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Roulhac D. Toledano and Marc Van de Velde* *The authors would like to thank Michael A. Maloney, MB, BAO, ChB, for his help with the tables and figures. INTRODUCTIONClinical indications for epidural anesthesia and analgesia have expanded significantly over the past several decades. Epidural analgesia is often used to supplement general anesthesia (GA) for surgical procedures in patients of all ages with moderate-to severe comorbid disease; provide analgesia in the intraoperative, postoperative, peripartum, and end-of-life settings; and can be used as the primary anesthetic for surgeries from the mediastinum to the lower extremities. In addition, epidural techniques are used increasingly for diagnostic procedures, acute pain therapy, and management of chronic pain. Epidural block may also reduce the surgical stress response, the risk of cancer recurrence, the incidence of perioperative thromboembolic events, and, possibly, the morbidity and mortality associated with major surgery. This chapter covers the essentials of epidural anesthesia and analgesia. After a brief history of the transformation from single-shot to continuous epidural catheter techniques, it reviews (1) indications for and contraindications to epidural block; (2) basic anatomic considerations for epidural placement; (3) physiologic effects of epidural block; (4) pharmacology of drugs used for epidural anesthesia and analgesia; (5) techniques for successful epidural placement; and (6) major and minor complications associated with epidural block. This chapter also addresses several areas of controversy concerning epidural techniques. These include controversies about epidural space anatomy, the traditional epinephrine test dose, methods used to identify the epidural space, and whether particular clinical outcomes may be improved with epidural techniques when compared to GA. More detailed information about local anesthetics (LAs), the mechanism of neuraxial block, the combined spinal-epidural (CSE) technique, obstetric anesthesia, and complications of central neuraxial block is provided following the links. From the Compendium of Regional Anesthesia: Epidural anesthesia infographic. BRIEF HISTORYThe neurologist J. Leonard Corning proposed injecting an anesthetic solution into the epidural space in the 1880s, but devoted his research primarily to subarachnoid nerve blocks. Despite coining the term spinal anesthesia, he may unknowingly have been investigating the epidural space. The French physicians Jean Sicard and Fernand Cathelin are credited with the first intentional administration of epidural anesthesia. At the turn of the 20th century, they independently introduced single-shot caudal nerve blocks with cocaine for neurologic and genitourinary procedures, respectively. Nineteen years later, the Spanish surgeon Fidel Pagés Miravé described a single-shot thoracolumbar approach to “peridural” anesthesia, identifying the epidural space through subtle tactile distinctions in the ligaments. Within a decade and seemingly without the knowledge of Pagés’s work, the Italian surgeon Achille Dogliotti popularized a reproducible loss-of-resistance (LOR) technique to identify the epidural space. Contemporaneously, the Argentine surgeon Alberto Gutiérrez described the “sign of the drop” for identification of the epidural space. A number of innovations by Eugene Aburel, Robert
Hingson, Waldo Edwards, and James Southworth, among others, attempted to prolong the single-shot epidural technique. However, Cuban anesthesiologist Manual Martinez Curbelo is credited with adapting Edward Tuohy’s continuous subarachnoid technique for the epidural space in 1947. His efforts were facilitated by an extensive knowledge of anatomy, a first-hand experience observing Tuohy at the Mayo Clinic, and the availability of 16-gauge Tuohy needles and small, gradated 3.5-French ureteral
catheters, which curved as they exited the tip of the needle. Several modifications of the Tuohy needle, itself a modification of the Huber needle, have since emerged. INDICATIONSThis section presents common and controversial indications for the use of lumbar and thoracic epidural block in lower extremity, genitourinary, vascular, gynecologic, colorectal, and cardiothoracic surgery. It also reviews less common and novel indications for epidural anesthesia and analgesia, including for the treatment of patients with sepsis and uncommon medical disorders (Table 1). TABLE 1. Examples of applications for epidural block.
Lumbar Epidural blockEpidural anesthesia has been administered most commonly for procedures involving the lower limbs, pelvis, perineum, and lower abdomen but is increasingly being used as the sole anesthetic or as a complement to GA for a greater diversity of procedures. This section examines several common indications for lumbar epidural block, including lower extremity orthopedic surgery, infrainguinal vascular procedures, and genitourinary and vaginal gynecologic surgeries. When applicable, it reviews the benefits and drawbacks of the use of neuraxial techniques versus GA for specific procedures. Lower Extremity Major Orthopedic Surgery Major
orthopedic procedures that can be performed under epidural, CSE, or integrated epidural and GA include primary hip or knee arthroplasty, surgery for hip fracture, revision arthroplasty, bilateral total knee arthroplasty, acetabular bone grafting, and insertion of long-stem femoral prostheses (Table 2).
Spinal anesthesia may be the preferred technique in some of these cases, particularly if anticipated postoperative pain is slight or negligible (eg, total hip arthroplasty) or if a supplemental peripheral nerve block is planned. TABLE 2. Orthopedic surgeries suitable for epidural, combined spinal-epidural, or integrated epidural–general anesthesia.
Anesthesia to T10 with needle placement at L3 to L4 is adequate for most of these procedures. The use of neuraxial anesthesia for major orthopedic surgery is not without risks and challenges. Elderly patients, trauma victims, and individuals with hemophilia who develop complications from recurrent bleeding into their joints may not be appropriate candidates for regional block. In general, epidural procedures are well tolerated in patients with age-related comorbidities, such as restrictive pulmonary disease, prolonged hepatic clearance of drugs, hypertension (HTN), coronary artery disease (CAD), and renal insufficiency. Elderly patients may benefit from the decreased postoperative confusion and delirium associated with regional anesthesia, provided intraoperative hypotension is kept to a minimum. However, prevention of excessive sympathectomy-induced hemodynamic changes can be challenging, as these patients are both less capable of responding to hypotension and more prone to cardiac decompensation and pulmonary edema in response to rapid fluid administration. An epidural technique with a sensory level below T10, as appropriate for many orthopedic surgeries, and judicious administration of fluids and vasopressors may minimize these risks. Elderly patients commonly present for surgery on anticoagulant or antiplatelet medications and may pose a risk for neurologic injury related to central neuraxial block. If an epidural technique is selected for these or other high-risk patients, appropriate timing of both block initiation and catheter removal relative to the timing of anticoagulant drug administration must be taken into account. For trauma patients, attaining proper positioning for administration of epidural anesthesia may present a challenge. Initiation of neuraxial block in the lateral position may improve chances of success. Intraoperatively, tourniquet pain can be anticipated with either spinal or epidural block, but occurs more frequently with the latter. While the mechanism remains poorly understood, it commonly presents within an hour of tourniquet inflation, increases in intensity over time, and is accompanied by tachycardia and elevated blood pressure. The administration of intrathecal or epidural preservative-free morphine may delay the onset of tourniquet pain. Lower Limb Vascular Surgery Consideration must also be given to the type of vascular procedure to be performed, the anticipated length of the procedure, the possible need for invasive monitoring, and the timely removal of the epidural catheter before transitioni ng to oral anticoagulation therapy. Maintaining normothermia, ensuring that motor strength can be promptly assessed postoperatively, and providing appropriate sedation during lengthy procedures are additional challenges. Infrainguinal vascular procedures that are suitable for epidural block include arterial bypass surgeries, arterial embolectomy, and venous thrombectomy or vein excision (Table 3). TABLE 3. Examples of vascular procedures performed with epidural block.
Slow titration of LAs to attain a T8–T10 level, while maintaining hemodynamic stability, is optimal. The addition of epinephrine to LAs is controversial due to concerns that its vasoconstrictive effect may jeopardize an already-tenuous blood supply to the spinal cord. Studies to date have failed to demonstrate a difference in cardiovascular and pulmonary morbidity and mortality with the use of epidural anesthesia as compared with GA for these procedures, although epidural techniques may be superior for promoting graft survival. Lower Genitourinary Procedures TABLE 4. Benefits of central neuraxial block versus general anesthesia for transurethral resection of the prostate.
Other transurethral procedures, such as cystoscopy and ureteral stone extraction, can be performed under GA, topical anesthesia, or neuraxial block, depending on the extent and complexity of the procedure, patient comorbidities, and patient, anesthesiologist, and surgeon preference. Of note, paraplegic and quadriplegic patients comprise a subset of patients who present for repeated cystoscopies and stone extraction procedures; neuraxial anesthesia is often
preferred in these patients because of the risk of autonomic hyperreflexia (AH) (see separate section on this topic).
TABLE 5. Sensory level required for genitourinary procedures.
Vaginal Gynecologic Surgeries TABLE 6. Vaginal gynecologic procedures suitable for epidural block.
If neuraxial anesthesia is selected, a T10 sensory level is appropriate. While outpatient diagnostic hysteroscopy can be performed under LA, hysteroscopy with distention media typically requires general or neuraxial anesthesia. Epidural anesthesia may have the disadvantage of increased glycine absorption compared to GA. However, mental status changes related to absorption of the hypotonic irrigation solution are more easily detected in awake patients. For urinary incontinence procedures, epidural anesthesia offers the advantage of permitting the patient to participate in the intraoperative cough test, which theoretically decreases the risk of postoperative voiding dysfunction, although the incidence of this untoward outcome does not appear to be increased under GA. A T10 sensory level provides sufficient anesthesia for bladder procedures, but the level should be extended to T4 if the peritoneum is opened. Vaginal hysterectomy can be performed under general or neuraxial (most commonly spinal) anesthesia. A T4–T6 sensory level is appropriate for uterine procedures. Thoracic Epidural Anesthesia and AnalgesiaThe benefits of and indications for thoracic epidural anesthesia (TEA) are expanding (Table 7). TEA offers superior perioperative analgesia compared with systemic opioids, decreases postoperative pulmonary complications, decreases the duration of postoperative ileus, and
decreases mortality in patients with multiple rib fractures, among other things. This section explores the role of TEA as either a primary anesthetic or as an adjuvant to GA for cardiac, thoracic, abdominal, colorectal, genitourinary, and gynecologic surgery (Figure 1). It also reviews the expanding role of TEA for video-assisted thoracic surgery (VATS) and laparoscopic surgery. TABLE 7. Benefits of thoracic epidural anesthesia and analgesia.
Figure 1. Level of placement in surgeries performed with thoracic epidural anesthesia and analgesia. Cardiac Surgery Several of these potential benefits can be attributed to selective block of cardiac sympathetic innervation (the T1–T4 spinal segments). However, the insertion of an epidural catheter in patients requiring full heparinization for CPB carries the risk of epidural hematoma. The evidence in support of high TEA for cardiac surgery is not conclusive. A study by Liu and colleagues comparing TEA with traditional opioid-based GA for coronary artery bypass grafting (CABG) with CPB found no difference in the rates of mortality or myocardial infarction, but demonstrated a statistically significant reduction in the risk of postoperative cardiac arrhythmias and pulmonary complications, improved pain scores, and earlier tracheal extubation in the TEA group. In contrast, a recent randomized control trial comparing the clinical effects of fast-track GA with TEA versus fast-track GA alone in over 600 patients undergoing elective cardiac surgery (both on pump and off pump) found no statistically significant difference in 30-day survival free from myocardial infarction, pulmonary complications, renal failure, or stroke. The duration of mechanical ventilation, length of intensive care unit (ICU) stay, length of hospital stay, and quality of life at 30-day follow-up were also similar for the two groups. Overall, the role of TEA as an adjuvant to GA for cardiac surgery with CPB remains controversial. The role of high TEA in off-pump coronary artery bypass (OPCAB) surgery is also debated in the literature. TEA offers the advantages of avoiding intubation of the trachea in selected CABG cases, earlier extubation in patients receiving GA, and reduced postoperative pain and morbidity. But, concerns remain about compromised ventilation with a high sensory block, hypotension due to sympathicolysis, and epidural hematoma, despite the vastly reduced heparin dose compared with CPB cases. A recent prospective, randomized controlled trial of more than 200 patients undergoing OPCAB surgery found that the addition of high TEA to GA significantly reduced the incidence of postoperative arrhythmias, improved pain control, and improved the quality of recovery. Until more definitive outcome data are available, the role of neuraxial techniques in OPCAB surgery remains uncertain. Thoracic and Upper Abdominal Surgical Procedures TABLE 8. Indications for thoracic epidural anesthesia and analgesia.
It is less commonly used for VATS, unless conversion to an open procedure is highly anticipated or if the patient is at high risk for complications from GA. Epidural block for many of these procedures commonly serves as an adjuvant to GA and as an essential component of postoperative pain management. Concurrent administration of high TEA with GA, however, carries risks of intraoperative bradycardia, hypotension, and changes in airway resistance. There is some debate regarding whether intraoperative activation of epidural block is required to appreciate the analgesic benefits of TEA or if postoperative activation produces equivalent benefits. A systematic review by Møiniche and colleagues found that the timing of several types of analgesia, including epidurals, intravenous opioids, and peripheral LAs, did not influence the quality of postoperative pain control. Thoracic epidural anesthesia initiated at the mid- to upper thoracic region can also be used for breast procedures. Benefits may include superior postoperative analgesia, decreased incidence of postoperative nausea and vomiting (PONV), improved patient satisfaction, and avoiding tracheal intubation in patients with moderate-to-severe comorbidities. The sensory level required depends on the procedure: A level extending from T1–T7 is adequate for breast augmentation; C5–T7 is required for modified radical mastectomy; and C5–L1 is required for mastectomy with transverse rectus abdominis myocutaneous (TRAM) flap reconstruction (Table 9). The epidural catheter can be introduced at T2–T4 to achieve segmental block of the thoracic dermatomes for most breast procedures; placement at T8–T10 is appropriate for TRAM flap reconstruction. TABLE 9. Sensory level required for breast procedures.
Epidural block provides a useful adjuvant to GA for procedures within the thoracic cavity, such as lung and esophageal surgery. The benefits of TEA for these procedures include enhanced postoperative analgesia; reduced pulmonary morbidity (eg, atelectasis, pneumonia, and hypoxemia); swift resolution of postoperative ileus; and decreased postoperative catabolism, which may spare muscle mass. Segmental epidural block of T1–T10 provides sensory block of the thoracotomy incision and the chest tube insertion site. Upper abdominal surgeries that can be performed with epidural anesthesia and analgesia include esophagectomy, gastrectomy, pancreatectomy, hepatic resection, and cholecystectomy. Laparoscopic cholecystectomy with epidural block30 and distal gastrectomy with a combined general-epidural anesthetic have also been reported. Midthoracic epidural catheter placement with segmental block extending from T5 (T4 for laparoscopic surgery) to T8 is appropriate for most upper abdominal procedures and, due to lumbar and sacral nerve root sparing, has minimal risk of lower extremity motor deficits, urinary retention, hypotension, and other sequelae of lumbar epidural anesthesia. Suprainguinal Vascular Procedures Extracorporeal Shock Wave Lithotripsy,Prostatectomy, Cystectomy, Nephrectomy Open prostate surgery, radical cystectomy and urinary diversion, and simple, partial, and radical nephrectomy can be performed under neuraxial block, either alone or in combination with GA, depending on the procedure. Some potential advantages of neuraxial compared with GA for radical retropubic prostatectomy include decreased intraoperative blood loss and transfusions, a decreased incidence of postoperative thromboembolic events, improved analgesia and level of activity up to 9 weeks postoperatively, faster return of bowel function, and several other still-disputed advantages of neuraxial anesthesia, such as faster time to hospital discharge and reduced hospital costs. For the open procedure, patients may require generous sedation in the absence of a combined general-neuraxial technique. A T6 sensory level is required, with catheter placement in the midthoracic region. Radical cystectomy is performed on patients with invasive bladder cancer and may have improved outcomes with a combined general-epidural anesthetic compared to GA alone. Epidural block can provide controlled hypotension intraoperatively, contributing to decreased blood loss, and optimize postoperative pain relief. A midthoracic epidural with a T6 sensory level is appropriate. Although GA is often required for radical nephrectomy due to concerns for patient positioning, intraoperative hypotension, and the potential for significant intraoperative blood loss, epidural analgesia provides more effective postoperative pain relief than systemic opioids while avoiding the adverse effects of the latter. Several other urologic-related surgeries can be performed with neuraxial block as the sole anesthetic or as an adjuvant to GA. The use of a combined GA-epidural technique in patients with functional adrenal tumors undergoing laparoscopic adrenalectomy is safe and effective and may have the added benefit of minimizing fluctuations in hormone levels. Of note, however, epidural block may not diminish the pressor effects of direct tumor stimulation. The use of epidural anesthesia for retroperitoneal laparoscopic biopsy for patients who are not candidates for percutaneous biopsy has also been reported. Lower Abdominal and Gyneacologic Surgeries Open and laparoscopic colectomy, sigmoidectomy, and appendectomy are among other lower abdominal surgeries that can be performed under neuraxial anesthesia, with or without GA. Of particular interest in patients undergoing bowel surgery thoracic epidural block decreases the duration of postoperative ileus, possibly without affecting anastomotic healing and leakage. The superior postoperative analgesia associated with continuous epidural infusions, with or without opioids, most likely improves postoperative lung function in patients undergoing gastrointestinal (GI) surgery, although specific randomized controlled trials have not been conducted. In combination with early feeding and ambulation, TEA plays a role in early hospital discharge after certain GI surgeries. A similar outcome has been demonstrated after laparoscopic colonic resection, followed by epidural analgesia for 2 days and early oral nutrition and mobilization (ie, multimodal rehabilitation). Epidural catheter placement between T9 and T11 is usually appropriate for lower abdominal procedures; a sensory block extending to T7 or T9 is required for most colonic surgeries (sigmoid resection, ileotransversostomy, hemicolectomy). Uncommon Medical Disorders and Clinical ScenariosEpidural anesthesia and analgesia may also be indicated in the perioperative management of patients with specific medical conditions or coexisting disease, such as myasthenia gravis (MG), AH, malignant hyperthermia (MH), COPD, pheochromocytoma (see previous discussion), and sepsis. Several other subsets of patients may benefit from continuous epidural catheter techniques, including palliative care patients, parturients with comorbidities, and patients at risk for recurrent malignancy. Myasthenia Gravis Autonomic Hyperreflexia Malignant Hyperthermia Whenever suitable, local, peripheral, or central neuraxial nerve blocks are recommended, as these techniques are reported to be safer than the use of GA. Both ester and amide LAs are considered safe in MH-susceptible patients, as is epinephrine, although controversy remains in the literature. Chronic Obstructive Pulmonary Disease Pediatric Surgery The single-shot caudal approach to the epidural space, with or without sedation, is
commonly used in pediatric patients for a variety of surgeries, including circumcision, hypospadias repair, inguinal herniorrhaphy, and orchidopexy. Ambulatory Surgery Labor Analgesia and Anesthesia However, surface anatomic landmarks may be difficult to appreciate in obstetric patients and may not reliably identify the intended interspace in this subset of patients due to both the anterior rotation of the pelvis and exaggerated lumbar lordosis. Several other factors may affect the ease of epidural placement and spread of epidurally administered LAs in parturients, including engorgement of epidural veins, elevated hormonal levels, and excessive weight gain. Refer to “Obstetric Regional Anesthesia” for additional information on epidural techniques in laboring patients. Miscellaneous There is a growing body of literature devoted to the potential beneficial effects of epidural analgesia in patients with cancer, although the data are preliminary and at times contradictory. Surgical stress and certain anesthetic agents suppress the host’s immune function, including its ability to eliminate circulating tumor cells, and can predispose patients with cancer to postoperative infection, tumor growth, and metastasis. Recent studies have demonstrated improved perioperative immune function with the use of TEA in patients undergoing elective laparoscopic radical hysterectomy for cervical cancer. Regional adjuncts to anesthesia have also been shown to have beneficial effects against recurrence of breast and prostate cancer. These protective effects may reflect both the decreased opioid requirements and the reduced neurohumoral stress response associated with epidural block. CONTRAINDICATIONSSerious complications of epidural techniques are rare. However, epidural hematomas, epidural abscesses, permanent nerve injury, infection, and cardiovascular collapse, among other adverse events, have been attributed to neuraxial block. As a result, an understanding of the conditions that may predispose certain patient populations to these and other complications is essential. This section reviews the absolute, relative, and controversial contraindications to epidural placement (Table 10). Ultimately, a risk-benefit analysis with particular emphasis on patient comorbidities, airway anatomy, patient preferences, and type and duration of surgery is recommended prior to initiation of epidural block. TABLE 10. Contraindications to epidural block.
Absolute ContraindicationsAlthough the contraindications to epidural block have been classified historically as absolute, relative, and controversial, opinions regarding absolute contraindications have evolved with advances in equipment, techniques, and practitioner experience. Currently, patient refusal may be considered the only absolute contraindication to epidural block. Although coagulopathy is considered a relative contraindication, initiating neuraxial block in the presence of severe coagulation abnormalities, such as frank disseminated intravascular coagulation (DIC), is contraindicated. Most other pathologic conditions comprise relative or controversial contraindications and require careful risk-benefit analysis prior to initiation of epidural block. Relative and Controversial ContraindicationsSepsis Increased
Intracranial Pressure TABLE 11. Signs and symptoms of elevated intracranial pressure.
Figure 2. Safety algorithm for neuroaxial block in patients with intracranial space-occupying lesions. CSF = cerebrospinal fluid. (Reproduced with permission from Leffert LR, Schwamm LH: Neuraxial anesthesia in parturients with intracranial pathology: a comprehensive review and reassessment of risk. Anesthesiology. 2013 Sep;119(3):703-718.) Coagulopathy NYSORA Tips• Epidural needle and catheter placement both carry a risk of epidural hematoma in patients on anticoagulants. Similar precautions should be observed during placement and removal of epidural catheters. The American Society of Regional Anesthesia and Pain Medicine periodically updates its guidelines for the initiation of regional anesthesia in patients receiving antithrombotic or thrombolytic therapy. Briefly, neuraxial techniques in patients receiving subcutaneous unfractionated heparin (UFH) with dosing regimens of 5000 U every 12 hours are considered safe (Table 12). TABLE 12. Epidural block in patients receiving antithrombotic therapy.
The risks and benefits of thrice-daily UFH or more than 10,000 U daily should be assessed on an individual basis; vigilance should be maintained to detect new or worsening neurodeficits in this setting. For patients receiving heparin for more than 4 days, a platelet count should be assessed before neuraxial nerve block or catheter removal due to concerns for heparin-induced thrombocytopenia (HIT). In patients who receive systemic heparinization, it is recommended to assess the activated plasma thromboplastin time (aPTT) and discontinue heparin for 2 to 4 hours prior to catheter manipulation or removal. Administration of intravenous heparin intraoperatively should be delayed for at least 1 hour after epidural placement; a delay before administration of subcutaneous heparin is not required. In cases of full heparinization for CPB, additional precautions include delaying surgery for 24 hours in the event of a traumatic tap, tightly controlling the heparin effect and reversal, and removing catheters when normal coagulation is restored. Epidural block in patients taking aspirin and nonaspirin NSAIDs is considered safe, as the risk of epidural hematoma is low. Needle placement should be delayed for 12 hours in patients receiving low molecular weight heparin (LMWH) thromboprophylaxis and for 24 hours in those receiving therapeutic doses. It is recommended that warfarin be discontinued for several days prior to surgery and that the international normalized ratio (INR) return to baseline prior to initiation of epidural techniques. An INR below 1.5 is considered sufficient for catheter removal, although many clinicians may be comfortable manipulating catheters with higher INR values. Refer to Chapter 52 for more detailed information on these and newer agents. Neuraxial techniques are contraindicated in the setting of DIC, which may complicate sepsis, trauma, liver failure, placental abruption, amniotic fluid embolism, and massive transfusion, among other disease processes (Table 13). If DIC develops after epidural placement, the catheter should be removed once normal clotting parameters have been restored. TABLE 13. Conditions associated with disseminated intravascular coagulation.
Thrombocytopenia and Other Common Bleeding Disorders While there is currently no universally accepted platelet count below which epidural placement should be avoided, many clinicians are comfortable with a platelet count above 70,000 mm3 in the absence of clinical bleeding. The cutoff may be higher or
lower, however, depending on the etiology of the thrombocytopenia, the bleeding history, the trend in platelet number, individual patient characteristics (eg, a known or suspected difficult airway), and provider expertise and comfort level. In general, platelet function is normal in conditions such as gestational thrombocytopenia and immune thrombocytopenic purpura (ITP). NYSORA Tips• The etiology of thrombocytopenia, the patient’s bleeding history, and the trend in platelet count must be taken into account when determining the safety of initiation of epidural block in thrombocytopenic patients. Certain conditions, such as ITP and gestational thrombocytopenia, are associated with functioning platelets despite a low platelet count. A platelet count below 50,000 mm3 in the setting of ITP may respond to corticosteroids or intravenous immunoglobulin (IVIG), when necessary. Functional platelet defects may be present in several less-common conditions, such as HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count); thrombotic thrombocytopenic purpura (TTP); and hemolytic uremic syndrome (HUS). Other conditions such as systemic lupus erythematous (SLE), antiphospholipid syndrome, type 2B von Willebrand disease (vWD), HIT, and DIC are associated with thrombocytopenia of varying degrees (Table 14). TABLE 14. Causes of thrombocytopenia.
A standard platelet count has not been established for catheter removal. While some sources suggest 60,000 mm3 is appropriate, catheter removal without adverse sequelae has been reported at counts below that cutoff. If platelet number or function is impaired after an epidural catheter has been placed, such as in the case of intraoperative DIC, the catheter should remain in situ until the coagulopathy has resolved. Other common bleeding diatheses that comprise relative contraindications to the initiation of epidural block include hemophilia, vWD, and disorders related to lupus anticoagulants and anticardiolipin antibodies. Hemophilia A and B are X-linked diseases characterized by deficiencies in factors VIII and IX, respectively. Although specific guidelines are lacking, neuraxial procedures are considered safe in carriers of the disease with normal factor levels and no bleeding complications. Neuraxial techniques have been performed without adverse sequelae in homozygous patients after factor replacement therapy once factor leve ls and the aPTT have normalized. Patients with lupus anticoagulants and anticardiolipin antibodies are predisposed to platelet aggregation, thrombocytopenia, and, because of interactions between antibodies and platelet membranes, thrombosis. As a result, many of these patients are anticoagulated with heparin in the peripartum or perioperative period. Heparin levels should be monitored with a blood heparin assay, thrombin time, or activated clotting test prior to performing neuraxial block. Of note, the aPTT is elevated at baseline in these patients and is likely to remain elevated after discontinuation of heparin due to interactions between the circulating antibodies and the coagulation tests. Von Willebrand disease is the most common inherited bleeding disorder. It is characterized by either a quantitative (type 1 and type 3) or qualitative (type 2) deficiency in von Willebrand factor (vWF), a plasma glycoprotein that binds to and stabilizes factor VIII and mediates platelet adhesion at sites of vascular injury. The clinical presentation of vWD varies: Patients with type 1, the most common type, experience mucocutaneous bleeding, easy bruising, and menorrhagia; patients with type 2 vWD may experience moderate-to-severe bleeding and, in the case of type 2B, thrombocytopenia; type 3, which is rare, presents with severe bleeding, including hemarthroses (Table 15). TABLE 15. Classification of von Willebrand disease.
Both treatment options and the decision to proceed with neuraxial block also vary with the different disease presentations. Type I responds to desmopressin (DDAVP), which promotes secretion of stored vWF from endothelial cells and results in a rapid rise in both plasma vWF and factor VIII. Factor VIII concentrates and cryoprecipitate are treatment options for type 2 and type 3 vWD. Specialized laboratory tests may help confirm the diagnosis and type of vWD but are not widely available; standard coagulation tests may serve to rule out other bleeding disorders. In addition to a thorough history and physical examination, collaboration with a hematologist and other team members, and a review of any pertinent laboratory results, a risk-benefit analysis should be performed prior to initiation of epidural procedures in patients with vWD. Preexisting Central Nervous System Disorders The decision to perform epidural anesthesia in patients with PPS, the most prevalent motor neuron disease in North America, requires careful analysis of the potential risks and benefits on a case-by-case basis. PPS is a late-onset manifestation of acute poliomyelitis infection that presents with fatigue, joint pain, and muscle atrophy in previously affected muscle groups. Epidural techniques in this patient population can be complicated by difficult puncture related to abnormal spinal anatomy, potential worsening of symptoms, and transient respiratory weakness. Alternatively, GA presents challenges related to sensitivity to muscle relaxants and sedatives and risks of respiratory compromise and aspiration. Although data are limited, there is no evidence that epidural techniques contribute to worsening of neurologic symptoms in patients with PPS. Evidence linking epidural techniques to either activation or recurrence of GBS is also lacking. GBS presents with progressive motor weakness, ascending paralysis, and areflexia, most likely attributable to a postinfection inflammatory response. Older age at onset and severe initial disease are among the risk factors for prolonged neurologic dysfunction. Epidural anesthesia has been used successfully in patients with GBS, most commonly in obstetric patients, although exaggerated hemodynamic responses (hypotension and bradycardia), higher-than-normal spread of LAs, and worsening of neurologic symptoms have been reported. As always, a risk-benefit analysis is warranted prior to performance of epidural block in patients with GBS, as are assessment and documentation of neurologic examination of the patient and a thorough discussion of the risks of anesthesia. It is reasonable to avoid regional techniques during periods of acute neuronal inflammation. Patients with spina bifida may also present a unique challenge to anesthesiologists. Spina bifida occulta occurs when the neural arch fails to close without herniation of the meninges or neural tissues. It is most commonly limited to one vertebra, although a small percentage of affected individuals have involvement of two or more vertebrae with associated neurologic abnormalities, underlying cord abnormalities, and scoliosis. In general, the use of epidural techniques is not contraindicated in patients with spina bifida occulta, although placement at the level of the occulta lesion, most commonly at L5 to S1, may have an increased risk of dural puncture and patchy or higher-than-normal response to LAs. In contrast, epidural placement in patients with spina bifida cystica has several potential risks, including risk of direct injury to the cord due to a low-lying conus medullaris, unpredictable or higher-than-expected spread of LAs, and increased risk of dural puncture. Fever or Infection Historically, there have been concerns about the safety of neuraxial procedures in individuals infected with HIV due to both the theoretical risk of inoculation of the virus into the CNS and the possibility that neurologic manifestations of HIV may be attributed to the anesthetic technique. However, the CNS is infected early in the course of HIV infection, and there is no evidence that neuraxial instrumentation, including an epidural blood patch (EBP) for the treatment of PDPH, confers additional risk of viral spread to the CNS. There also is no evidence that the introduction of HIV-infected blood into the CSF might exacerbate a preexisting CNS infection, such as meningitis. Concerns that neurologic sequelae of HIV might be attributed to the neuraxial technique also appear to be unsubstantiated, as a temporal relationship between the epidural placement and the onset of neurologic deficits is unlikely. Nonetheless, thorough documentation of any preexisting neurologic deficit is recommended, given that neurologic complications of HIV are not uncommon and that HIV-positive individuals are at high risk for other sexually transmitted diseases that affect the CNS. Potential risks should be discussed in advance, and, as always, strict aseptic technique to protect both the patient and the anesthesiology provider must be maintained. Areas of concern regarding the use of regional anesthesia in patients with
HSV-2 include the risk of introducing the virus into the CNS during administration of neuraxial anesthesia; the possibility that a disseminated infection that develops after a regional anesthetic might be ascribed to the anesthetic itself, despite the lack of a causal relationship; and the safety of neuraxial techniques in primary HSV-2 outbreaks, which may be silent and difficult to distinguish from secondary outbreaks, but more commonly present with viremia, constitutional symptoms, genital
lesions, and, in a small percentage of patients, aseptic meningitis. There are no documented cases of septic or neurologic complications following neuraxial procedures in patients with secondary (ie, recurrent) HSV infection; however, the safety of regional anesthesia in patients with primary infection has not been established. Crosby and colleagues conducted a 6-year retrospective analysis of 89 patients with secondary HSV infection who received epidural anesthesia for cesarean delivery
and reported that no patients suffered septic or neurologic complications. Previous Back Surgery, Preexisting Neurologic Injury, and Back Pain Preload-Dependent States Epidural Placement in Anesthetized Patients Needle Insertion Through a Tattoo ANATOMYAn understanding of the anatomy of the vertebral column, spinal canal, epidural space and its contents, and commonly encountered anatomic variations among individuals is essential for the safe and effective initiation of epidural block. A three-dimensional mental image of vertebral column anatomy also aids in troubleshooting when identification of the epidural space is equivocal or when complications of epidural catheterization, such as unilateral block, intravascular cannulation, or catheter migration, occur. This section presents the basic anatomic considerations for successful epidural anesthesia and analgesia and reviews several controversies in the field of applied anatomy, including the accuracy of anatomic landmarks to estimate the spinous process level, the existence (or lack thereof) of a subdural compartment, and the contents of the epidural space. Vertebral ColumnGeneral
Appearance Figure 3. Physiologic spinal curves: anterior, posterior, and lateral views (left to right). The four physiologic spinal curves are fully developed by 10 years of age and become more pronounced during pregnancy and with aging.
In the supine position, C5 and L3 are positioned at the highest points of the lordosis; the peaks of kyphosis occur at T5 to T7 and at S2. NYSORA TipsC5 and L3 comprise the highest points of lordosis in the supine position; the highest points of kyphosis are T5 to T7 and S2. Structure of Vertebrae Figure 4. Size and shape of the vertebral bodies at different spinal levels. The thoracic vertebral bodies are larger than the cervical vertebral bodies and are wider in the posterior than anterior dimension, contributing to the characteristic thoracic curvature. The long and slender thoracic spinous processes, with tips that point caudally, are most sharply angled between T4 and T9, making insertion of the epidural needle in the midline more difficult in the midthoracic region. Beyond T10, they increasingly resemble those in the lumbar region. Each thoracic vertebra articulates with ribs along the dorsolateral border of its body, a feature that may help distinguish the lower thoracic and upper lumbar regions. The inferior angle of the scapula and the 12th rib are widely used in clinical practice to estimate the level of the cross the L1 spinous process (Table 16). TABLE 16. Anatomic landmarks to identify spinous processes of T7 and T12, respectively. The imaginary line connecting the caudal-most margin of the 12th ribs is often presumed to vertebral levels.
The lumbar vertebrae are the largest movable segments, with thicker anterior than posterior dimensions that contribute to the characteristic lumbar curvature. The spinous processes in this region are blunt and large, with tips that point posteriorly. Anatomic variations in the lumbosacral region that may have clinical implications are not uncommon. Sacralization of the last lumbar vertebra, marked by fusion of L5 to the sacral bone, and lumbarization of S1 and S2, in which fusion is incomplete, may make numbering and identification of the correct lumbar level difficult. Although probably not of clinical significance, patients with sacralization have also been found to have a higher position of the conus medullaris, which demarcates the cone-shaped terminus of the spinal cord, than those with lumbarization or without lumbosacral transitional vertebrae. In the absence of these transitional vertebrae, the largest and most easily palpable interspace corresponds to L5 to S1. Surface Anatomic Landmarks to Identify the Spinal Level Figure 5. Skeletal landmarks used to determine the level of epidural placement. However, palpation and inspection of surface anatomical landmarks may fail to help localize the correct intervertebral space, particularly when considering individual variations in the vertebral level of these landmarks, the varying termination of the conus medullaris between the middle third of T12 and the upper third of L3, and anesthesiologists’ poor record of identifying the correct
interspace. Joints and Ligaments of the Vertebral ColumnGeneral The Longitudinal Ligaments Figure 6 Ligaments of the vertebral canal. NYSORA Tips• Disk herniation occurs primarily at weak points in the posterior longitudinal ligament in an area that comprises the anterior epidural space, as opposed to the more clinically relevant posterior epidural space. Nonetheless, thorough documentation of preexisting pain and neurologic deficits in patients with known disk herniation is recommended prior to initiation of epidural anesthesia. Also of clinical relevance, a membranous lateral extension of the posterior longitudinal ligament may serve as a barrier to the spread of epidural solutions and appears to cordon the veins anterior to the dura away from the rest of the epidural space. NYSORA Tips• A membranous lateral extension of the posterior longitudinal ligament appears to cordon off the veins in the anterolateral epidural space, where epidural vein puncture and catheter cannulation are more likely to occur. The Supraspinous and Interspinous Ligaments The
Ligamentum Flavum TABLE 17. Thickness of the ligamentum flavum at different vertebral levels.
NYSORA Tips• The ligamentum flavum varies in thickness at different spinal levels and is thickest in the lumbar region. Its thickness also varies within each interspace. Clinically, these varying degrees of thickness may influence the risk of inadvertent dural puncture or determine whether injection of an anesthetic solution into the epidural space is possible with the skin infiltration needle. Another controversy concerns the incidence and location of gaps formed by the incomplete fusion of the right and left ligamentum flava. In their study of 52 human cadavers, Lirk and colleagues found that up to 74% of the flava in the cervical region are discontinuous at midline. These gaps vary in location, with some occupying the entire height of the ligamentum flavum between successive vertebral arches and others occupying the caudal third portion only (Figure 7).
Figure 7. Ligamentum flavum with different types of midline gaps. Veins connecting the posterior external and internal vertebral venous plexuses not uncommonly traverse the caudal portion of the
gaps. In another cadaveric study, Lirk et al determined that thoracic midline gaps were less frequent than cervical gaps but more frequent than those in the lumbar region, with an incidence as high as 35.2% at T10 to T11. In cadaveric studies of the lumbar ligamentum flavum, gaps were found most commonly at L1 and L2 (22.2%) and decreased caudally (11.4% at L2 to L4; 9.3% at L4 to L5; 0% at L5 to S1). Clinically, these gaps may contribute to failure to identify the epidural space using the LOR
technique at midline. The characteristic “pop” sound and tactile sensation conferred by penetration of the elastic fibers of the ligamentum flavum may be absent in the setting of a discontinuous ligamentous arch. The depth to the epidural space at midline may also be affected. NYSORA Tips• Ligamentum flavum midline gaps represent incomplete fusion of the right and left ligamentum flava. They are common in the cervical spine and decrease in frequency in the thoracic and lumbar regions. The variable thickness of the ligamentum flavum and the presence of midline gaps may contribute to failure to identify the epidural space. The Spinal Canal GeneralThe vertebrae serve primarily to support the weight of the head, neck, and trunk; transfer that weight to the lower limbs; and protect the contents of the spinal canal, including the spinal cord. An extension of the medulla oblongata, the spinal cord serves as the conduit between the CNS and the peripheral nerves via 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal) (Figure 8). The adult cord measures approximately 45 cm or 18 inches and has two regions of enlarged diameter at C2–T2 and at T9–L2, areas that correspond with the origin of the nerve supplies to the upper and lower extremities. However, its level of termination varies with age, as well as among individuals of similar age groups. As a result of a discrepancy in the pace of growth of the spinal cord and vertebral column during development, the spinal cord at birth ends at approximately L3. By 6–12 months of age, the level of termination parallels that of adults, most commonly at L1. Below the conus medullaris, the long dorsal and ventral roots of all the spinal nerves below L1 form a bundle known as the cauda equina, or horse’s tail. A collection of strands of neuron-free fibrous tissue enveloped in pia mater comprises the filum terminale and extends from the inferior tip of the conus medullaris to the second or third sacral vertebra. Figure 8. Vertebral column with spinal nerves. Spinal
Nerves TABLE 18. Surface landmark correlation to dermatomal level.
An intricate relationship exists between the spinal nerves and the autonomic nervous system (Figure 10). Preganglionic sympathetic nerve fibers originate in the spinal cord from T1 to L2 and are blocked to varying degrees during epidural anesthesia. Figure 9. Distribution of dermatomes. Figure 10. Sympathetic nervous system. Cranial and sacral components comprise the parasympathetic nervous system. The vagus nerve, in particular, provides parasympathetic innervation to a broad area, including the head, neck, the thoracic organs and parts of the digestive tract. Parasympathetic innervation of the bladder, the descending large intestine, and the rectum originate at spinal cord levels S2 to S4. Spinal Meninges Figure 11. Spinal meninges. The flexible arachnoid mater, the middle meningeal layer, is loosely attached to the inner aspect of the dura and encloses the spinal cord and surrounding CSF within the subarachnoid space. It is composed of layers of epithelial-like cells connected by tight and occluding junctions, which impart its low permeability. NYSORA TipsClefts may form at the arachnoid-dura interface as a result of mechanical stress and direct trauma. Injection of a large volume of LA intended for the epidural space in this area may result in a subdural nerve block. Blood Supply Figure 12. Blood supply of the spinal cord. Epidural Space In contrast to traditional dogma, these vessels are located primarily in the anterior epidural space, where they are largely confined by the membranous extension of the posterior longitudinal ligament106 (Figure 13). This area is probably a common site of epidural catheter blood vessel puncture. Also of clinical significance, the subatmospheric pressure of the epidural space diminishes significantly in the lumbar region, potentially affecting both the hanging-drop and the epidural pressure waveform techniques of identification of the epidural space. The contents of the epidural space and their clinical implications have been debated extensively in the literature. The amount of adipose tissue in the epidural space appears to affect the spread of LA, but it remains unclear whether epidural fat prolongs nerve block duration by serving as a reservoir or decreases the amount of available drug, thereby slowing onset, or both. The reduction of adipose tissue with age is speculated to account in part for the higher levels and faster onset of epidural anesthesia in the elderly. Figure 13. Epidural vein distribution in the lumbar region. Similarly, the increase in adipose tissue in the lower lumbar area where the dural sac tapers may contribute to the variable effects of LA injections below L4–L5. Finally, adipose tissue in the midline gap, where the ligamentum flava fuse, may alter the tactile sensation that is normally appreciated during the LOR technique. Distance From Skin to Epidural Space PHYSIOLOGIC EFFECTS OF EPIDURAL blockEpidural block provides surgical anesthesia, intraoperative muscle relaxation, and intrapartum and postoperative pain relief with widespread direct and indirect effects on several physiologic systems. The extent of these physiologic effects depends on the level of placement and the number of spinal segments blocked. In general, high thoracic epidural nerve blocks (ie, above T5) and extensive epidural nerve blocks are associated with more profound physiologic changes than nerve blocks with low sensory levels (ie, below T10). This section reviews the physiologic alterations related to epidural anesthesia and analgesia. Differential blockDifferential block occurs when sensory, motor, and sympathetic nerve functions are obtunded at different rates and to different degrees. It may be observed at both onset and regression of the nerve block. In general, sympathetic block, which is not uncommonly incomplete, extends two to six dermatomes higher than sensory block, which in turn is
higher than the motor block. Sensory block also occurs with a lower concentration or total dose of LA and develops faster than motor block. Among sensory functions, temperature is blocked first, followed by pinprick and, finally, touch. Central Nervous System EffectsCerebral blood flow (CBF) is autoregulated and is not affected by epidural block unless the patient experiences pronounced hypotension. However, neuraxial anesthesia does appear
to have a sedative effect and to reduce anesthetic requirements for several agents, including midazolam, propofol, thiopental, fentanyl, and volatile agents. The degree of sedation and minimum alveolar concentration (MAC) sparing effect appear to correlate with the height and level of the sensory nerve block; block of the middle thoracic dermatomes is associated with greater sedative effects than block of the lower lumbar segments. Although data are conflicting, higher-concentration LAs may
contribute to a greater MAC-sparing effect. The addition of opioid adjuvants, such as morphine, to the epidural LA solution does not appear to reduce volatile agent requirements any further, although it does contribute to better postoperative pain scores. Overall, decreased anesthetic requirements have most commonly been attributed to decreased afferent input induced by the neuraxial nerve block rather than to systemic effects of LAs, altered pharmacokinetics, or direct action of LAs on the
brain. Cardiovascular and Hemodynamic EffectsCardiovascular changes associated with epidural anesthesia and analgesia result primarily from block of sympathetic nerve fiber conduction. These changes include venous and arterial vasodilation, reduced SVR, changes in chronotropy and inotropy, and associated alterations in blood pressure and CO. The type and intensity of these changes are related to the level of nerve block, the total number of dermatomes blocked, and, relatedly, the type and dose of LA administered. In general, lumbar epidural or low thoracic nerve blocks are not associated with significant hemodynamic changes, while higher thoracic nerve blocks (particularly those involving the T1–T4 sympathetic fibers) can cause more marked changes, not all of which are detrimental. However, factors such as pregnancy, age, comorbidities, patient positioning, and hypovolemia can complicate the clinical scenario and the anticipated cardiovascular effects. Hypotension Heart Rate and Cardiac Function Pulmonary EffectsThe motor and sympathetic changes associated with epidural anesthesia may affect lung function, depending on the level of block. In general, tidal volume remains unchanged even during high neuraxial nerve blocks, while vital
capacity may be reduced due to the decrease in expiratory reserve volume that occurs as accessory muscles involved in expiration are blocked. Gastrointestinal EffectsThe sympathetic outflow to the GI tract arises from T5 to T12, while parasympathetic innervation is supplied by the vagus nerve. Sympathectomy associated with epidural block in the mid- to low-thoracic levels results in unopposed vagal tone, which manifests clinically with increased peristalsis, relaxed sphincters, an increase in GI secretions, and, likely, more rapid restoration of GI motility in the postoperative phase. Nausea and vomiting commonly accompany hyperperistalsis and can be treated effectively with intravenous atropine. Theoretically, increased intestinal motility could contribute to breakdown of surgical anastomoses, but this has not been demonstrated in the literature. Rather, TEA may decrease the risk of anastomotic leakage and improve perioperative intestinal perfusion, although the data are somewhat conflicting. Numerous experimental and clinical studies have demonstrated that TEA protects against splanchnic hypoperfusion and reduces postoperative ileus. However, similar benefits are not seen with lumbar epidural anesthesia. Renal/Genitourinary EffectsBecause renal blood flow (RBF) is maintained through autoregulation, epidural anesthesia has little effect on renal function in healthy individuals. Compensatory and feedback mechanisms (afferent arteriolar dilation and efferent arteriolar vasoconstriction) ensure constant RBF over a broad range of pressures (50–150 mHg). During transient periods of hypotension below 50 mm Hg, oxygen delivery to the kidneys is adequately
maintained. Neuroendocrine EffectsSurgical stress produces a variety of
changes in the host’s humoral and immune response. Increased protein catabolism and oxygen consumption are common. Increased plasma concentrations of catecholamines, vasopressin, growth hormone, renin, angiotensin, cortisol, glucose, antidiuretic hormone, and thyroid-stimulating hormone have been documented after sympathetic stimulation associated with both minimally invasive and major open surgery. Perioperative manifestations of the surgical stress response may include HTN, tachycardia,
hyperglycemia, suppressed immune function, and altered renal function. Increased catecholamine levels can also cause increased left ventricular afterload and, in combination with other pathologic responses to stress (eg, proinflammatory responses that may lead to plaque instability via activation of matrix metalloproteinase; raised corticotropin-releasing hormone levels that reduce cardiac nitric oxide release, increase endothelin production, and aggravate coronary endothelial dysfunction),
trigger acute coronary syndromes and myocardial infarctions in patients with coexisting cardiac disease. Afferent sensory information from the surgical site is thought to play a pivotal role in this response. ThermoregulationHypothermia has significant side effects, such as increased cardiac morbidity, impaired coagulation, increased blood loss, and increased risk for infection. The rate and severity of hypothermia associated with epidural anesthesia is similar to that observed during cases under GA. Hypothermia associated with neuraxial anesthesia is primarily due to peripheral vasodilation resulting in heat redistribution from the core to the periphery. In addition, reduced heat production (due to reduced metabolic activity) results in a negative heat balance due to unchanged heat loss. Finally, thermoregulatory control is impaired. Of note, rewarming with forced air warming devices occurs more rapidly with neuraxial anesthesia as compared to GA due to peripheral vasodilation. Coagulation SystemThe postoperative period is a marked hypercoagulable state. Neuraxial block is associated with a decreased risk of DVT and pulmonary embolism, as well as a decreased risk of arterial and venous thrombosis. PHARMACOLOGY OF EPIDURAL blockAn understanding of the physiology of nerve conduction and the pharmacology of LAs is essential for successful epidural block. Potency and
duration of LAs, preferential block of sensory and motor fibers, and the anticipated duration of surgery or need for postoperative analgesia are factors that should be considered before initiating epidural block. This section covers several practical aspects of attaining effective epidural anesthesia and analgesia. Choice of Local AnestheticsDrugs used for epidural block can be categorized into short-, intermediate-, and long-acting LAs. Onset of epidural block in the dermatomes immediately surrounding the site of injection can usually be detected within 5 or 10 minutes, if not sooner. The time to peak effect varies with the type of LA and the dose/volume administered (Table 19). TABLE 19. Commonly used local anesthetics for epidural anesthesia and analgesia.
The shortest-acting LA for neuraxial block is chloroprocaine, an ester. In the past, chloroprocaine was associated with adhesive arachnoiditis when large volumes were accidentally administered into the subarachnoid space. In addition, severe back pain was not uncommonly reported when large volumes were administered in the epidural space, most likely due to the ethylenediaminetetraacetic acid (EDTA) and bisulfite preservatives in the solution. Since 1996, preservative-free chloroprocaine has been available and has not been associated with either neurotoxic effects or back pain. In ambulatory settings and for emergency cesarean deliveries with in situ epidurals, chloroprocaine can provide excellent surgical anesthesia quickly, without delaying recovery room discharge. Delivered via the epidural route, 2% lidocaine is an intermediate-acting LA commonly used for surgical anesthesia. When epinephrine is added to the solution (1:200,000), it prolongs the duration of action by up to 60%. Long-acting LAs used for epidural block are bupivacaine, levobupivacaine (no longer available in the United States), and ropivacaine. Dilute concentrations (eg, 0.1% to 0.25%) can be used for analgesia, while higher concentrations (eg, 0.5%) may be more appropriate for surgical anesthesia. The addition of epinephrine to these solutions can prolong the duration of action, although this effect is less reliable with long- versus intermediateacting agents. Severe cardiotoxic reactions (hypotension, atrioventricular nerve block, ventricular fibrillation, and torsades de pointes) refractory to usual resuscitation methods can result from accidental intravascular injection of bupivacaine. The rationale for the resistance to resuscitative measures lies in its high degree of protein binding and more pronounced effect on cardiac sodium channel block. Levobupivacaine, the S-enantiomer of bupivacaine, has a similar profile to bupivacaine but with lesspronounced cardiotoxic effects. Ropivacaine, a mepivacaine analogue, has a similar profile of action to bupivacaine. In most studies, ropivacaine has demonstrated a slightly shorter duration of action than bupivacaine, potentially with a less-dense motor nerve block at equipotent doses. A deterrent to the broader use of ropivacaine in clinical practice is its higher cost. Onset and Duration of Local AnestheticsAlkalinization of the LAs, which are marketed
in a water-soluble, ionized state, hastens onset. By increasing the concentration of the nonionized form, more lipid-soluble LA is available to penetrate the neural sheath and nerve membrane. Adding sodium bicarbonate immediately before injection of lidocaine, mepivacaine, or chloroprocaine produces a clinically significant faster onset of anesthesia and may also contribute to a denser nerve block. However, ropivacaine and bupivacaine will precipitate with the addition of bicarbonate unless a
very low concentration is used. Combining short- and long-acting drugs for rapid onset and a prolonged sensory nerve block has not been proven to be effective. For example, mixing 2-chloroprocaine with bupivacaine for the rapid onset of the former and long duration of the latter results in shortening the duration and effectiveness of the bupivacaine.160 Continuous drug administration and the use of additives obviate the need for mixing LAs. NYSORA Tips Combining
short- and intermediate- or long-acting LAs for rapid onset with prolonged duration of action has not been proven to be effective. Continuous drug Adding epinephrine to certain LAs can increase the duration of action, most likely by decreasing vascular absorption. The effect is greatest with 2-chloroprocaine, lidocaine, and mepivacaine and is less effective with the longer-acting agents. Other vasoconstrictors, such as phenylephrine, have not been proven to be as effective in reducing the peak blood levels of LAs as epinephrine. Adjuvants to Local Anesthetics in the Epidural SpaceA variety of other classes of drugs have been studied more recently to try to improve the quality of neuraxial block. In addition to several opioids (eg, fentanyl, sufentanil, and preparations of morphine); α-adrenergic agonists; cholinesterase inhibitors; semisynthetic opioid
agonist-antagonists; ketamine; and midazolam have been studied, with mixed results. The administration of clonidine in the epidural space has been studied extensively. An α2-adrenergic agonist, clonidine appears to prolong the duration of action of LAs, although the mechanism remains unclear. Animal studies have shown that clonidine reduces regional spinal cord blood flow, therefore slowing the rate of drug elimination. Kroin and colleagues demonstrated that the mechanism by which
clonidine prolongs the duration of a nerve block when mixed with LAs is not mediated by α-adrenoreceptors; rather, it is more likely related to the hyperpolarization-activated cation current Ih. 1. Prolongation and enhancement of the effects of epidural LAs without an additional risk of hypotension Side effects that are commonly associated with epidural clonidine include dose-independent hypotension, bradycardia, sedation, and dry mouth. Combining clonidine with other
agents, such as opioids, anticholinergics, opioid agonist-antagonists, and ketamine, may enhance the beneficial effects of these drugs while minimizing adverse side effects. Other Factors Affecting Epidural block Injection SiteThe epidural block is most effective when the nerve block or the catheter is inserted in a location that corresponds to the dermatomes covered by the surgical incision. The most rapid onset and the densest nerve block occur at the site of injection. By inserting the catheter closer to the dermatomal distribution of the surgical site, a lower dose of drug can be given,
thereby reducing side effects. This concept is especially important when thoracic epidural analgesia is used for postoperative analgesia. Dose, Volume, and Concentration TABLE 20. Redosing local anesthetics.
Patient Positioning Patient Characteristics: Age, Weight, Height, and Pregnancy Intermittent Versus Continuous Epidural Nerve Block EPIDURAL TECHNIQUESeveral factors influence the success of epidural block, including the clinician’s experience and knowledge of anatomy, patient preparation and positioning, the level of epidural catheter insertion, and the technique used to initiate the procedure. Patient EvaluationAs in the case with any anesthetic, the risks and benefits of epidural placement should be discussed with the
patient in a manner consistent with informed consent. Any concerns and questions should be addressed prior to the administration of premedication. When a language barrier exists, trained interpreters or telephone translation services should be utilized. The patient’s medical history and active medication list should be reviewed prior to the initiation of epidural block, with particular emphasis on the presence of conditions that may predispose the patient to serious complications. Drug
therapy that influences the patient’s clotting function or physiologic response to block of the sympathetic preganglionic fibers should be taken into consideration, including when the last dose was administered. The patient’s last oral intake should also be documented. For those patients receiving epidural block as the sole anesthetic or as an adjuvant to GA for elective surgical procedures, the ASA guidelines for nothing by mouth should be enforced. Patients with medical conditions that worsen
with reduced afterload or preload (eg, severe AS, mitral stenosis, hypertrophic cardiomyopathy) and patients who may experience worsening shortness of breath, such as those with restrictive lung disease or severe COPD, may require additional testing. Clinical conditions that predispose patients to neuraxial infections, such as immunosuppression, DM, pancreatitis, and alcohol or drug abuse, may require further evaluation or laboratory studies. Preexisting neurologic deficits or CNS disorders
should be assessed and documented. History of sensitivity or adverse reaction to opioids or LAs and complications related to prior epidural procedures require further investigation. NYSORA Tips • Routine laboratory studies are not required for initiation of epidural block in healthy patients for routine procedures. PreparationA large-bore intravenous catheter for fluid or emergency drug administration must be secured prior to initiation of epidural block. Fluid preloading is not required and may be harmful in certain subsets of patients with decreased serum colloid oncotic pressure (eg, those with burns, preeclamptic
patients). TABLE 21. Emergency equipment and drugs for initiation of neuraxial block.
Communication With Surgical StaffA discussion with the surgical staff regarding the operative approach, the desired positioning of the patient, the estimated length of the surgical procedure, the anesthetic or analgesic goals of the block, and postoperative analgesic requirements can help to determine whether a continuous epidural, a single-shot epidural, or a CSE is preferable. The surgical staff can also share information about the patient that is
not readily available in the chart or immediately apparent during the preoperative interview. EquipmentCommercially prepared, sterile, disposable epidural trays are available from several manufacturers. A standard kit typically includes the following: a sterile drape; prep swabs; 4 × 4 gauze sponges; a paper towel; povidone-iodine solution; an ampoule of 0.9% preservative-free sodium chloride; a 5-mL ampoule of 1.5% lidocaine with epinephrine 1:200,000; a 5-mL ampoule of 1% lidocaine for skin infiltration; a filtering device (needle or straw); a bacterial filter; needles and syringes of
various sizes; a styletted epidural needle with cm markings; a 5- or 10-mL glass or plastic LOR syringe (either Luer lock or Luer slip); a catheter connector securing device; an epidural catheter with centimeter gradations and a connector/adapter; a thread assist device (TAD); a needle guard for sharps disposal; and labels. Figure 14. Epidural needles: bevel and wing configuration. Epidural needles with a back-eye opening for exit of a spinal needle (for CSEs) and double-lumen needles with separate openings for the spinal needle
and catheter are also available. Figure 15. Single end-hole wire-reinforced catheter. (Used with permission from Epimed International.) Many commercially available nylon and wire-reinforced catheters are manufactured in both single end-hole and multiorifice versions (Figure 16). A lack of robust data precludes a full assessment of whether clinical outcomes, such as the incidence of paresthesias, epidural vein cannulation, intrathecal migration, and adequate analgesia, are improved with the uniport or multiport design. However, a 2009 prospective, single-blind, randomized controlled trial by Spiegel et al investigated the success of labor analgesia, the number of episodes of breakthrough pain requiring supplemental medicine, and the occurrence of complications, such as paresthesias and intravascular and intrathecal catheter placement, in 493 parturients who received either a single end-hole, wire-reinforced polyurethane catheter or a multiorifice, wire-reinforced nylon catheter. The authors found no statistically significant difference in outcomes between the two groups and postulated that the flexibility afforded by the wire coil may eliminate any of the potential advantages of the multiport design. Figure 16. Multi-orifice wire-reinforced catheter. (Used with permission from Epimed International.) NYSORA Tips • The use of wire-reinforced epidural catheters appears to reduce the incidence of complications associated with epidural techniques, including epidural vein cannulation, paresthesias, and inadequate analgesia. Additional equipment that may be needed for initiation of epidural procedures includes 0.5% chlorhexidine with ethanol (Hydrex®) or 2% chlorhexidine with 70% isopropyl alcohol (ChloraPrep®), which is not supplied in epidural trays; a transparent sterile, occlusive dressing for the puncture site; and tape to secure the catheter. To minimize the remote risk of chemical arachnoiditis, the skin disinfection solution should not make contact with the epidural drugs or equipment and should be given adequate time to dry. Usually a large clear dressing (eg, Tegaderm”) and adhesive tape are sufficient to prevent catheter dislodgement and to keep the epidural insertion site visible and clean. A sterile pen to label medications and a 25- or 27-gauge spinal needle (for CSEs) can be dropped onto the sterile field. NYSORA Tips • A clear sterile occlusive dressing is recommended to prevent catheter dislodgement. Analgesia and Sedation During Nerve Block InitiationAnalgesia or sedation can be provided to improve patient comfort during neuraxial block. However, there is emerging evidence that intravenous sedatives may increase pain perception in an agent-type- and pain-type-specific manner.
Light sedation with a benzodiazepine (most commonly midazolam) or a short-acting opioid prior to epidural placement is usually sufficient. This may also be appropriate for obstetric patients. In a small, double-blind randomized study, Frölich and colleagues found that maternal analgesia and sedation with fentanyl and midazolam prior to spinal placement was not associated with adverse neonatal effects. Importantly, mothers in both the group that received premedication and the control group showed
no difference in their ability to recall the births of their babies. NYSORA Tips The following tips may serve to reduce pain on injection of LA for skin infiltration: Patient PositioningOptimal patient positioning is essential for successful epidural placement. Depending on the patient’s medical status (eg, body habitus and ability to cooperate), the planned procedure, the anesthesia provider’s experience, the baricity of the intrathecal solution (for CSE placement), and several other factors, the sitting, lateral decubitus,
jackknife, or prone position can be used. Sitting Position TABLE 22. Advantages of sitting position for initiation of neuraxial block.
If the sitting position is chosen, the patient should be assisted to sit on the operating room table or bed with the backs of the knees touching the edge of the bed and the feet resting on a stool or hanging over the bed. The patient should relax the shoulders and curve the back out toward the clinician, assuming a “slouched” or “mad-cat” position. It is useful to have an assistant stand in front of the patient and help the patient attain maximal spinal flexion (Figure 17). Flexing the neck should help to flex the lower spine and open the vertebral spaces (Figure 18). Asking the patient to hug a pillow may also help with positioning. Figure 17. A, B: Epidural placement in the sitting position with assistant helping to position the patient. Figure 18. Flexion versus extension during epidural placement. Lateral Decubitus Position TABLE 23.
In the lateral decubitus position, the patient’s back should be fully aligned with the edge of the table or bed (Figure 19). Figure 19. Epidural placement in the lateral position. The left lateral recumbent position may be preferable for righthanded physicians and may provide improved hemodynamic stability for parturients. The coronal plane of the patient should be perpendicular to the floor, with the tips of the spinous processes pointing toward the wall. The thighs should be flexed toward the abdomen and the knees drawn to the chest; the neck should be in a neutral position or flexed so that the chin rests on the chest. Asking the patient to “assume the fetal position” may help maximally flex the spine. The hips should be aligned one above the other, and the nondependent arm should extend toward and rest on the nondependent hip. The patient’s head may need to be elevated with a pillow to avoid rotation of the spine. Obese patients or those with larger hips may require additional pillows to maintain proper alignment. Directing the needle toward an imaginary line that extends cephalad and caudad from the umbilicus may optimize chances of midline insertion, which is particularly important during initiation of CSEs (Table 24). The bevel of the epidural needle is directed toward the patient’s head. TABLE 24. Tips for attaining optimal lateral position.
Infection ControlAdherence to strict aseptic techniques is essential during initiation and maintenance of neuraxial block. The ASA Task Force on Infectious Complications Associated With Neuraxial Techniques advises the following measures: remove jewelry on fingers and wrists; use careful hand washing before gloving; use caps, masks (changed with each new patient encounter), and sterile gloves; use chlorhexidine with alcohol for skin
preparation; drape the patient under sterile conditions; and cover the catheter insertion site with a sterile occlusive dressing. A single application of chlorhexidine with alcohol appears as efficacious as two applications for skin disinfection. When chlorhexidine, which is not supplied in epidural kits, is not available, the use of povidone-iodine with alcohol is preferable to povidone-iodine alone. All antiseptic solutions are considered neurotoxic if they come into direct contact with
the meninges; care should be taken to keep needles and drugs in the epidural tray separate from the skin disinfectants. Bacterial filters may be helpful for patients with chronic or extended continuous epidural infusions, but there are no data to support that they decrease the incidence of catheter-related infections. The catheter should TABLE 25. Aseptic technique during epidural block initiation and maintenance.
Techniques to Identify the Epidural SpaceThree techniques can be used to identify the epidural space: LOR, hanging drop, and ultrasonography. Despite increasing interest in ultrasound-assisted neuraxial procedures, the LOR technique, which relies on the different tissue densities as the needle passes through ligaments into the epidural space, is the most commonly used technique. Both LOR to fluid, with or without an air bubble, and air are recognized
as acceptable means of identifying the epidural space. Randomized trials comparing saline to air for LOR have suggested that saline is superior. However, these trials may overstate the difference between the two media by forcing the anesthesia provider to use a less-preferred technique. Regardless of which technique is used during routine epidural placement, it is important to bear in mind that LOR to air is not recommended for EBP procedures. Loss of Resistance to Air TABLE 26. Complications associated with loss of resistance to air.
The incidence of PDPH and the onset of symptoms may also be higher when the LOR to air technique is used to identify the epidural space. In addition, the LOR to air technique has been associated with a higher incidence of unblocked segments or patchy pain relief and neurologic deficits related to compression of nerve roots or the spinal cord by air bubbles. Venous air embolism (VAE) in the presence of tears in the epidural venous plexus or if the pressure from
the air source is higher than the venous pressure has been reported. Finally, both an increased incidence of epidural venous cannulation and difficult catheter insertion have been associated with LOR to air, particularly in the absence of fluid predistension of the epidural space, although the data are conflicting. To identify the epidural space with the LOR to air technique, advance the needle slowly, exerting either continuous or intermittent pressure on the LOR syringe. As the needle enters the ligamentum flavum, there is usually a distinct sensation of increased resistance followed by a subtle “give” when light pressure is exerted on the plunger. Avoid injecting air on identifying the epidural space due to concerns for pneumocephalus (in the event of ADP) and patchy, inadequate analgesia. Loss of Resistance to Saline With or Without an Air Bubble The Hanging Drop Technique Ultrasonography Technique of Epidural blockThere are four common approaches to the epidural space: midline, paramedian, Taylor (modified paramedian), and caudal. Clinical expertise in each of these techniques gives the anesthesiologist more flexibility when performing epidural block. For all approaches, monitors should be in place and the skin should be prepped and draped in a sterile fashion before initiation of the procedure. Emergency equipment and medication must be immediately available. Sedation may be used, as appropriate. In general, the epidural needle bevel should be facing cephalad regardless of the approach used to access the epidural space unless an intentional unilateral nerve block is desired (eg, for lower extremity orthopedic procedures performed under CSE). Midline Approach Figure 20. Epidural needle engaged in midline ligament. NYSORA Tips • The epidural needle advances through skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, and ligamentum flavum before reaching the epidural space. Determining which ligaments are traversed is an acquired skill. The interspinous ligament may feel “gritty” against the advancing needle, while the ligamentum flavum offers more resistance. However, midline gaps in the ligamentum flavum are not uncommon, and obstetric patients may have softer ligaments. The depth from the skin to the ligamentum flavum generally ranges from 4 to 6 cm in normal-size adults, although there is a great deal of variability. After the ligaments are penetrated, it is no longer advisable to change the direction of the needle tip without withdrawing the needle several centimeters or to the skin level. The stylet should be placed in the epidural needle while redirecting to avoid the accumulation of bony debris or soft tissue plugs that may hinder the flow of CSF in the event of an ADP. 5. Remove the stylet from the epidural needle and attach the LOR syringe with air or saline (with or without an air bubble) firmly to the hub of the needle. Glass or lowresistance plastic LOR syringes are appropriate. Care should be taken to ensure that glass syringes are not “sticky.” Multiple hand positions are appropriate to advance the epidural needle into the epidural space: The back of the nondominant hand can rest firmly on the patient’s back, with the thumb and forefinger grasping the needle shaft, while pressure is exerted on the LOR plunger either continuously or intermittently by the thumb of the dominant hand. The nondominant hand can rest on the patient’s back with the thumb and forefinger extending to and stabilizing the needle hub, while the thumb of the dominant hand applies pressure (Figure 21). Or, the middle through fourth or fifth fingers of the nondominant hands can rest on the back, with both thumbs and forefingers grasping the wings of the epidural needle and the dominant hand intermittently releasing its position and exerting pressure on the LOR syringe plunger (Figure 22). Figure 21. Advancing epidural needle: nondominant hand on patient’s back with thumb and forefinger on needle hub. Figure 22. Advancing epidural needle: thumbs and index fingers grasping wings. As the needle enters the epidural space, the plunger of the LOR syringe suddenly “gives.” Avoid injecting the full contents of the syringe, particularly with LOR to air, if possible. For continuous epidurals, a small volume of saline can be injected into the epidural space to dilate the space, thereby reducing the risk of epidural vein cannulation and facilitating catheter
insertion. Note the depth of the needle at the skin. The marking on the needle at the skin represents the depth from the skin to the epidural space. Because the centimeter markings are not numbered, it may help to count the number of centimeter markings between the skin and the epidural needle hub and subtract that number from the length of the needle. For example, if 4 markings remain visible between the skin and the needle hub, subtract 4 from 9 (the common length of an epidural needle) to
determine that the depth to epidural space is 5 cm. Figure 23. Inserting the epidural catheter. NYSORA Tips• An easy way to measure depth to epidural space when using the LOR technique is to count the number of centimeter markings that are visible between the skin and the needle hub. Subtract that number from the length of the needle. For example, most epidural needles are 9 cm in length. If 4 centimeter markings are visible after epidural space identification, subtract 4 from 9 to conclude that the depth to space is 5 cm. The epidural catheter should be inserted no more than 5 or 6 cm beyond that distance (ie, taped at 10–11 cm at the skin). For the less-common single-shot epidural technique, the LA may be administered directly through the needle in divided doses over several minutes. This technique, however, requires that the patient remain immobile during dosing and may result in painful pressure with large volumes. For the continuous catheter technique, administering LA through the needle is not recommended, as correct catheter placement cannot be verified. A clear occlusive dressing should be applied over the insertion site to allow inspection of the catheter. The catheter should be secured to the patient’s back with the connector at the patient’s shoulder. Using clear tape has the advantage of permitting the practitioner to visualize the proximal and distal “flashback” windows of the catheter prior to administering boluses of LA. Paramedian Approach Figure 24. Paramedian epidural technique. Taylor
Approach Caudal
Approach Figure 25. Caudal approach for epidural catheter placement. If fluoroscopy is not used, there are two methods to identify the hiatus:(1) The sacral hiatus lies at the apex of an equilateral triangle connecting the posterior superior iliac spines and pointing caudad. (2) The bony protuberances (the sacral cornua) that surround the sacral hiatus can be palpated by applying firm pressure with the index finger as it moves cephalad from the coccyx. 5. After LOR is encountered, advance the needle slightly into the caudal canal. Advancing too far may lead to ADP or unintended intravascular injection or epidural vein cannulation during catheter placement. If LOR is equivocal, several milliliters of saline can be
injected through the caudal needle while palpating the skin overlying the sacrum. The needle is likely positioned correctly if a skin bulge does not develop. Cervical Epidural blockSingle-shot or continuous cervical epidural techniques are used for a variety of surgical and pain procedures, including carotid endarterectomy,
thyroidectomy, and chronic neck pain conditions. Both the midline and paramedian approaches are used to perform cervical procedures, although fluoroscopic guidance is becoming increasingly common. Cervical epidural block can be initiated in the prone, lateral, or sitting position. The prone position is used most commonly for fluoroscopic-assisted procedures, although the sitting position can be used. Whichever position is used, flexion of the neck serves to increase the distance from the
ligamentum flavum to the dura mater, increasing the margin of safety for these procedures, and to expand the interlaminar space. Initiation and Management of Epidural blockTest Dose Dosing Regimen Top-Up Dosing Problem SolvingEpidural placement presents unique challenges that are directly related to practitioner experience, the clinical scenario, and patient characteristics, among other things. Most of these problems can be overcome if the clinician recognizes the problem, is familiar with vertebral column anatomy, and knows how to make adjustments in technique (Table 27). TABLE 27. Problem solving during initiation of epidural block.
Difficulty Identifying the Epidural Space If resistance is met, continue injecting the saline into the soft tissue and then resume the original LOR technique. Often, the familiar feedback from the LOR syringe returns after saline has dissipated throughout the soft tissue planes. Paresthesias During Epidural Needle or Catheter Placement Accidental Dural Puncture Difficulty Threading the Catheter Unilateral Nerve Block Blood in the Epidural Needle or Catheter Pain Despite Adequate Nerve Block Height and Density Inadequate Analgesia Despite Fully Dosed Epidural Catheter Dissipating Nerve Block Requiring Larger Doses Failed Epidural Analgesia Difficulty Removing the Epidural Catheter COMPLICATIONS AND COMMON SIDE EFFECTSComplications of epidural block can be classified broadly as either drug or procedure related. Potential drug-related complications include LAST, allergy to LAs, direct LA-induced nervous tissue injury, and drug or mode of delivery errors. Procedure-related complications may be mild to moderate or transient, such as back pain, pneumocephalus, and PDPH. Potentially life-threatening complications include subdural injection of LAs, total or high spinal, infectious or aseptic meningitis, cardiac arrest, SEA, epidural hematoma formation, and permanent neurologic injuries. In contrast to complications, several known or expected side effects accompany initiation and maintenance of epidural block without adversely affecting long-term patient outcomes. This section reviews both the complications and the common side effects associated with epidural block, with emphasis on risk factors, preventive measures, and treatment. Several of the complications are covered in greater detail elsewhere in this textbook. Local Anesthetic Systemic ToxicityLocal anesthetic systemic toxicity results from excessive plasma concentration in the blood due to unintentional intravascular injection or, less commonly, systemic absorption from the injection site. Direct intravascular injection can occur with unintentional epidural vein cannulation during catheter placement or subsequent catheter migration into a vessel. Risk factors for intravascular cannulation include trauma to the epidural vessels during nerve block initiation, the use of stiff catheters, pregnancy, and patient positioning during epidural placement, among others (Table 28). TABLE 28. Risk factors for epidural vein cannulation.
The risk of epidural vein cannulation in obstetric patients may be reduced with initiation of epidural block in the lateral position, the use of wire-reinforced catheters, the use of a single end-hole (versus multiorifice) catheters, fluid predistention with normal saline prior to threading the catheter, and limiting the depth of catheter to 6 cm or less (Table 29). Limiting the number of attempts at epidural placement; avoiding the lateral epidural space, where vessel puncture is more likely; and avoiding direct administration of LAs through the epidural needle may also reduce the risk of direct intravascular injection. TABLE 29. Strategies to avoid epidural vein cannulation.
Although the data are inconclusive regarding the role of catheter material and tip configuration, the use of flexible catheters may reduce the risk of subsequent catheter migration into a vessel. Because of preferential efflux from the proximal port of multiport catheters during continuous infusion techniques, there remains a remote possibility that a distal port may migrate into a vessel unnoticed until a manual bolus is administered. This can be avoided with
the use of a single-orifice catheter.
TABLE 30. Relative order of peak plasma concentration of local anesthetic associated with regional anesthesia (descending order).
However, trauma to the vessels during initiation of the epidural procedure may lead to more rapid intravascular absorption from the epidural space than anticipated. The addition of epinephrine to the LA solution diminishes systemic absorption but may not be appropriate in highly vascular areas, where systemic absorption is likely, or for all patient populations. Epinephrine may also unnecessarily prolong the duration of action of LAs. Toxicity associated
with systemic absorption of LAs can be reduced by careful patient selection, remaining vigilant for signs and symptoms of toxicity, limiting the total dose of LA administered, use of appropriate LA concentrations, and, possibly, by using the newer amide LAs, such as ropivacaine and levobupivacaine. TABLE 31. Signs and symptoms of local anesthatic systemic toxicity.
Allergy to Local AnestheticsTrue allergic reactions to LAs can occur, but fortunately are rare. Most documented reactions are not mediated by immunoglobulin E (IgE) and can be attributed to reactions to other agents administered concomitantly (eg, additives, epinephrine, preservatives, antibiotics) or to a delayed type IV hypersensitivity reaction (ie, mild contact dermatitis). Alternatively, reported reactions may be due to anxiety, a vasovagal
episode, endogenous sympathetic stimulation, or an adverse patient response to the surgical, dental, ophthalmic, or obstetric procedure itself. ArachnoiditisArachnoiditis is a rare disorder marked by inflammatory changes in the arachnoid mater. Although the precise mechanism remains unclear, fibrosis develops and adhesions form between the nerve roots and the membranes that surround the brain, spinal cord, and cauda equina. In chronic, adhesive cases, collagen deposits ultimately encapsulate the nerve roots, creating nerve root atrophy as a result of an interruption to the blood supply. Trauma, surgery,
infections, contaminants, disinfectants, contrast media, tumors, subarachnoid hemorrhage, and the subarachnoid administration of irritants (eg, steroids) can precipitate these inflammatory changes. Accidental intrathecal administration of large volumes of chloroprocaine containing the preservative sodium bisulfite has also been linked to arachnoiditis, although the role of the preservative has been called into question in recent studies. TABLE 32. Clinical presentation of arachnoiditis.
Unfortunately, significant neurologic improvement is unlikely with current therapies, including intravenous corticosteroids, NSAIDs, and antibiotic therapy. Deficits may progress to severe and permanent disability. BackacheBack pain is a common postoperative complaint, with an incidence that ranges from 3% to 31% after nonobstetric surgery, regardless of the anesthetic technique. Although the etiology is multifactorial, both postoperative and
peripartum back pain are often attributed to neuraxial techniques when a temporal association exists. Postdural Puncture HeadachePostdural
puncture headache is a common complication of spinal anesthesia, lumbar punctures (“spinal taps”), and epidural procedures complicated by ADP or unrecognized dural tear. The incidence of ADP is generally accepted to be at or below 1%; up to 80% of patients may experience PDPH following ADP. Although the precise mechanism remains poorly understood, signs and symptoms of PDPH appear to result from CSF leakage through the dural hole. In the upright position, the brain tissue sags in the
cranial vault, creating painful traction on the dura, falx cerebri, cerebral blood vessels, tentorium, cranial nerves, and nerve roots. This traction also contributes to the cranial nerve palsies that are not uncommonly seen in patients with PDPH. Compensatory cerebral vasodilation in response to the decrease in CSF also appears to play a role in the genesis and severity of PDPH. TABLE 33. Signs and symptoms of postdural puncture headache.
PDPH typically resolves spontaneously within 1 to 2 weeks but may last months or even years; a substantial percentage of patients may develop chronic headaches after ADP with a largebore Tuohy needle. Risk factors for PDPH include younger age, female gender, lower BMI, pregnancy, pushing during the second stage of labor, the use of cutting versus atraumatic spinal needles, and the use of larger-gauge needles (Table 34). There is lesscompelling evidence regarding the role of needle bevel orientation, the number of dural punctures, the approach used to enter the epidural space (paramedian vs. midline), patient positioning during initiation of the epidural procedure, and the technique used to identify the epidural space (LOR to air versus saline with or without an air bubble). TABLE 34. Risk factors for postdural puncture headache.
Several interventions for the prevention or treatment of PDPH have been proposed. There appears to be little benefit from conservative measures, such as bed rest and aggressive fluid administration. However, symptomatic relief may be obtained with analgesics, pharmacologic agents with vasoconstricting properties (caffeine, theophylline, sumatriptan), and, possibly, corticotropin (ACTH). In a quantitative systematic review of available evidence for measures to
prevent PDPH, Apfel et al found that the administration of epidural morphine prior to removal of the catheter may confer some advantage, but this conclusion was based on one small randomized controlled trial. In a recent meta-analysis, Heesen et al. suggested that insertion of an intrathecal catheter following ADP may protect against PDPH and may reduce the need for an EBP, but additional studies are warranted. The evidence to date regarding the routine use of prophylactic EBP is not conclusive.
There are limited data to support epidural patching with normal saline, dextran 40, and gelatin and fibrin glue. Prior to performing an EBP, other causes of headache, such as preeclampsia/eclampsia and meningitis, should be ruled out. In certain clinical scenarios, it may also be necessary to rule out elevated ICP. Using sterile techniques, the epidural space at or below the level of prior ADP is identified using LOR to normal saline. The air bubble is omitted due to the concern that air may enter the dural breach, leading to pneumocephalus. Up to 20 mL of the patient’s blood (drawn aseptically) is slowly injected into the space; the clinician should stop injecting blood if the patient experiences moderate-to-severe pain or pressure in the lower back or neck region. Although the optimal volume of blood remains to be determined, injection of more than 20 mL appears to confer no additional benefit. The patient typically remains supine for at least 1 hour after the EBP. Back pain and, less frequently, neck pain are commonly experienced during the procedure and, when severe, may alert the clinician to stop injecting blood. To minimize the risk of infections and related sequelae, both the acquisition of autologous blood and identification of the epidural space should be performed using strict aseptic techniques. For a more in-depth discussion of PDPH, refer to Postdural Puncture Headache. Subdural InjectionThe subdural space has been described historically as a potential space between the normally closely adherent arachnoid mater and the overlying dura mater,
although it may represent a cleft along the dural border cell layer that results only from direct tissue damage. Injection of a small dose of LA into the area can have profound hemodynamic and sympatholytic effects. TABLE 35. Clinical presentation of a subdural nerve block.
Total Spinal AnesthesiaTotal spinal block, which complicates an estimated 1 in 1400 attempted epidural procedures may result from unrecognized ADP with unintentional injection of an epidural dose of LA, the administration of a large dose of LA into the subdural compartment, and undetected migration of the epidural catheter tip into the subarachnoid space. It has also been observed when one hole of a multiorifice catheter is lodged in the subarachnoid space; with translocation of LA through an accidental or intentional dural breach; after CSE techniques; and after a failed epidural block is replaced with a spinal technique. Total spinal anesthesia usually develops within minutes of LA administration, although it may occur unexpectedly later with changes in patient positioning or after a previously functioning epidural catheter has migrated into the subarachnoid space. During total spinal block, the LA spreads high enough to
nerve block the entire spinal cord and, occasionally, the brainstem. Ascending sensory and motor changes develop rapidly, followed by profound hypotension, bradycardia, dyspnea, and difficulty phonating and swallowing. Unconsciousness and apnea may result from direct LA action on the brainstem, respiratory muscle paralysis, and cerebral hypoperfusion. Treatment includes airway support and, if necessary, endotracheal intubation; the administration of 100% oxygen; and hemodynamic support with
intravenous fluids and vasopressors. Epinephrine should be used early and in escalating doses to stabilize the heart rate and blood pressure in unstable patients. As the nerve block recedes, the patient will regain consciousness and control of breathing followed by recovery of motor and sensory function. The administration of sedation until the nerve block regresses may be appropriate once the patient is stable. Spinal Epidural AbscessSpinal epidural abscess is a rare disorder that affects elderly and immunocompromised patients disproportionately. Individuals with prolonged intensive care unit stays, intravenous drug users, and patients with bacteremia, DM, alcohol dependence, cancer, HIV, and end-stage renal disease are at increased risk compared with the general population (Table 36). In recent decades, the incidence of SEA has increased, in part due to the increase in spinal instrumentation, the rise of illicit drug use, and the aging population. TABLE 36. Predisposing conditions for spinal epidural abscess.
An estimated 5% of SEAs are associated with epidural procedures. Risk factors for this rare complication include extended epidural catheter infusions and localized or systemic infection at the time of initiation of the nerve block. The site of epidural placement also appears to place some patients at higher risk for SEA formation, with thoracic and lumbar catheters implicated more often than cervical catheters. Poor adherence to sterile technique and, possibly,
multiple attempts at epidural placement may place patients at additional risk. Early diagnosis, prompt treatment, and consistent follow-up are essential to avoid irreversible neurologic
damage from SEA. The most common clinical symptoms are back pain, fever, and neurologic changes, such as leg weakness or sensory deficits, but a majority of patients do not present with this triad. Instead, patients may present with bladder dysfunction, sepsis, meningitis, paraplegia or quadriplegia, urinary tract infection (UTI), mental status changes, inflammation at the catheter site, headache, neck stiffness, or nausea and vomiting. Symptoms most commonly present within 7 days but may
be delayed for 60 days or more. Elevated white blood cell (WBC) count and elevated erythrocyte sedimentation rate (ESR) or C-reactive protein may also be present, but these laboratory findings are nonspecific. If SEA is suspected, gadolinium-enhanced MRI is the diagnostic tool of choice. Some investigators have proposed that MRI scanning be considered in patients who have received epidural catheters if systemic and local signs of infection (eg, pus or erythema at the epidural insertion site)
develop, even in the absence of neurologic deficits. MeningitisBacterial
meningitis following epidural anesthesia is a rare event. Microorganisms can be transmitted via syringes, catheters, needles, infusion tubing, and medications injected into the epidural space, as well as from the clinician or patient. Similar infectious complications can occur with nonanesthetic procedures, such as EBP, myelography, epidural steroid injection, and diagnostic lumbar puncture. Most cases appear to be caused by contamination of the puncture site by organisms from the naso- or
oropharynx of the health care provider. Less commonly, contaminants from incompletely sterilized skin and direct or hematogenous spread from an endogenous infectious site are implicated. A dural puncture, such as in the setting of a CSE, spinal, or an ADP, is believed to place patients at higher risk by allowing transfer of blood-borne pathogens across the blood-brain barrier. However, the incidence of bacterial meningitis remains low despite the increasing use of CSE and spinal techniques.
Also, diagnostic lumbar puncture in the setting of bacteremia is rarely associated with meningitis. Additional risk factors include breaches in aseptic technique, reinsertion of the stylet that has been exposed to ambient air, difficulty performing the neuraxial procedure, and, relatedly, multiple attempts at spinal or epidural placement. TABLE 37. Signs and symptoms of bacterial meningitis.
Symptoms usually present within 6 to 36 hours after the anesthetic procedure. Because the initial clinical presentation is similar to that of a PDPH, the diagnosis of meningitis can be delayed. Meningitis can be distinguished from PDPH by the presence of a fever, mental status changes (ie, lethargy and confusion), and a headache that is not positional in nature. The diagnosis is confirmed with CSF analysis and culture with or without prior head CT. The CSF is often cloudy, with leukocytosis (predominantly neutrophils), elevated protein content, and low glucose concentration. Early diagnosis is essential. Common pathogens include Streptococcus salivarius and other strains of viridans streptococci, S. aureus, P. aeruginosa, Neisseria meningitidis, and Enterococcus faecalis. In many cases, no organism is isolated. Treatment of bacterial meningitis includes immediate empiric broad-spectrum antibiotic therapy, such as vancomycin with a third-generation cephalosporin, ultimately tailored to blood or CSF culture results. Neurologic sequelae may include cranial nerve palsies, hemiparesis, quadriparesis, and aphasia. If diagnosis and treatment are delayed, death may result. Adherence to full aseptic precautions, including removal of jewelry, hand washing, appropriate skin preparation with individual packets of antiseptic solution (preferably chlorhexidine with alcohol), the use of a sterile drape and dressing, and, at a minimum, the use of caps, sterile gloves, and face masks (changed between each patient encounter), is critical to minimize the risk of bacterial meningitis associated with neuraxial instrumentation. Alternatives to neuraxial techniques should be offered to patients at high risk for infectious complications, and patients with known or suspected bacteremia should be started on antibiotic therapy prior to neuraxial instrumentation. Spinal Cord and Nerve Root InjuryNeurologic deficits can be caused by direct trauma to the spinal cord or spinal nerves, from spinal cord ischemia, from accidental injection of neurotoxic drugs or chemicals, or from hematomas or abscesses. Fortunately, serious neurologic injury is an extremely rare complication of neuraxial anesthesia, with an estimated incidence of 0.03%–0.1%. Horlocker and colleagues evaluated the records of over 4000 patients who had received lumbar epidurals for thoracic surgery while under GA and found no cases of neurologic complications. In another extensive review of 45,000 patients undergoing epidural placement, 40 cases of neurologic injuries were reported. Of note, 22 of these patients experienced paresthesias during the epidural procedure. There have been a few case reports of myelopathy and paraplegia occurring with thoracic epidurals placed in anesthetized patients, but these complications are exceedingly rare. Most peripheral neuropathies associated with neuraxial techniques resolve spontaneously. Those that become permanent are usually limited to persistent paresthesias and limited motor weakness. Cauda Equina SyndromeCauda equina syndrome (CES), a rare state of neurologic compromise due to lumbosacral root compression, is characterized by bowel and bladder dysfunction, low-back pain, perineal sensory loss and other patchy sensory deficits, unilateral or bilateral sciatica, and lower extremity motor weakness. It has been associated with trauma, infection, lithotomy position, and ischemic
compression by a hematoma, abscess, tumor, prolapsed intervertebral disk, or spondylolisthesis. CES has also been linked to direct neurotoxicity from large volumes or high concentrations of hyperbaric LAs in the sacral CSF. The nerve roots of the cauda equina have a poorly developed epineurium and limited blood flow and appear to be particularly susceptible to the pooling of LAs that may accompany continuous spinal infusions with microbore catheters, accidental intrathecal injection of large
doses of LA intended for epidural anesthesia, and repeat intrathecal injections after failed spinal nerve block. Cases of CES have also been reported after single-shot spinals. Epidural HematomaEpidural hematoma is a rare occurrence that can lead to cord compression, cord ischemia, or myelopathy similar to that caused by a space-occupying tumor. The incidence of hematoma associated with epidural block is estimated at 1:150,000, somewhat higher than that of spinal anesthetics (1:220,000). However, the incidence
varies dramatically with the patient population and may be significantly higher in a subset of patients with a less-compliant epidural space and a greater likelihood of coagulation disorders. Indeed, hemostatic abnormalities during either initiation of epidural block or removal of the epidural catheter are present in the majority of reported cases, although a large proportion of the documented cases also occur spontaneously, with no predisposing factors. Anterior Spinal Artery SyndromeAnterior spinal artery syndrome (ASAS) occurs most commonly in patients with vascular disease and concomitant decreased spinal blood flow due to obstruction, compression, or hypotension. However, it has also been described in the setting of acute thoracic disk herniation, spondylosis, arteriovenous malformation, and similar pathologic conditions that can disrupt the tenuous blood flow in the anterior spinal artery distribution. ASAS is the most common neurologic complication after abdominal aortic surgery but has also been reported after surgery on the thoracic spine. Massive blood loss and persistent hypotension induced by neuraxial anesthesia have been implicated in the intraoperative development of this potentially life-threatening syndrome. ASAS presents with immediate, painless paraplegia and loss of lower extremity sensory function. Proprioception and vibration sense are spared. Prognosis is poor, with permanent and disabling neurologic deficits. Correction of intraoperative hypotension is essential in patients at high risk for ASAS. Cardiac ArrestCardiac arrest resulting in death or brain damage is a rare complication of epidural block. Causes include unintentional total spinal anesthesia, LAST, myocardial ischemia, respiratory compromise, or any of several circulatory events that do not fall within these categories, such as complete block of the preganglionic cardiac accelerator fibers or vagal predominance in the setting of sympathetic block. Although the mechanism of increased vagal
tone has not been fully elucidated, block of the sympathetic efferents results in vasodilation and a decrease in venous return. Decreased preload, in turn, may enhance cardiac vagal tone. Bradycardia, reduced CO, and cardiac arrest may result and can be attributed in part to reflex activity. The paradoxical Bezold-Jarisch reflex, for example, triggers slowing of the heart rate in response to decreased ventricular volume to permit more time for complete filling of the heart. Side EffectsSeveral common side effects accompany epidural procedures, including transient fever in obstetric patients, nausea and vomiting, pruritus associated with neuraxial opioids, shivering, and urinary retention. Numerous studies have found an association between epidural labor analgesia and new-onset maternal intrapartum fever, although the relationship may not be causal. The increase in maternal temperature is often subclinical and self-limited and does not appear
to have an adverse effect on the fetus. TABLE 38. Treatment of hypotension following neuraxial block.
SUMMARYBoth the indications for neuraxial techniques and the patient population that is considered appropriate for these procedures have expanded over the past several decades. Epidural block is currently being advocated as an adjuvant to GA for cardiothoracic, major vascular, and other high-risk surgeries; as the sole anesthetic in surgeries that were previously performed exclusively under GA; and for acute and chronic pain management. Neuraxial
techniques are also increasingly being used in the ambulatory setting, where the decrease in PONV and improved pain relief permit earlier discharge; for a variety of diagnostic procedures; and to alleviate pain in adults and children in the end-of-life setting. This text is a sample of content from the Compendium of Regional Anesthesia on the NYSORA LMS. NYSORA’s Compendium of Regional Anesthesia is simply the most comprehensive, and practical curriculum on Regional Anesthesia from A to Z, featuring NYSORA’s Premium content. As opposed to textbooks and e-books, the Compendium is continuously updated and features NYSORA’s newest videos, animations, and visual content. The Compendium is one of several gold-standard educational courses on NYSORA’s Learning System (the NYSORA LMS), and registration to NYSORALMS.com is free. The FULL access to the Compendium, however, is based on an annual subscription, as it requires an army of illustrators, video editors, and an educational team to continue making it the BEST tool for education on everything regional anesthesia. While you can think of the compendium as an ebook on steroids, a quick test drive will give you a real-time feel of how incredible the Compendium really is. Your subscription will transform the way you read about regional anesthesia:
Even if you do not wish to subscribe to the Compendium, do register to the NYSORA LMS, be the first to know what’s new in regional anesthesia, and get involved in case discussions. Here’s what the activity feed on NYSORA LMS looks like: We are convinced that once you experience the Compendium on the NYSORA LMS, and you’ll never go back to your old books, and your subscription will support keeping NYSORA.com free for the rest of the world. Additional Reading
What are the complications of an epidural?Epidurals are usually safe, but there's a small risk of side effects and complications, including:. low blood pressure, which can make you feel lightheaded or nauseous.. temporary loss of bladder control.. itchy skin.. feeling sick.. headaches.. nerve damage.. What are 2 adverse effects of epidural anesthesia?Side effects Epidural. Low blood pressure. It's normal for your blood pressure to fall a little when you have an epidural. ... . Loss of bladder control. ... . Itchy skin. ... . Feeling sick. ... . Inadequate pain relief. ... . Headache. ... . Slow breathing. ... . Temporary nerve damage.. What does a nurse need to assess when a patient has an epidural?Assess the patient's emotional and physiologic responses to request modification of the plan of care. When local anesthetics are infused through an epidural catheter, assess sensory block and motor function, vital signs, level of consciousness, and perception of pain.
What are potential serious complications of epidural administration of analgesics?While rare, serious complications are possible after an epidural steroid injection and are discussed below.. Infection. ... . Bleeding. ... . Dural puncture. ... . Nerve damage. ... . Cardiovascular system (heart) complications. ... . Risk associated with local anesthetics. ... . Risk associated with particulate steroids.. |