Perioperative fluid management in microvascular surgery.

The aim of intravenous fluid therapy in microvascular surgery is to maintain intravascular fluid volume for optimal tissue blood flow and oxygen transport to all tissues, including the free transferred tissue. General problems include the prolonged surgical procedures, frequently resulting in hypothermia and peripheral vasoconstriction, which may affect blood flow to the transplanted tissue. The surgical wounds may also be extensive, and can cause profound and sometimes underestimated fluid and blood loss. The choice of fluids is important, since free flaps and replants are at increased risk of developing edema, due to lack of lymphatic drainage and a decreased ability to reabsorb excessive interstitial fluid. Therefore, it is suggested that crystalloids be used only for insensible fluid loss, but that synthetic colloids (preferably pentastarch) be used for the replacement of plasma constituents. Hypertonic saline may have beneficial effects in ischemic and edematous flaps and replants. To optimize blood flow to the free flap, it is advisable to use moderate hemodilution. This facilitates the maintenance of high cardiac output and low peripheral vascular resistance. In addition, body temperature should be kept as close to normal as possible and, after completion of the microvascular anastomosis, arterial blood pressure should be kept near normal, to insure adequate perfusion pressure.