In which period of skeletal muscle ischemia-reperfusion injury is local hypothermia more effective?

Objectives: We investigated the potential beneficial effects of local hypothermia applied during different periods of ischemia-reperfusion injury in a rat model. Methods: An isolated gracilis muscle model of ischemia-reperfusion injury was used consisting of four groups, each with six rats. Ischemic injury was induced by clamping the femoral artery for six hours. Local hypothermia at 10 °C was applied during only ischemia (IH), during reperfusion (RH) for four hours, and during both ischemia and reperfusion (IRH). The control group remained untreated. After 24 hours of perfusion, the rats were sacrificed and the gracilis muscles were removed to determine muscle edema (wet-to-dry weight ratio), polymorphonuclear leukocytes (PMNL), and the percentage of necrosis. Results: Compared to the control group (193.7 ±38.9), the PMNL count was significantly lower in the IH, RH, and IRH groups (111.5±36.2, p<0.004; 82±18.6, p<0.002; 54.5±21.8, p<0.002, respectively). The only significant difference in the PMNL count was between the IH and IRH groups (p<0.004). In all the hypothermia groups, the percentage of necrosis was found significantly less than that of the control group (22.5±5.2% vs 11.7±5.2% in IH, p<0.004; 10.8±3.8% in RH, p<0.004; 6.7±2.6% in IRH, p<0.002).Similarly, muscle edema was significantly decreased in the study groups (control, 2.89±0.46 vs 2.01±0.26 in IH, p<0.001; 1.98±0.34 in RH, p<0.001; 1.97±043 in IRH, p<0.001). There were no significant differences between the three hypothermia groups with respect to the percentage of necrosis and muscle edema. Conclusion: Our results show that local hypothermia applied during ischemic and reperfusion periods is significantly effective in reducing ischemia-reperfusion injury.