Effects of timing and duration of hypothermia on survival in an experimental gerbil model of global ischaemia.

PURPOSE Despite the use of animal models to study post-cardiac-arrest resuscitation, the effects of hypothermia on physiological circulatory parameters are still not fully understood. In this study, using a gerbil model of global ischaemia/reperfusion, we aimed to assess the effects of hypothermia on physiological parameters and evaluated the optimal timing for the induction of hypothermia to achieve a better survival rate. METHODS Survival rates at 72 h after reperfusion were evaluated by varying the degree of hypothermia and/or duration of ischaemia, and then examined by varying induction timing and/or extending the duration of ischaemia. Physiological parameters were measured using an intravital microscopy system. RESULTS Under normothermic cerebral ischaemia, the survival rate was dramatically decreased by the induction of 15-20 min of ischaemia. Induction of hypothermia significantly improved the survival rate only when it occurred less than 10 min after ischaemic onset. In the hypothermia-treated groups, post-ischaemic hyperperfusion was significantly suppressed, and post-ischaemic vasoconstriction of the pial arteriole was prevented. CONCLUSIONS Hypothermia-induced suppression of post-ischaemic hyperperfusion and the prevention of vasoconstriction of the pial arteriole play an important role in improving the survival rate after global ischaemia/reperfusion, but the time window for induction of hypothermia remains relatively narrow.