Anesthesia for Orthopedic Surgery

d. Minimally invasive surgery techniques have not been shown to be justified by superior clinical benefits.

2. Anesthetic Management. General anesthesia is preferred for essentially all thoracic and lumbar spine surgery (airway access, less nausea and vomiting, greater patient acceptance). SCh should be avoided if the patient has progressive neurologic deficits.

D. Spinal Cord Monitoring. Paraplegia is a feared complication of major spine surgery. The incidence of neurologic injuries associated with scoliosis correction is 1.2%. When patients awaken with paraplegia, neurologic recovery is unlikely, although immediate removal of instrumentation improves the prognosis. It is therefore essential that any intraoperative compromise of spinal cord function be detected as early as possible and reversed immediately. The two methods for detecting intraoperative compromise of spinal cord function are the “wake-up test” and neurophysiologic monitoring.

1. The wake-up test consists of intraoperative awakening of patients after completion of spinal instrumentation. Surgical anesthesia (often including opioids) and neuromuscular blockers are allowed to dissipate, and the patient is asked to move his or her hands and feet before anesthesia is re-established. Recall may occur but is rarely viewed as unpleasant, especially if the patient is fully informed before surgery.

2. Neurophysiologic monitoring (as an adjunct or an alternative to the wake-up test) includes somatosensory-evoked potentials (SSEPs) (waveforms may be altered by volatile anesthetics, hypotension, hypothermia, hypercarbia), motor-evoked potentials (MEPs) (neuromuscular blocking drugs cannot be used), and electromyography.

a. SSEPs reflect the dorsal columns of the spinal cord (proprioception and vibration) supplied by the posterior spinal artery.

b. MEPs reflect the motor pathways and the portion of the spinal cord supplied by the anterior spinal artery.

c. The combined use of SSEPs and MEPs may increase the early detection of intraoperative spinal cord ischemia.

d. If both SSEPs and MEPs are to be monitored during major spine surgery, one might consider providing anesthesia with an ultrashort-acting opioid infusion with a low dose of inhaled anesthetic and monitoring the electroencephalogram to minimize the potential for intraoperative awareness.

E. Blood Loss. Most of the blood loss in spinal instrumentation and fusion occurs with decortication and is proportional to the number of vertebral levels decorticated.

1. Measures to decrease blood loss and transfusion requirements include preoperative autologous donations, proper positioning, intraoperative blood salvage, induced hypotension, intraoperative normovolemic hemodilution, and administration of tranexamic acid. (Aprotinin use has been suspended owing to cardiac safety questions.)

2. Perioperative coagulopathy from dilution of coagulation factors, platelets, or fibrinolysis may be predicted from measurement of either the prothrombin time or activated partial thromboplastin time.

F. Visual Loss after Spine Surgery. The American Society of Anesthesiologists Visual Loss Study Group has identified risk factors for ischemic optic neuropathy after spinal surgery to include male gender, obesity, use of the Wilson frame, anesthetic duration, increased blood loss, and the use of noncolloid for fluid replacement.

G. Venous Air Embolus. Venous air embolism can occur in all positions used for laminectomies because the operative site is above the heart level. Presenting signs are usually unexplained hypotension and an increase in the end-tidal nitrogen concentration.

H. Postoperative Care

1. Most patients’ tracheas can be extubated immediately after posterior spinal fusion operations if the procedure was relatively uneventful and preoperative vital capacity values were acceptable. The presence of severe facial edema may prevent prompt tracheal extubation.

2. Aggressive postoperative pulmonary care, including incentive spirometry, is necessary to avoid atelectasis and pneumonia.

3. Continued hemorrhage in the postoperative period is a concern.

4. Postoperative analgesia is typically provided by systemic and/or intrathecal opioids and instillation of local anesthetics at the surgical site. Multimodal analgesia including an oral regimen may be an alternative to IV opioids.

TABLE 50-6 CHANGES AFTER MAJOR SPINE SURGERY THAT MAY INFLUENCE THE ABILITY TO PERFORM EPIDURAL OR SPINAL ANESTHESIA

Degenerative changes (spondylothesis below level of fusion) that increase the chance of spinal cord ischemia and neurologic complications with regional anesthesia

Ligamentum flavum injury from prior surgery results in adhesions and possible obliteration of the epidural space or interference with spread of local anesthetic solution (“patchy block”)

Increased incidence of accidental dural puncture if the epidural space is altered by prior surgery (blood patch is difficult to perform if needed)

Prior bone grafting or fusion may prevent midline insertion of the needle

I. Epidural and Spinal Anesthesia after Major Spine Surgery

1. Postoperative anatomic changes make needle or catheter placement more difficult after major spine surgery (Table 50-6).

2. Spinal anesthesia may be a more reliable technique than epidural anesthesia if a regional technique is selected.

3. The presence of postoperative spinal stenosis or other degenerative changes in the spine or pre-existing neurologic symptoms may preclude the use of regional anesthesia in these patients.

IV. SURGERY TO THE UPPER EXTREMITIES. Orthopedic surgical procedures to the upper extremities are well suited to regional anesthetic techniques (Table 50-7). Upper extremity peripheral nerve blocks may be used in the treatment and prevention of reflex sympathetic dystrophy. Continuous catheter techniques provide postoperative analgesia and facilitate early limb mobilization. The patient should be examined preoperatively to document any neurologic deficits because orthopedic surgical procedures often involve peripheral nerves with pre-existing deficits (ulnar nerve transposition at the elbow, carpal tunnel release of the median nerve at the wrist) or may be adjacent to neural structures (total shoulder arthroplasty or fractures of the proximal humerus). Improper surgical positioning, the use of a tourniquet, and the use of constrictive casts or dressings may also result in perioperative neurologic ischemia. Local anesthetic selection should be based on the duration and degree of sensory or motor block required. Prolonged anesthesia in the upper extremity in contrast to the lower extremity is not a contraindication to hospital discharge.

TABLE 50-7 REGIONAL ANESTHETIC TECHNIQUES FOR UPPER EXTREMITY SAURGERY*

^*The duration of the block performed with long-acting local anesthetic (bupivacaine, ropivacaine) is 12–20 hours; intermediate-acting agents (lidocaine, mepivacaine) resolve after 4–6 hours.

A. Surgery to the Shoulder and Upper Arm

1. A significant incidence of neurologic deficits in patients undergoing this type of surgery demonstrates the importance of clinical examination before regional anesthetic techniques are performed.

a. Total shoulder arthroplasty may be associated with a postoperative neurologic deficit (brachial plexus injury) that is at the same level of the nerve trunks at which an interscalene block is performed. It is impossible to determine a surgical or anesthetic cause. Most of these injuries represent neuropraxia and resolve in 3 to 4 months.

b. Radial nerve palsy is associated with humeral shaft fractures, and axillary nerve injury is associated with proximal humeral shaft fractures.

2. Surgical Approach and Positioning

a. Typically, the patient is flexed at the hips and knees (“beach chair position”) and placed near the edge of the operating table to allow unrestricted access by the surgeon to the upper extremity.

b. The head and neck are maintained in a neutral position because excessive rotation or flexion of the head away from the side of surgery may result in stretch injury to the brachial plexus.

c. Case reports of stroke after general anesthesia in the sitting position have been reported. (The risk of induced hypotension in such patients is undetermined.)

3. Anesthetic Management. Surgery of the shoulder and humerus may be performed under regional (interscalene or supraclavicular brachial plexus block) or general anesthesia. The ipsilateral diaphragmatic paresis and 25% loss of pulmonary function produced by interscalene block mean that this block is contraindicated in patients with severe pulmonary disease.

B. Surgery to the Elbow. Surgical procedures to the distal humerus, elbow, and forearm are suited to regional anesthetic techniques. Supraclavicular block of the brachial plexus is more reliable than the axillary approach (which may miss the musculocutaneous nerve) but introduces the risk of pneumothorax (which typically manifests 6–12 hours after hospital discharge such that postoperative chest radiography may not be useful).

C. Surgery of the Wrist and Hand

1. Brachial plexus block (axillary approach) is most commonly used for surgical procedures of the forearm, wrist, and hand. The interscalene approach is seldom used for wrist and hand procedures because of possible incomplete block of the ulnar nerve (15%–30% of patients), and the supraclavicular approach introduces the risk of pneumothorax.

2. IV regional anesthesia (“Bier block”) permits the use of a tourniquet but has disadvantages of limited duration (90–120 minutes), possible local anesthetic systemic toxicity, and rapid termination of anesthesia (and postoperative analgesia) on tourniquet deflation.

D. Continuous Brachial Plexus Anesthesia

1. Catheters placed in the sheath surrounding the brachial plexus permit continuous infusion of local anesthetic solution. Bupivacaine 0.125% prevents vasospasm and improves circulation after limb reimplantation or vascular repair.

2. Indwelling catheters may be left in place for 4 to 7 days after surgery.

V. SURGERY TO THE LOWER EXTREMITIES. Orthopedic procedures to the lower extremity may be performed under general or regional anesthesia, although regional anesthesia may provide some unique advantages (Table 50-8).

A. Surgery to the Hip

1. Surgical Approach and Positioning. The lateral decubitus position is frequently used to facilitate surgical exposure for total hip arthroplasty, and a fracture table is often used for repair of femur fractures. The patient must be carefully monitored for hemodynamic changes during positioning when under general or regional anesthesia. Adequate hydration and gradual movement minimize blood pressure decreases. Care should be taken to pad and position the arms and to avoid compression of the brachial plexus. A “chest roll” is placed caudad to the axilla to support the upper part of the dependent thorax.

2. Anesthetic Technique. Spinal or epidural anesthesia is well suited to procedures involving the hip. Deliberate hypotension can also be used with general anesthesia as a means of decreasing surgical blood loss.

B. Total Knee Arthroplasty (TKA)

1. Patients undergoing TKA experience significant postoperative pain, which impedes physical therapy and rehabilitation.

TABLE 50-8 LUMBOSACRAL TECHNIQUES FOR MAJOR LOWER EXTREMITY SURGERY

^*The duration of the block performed with long-acting anesthetic (bupivacaine, ropivacaine); intermediate-acting agents (lidocaine, mepivacaine) resolve in 4 to 6 hours.

^†Outcomes are most marked in patients who receive a continuous lumbar plexus catheter with infusion of 0.1% to 0.2% bupivacaine or ropivacaine at 6 to 12 mL/hr for 48 to 72 hours.

PCA = patient-controlled analgesia; THA = total hip arthroplasty; TKA = total knee arthroplasty.

Only gold members can continue reading. Log In or Register to continue