Effects of tissue expansion on secondary ischemic tolerance in experimental free flaps

The effects of tissue expansion on free flap tolerance and metabolic response to secondary ischemia were evaluated. A total of 178 male syngeneic Lewis rats were used: 28 in perfusion study and 75 donor and 75 recipient animals in flap survival study. Animals were organized in three experimental groups: control, sham operation, and expansion group. Sham group animals had the expander implanted but not insufflated. After 4 weeks of tissue expansion, 3 x 5-cm epigastric free flaps were transplanted to recipient animals. Twenty-four hours later, secondary ischemia was produced by 3-hour venous occlusion. Flap survival, perfusion, and enzyme activities were determined. Pre-expanded skin flaps had an increase in perfusion of approximately 700% as measured by fluorescein levels compared with control flaps (p < 0.001) and demonstrated a better success rate (76%) compared with those of the control (40%) (p < 0.05) and sham (28%) groups (p < 0.05). Glutathione peroxidase, glutathione reductase, and glucose 6-phosphate dehydrogenase of the antioxidant defense systems significantly increased in skin in both the sham and the expansion groups. In response to secondary ischemia, the control and sham groups exhibited a decrease in enzyme activities of the glutathione redox cycle, whereas the expansion group showed no significant changes from the elevated baseline activities. Tissue expansion improved flap tolerance to secondary ischemia by increasing flap circulation and probably by augmenting tissue metabolic response to oxidative stress.