• Harris W Kashtan, Meryl A Simon, Carl A Beyer, Andrew Wishy, Guillaume L Hoareau, J Kevin Grayson, and M Austin Johnson.
• Clinical Investigation Facility, David Grant USAF Medical Center, 101 Bodin Cir, Travis Air Force Base, CA.
• Mil Med. 2020 Jan 7; 185 (Suppl 1): 42-49.

IntroductionExternal cooling of ischemic limbs has been shown to have a significant protective benefit for durations up to 4 hours.Materials And MethodsIt was hypothesized that this benefit could be extended to 8 hours. Six swine were anesthetized and instrumented, then underwent a 25% total blood volume hemorrhage. Animals were randomized to hypothermia or normothermia followed by 8 hours of Zone 3 resuscitative endovascular balloon occlusion of the aorta, then resuscitation with shed blood, warming, and 3 hours of critical care. Physiologic parameters were continuously recorded, and laboratory specimens were obtained at regular intervals.ResultsThere were no significant differences between groups at baseline. There were no significant differences between creatine kinase in the hypothermia group when compared to the normothermia group (median [IQR] = 15,206 U/mL [12,476-19,987] vs 23,027 U/mL [18,745-26,843]); P = 0.13) at the end of the study. Similarly, serum myoglobin was also not significantly different in the hypothermia group after 8 hours (7,345 ng/mL [5,082-10,732] vs 5,126 ng/mL [4,720-5,298]; P = 0.28). No histologic differences were observed in hind limb skeletal muscle.ConclusionWhile external cooling during prolonged Zone 3 resuscitative endovascular balloon occlusion of the aorta appears to decrease ischemic muscle injury, this benefit appears to be time dependent. As the ischemic time approaches 8 hours, the benefit from hypothermia decreases.Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2020.

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