Prediction of border necrosis in skin flaps of pigs with microdialysis

Metabolic changes were studied in newly-raised pedicled skin flaps of pigs. These flaps were constructed so that their distal parts were predestined t o necrotize. The objective was to find new ways of making early postoperati ve prognostications about future flap viability. For that purpose, the fluo rescein penetration technique was compared with microdialysis monitoring of interstitial tissue concentrations of glucose, lactate, and glycerol. Thes e parameters were measured 6 to 24 hr postoperatively, and collected at fiv e different sites, ranging from base to end of the flap. The fluorescein pe netration border appeared closer to the flap base than a subsequent necroti c border, thereby confirming that this technique-when applied early in the postoperative period-underestimates flap viability. The authors also observ ed that glucose concentration in the flap declined at an early stage close to the border of fluorescein penetration. No further change was seen in mor e distal parts of the flap. Consequently, glucose concentration underestima tes the viable flap area just as fluorescein does. In contrast, both glycer ol and lactate concentrations began to increase closer to the necrotic bord er. Both increased significantly on passing the border between viable tissu e and tissue which later on would become necrotic, and reached levels in th e necrotic portion which were never seen in the viable parts. These results were obtained within the first postoperative hours. They suggest that micr odialysis monitoring of lactate and glycerol concentrations in skin flaps o f pigs can be used to estimate at an early stage where the necrotic border will appear later on. If these results hold true in humans, they may have i mportant clinical applications.