Recipient bed vascularity and the survival of ischaemic flaps

The purpose of this study was to identify the length of the ischaemic period required to induce the 'no-reflow' phenomenon in a rat epigastric flap on an avascular recipient site. The vascularity of the recipient bed may affect flap survival in the early postischaemic stage after flap transfer. Initially, we designed epigastric flaps in 300-350 g Sprague-Dawley rats and separated the rats into four groups of 5 rats each (total 20 rats). In groups 1, 2, 3, the flaps were made ischaemic for 1 hour, 6 hours and 10 hours, respectively, by temporarily clipping the epigastric artery and vein. In group 4, the epigastric artery and vein were divided to create permanent ischaemia. In groups 1, 2 and 3, ischaemia was ended by removing the clips. After the ischaemic flaps were reperfused, their viability was studied by measuring the flap survival rate at postoperative day 7. Flap survival was studied by direct observations, laser Doppler flowmeter measurement of flap blood flow, histopathology, and carbon particle perfusion of the flap vasculature. Ischaemic flaps of groups 1 and 2 recovered almost completely after reperfusion due to the short period of ischaema. In a second series of experiments, in order to evaluate the contribution to flap survival of the recipient vascularised bed, another four groups of epigastric flaps (of 5 animals each, using the same time periods as above) were raised and a piece of Biobrane was interposed between the flap and the recipient bed before the flap wound was closed, to eliminate all nutrient supply from the recipient bed. THe results showed that the combined effect of the reperfused flap vasculature plus the metabolic contribution of the recipient bed significantly (P < 0.01) increased the extent of flap survival of the 6- and 10-hour ischaemic flaps as well as the divided pedicle flaps, which were never reperfused. An absolute 'no-reflow' rat model flap for further flap salvage studies was also developed.