Delay in cooling negates the beneficial effect of mild resuscitative cerebral hypothermia after cardiac arrest in dogs: A prospective, randomized study

ObjectivePreviously, we documented that mild hypothermia (34°C) induced immediately with reperfusion after ventricular fibrillation cardiac arrest in dogs improves functional and morphologic cerebral outcome. This study was designed to test the hypothesis that a 15-min delay in the initiation of cooling after reperfusion would offset this beneficial effect. DesignProspective, randomized, controlled study. SettingAnimal intensive care unit. SubjectsA total of 22 custom-bred coonhounds. InterventionsEighteen dogs underwent normothermic ventricular fibrillation arrest (no blood flow) of 12.5 mins, reperfusion with brief cardiopulmonary bypass, defibrillation within 5 mins, intermittent positive-pressure ventilation to 20 hrs, and intensive care to 96 hrs. Three groups of six gogs each were studied: group 1, normothermic controls; group 2, core temperature 34°C from reperfusion to 1 hr; and group 3, delayed initiation of cooling until 15 mins after normothermic reperfusion, and 34°C from 15 mins to 1 hr 15 mins after cardiac arrest. Measurements and Main ResultsTympanic membrane temperature (which represented brain temperature) in group 2 reached 34°C at 6 ± 3 (SD) mins after reperfusion; and in group 3 at 29 ± 1 mins after reperfusion. Best overall performance categories achieved (1, normal; 5, brain death) compared with group 1, were better in group 2 (p <.05) but not in group 3 (NS). Similar results were found with best neurologic deficit scores (0%, normal; 100%, brain death), i.e., 44 ± 4% in group 1, 19 ± 15% in group 2 (p<.01), and 38 ± 9% in group 3 (NS). Total brain histologic damage scores (< 30 minimal damage; > 100 severe damage), however, were 150 ± 32 in group 1, 81 ± 13 in group 2 (p<.001 VS. group 1), and 107 ± 17 in group 3 (p<.05 VS. group 1). ConclusionsMild, resuscitative cerebral hypothermia induced immediately with reperfusion after cardiac arrest improves cerebral functional and morphologic outcome, whereas a delay of 15 mins in initiation of cooling after reperfusion may not improve functional outcome, although it may slightly decrease tissue damage. (Crit Care Med 1993;21:1348–1358)