The rate of induction of hypothermic arrest determines the outcome in a swine model of lethal hemorrhage

Background: Lethal injuries can be surgically repaired under asanguineous hypothermic condition (suspended animation) with excellent outcome. However, the optimal rate for the induction of hypothermic metabolic arrest following uncontrolled lethal hemorrhage (ULH) is unknown. Methods: ULH was induced in 32 female swine (80-120 lbs) by creating an iliac artery and vein injury, followed 30 minutes later by laceration of the descending thoracic aorta. Through a left thoracotomy approach, total body hypothermic hyperkalemic metabolic arrest was induced by infusing organ preservation fluids into the aorta. Experimental groups were: normothermic controls (no cooling, NC), or hypothermia induced at a rate of 0.5degreesC/min (slow, SC), 1degreesC/min (medium, MC), or 2degreesC/min (fast, FC). Vascular injuries were repaired during the 60 minutes of profound (10degreesC) hypothermic arrest. Hyperkalemia was reversed by hypokalemic fluid exchange, and blood was infused for resuscitation during the re-warming (0.5degreesC/ minute) period. The survivors were monitored for 6 weeks. Results: The 6 week survival rates were 0% (NC), 37.5% (SC), 62.5% (MC), and 87.5% (FC) respectively (p < 0.05 MC&FC versus NC). All of the surviving hypothermic arrest animals were neurologically intact and displayed no long term organ dysfunction. Conclusion: Hypothermic metabolic arrest can be used to maintain viability of key organs during repair of lethal injuries. Survival is influenced by the rate of cooling with the best outcome following rapid induction of hypothermia.