Temperature regulation is extremely important during and after microvascular surgery. Hypothermia is a major cause of peripheral vasoconstriction intraoperatively, and more importantly, postoperatively.

BLOOD AND FLUID REPLACEMENT

Intravascular volume must be maintained to provide adequate cardiac output. Blood loss during microvascular surgery is slow and insidious. Often more blood is lost in the surgical drapes than on sponges or in the suction. Careful monitoring of the estimated blood loss, checking of the hematocrit, and monitoring of the vital signs and urine output are essential to maintaining adequate intravascular volume. Central venous pressure monitoring may be helpful in rapid or large-volume blood loss. We usually find that maintaining a urine output greater than 1 cc/kg/hr indicates adequate vascular volume. We do not advocate the routine use of pulmonary artery catheterization and usually do not monitor the central venous pressure. We believe that there is insufficient evidence to support the use of colloid over crystalloid for fluid replacement. Therefore we routinely use isotonic crystalloid for this replacement.

VASODILATING AGENTS

Trimethaphan, nitroglycerin, sodium nitroprusside, hydralazine, phenoxybenzamine, and thymoxamine have all been advocated for intraoperative use. Trimethaphan, a ganglionic blocking agent, and phenoxybenzamine and phentolamine, alpha-adrenergic blockers, can produce vasodilation, but do not protect against direct smooth muscle contraction resulting from surgical manipulation. Nitroglycerin, sodium nitroprusside, and hydralazine are direct vascular, smooth muscle relaxants. Nitroglycerin tends to act more on the venous circulation. Hydralazine is a longer-acting agent and is therefore less controllable. Sodium nitroprusside theoretically provides the most appropriate direct arteriolar vasodilation. Its use is advocated by Christopher et al.2 These authors aimed to produce vasodilation while maintaining systolic blood pressure at no less than 100 mm of mercury. In a 2-year period, 34 of their patients underwent transplants (free flaps), of which 28 were successful. These patients received sodium nitroprusside intraoperatively by means of central line. Nitroprusside or hydralazine was used as needed postoperatively.

We agree with McDonald,3 however, that these agents are seldom required. A thoughtfully planned general anesthetic with care to maintain intravascular volume and normal temperature have proved reliable for us. If necessary, topical papaverine, marcaine, or lidocaine can be used successfully to treat intraoperative vasospasm caused by surgical manipulation.

ANESTHETIC TECHNIQUES AND AGENTS

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