Tourniquet-induced changes of energy metabolism in human skeletal muscle monitored by microdialysis

Background: Tourniquets are often used as part of orthopedic surgery but ma y cause local and remote organ injury. The authors hypothesized that the pr ocedures used to induce ischemia (circulatory occlusion or exsanguination) may have differential effects on the metabolic state of the muscle that sho uld be reflected in the interstitial levels of metabolites. Methods: Microdialysis probes were implanted in both quadriceps femoris mus cles of 18 patients. Interstitial fluid was obtained during tourniquet-indu ced ischemia and reperfusion and was analyzed for glucose, lactate, choline , and purines by high-performance liquid chromatography. Results: At a flow rate of 2 mul/min, the average baseline concentrations i n the dialysate were 2.5 mM for glucose, 1.7 mM for lactate, 5.2 muM for ch oline, and 14.3 muM for hypoxanthine. Circulatory occlusion by tourniquet c aused a 40% decrease of the extracellular glucose concentration within 30 m in. Concomitantly, the interstitial levels of lactate and hypoxanthine incr eased in a linear fashion to 206% (lactate) and 241% (hypoxanthine) of basa l values. The extracellular concentration of choline was also significantly elevated. After exsanguination, the glucose levels were significantly more reduced (by 65%), and the levels of lactate (to 268%) and hypoxanthine (to 286%) were more increased than after circulatory occlusion alone. Conclusion: Our microdialysis results demonstrate that the interstitial con centrations of glucose, lactate, and hypoxanthine, which are indicators of tissue ischemia, change more prominently after exsanguination than after ci rculatory occlusion alone.