Microdialysis – a new technique for free flap surveillance: methodological description

Early detection of impaired circulation in free flaps is vital for their survival. In the present investigation metabolic changes, known to occur in various tissues during ischemia, were studied using microdialysis. Five patients provided with free flaps, were included in the study. Microdialysis catheters were placed in the flap and in normal control tissue. Laser Doppler flowmetry was used postoperatively to verify circulatory changes. During flap transfer, and the ischemia that was induced by the operation, the glucose concentration in the interstitial flap tissue decreased substantially, whereas the lactate and glycerol concentrations both increased. When vascular anastomoses had been completed these three parameters tended to return to preoperative levels. This metabolic pattern was not seen in the control tissue, thus suggesting that it may be typical for local ischemia. In two of the patients the pattern reappeared in connection with postoperative venous thrombosis, and disappeared when the thromboses were surgically removed. This observation lends further support to the notion that transcient ischemia induces a specific metabolic pattern which can be detected by microdialysis. Consequently, microdialysis appears to be a useful tool in the surveillance of microsurgical free flaps.