Abstract 319: Mild Hypothermia Preserves Cerebral Cortex Microcirculation After Resuscitation in a Rat Model of Cardiac Arrest

Introduction: Mild hypothermia is one of the effective treatments in comatose patients after cardiac arrest. However, its neuroprotective mechanism is not fully clear. In the present study, we investigated the effect of mild hypothermia on cerebral cortex microcirculation and cerebral oxygen extraction ratio (CERO2). Hypothesis: Mild hypothermia is associated with an improved cerebral cortex microcirculation and a decreased CERO2. Methods: Twenty-five male Sprague-Dawley rats were randomized into 3 groups: hypothermic (HT, n=10), normothermic (NT, n=10) or sham control group (SC, n=5). Ventricular fibrillation was electrically induced and untreated for 8 mins, followed by 8 mins of precordial compressions and mechanical ventilations. Core temperature was reduced to 33±0.5°C at 14 mins after return of spontaneous circulation (ROSC) with a combination of ice packs, an electrical fan and a cooling blanket. The temperature was maintained at 33°C for 8 hrs. Hemodynamics, jugular venous and aortic blood gas, and cerebral cortex microcirculation were measured at baseline, 2, 4 and 8 hrs after ROSC. Results: Of the 20 experimental rats, 15 were successfully resuscitated. There was no significant difference in the rate of ROSC in the NT and HT groups (7/10 vs. 8/10; p>0.05). Microvascular flow index was significantly reduced at 2, 4 and 8 hrs after ROSC but was significantly improved by mild hypothermia (Figure 1). Mild hypothermia significantly reduced the CERO2 after ROSC (Figure 2). Conclusions: Mild hypothermia improves the cerebral cortex microcirculatory blood supply/oxygen uptake mismatching after ROSC, which may provide one additional mechanism of cerebral protection.