Effect of hypothermia on blood-flow responses in pedicled groin flaps in rats

Cooling is widely used for preserving tissues such as kidneys before transplantation and for preserving extremities before replantation. Hypothermia has also been shown to be effective in the temporary storage of free flaps. However, in the intact living body, cooling can be damaging to tissue and the body system. We used a custom-designed clamping method (after flap elevation, occlusion and release of the flap-feeding artery) and continuous laser Doppler flowmetry to investigate the effects of hypothermia on blood flow and postocclusive reactive hyperaemia in the flaps. The animal model used was the partially elevated epigastric flap of adult Sprague-Dawley rats. In the hypothermia group (n=12), the core temperature and the flap temperature were allowed to fall during anaesthesia. At core temperatures of 34.58 degrees C and 338 degrees C and after rewarming of the rat, the feeding artery was occluded for 30 s and 120 s to observe the changes in blood flow and postocclusive reactive hyperaemia in the flap. In the control group (n=12), the core temperature was maintained at more than 378 degrees C throughout the experiment. To compare the flap blood-flow responses to occlusion of the femoral artery in the hypothermia group and the control group, the postocclusive reactive hyperaemia periods (i.e. blood flow above baseline after clamp release) were analysed. Statistical analysis of the responses showed that the magnitude (P=0.024), duration (P<0.001) and amplitude (i.e. peak flow) (P=0.037) of postocclusive reactive hyperaemia were significantly decreased in the hypothermia group. Our results suggest that hypothermia significantly decreases blood flow and postocclusive reactive hyperaemia in the rat epigastric flap. This may increase the risk of ischaemic flap complications unless rewarming is performed.