Background: Rapid induction of profound hypothermia can improve survival from uncontrolled lethal hemorrhage. However, the optimal depth of hypothermia in this setting remains unknown. This experiment was designed to compare the impact of deep (15°C), profound (10°C), and ultraprofound (5°C) hypothermia on survival and organ functions. Methods: Uncontrolled lethal hemorrhage was induced in 32 swine (80-120 lb) by creating an iliac artery and vein injury, followed 30 minutes later by laceration of the descending thoracic aorta. Hypothermia was induced rapidly (2°C/min) by infusing cold organ preservation solution into the aorta through a thoracotomy. The experimental groups were (n = 8 per group): a normothermic control, and 3 hypothermic groups in which the core temperature was reduced to 15°C, 10°C, and 5°C. Vascular injuries were repaired during 60 minutes of hypothermia. Animals were then rewarmed (0.5°C/min) and resuscitated on cardiopulmonary bypass, and monitored for 6 weeks for neurologic deficits, cognitive function, and organ dysfunction. Results: All normothermic animals died, whereas 6-week survival rates for the 15°C, 10°C, and 5°C groups were 62.5%, 87.5%, and 25%, respectively (P < .05: normothermic vs 15°C and 10°C; 10°C vs 5°C). The surviving animals from the 15°C and 10°C groups were neurologically intact, displayed normal learning capacity, and had no long-term organ dysfunction. The survivors from the 5°C group displayed slower recovery and impaired cognitive functions. Conclusions: In a model of lethal injuries, rapid induction of profound hypothermia can prevent death. The depth of hypothermia influences survival, with a better outcome associated with a core temperature of 10°C compared with 5°C.
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