BENEFICIAL EFFECT OF MILD HYPOTHERMIA AND DETRIMENTAL EFFECT OF DEEP HYPOTHERMIA AFTER CARDIAC-ARREST IN DOGS

Background and Purpose: Mild cerebral hypothermia (34-degrees-C) induced immediately after cardiac arrest improves outcome. Deep postarrest hypothermia (15-degrees-C) has not been studied. Methods: We used our dog model of normothermic ventricular fibrillation (no blood flow) of 12.5 minutes, reperfusion by brief cardiopulmonary bypass, controlled ventilation to 20 hours, and intensive care to 72 hours. Head surface cooling and bypass cooling were performed from start of reperfusion to 1 hour. Five groups of six dogs each were compared: group I, normothermic controls; group II, deep hypothermia (15-degrees-C); group III, moderate hypothermia (30-degrees-C); group IV, mild hypothermia (34-degrees-C); and group V, mild hypothermia with head surface cooling begun during no flow. Results: In control group I, five dogs remained comatose (overall performance category [OPC] 4) and one severely disabled (OPC 3). In group II, four dogs achieved OPC 4 and two dogs OPC 3 (NS versus group I). Compared with group I, OPCs were better in group III (p < 0.05), group IV (p < 0.05), and group V (p<0.05). Neurological deficit scores were also better in groups III, IV, and V than in groups I or II (p<0.05). Total brain histological damage scores were better in group III (p=0.02), group IV (p=0.06), and group V (p<0.05) than in group I. In group II, OPC and neurological deficit scores were the same and histological damage scores numerically worse than in group I and all were worse than in groups III, IV, and V (p<0.05). Cardiovascular complications and myocardial morphological damage in groups II and III were worse than in groups I, IV, and V (p<0.05). Conclusions: Mild or moderate cerebral hypothermia induced immediately after cardiac arrest improves cerebral outcome, more likely when initiated during arrest, whereas deep postarrest hypothermia can worsen cerebral and cardiac outcome.