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 to necrotize. The objective was to find new ways of making early postoperative prognostications about future flap viability. For that purpose, the fluorescein penetration technique was compared with microdialysis monitoring of interstitial tissue concentrations of glucose, lactate, and glycerol. These parameters were measured 6 to 24 hr postoperatively, and collected at five different sites, ranging from base to end of the flap. The fluorescein penetration border appeared closer to the flap base than a subsequent necrotic border, thereby confirming that this technique--when applied early in the postoperative period--underestimates flap viability. The authors also observed that glucose concentration in the flap declined at an early stage close to the border of fluorescein penetration. No further change was seen in more distal parts of the flap. Consequently, glucose concentration underestimates the viable flap area just as fluorescein does. In contrast, both glycerol and lactate concentrations began to increase closer to the necrotic border. Both increased significantly on passing the border between viable tissue and tissue which later on would become necrotic, and reached levels in the necrotic portion which were never seen in the viable parts. These results were obtained within the first postoperative hours. They suggest that microdialysis monitoring of lactate and glycerol concentrations in skin flaps of 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 important clinical applications.