TOURNIQUET-INDUCED EXSANGUINATION IN PATIENTS REQUIRING LOWER-LIMB SURGERY - AN ISCHEMIA-REPERFUSION MODEL OF OXIDANT AND ANTIOXIDANT METABOLISM

Background: Surgically induced ischemia and reperfusion is frequently accompanied by local and remote organ injury. It was hypothesized that this procedure may produce injurious oxidants such as hydrogen peroxi de (H2O2), which, if unscavenged, will generate the highly toxic hydro xyl radical (. OH). Accordingly, it was proposed that tourniquet-induc ed exsanguination for limb surgery may be a useful ischemia-reperfusio n model to investigate the presence of oxidants, particularly H2O2. Me thods: In ten patients undergoing knee surgery, catheters were placed in the femoral vein of the limb operated on for collection of local bl ood and in a vein of the arm for sampling of systemic blood. Tournique t-induced limb exsanguination was induced for about 2 h. After tourniq uet release (reperfusion), blood samples were collected during a 2-h p eriod for measurement of H2O2, xanthine oxidase activity, xanthine, ur ic add (UA), glutathione, and glutathione disulfide. Results: At 30 s of reperfusion, H2O2 concentrations increased (approximate to 90%) fro m 133 +/- 5 to 248 +/- 8 nmol .. ml(-1) (P < 0.05) in local blood samp les, but no change was evident in systemic blood. However, in both loc al and systemic blood, xanthine oxidase activity increased approximate to 90% (1.91 +/- 0.07 to 3.93 +/- 0.41 and 2.19 +/- 0.07 to 3.57 +/- 0.12 nmol UA . ml(-1). min(-1), respectively) as did glutathione conce ntrations (1.27 +/- 0.04 to 2.69 +/- 0.14 and 1.27 +/- 0.03 to 2.43 +/ - 0.13 mu mol . ml(-1), respectively). At 5 min reperfusion, in local blood, H2O2 concentrations and xanthine oxidase activity peaked at 796 +/- 38 nmol . ml(-1) (approximate to 500%) and 11.69 +/- 1.46 nmol UA . ml(-1). min(-1) (approximate to 520%, respectively. In local blood, xanthine and UA increased from 1.49 +/- 0.07 to 8.36 +/- 0.33 nmol . ml(-1) and 2.69 +/- 0.16 to 3.90 +/- 0.18 mu mol . ml(-1), respectivel y, whereas glutathione and glutathione disulfide increased to 5.13 +/- 0.36 mu mol . ml(-1) and 0.514 +/- 0.092 mu mol . ml(-1), respectivel y. In systemic blood, xanthine oxidase activity peaked at 4.75 +/- 0.2 0 UA nmol . ml(-1). min(-1). At 10 min reperfusion, local blood glutat hione and UA peaked at 7.08 +/- 0.46 mu mol . ml(-1) and 4.67 +/- 0.26 mu mol . ml(-1), respectively, while the other metabolites decreased significantly toward pretourniquet levels. From 20 to 120 min, most me tabolites returned to pretourniquet levels; however, local and systemi c blood xanthine oxidase activity remained increased 3.76 +/- 0.29 and 3.57 +/-: 0.37 nmol UA . ml(-1). min(-1), respectively. Systemic bloo d H2O2 was never increased during the study. During the burst period ( approximate to 5-10 min), local blood H2O2 concentrations and xanthine oxidase activities were highly correlated (r = 0.999). Conclusions: T hese studies suggest that tourniquet-induced exsanguination for limb s urgery is a significant source for toxic oxygen production in the form of H2O2 and that xanthine oxidase is probably the H,O-2-generating en zyme that is formed during the Ischemia-reperfusion event. In contrast to the reperfused leg, the absence of H2O2 in arm blood demonstrated a balanced oxidant scavenging in the systemic circulation, despite the persistent increase in systemic xanthine oxidase activity.