Ischemic preconditioning of musculocutaneous flaps: effects of ischemia cycle length and number of cycles.

Previous work in our laboratory has indicated that ischemic preconditioning improves musculocutaneous flap survival 2.5 times that of the control flap area when the flaps are subsequently subjected to 4 hours of global ischemia. The preconditioning protocol used in this study was arbitrarily designed to be 10 minutes of pedicle clamping followed by 10 minutes of reperfusion. This sequence was repeated for three cycles with a total preconditioning time of 1 hour. There are no published works comparing different preconditioning protocols in musculocutaneous flaps. The goal of this study was to determine if the ischemic cycle time and the number of cycles influenced the effectiveness of ischemic preconditioning. Fifty-one male Sprague-Dawley rats were divided into one control and six treatment groups of 6 to 10 animals in each group. A transverse rectus abdominis musculocutaneous flap based on the inferior epigastric vessels was elevated in each animal. Flaps were preconditioned by pedicle clamping and reperfusion for either 5 or 10 minutes per cycle. This was repeated for one, two, or three cycles. Controls were simply perfused for 30 minutes. Each flap was then subjected to 4 hours of global ischemia. Flap surface survival area was calculated on the fifth postoperative day by computerized video planimetry. Differences in survival areas between control and preconditioned flaps were compared using analysis of variance and t-tests. There was an overall statistical significance in the comparison of flap survival of preconditioned flaps with that of controls. A single 5-minute cycle improved flap survival 2.5 times the mean control area. Two and three 5-minute cycles resulted in a reduction of the preconditioning effect, with flap survival no different than controls. Ten-minute preconditioning cycles increased flap survival 1.5 to 3 times the mean control area. Flap survival was improved by increasing the number of 10-minute cycles. Cycle time and number of cycles have definite effects on the survival areas of preconditioned musculocutaneous flaps. Ischemic preconditioning with 10-minute cycles is superior to 5-minute cycles. Three cycles of 10-minute preconditioning is statistically superior to one or two cycles. Future studies are planned to study four or more cycles and longer cycle times.