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The free epigastric rabbit flap was used to observe morphological alterations in the microvasculature following prolonged hypothermic ischemic intervals. Free flaps were raised, cooled 1-6 days, and reanastomosed. The epigastric artery, vein, and dermal vessels were examined by electron microscopy. Efforts to keep flap tissues in the cold less than or equal to 5 days were successful (85% of flaps survived following reanastomosis N = 15). Flap failures were accompanied by extensive disruption to the endothelial cells of the epigastric vein. The findings support the efficacy of a cooling period less than or equal to 5 days for free flaps. The morphological alterations in the venous endothelium of the flap also suggest a plausible explanation for flap failures which occur in spite of patent anastomotic sites.

Cellular function and blood flow in acute, steroid-treated, and surgically delayed random skin flaps have been examined. In these studies, the period following flap elevation could be divided into early (0-2 hr), intermediate (4-6 hr), and late (12 hr) periods of ischemia, based on the cutaneous blood flow and cellular function measured by thallium-201 uptake. There was a close correlation (r = 0.98, 2 hr) between blood flow and cellular function during the early period of ischemia which became worse with time (r = 0.78, 12 hr). Blood flow studies demonstrated a significant difference (P less than 0.05) between the early and intermediate periods of ischemia which was abolished by surgical delay. Improvement in cellular function was accomplished by improved blood flow in the surgically delayed flaps, while steroid-treated flaps enhanced cellular metabolism by another mechanism. Cellular function approximated blood flow during the early and immediate period of ischemia. Steroids may augment cellular function without improving blood flow, while surgical delay improves cellular function by improving blood flow.