COMPARISON OF SECONDARY ISCHEMIC TOLERANCE BETWEEN PEDICLED AND FREE ISLAND BUTTOCK SKIN FLAPS IN THE PIG

We compared the secondary ischemic tolerance of 8 x 12 cm surgically d enervated pedicled island skin flaps and skin free flaps raised contra laterally on the buttocks of 50 pigs. The pedicled flaps and fee flaps were subjected to 2 hours of primary warm global ischemia followed by 12 hours of reperfusion and 0, 2, 4, 6, or 10 hours of secondary warm global ischemia (n = 10 flaps). Skin necrosis was assessed 7 days aft er secondary ischemia. Pedicled skin flaps tolerated up to 10 hours of secondary ischemia without skin necrosis. However, incidences of skin necrosis (partial and total) in free flaps subjected to 0, 2, 4, 0, o r 10 hours of secondary ischemia were 0, 10, 50, 80, and 100 percent, respectively. In a separate experiment, skin blood flow and hematology were studied in contralateral pedicled flaps and free flaps (n = 20) subjected to 4 hours of secondary ischemia. The skill blood flow measu red by 15-mu m microspheres at 1.5 hours of reperfusion was significan tly higher (p < 0.01, n = 20) in pedicled skin flaps than in skin free flaps (1.91 +/- 0.35 versus 0.67 +/- 0.53 ml/min/100 gm). Under an op erating microscope, microthrombi were observed near the arterial and/o r venous anastomoses in 8 of 20 skin free flaps but none in the pedicl ed skin flaps. We obtained venous blood samples by cannulation of the major venae comitantes in 12 of the 20 skin free flaps in which there was no thrombosis in the vascular pedicle for hematologic studies. The venous plasma level of thromboxane by was significantly higher (p < 0 .05) in the skin free flaps thin in their contralateral pedicled skin flaps (195 +/- 19 versus 124 +/- 30 pg/ml). In addition, venous hemato crit, hemoglobin concentration, and while blood cell count also were s ignificantly (p < 0.05) higher in skin free flaps compared with their contralateral pedicled skin flaps, Taken together, these observations were interpreted to indicate that buttock skill fr ee flaps in the pig were less tolerant of secondary ischemia compared with their contrala teral pedicled skin flaps subjected to tile same ischemic protocol, an d this reduced ischemic tolerance in skin free maps was associated wit h compromised skin blood flow, hemoconcentration, and thrombosis in th e vascular pedicle.