Use of photoplethysmography to determine the survival length of skin flaps.

Photoplethysmography was used to evaluate 14 skin flaps in the pig. Eight skin flaps were 4x12 cm and were based dorsally. Six skin flaps were 4x18 cm and were based ventrally. All flaps were designed to undergo necrosis of the distal end. After elevation of the flap, blood flow to the skin flaps was estimated immediately by means of intravenously administered fluorescein. Photoplethysmography was used to determine blood flow to the skin flaps at 3, 24, 72, and 144 hours after elevation. Surviving length of the skin flaps was measured at nine days. Fluorescein accurately predicted the surviving length of the skin flaps. Photoplethysmography did not show a decrease in blood flow at the level of fluorescein penetration 3 or 48 hours after elevation. However, 72 and 144 hours after elevation, an abrupt decrease in blood flow was noted by photoplethysmography at the level of eventual skin necrosis.