Local hypothermia during ischemia or reperfusion in skeletal muscles

A modified rat hindlimb tourniquet model was used to measure postischemic muscle necrosis. The effect of moderate local hypothermia to 20 degrees C during ischemia and reperfusion was investigated. Eighteen animals were kept in an incubator at 27 degrees C, and complete circulatory arrest was maintained for 3.5 h before release of the vascular occlusion. After survival for 72 h the degree of necrosis in the anterior tibial muscles was measured morphometrically on histological slides. Areas of necrosis with intact capillary structure and resorption of muscle fibers, and areas without resorption and capillary disintegration were measured separately. Three experimental groups (six animals in each) were included in the series. In the first group local cooling to 20 degrees C was performed during the initial 1.5 h of ischemia. The second group was cooled for 1.5 h during the initial phase of reperfusion. The animals in the third group served as controls without cooling. The total areas of necrosis in the three groups were 0, 90 and 90%, and the areas of no-resorption 0, 23 and 39%, respectively. Cooling during ischemia thus had a marked effect, while no significant differences were found between the control group and the group cooled during reperfusion. The study shows that moderate cooling during initial ischemia protects effectively against postischemic muscle necrosis, while cooling during reperfusion has no such effect.