The most common complication in flap surgery is of a circulatory nature. Impeded blood flow leads to altered metabolism in the tissue. Possible metabolic differences between different zones of the transverse rectus abdominis muscle (TRAM) flap were studied and the metabolism of pedicled and free TRAM flaps was compared intraoperatively and postoperatively. The method used was microdialysis, which is a useful technique for following local metabolic changes continuously in various tissues.Twenty-two patients with a pedicled or free TRAM flap were monitored using the microdialysis technique. Two microdialysis catheters were placed subcutaneously in the flap (zone I and zone II), and a third one was placed subcutaneously in the flank to serve as a control. The flaps were monitored intraoperatively and postoperatively for 3 days with repeated analyses of extracellular glucose, lactate, and glycerol concentrations. An additional analysis of pyruvate was performed in some patients to calculate the lactate-to-pyruvate ratio. This study showed that glucose, lactate, and glycerol change in a characteristic way when complete ischemia (i.e., complete inhibition of the blood circulation) is present. A slower stabilization with prolonged metabolic signs of ischemia, such as lower glucose and higher lactate and glycerol concentrations, was seen in zone II compared with zone I, and more pronounced metabolic signs of ischemia, but with a faster recovery, were detected in the free TRAM flap group than in the pedicled TRAM flap group. The fact that the metabolites returned to normal earlier in free flaps than in pedicled flaps may indicate that free TRAM flaps sustain less ischemic damage because of better and more vigorous perfusion.

The aim of this investigation was to follow the metabolism of myocutaneous flaps using microdialysis. After subcutaneous implantation of a microdialysis catheter into the flap tissue, serial samples were collected and changes in composition of the extracellular fluid assessed. Ten women underwent reconstructions with transverse rectus abdominis myocutaneous (TRAM) or latissimus dorsi flaps. Glucose, glycerol, and lactate concentrations were measured in the flaps and compared with those in adipose control tissue located over the hip. A transient rise in glucose was observed initially in the flaps. The glycerol concentration also increased significantly, and remained increased for approximately 12 hours after the operation. The lactate concentration changed in the same direction, but stayed elevated in the flap tissue during the entire investigation (24 hours). Neither of these parameters changed to the same extent in the control tissue. In one of the patients a haematoma developed postoperatively in the flap. This incident was accompanied by a sharp decline in glucose, and marked additional increases in glycerol and lactate concentrations. It may well be that this "metabolic pattern" in flap tissue signals threatening flap ischaemia. If so, this new microdialysis technique may be useful as a postoperative surveillance tool in myocutaneous flap surgery.

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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.