Mild hypothermia preserves cerebral cortex microcirculation after resuscitation in a rat model of cardiac arrest.

Objective: Mild hypothermia improves the outcomes of comatose patients after cardiac arrest. Its neuroprotective mechanism is not fully understood. We investigated the effects of mild hypothermia on cerebral cortex microcirculation and cerebral oxygen extraction ratio.

Methods: Twenty-five rats were randomized into the hypothermic group (HT), normothermic group (NT) or the sham control group. Ventricular fibrillation was electrically induced and untreated for 8 min, followed by 8 min of precordial compressions and mechanical ventilations. The core temperature in the HT group was reduced to 33±0.5 °C at 14 min after ROSC with a combination of ice packs, an electrical fan and a cooling blanket. The temperature was maintained at 33 °C for 8h. Hemodynamics, arterial and jugular venous blood gases and cerebral cortex microcirculation were measured at baseline, 2, 4 and 8h after ROSC.

Results: Microvascular flow index was significantly reduced in the NT and HT groups when compared with the SC group. A significant lesser reduction in microvascular flow index was observed in the HT group when compared with the NT group. Mild hypothermia reduced the cerebral oxygen extraction ratio after resuscitation when compared with the NT group.

Conclusion: Mild hypothermia improves the cerebral cortex microcirculatory blood supply/oxygen uptake mismatching after resuscitation. This may provide an additional cerebral protection.