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Anesthesia for Extremity Surgery
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A general anesthetic can be used as the anesthetic of choice for all orthopedic procedures. However, a regional anesthetic technique can be used to provide both anesthesia and postoperative analgesia for a variety of orthopedic procedures, including arthroscopic, fracture, and joint replacement surgery. For lower limb surgery, central neuroaxial techniques can be used in addition to peripheral nerve blocks.
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Upper Extremity Surgery
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The variety of brachial plexus blocks available means that several options for block technique can be used for upper extremity procedures.25 The most important factor in choosing a block is the anticipated location of the incision, although other variables can affect the decision. Patient factors, such as weight, degree of pulmonary dysfunction, and coagulation status, also play a role. Choice of local anesthetic depends on balancing the time of onset with the desired duration of block. For procedures on the shoulder, interscalene block using 30 to 40 mL of local anesthetic is the preferred technique. This dose should ensure block of the suprascapular nerve, which branches off from the plexus quite proximally. Superficial cervical plexus block also is important, although it usually is achieved as an effect of an interscalene block. To cover anterior incision sites, supplemental intercostobrachial nerve block is needed as well. The sensory distribution of this nerve is highly variable. To cover posterior incision sites, paravertebral blocks of the T1 and T2 nerve roots or skin infiltration by the surgeon are necessary. If paravertebral blocks are used, separate injection of the intercostobrachial nerve is unnecessary. Anesthesia from the midhumerus to the hand can be achieved with a supraclavicular, infraclavicular, or axillary block. Each of these techniques has unique advantages and drawbacks that may make that technique particularly useful in a given patient. Ultrasonography is playing an increasing role, particularly in more superficial upper extremity blocks (Fig. 65-2). Supplemental injection of the peripheral nerves more distally can be performed to salvage partially successful proximal blocks. Bier block can be used to perform short-duration forearm and hand surgery, but it does not provide postoperative analgesia. A description of the various peripheral nerve block techniques is given in Chapter 48.
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Shoulder Replacement Surgery
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More than 80000 shoulder arthroplasty procedures are performed annually in the United States. Shoulder replacement surgery, similar to knee and hip replacement surgery, can result in significant postoperative pain. Both general anesthesia and interscalene nerve blocks can be used for anesthesia, either alone or combination. Increasingly more shoulder procedures are performed on an outpatient basis, which has necessitated the use of a variety of techniques to improve postoperative pain. Use of interscalene nerve blocks alone for anesthesia and analgesia offers patients a significant advantage in terms of pain scores, time to ambulation, time to discharge, and need for unexpected admission compared with general anesthesia.26 Other techniques used for postoperative pain include intra-articular infusions of local anesthetics and suprascapular nerve blocks. The continuous delivery of intra-articular local anesthetic via means of an indwelling-catheter has recently been discredited because of the erosion of the articular cartilage by the local anesthetic infusion. Suprascapular nerve blocks have been shown to be superior compared with patient-controlled IV analgesia.27 Potential benefits of suprascapular nerve block compared with interscalene nerve block are ease of performance, lower volumes of local anesthetics needed, and fewer complications such as phrenic nerve paralysis and intrathecal injection. The major drawback of suprascapular block compared with interscalene nerve block is that suprascapular nerve block must be combined with general anesthesia, thus necessitating airway manipulation and exposing the patient to the deleterious physiologic changes associated with general anesthesia. In some studies, intra-articular infusion of bupivacaine has shown no benefit compared with placebo.28 Many shoulder surgeries are undertaken with the patient placed in a 45-degree semirecumbent position (beach chair position). This position presents problems related to potential difficulties with airway access if a regional anesthetic is the sole anesthetic technique. It is essential to test whether the interscalene block is adequate for the surgical procedure before the procedure is started because access to the airway during the case can be difficult. Another problem with this position is reduced venous return to the right side of the heart, resulting in reduced preload and potential hypotension, especially with use of general anesthesia. This condition may result in the need for increased fluid resuscitation. Lower extremity noninvasive blood pressure measurements should be used with caution, if at all, because these measurements do not provide accurate information for determining cerebral perfusion pressure for the patient in a beach chair position. To ensure cerebral perfusion is adequate, continuous processed electroencephalogram or cerebral oximetry should be monitored on some patients in the beach chair position.29 These considerations include patients with previous neurologic ischemic events, carotid stenosis, arterial vascular disease, and significant cardiovascular risk.
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Patients with significant cardiovascular problems should be positioned slowly, and the anesthesiologist should always be aware of the potential for venous air embolism, particularly with patients in the sitting position.
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The problems of embolic phenomenon, as seen in hip or knee replacement surgery, are generally not seen in shoulder replacement surgery. In general, use of invasive lines, such as central lines and arterial lines, is not required for these cases, depending on the presence of comorbidities.
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Lower Extremity Surgery
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Many different regional anesthesia techniques are available for lower extremity orthopedic surgery.30 Neuraxial techniques are appropriate for any lower extremity procedure in most patients, but aggressive use of postoperative anticoagulation for prevention of DVT and pulmonary embolism (PE) may limit the use of postoperative epidural analgesia. Peripheral nerve blocks with or without continuous catheter use offer an alternative to neuraxial techniques, which may be safer in the setting of perioperative anticoagulation with efficacy at least equal to that of epidural analgesia. For procedures on the hip and proximal femur, lumbar plexus block30 in conjunction with a proximal sciatic nerve block30,31 provides acceptable analgesia. A femoral nerve block can be used instead of a lumbar plexus block, although it is less likely to provide block of the obturator and lateral femoral cutaneous nerves.32 Addition of paravertebral nerve blocks at the first and second lumbar levels may be needed to provide complete anesthesia. Alternatively, the procedure can be accomplished using a spinal anesthetic alone or a combination of spinal anesthesia with a lumbar plexus and sciatic blocks or catheters for postoperative analgesia. Epidural or combined spinal epidural anesthesia provides a simpler route of anesthesia and analgesia33 and may be acceptable for postoperative use if the epidural is managed in accordance with the third consensus statement on neuraxial anesthesia and anticoagulation of the American Society of Regional Anesthesia and Pain Medicine (ASRA) (2010).34 The main goal of these guidelines is to decrease the occurrence of neuraxial hematoma. In general, hip procedures are associated with less postoperative pain than are knee procedures, making prolonged regional analgesia less important. Anesthesia and analgesia for procedures involving the knee and distal femur can be accomplished with either neuraxial techniques or peripheral nerve blocks. Lumbar plexus block offers more complete anesthesia of the thigh than does femoral block but is deeper and may be more difficult in obese patients and those with a history of lumbar spine surgery.32 Sciatic nerve block is crucial for coverage of the posterior cutaneous nerve of the thigh and for the knee joint itself.35 Procedures involving the foot and ankle, as well as those involving the tibia and fibula, are primarily covered by a sciatic nerve block. This can be achieved by blockade of the sciatic nerve at the popliteal level. Figure 65-3 shows an ultrasound scan of the popliteal nerve. Block of the saphenous nerve may be necessary, depending on the location of the incision and the need for tourniquet. The saphenous nerve can be blocked via either femoral nerve block or a distal dedicated saphenous nerve block. Blocking the saphenous nerve at the femoral nerve level results in weakness of the quadriceps femoris with an inability to extend knee. This may make mobilization more problematic compared with performing a dedicated saphenous block, which is purely sensory. Recently, ultrasound techniques have been described in which the saphenous nerve is blocked in the adductor canal just below the sartorius muscle36 (Fig. 65-4). Ankle block without the use of epinephrine is adequate for procedures on the foot if no tourniquet use is expected.
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The question as to whether general or regional anesthesia is superior with respect to outcome is controversial. A number of studies have shown no improvement in outcome with respect to mortality and morbidity.37,38 However, other studies have shown that regional anesthesia and analgesia may reduce morbidity and mortality after surgery.39-41 In a meta-analysis study, Rodgers et al40 showed a 33% reduction in mortality. They also showed a significant decrease in the incidences of myocardial ischemic events, respiratory depression, rate of DVT formation, and blood loss. Wu et al42 showed a death rate of 5.8 per 1000 (95% confidence interval [CI], 2.9-8.7) at 30 days postsurgery for cases using epidurals versus a death rate of 9.9 per 1000 (95% CI, 8.6-11.3) for cases using only general anesthesia. However, this benefit to patients must be considered in the context of the risk of epidural hematomas when neuroaxial anesthesia is given in the presence of anticoagulants such as LMWH. The risk, although small, has led to the publication of guidelines for use of regional anesthesia in patients receiving anticoagulants.34 The 2010 guidelines depart from the 2003 guidelines by stating that LMWH should not be administered concomitantly with medications that affect hemostasis, such as antiplatelet drugs, standard heparin, or dextran. This has resulted in the reinvention and development of many peripheral nerve block techniques, including continuous peripheral nerve catheter techniques,43 and use of ultrasonography to place these regional nerve blocks.44,45
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Hip and Knee Joint Replacement Surgery
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With the population of the United States aging and the prospect of "baby boomers" reaching retirement age in the next couple of decades, the number of patients requiring joint replacement will increase greatly. It is estimated that more than 1 million joint replacement procedures per year will be performed in the United States during the next decade. A variety of anesthetic techniques, consisting of general, spinal, epidural, combined spinal and epidural, and peripheral nerve blocks, are available to anesthesiologists. These techniques have been shown to be superior to routine patient-controlled analgesia and as efficacious as epidural anesthesia but with fewer side effects.46-48 Some evidence suggests that regional techniques may result in earlier discharge and improved functional outcome.47,49 Knee replacement surgery is especially associated with significant postoperative pain, and patients undergoing this surgery benefit greatly from some form of postoperative regional analgesia. Use of epidurals in the joint replacement setting has been severely restricted by the widespread use of LMWH. The introduction of a new synthetic antithrombin III pentasaccharide sequence, fondaparinux, that has a half-life of 17 hours may have huge implications for the performance of regional techniques.50 Normal practice is to wait at least 2 half-lives after discontinuation of such drugs before placing a neuraxial block or manipulating epidural catheters. Unfortunately, this means that with fondaparinux, there will be no window of opportunity to perform the regional anesthesia techniques or remove an epidural catheter.
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A variety of peripheral nerve blocks have been used for analgesia in knee replacement surgery. They include psoas compartment blocks (lumbar plexus), femoral nerve blocks, and sciatic nerve blocks. The psoas compartment approach may be superior to the femoral approach because it is associated with greater success in blocking the 3 main components of the lumbar plexus: femoral, obturator, and lateral femoral cutaneous nerves. Capdevila et al51 showed a 95% probability of blockade of all 3 nerves if the psoas compartment approach is used versus 33% if the femoral approach is used. A study by Macalou et al52 showed that addition of an obturator nerve block to a 3:1 femoral nerve block resulted in superior postoperative pain relief compared with a 3:1 femoral nerve block alone. The addition of a sciatic nerve block for postoperative pain management is controversial. Studies have shown a significant improvement in postoperative pain management if the sciatic nerve block is also used.53,54 Other studies have shown no improvement in postoperative opioid requirements if a sciatic nerve block is used.55
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Whether the addition of peripheral nerve blocks to general anesthesia or spinal anesthesia offers any benefit to patients undergoing hip arthroplasty surgery is not as clear as in the case of knee replacement surgery. Biboulet et al56 compared patient-controlled analgesia with morphine and a single injection of either a femoral or psoas compartment block. No difference in morphine consumption or pain scores was noted 4 hours after extubation. Other investigators have reported similar results using psoas compartment block for postoperative pain.49 Thus, for hip replacement surgery, use of a spinal, epidural, or both may offer benefits to patients compared with general anesthesia in terms of mortality, morbidity, and pain control, but the addition of peripheral nerve blocks for postoperative pain appears to be of limited benefit. This may be in part because the pain after hip replacement surgery is of much shorter duration than in knee replacement surgery.49,56
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The maximum duration of a single-shot nerve block depends on the local anesthetic used and the site of injection (lidocaine 2%, mepivacaine 1.5%, 4-6 h of analgesia vs ropivacaine 0.5%, bupivacaine 0.5%, 8-16 h of analgesia). Administration of additives, such as clonidine (50-150 mcg), may prolong the nerve block by another 2 or 3 hours. Use of continuous catheters in knee replacement surgery can extend the block indefinitely and can help patients avoid the severe pain experienced when the single-shot nerve block wears off. Evidence indicates that use of a stimulating nerve catheter improves the success rate of nerve catheters by avoiding subsequent failure of the catheter when the initial nerve block wears off (so-called "secondary block failure"). Salinas et al43 showed a 100% success block rate when using a stimulating nerve catheter compared with an 85% success rate when using a nonstimulating nerve catheter. A recent semiquantitative systematic review including 11 randomized controlled studies has also shown improved analgesia with the use of stimulating catheters compared with nonstimulating catheters.57
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Early mobilization and rehabilitation are important for the functional outcome of the patient. Use of a continuous catheter with local anesthetic causes motor weakness. Close collaboration among the anesthesia, orthopedic, and physiotherapy teams is needed to allow early mobilization with adequate analgesia. Lower concentrations of local anesthetic infusions produce less motor block but also may produce inferior analgesia. Starting patients on some form of oral analgesics before discontinuing the peripheral nerve catheters is essential to maintain adequate postoperative analgesia.
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A new approach to postoperative pain management in patients undergoing lower limb joint replacement is the use of extended-release epidural morphine sulfate (DepoDur, SkyePharma, London, UK). This technology is based on liposomal products into which doses of 10 to 20 mg of morphine are incorporated (Fig. 65-5). This form allows the slow release of morphine into the epidural space over a 48-hour period without the need for an epidural catheter, thus avoiding anticoagulation issues. A study of hip replacement patients has shown a significant reduction in postoperative fentanyl requirements and pain scores.58 The side effects are similar to those of other neuroaxial opioids. The most serious potential side effect is respiratory depression,59 so patients must be monitored closely for 48 hours. Further developments of slow-release preparations of local anesthetics are awaited.
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Invasive monitoring with arterial or central venous lines is generally not required except in patients with significant comorbidities or in patients undergoing revision of a previous joint replacement. Blood loss tends to be higher during revision joint replacement procedures. Methods used to reduce the requirement for blood transfusion are relevant to all patients undergoing joint replacement surgery (discussed earlier in this chapter in the section on blood loss).
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Neck of Femur Fractures
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Repairing neck of femur fractures is a common surgical procedure at trauma institutions. Management is generally surgical and involves either internal fixation with screws or plates or a hemiarthroplasty. Hip arthroplasty for management of femoral neck fractures is associated with a nearly 10-fold increase in the rate of perioperative mortality compared with elective hip arthroplasty. The 30-day mortality is 10%, and 20% to 30% of patients die within 1 year of surgery.60,61 The reasons for this high mortality rate probably are the age of this population group (>70 years of age), the presence of comorbidities, and the high incidence of DVTs and PEs. Optimization of patient medical conditions before surgery is generally but not always recommended because delay in surgery caused by the need for management of comorbidities may increase the mortality rate by 2.5 times.62 Thus, appropriate and timely medical care is important before anesthesia and surgery.
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Anesthesia involvement in the management of patients with neck of femur fractures can occur before the need for anesthesia for surgery and may involve the placement of a 3:1 femoral nerve block or fascia iliaca block in the emergency department for analgesia. Preoperative use of a femoral 3:1 block has been shown to be simple and to reduce the pain experienced, with few side effects.63 The reduction in opioid doses required by patients can have substantial benefits. The question of whether general anesthesia or some form of regional anesthesia is best for these patients is controversial. The authors hold the opinion that regional anesthesia, including the use of spinal anesthesia, epidural anesthesia, combined spinal epidural anesthesia, or peripheral nerve blocks, is beneficial. Use of lumbar paravertebrals, lumbar plexus, and sciatic nerve block as the sole anesthetic technique for neck of femur fracture is a beneficial technique, especially in patients who, because of their comorbidities, cannot tolerate the drop in preload or afterload caused by spinal or epidural anesthesia.31,64 An alternative method in this group of patients is the use of a continuous spinal catheter.65 This method allows the anesthesiologist to titrate intrathecally the local anesthetic in small amounts while still obtaining the desired effect without the usual hemodynamic changes associated with a single large dose of intrathecal local anesthetic. Invasive line monitoring, such as arterial and central lines, may be needed, depending on the presence of comorbidities. The need for blood transfusion is uncommon, but adequate IV access and a blood cross-match should always be available. Keeping patients warm during the procedure is especially important in this elderly population. Finally, this group is at a much higher risk for development of DVT and subsequent PE. All patients must be adequately anticoagulated during the postoperative period to prevent this complication (see Deep Vein Thrombosis).
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Spinal surgery is frequently a challenge for anesthesiologists, involving a wide variety of procedures for treatment of different pathologies in the young to the very old patient population. It may involve surgery on the vertebrae of the spine in addition to the neural structures of the spinal cord.66 Common pathologic reasons for surgery are listed in Table 65-2.
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The required position of patients frequently is prone. The prone position requires extra care and attention because it may be associated with an increased incidence of complications. Major spinal surgery can be associated with extensive blood loss. Although the majority of spinal surgery is elective, urgent surgery may be required after trauma or when spinal cord viability is a concern. Some patients undergoing spinal procedures require repeat surgery and may have high requirements for analgesics in the postoperative period.
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The majority of spinal surgery is performed with the patient in the prone position, although an anterior approach is sometimes used, particularly for cervical spine surgery. In addition, an anterior or lateral approach may be used for lumbar and thoracic spinal surgery. The ideal position allows easy access and maximal exposure to the site of surgery while allowing for a good operative field with minimal bleeding. Decompression of the stomach and bladder using an orogastric tube and a urinary catheter along with avoiding compression of the abdomen results in decreased pressure in the epidural veins and decreased blood loss. The site of surgery may be above the level of the heart, resulting in low venous pressure and decreased blood loss; however, it also is associated with a risk of venous air embolism. Hence, appropriate positioning of the patient is essential while being careful to avoid many of the potential complications. Although many different surgical tables and positions largely determined by surgeons' preference are available to improve exposure to the surgical site, many of the pertinent issues are common to all cases. First, extreme care must be taken when turning the patient, particularly patients at risk for spinal cord compromise. Particular attention should be paid to positioning of the head, neck, and arms. Complications associated with malpositioning of the arms, including vascular and brachial plexus injury, have been reported (Table 65-3).67 Such injuries are least likely to occur when the arms are placed by the patient's side. However, this position may invade the surgeon's space and restricts the anesthesiologist's access to arterial and venous access. Therefore, the patient is frequently positioned with the arms resting on padded arm boards and flexed at the elbow (Fig. 65-6). The elbow should not be flexed more than 100 degrees because such a position is associated with increased pressure within the cubital tunnel.68 The abdomen, genitalia, and breasts all should be checked because prolonged surgery in the prone position can result in injury to these areas. Adequate protection and padding of the eyes and head are essential. Blindness resulting from surgery performed with the patient in the prone position has been reported. Although its etiology probably is multifactorial but still is incompletely understood, prolonged surgery, anesthetic length greater than 6 hours, hypotension, large blood loss (>1 L), anemia, edema, and changes in intraocular perfusion pressure all may contribute to blindness.69,70 Changes in ocular perfusion pressure resulting in decreased blood flow to the optic nerve may result in ischemic optic neuropathy. Increases in intraocular pressure or decreases in mean arterial pressure result in decreased ocular perfusion pressure.71,72 Avoidance of prolonged periods of hypotension and perioperative anemia may reduce the risk of perioperative blindness in patients in the prone position.73 In addition, direct pressure on the eye can result in injury to the eye. Tape marks and facial skin loss may result, especially in prone patients with significant facial edema and friable skin.
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The sitting position occasionally is used for surgery on the cervical spine. The risks and complications associated with surgery performed in the sitting position are described elsewhere in this textbook.
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A standard preoperative assessment is essential in patients undergoing spinal surgery. In addition to standard American Society of Anesthesiologists monitoring, use of invasive monitoring depends on patient comorbidities and the anticipated complexity of the surgical procedure and anticipated blood loss.66 Surgeries involving multiple levels, repeat operations, and procedures for treatment of trauma and neoplasms typically are associated with increased blood loss.
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A thorough airway examination should be performed. This assessment is critical, particularly in patients presenting for cervical spinal surgery and in patients with disease processes that affect the vertebral column, such as rheumatoid arthritis, ankylosing spondylitis, or generalized osteoarthritis. In addition, patients who have undergone previous neck surgery may have increased difficulty at intubation. The aim is to safely secure the airway while avoiding any damage to the spinal cord. This can be achieved safely in both awake and anesthetized patients using a variety of techniques, such as standard laryngoscopy, intubating aids, manual inline stabilization, laryngeal mask airways (LMAs; LMA North America, Inc., San Diego, CA), and fiberoptic intubations. The precise technique depends on the clinical situation; management of the difficult airway is discussed in Chapter 36. The majority of movement in the cervical spine during intubation occurs at the atlantooccipital joint and between the first 2 cervical vertebrae.74,75 Particular caution should be exercised in the airway management of patients with C1–C2 injury and at-risk patient populations (rheumatoid arthritis, Down syndrome) that are more prone to pathology of C1–C2. Use of rigid collars may increase the difficulty of intubation but does not affect the degree of cervical spine movement. After the airway is secured, the cervical collar alerts staff members that the patient may have a neck injury. Awake intubation allows neurologic examination after intubation and positioning of the patient, although this may be difficult in uncooperative patients. Thoracic spinal surgery may require use of a double-lumen tube or bronchial blocker if 1-lung ventilation is required with an anterior or lateral approach.
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Anesthesia induction can be either IV or inhalational, with IV induction appropriate for the majority of patients. Intubation and muscle relaxation can be facilitated with either nondepolarizing muscle relaxants or succinylcholine. Use of succinylcholine should be avoided in patients with muscular dystrophies and in patients with spinal cord injuries in whom an exaggerated hyperkalemic response may be seen. Use of succinylcholine probably is safe in the 48 hours immediately after spinal injury and again 9 months after the injury.76 Intraoperative use of muscle relaxants may be avoided depending on whether motor-evoked responses are monitored and surgeon preference. This is relevant in patients at risk for nerve root injury during surgery in which nerve root stimulation results in muscle movement. Anesthesia can be maintained using either a potent volatile anesthetic in a nitrous oxide–oxygen or air–oxygen mixture or IV anesthesia such as propofol infusions. Potent volatile agents may hinder the use of sensory and motor-evoked responses. If motor-evoked potentials are to be used by the surgeon, potent volatile agents are avoided completely, and a total IV infusion (TIVA) technique is used. Intubation can be accomplished with succinylcholine or under deep propofol-induced anesthesia. Nondepolarizing agents should not be used so as not to interfere with the motor-evoked potential. Many opioids have been used as part of a balanced anesthetic technique, with remifentanil having the advantage of providing potent analgesia and rapid offset of action. This may assist in the early assessment of the patient's neurologic status in the early postoperative period. Remember that all anesthetic agents may affect the use of somatosensory and motor-evoked potentials, which can be used to monitor spinal cord function (see Chapter 89). Changes in anesthetic concentrations and arterial blood pressure also affect the interpretation of evoked potentials. Spinal cord monitoring is discussed in Chapter 90.
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Measures for minimizing intraoperative blood loss and reducing allogeneic blood transfusion in spinal surgery are particularly important. Careful positioning, avoidance of abdominal compression, surgical technique, hypotensive techniques, use of preoperative autologous donation, intraoperative normovolemic hemodilution, and use of intraoperative cell savers all may help avoid the use of allogeneic blood products. However, combinations of these techniques to reduce requirements for homologous blood products have not produced consistent results.77,78 Use of antifibrinolytics may reduce intraoperative blood loss.79 Hypotensive anesthesia is very effective at reducing blood loss, although it may be a contributory factor to the rare but devastating complication of posterior optic neuropathy. These techniques are particularly important in spinal surgeries associated with large blood loss. Minimally invasive spinal surgery has increased substantially. Primarily by using endoscopic, computer navigation and microsurgical techniques, surgeries to treat a wide variety of conditions ranging from spinal stenosis to tumor removal can be performed through much smaller incisions. These techniques allow for a quicker recovery time, reduced blood loss, and decreased opioid requirements with fewer postoperative complications.80 Many of these new techniques use not only sensory-evoked potentials but also motor-evoked potentials. Many surgeons request the use of no muscle relaxants during the case as well as avoidance of potent inhalational agents to minimize disturbance on the motor-evoked potentials. To achieve this, a TIVA technique is required.
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Postoperative analgesia can be a challenge, particularly in patients who have experienced chronic back pain. Postoperative pain management has shifted from opioid-only patient-controlled analgesia to a multimodal approach. This multimodal approach uses drugs of various classes (e.g., NSAIDs, acetaminophen, gabapentenoids, antidepressants, ketamine) along with regional anesthesia to reduce or eliminate the amount of opioids required by the patient. Ketamine has made a resurgence of use in the management of some of our chronic pain patients undergoing orthopedic procedures. Ketamine is typically administered as an infusion during the case and occasionally continued postoperatively with great success. Perioperative infusion rates of ketamine range from 0.15 mg/kg/h to 0.35mg/kg/h. Use of NSAIDs is controversial. They may reduce opioid requirements by up to 40% and reduce the incidence of opioid-related side effects such as nausea, vomiting, sedation, and respiratory depression.81 However, they may interfere with bone healing.82 Initial studies using COX-2 inhibitors suggest minimal effect on bone healing, particularly when used for short durations.
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In some cases, surgeons insert a catheter under direct vision into the epidural space. Either epidural opioids or opioids in addition to local anesthetics may be infused. Low concentrations of local anesthetics typically are used to avoid a motor block, which may delay accurate diagnosis of motor dysfunction as a complication of surgery.83
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The majority of patients undergoing spinal surgery can be managed in the postsurgical unit postoperatively. Those who have undergone extensive surgery, experienced significant blood loss, received large fluid resuscitation, or experienced fluid shifts should be monitored postoperatively in an intensive care or stepdown unit. Patients with significant facial and airway edema may require ventilation postoperatively. In addition, patients who have undergone certain cervical and thoracic spinal procedures may require postoperative ventilation; those requiring extensive neurologic monitoring should be cared for in a monitored bed postoperatively.
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Neurogenic shock is characterized by loss of sympathetic tone, resulting in hemodynamic instability, as evident from significant hypotension and bradycardia. This may be accentuated by hypovolemia. Shock tends to occur in injuries above the T6 level caused by disruption of sympathetic outflow and unopposed vagal tone. Arterial and central venous pressure monitoring is helpful in the management of these patients. Fluid administration in addition to vasopressors may be required to treat the hypotension along with appropriate management of the bradycardia. Autonomic dysreflexia is a syndrome of sympathetic imbalance that may occur after the phase of spinal shock. It occurs more commonly in males and may result in hypertension associated with myocardial ischemia, retinal or cerebral hemorrhage, and seizures.
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Ambulatory Orthopedic Surgery
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The 1990s saw a dramatic increase in the number of surgical cases performed in the ambulatory setting. Nearly 60% of all cases now occur as outpatient procedures, with orthopedic surgery accounting for a large number of cases. This trend has huge socioeconomic implications, such as reduced costs, more rapid return to daily activity, and lower risk of nosocomial infections. Shoulder and knee procedures, including shoulder arthroplasty and anterior cruciate ligament repair, occur routinely on an outpatient basis. All ambulatory orthopedic surgical procedures can be performed under general anesthesia. However, these procedures may be most suited for a regional anesthetic technique, and improved analgesia seen in the perioperative period can be safely and effectively extended to the postoperative period with the use of perineural catheters.84 With more complicated procedures occurring on an outpatient basis, adoption of a multimodal approach to postoperative pain management is essential. This will allow better pain control with the need for less opioid medication, thus reducing the potential for side effects such as nausea and vomiting, which often can derail a timely discharge from the ambulatory center. The cornerstone of these techniques is frequently a peripheral nerve block. New disposable infusion devices allow patients to be discharged with peripheral nerve catheter infusions, further prolonging the effect of a single shot of peripheral nerve block.85 When general anesthesia is required, the aim should be to provide adequate anesthesia and analgesia while minimizing perioperative-related side effects such as nausea and vomiting.