ISCHEMIC PRECONDITIONING IMPROVES THE SURVIVAL OF SKIN AND MYOCUTANEOUS FLAPS IN A RAT MODEL

Inadequate blood supply of pedicle flaps results in partial necrosis, and prolonged ischemia during free-tissue transfer can result in parti al or complete flap necrosis. Recent research in the field of cardiova scular surgery has shown that ischemic preconditioning (repeated brief episodes of coronary artery occlusion followed by reperfusion) improv es myocardial muscle survival when the heart is subsequently subjected to prolonged ischemia. Preconditioning of skin or myocutaneous flaps as either pedicle or free flap models has never been studied. The goal of this investigation was to measure the effect of ischemic precondit ioning on myocutaneous and skin flap survival areas and total necrosis rates after variable periods of global ischemia. In 220 rats, 100 tra nsverse rectus abdominis myocutaneous flaps and 120 dorsal cutaneous f laps were randomized into treatment and control groups. The treatment flaps underwent preconditioning by three cycles of 10 minutes of pedic le clamping followed by 10 minutes of reperfusion for a total precondi tioning period of 1 hour. The control flaps were perfused without clam ping for 1 hour. Both control and treatment flaps then underwent globa l ischemia for 0, 2, 4, 6, 10, or 14 hours by pedicle clamping. Flap s urvival area was measured on the fifth postoperative day. Statistical analysis was performed with analysis of variance, student's t tests, a nd probit analysis. Preconditioning improved survival areas of pedicle myocutaneous flaps (0-hour group) from 47 +/- 16 percent (mean percen t area surviving +/- SD) to 63 +/- 5 percent. This difference was stat istically significant (t test, p < 0.04). There was no statistically s ignificant improvement in pedicle skin flap survival. For free flap mo dels (flaps undergoing global ischemia), preconditioning increased the survival areas of skin and myocutaneous flaps (analysis of variance, p < 10(-5)). For the skin flap model, statistical significance of the survival area difference was reached at 6, 10, and 14 hours of ischemi a (t test, p < 10(-4)). The magnitude of this effect was higher in the myocutaneous flap model and reached statistical significance at 2, 4, 6, and 10 hours of ischemia (p < 10(-3)). Preconditioned flap surviva l areas were increased by two to five times that of non-preconditioned flaps at these ischemia times. Preconditioning lowered total necrosis rates at all ischemia times for both flap models. The critical ischem ia time when 50 percent of skin flaps became totally necrotic (CIT50) improved from 6.9 to 12.4 hours by preconditioning. Similarly, precond itioning improved the CIT50 of myocutaneous flaps from 3.6 to 9.2 hour s. For the first time, statistically significant improvements of parti al necrosis areas and total necrosis rates have been demonstrated thro ugh intraoperative ischemic preconditioning of skin and myocutaneous f laps. In clinical practice, application of this technique may lead to improved survival during pedicled or free transfer of myocutaneous fla ps and free transfer of skin flaps.