Patients are assessed preoperatively according to the American Society of Anesthesia criteria. Electrocardiograms, arterial blood gases, and other tests are ordered on a case-by-case basis based on history and physical examination (Fig. 35-1).

Adequate hydration preoperatively, intraoperatively, and postoperatively is essential for optimal flap or replant circulation. Patients who are volume-depleted preoperatively may become significantly dehydrated during the prolonged operative time. Large surgical or traumatic wounds cause further significant fluid loss. Preoperative angiography may also contribute to dehydration. We have found, however, that volume status in most microsurgical patients is adequately monitored by assessment of vital signs and urine output. Rarely, central venous pressure measurements or pulmonary artery pressure and cardiac output determinations are required (See Chapter 39).

For purposes of circulatory hemodynamics, hematocrits of 25% to 30% are acceptable and even desirable in microsurgery patients. Wounds can heal well with hematocrits as low as 25%.6 If a patient's hematocrit is already in the 25% to 30% range, preoperative transfusion may be appropriate, depending on the anticipated blood loss.

In elective cases, aspirin is given the night before surgery to provide antiplatelet activity, which is desirable to prevent clotting in microvascular anastomoses. For clean cases, a short course of perioperative antibiotics (usually a cephalosporin) is begun immediately preoperatively. When a chronic wound is present, or in the instance of an infected fracture or osteomyelitis, appropriate antibiotic coverage is chosen for the cultured organism. Figure 35-1 shows typical preoperative orders for a healthy young patient.

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