Anesthetic Management

A variety of anesthesia techniques, including general anesthesia, regional (i.e., epidural or spinal) anesthesia, and combined techniques, have been used successfully for lower extremity reconstruction. General anesthesia is usually delivered by use of a balanced technique with opioids, potent inhalation anesthetics, nitrous oxide, and neuromuscular blockade. Induction of anesthesia should proceed in a controlled fashion such that a stable hemodynamic profile is maintained. Anesthetic maintenance may be accomplished with low-dose inhaled anesthetic (i.e., isoflurane, desflurane, or sevoflurane) in 50% nitrous oxide and opioid (3 to 5 μg/kg of fentanyl). Because virtually all patients are extubated in the operating room, high doses of opioid are generally avoided. The goal is to maintain stable hemodynamics and to prevent myocardial ischemia during the intraoperative and postoperative periods. Judicious use of β-blockers and vasoactive drugs is often necessary.

Regional anesthesia can be accomplished with spinal or epidural techniques. Disadvantages of spinal anesthesia include the limited duration of action in the setting of a surgical procedure that is somewhat unpredictable in length and complexity. The level of sympathetic block is somewhat less controllable than that of the epidural block. Hypotension can occur with either technique and should be promptly treated with judicious use of fluids and vasopressors. An advantage of an epidural technique is the ability to continue drug delivery into the postoperative period for analgesia and attenuation of the stress response. A lumbar epidural catheter is ideal for lower extremity vascular procedures. The dermatomes that need to be anesthetized are innervated at the same level where the catheter is inserted because the incision is usually in the L1 to L4 region. Small volumes of local anesthetic are recommended because a T10 block is usually sufficient. Usually, 9 to 12 mL (including the test dose) is sufficient for the initial dose, and more drug is given as needed. Because vascular surgery patients are generally advanced in age and prone to higher block levels, larger doses may result in high sympathetic block with significant hypotension.^[526] A high sympathetic block is problematic because of decreased coronary perfusion and excessive fluid and vasopressor requirements. Congestive heart failure may result in the postoperative period when the sympathectomy resolves and the intravascular space contracts. When the test dose is given, careful attention should be directed at the heart rate and the blood pressure. Blood pressure may be a more reliable indicator of an intravascular injection because vascular surgery patients may have little or no increase in heart rate due to β-blocker therapy or decreased α-adrenergic responsiveness resulting from aging.^[527] When hypotension results from sympathectomy, a low-dose phenylephrine infusion is helpful in reducing intravenous fluid requirements. I believe this approach is more physiologic than administration of large fluid volumes.