Effects of Extended Lower Extremity Cooling Following Zone 3 REBOA in a Porcine Hemorrhage Model.

Abstract

External cooling of ischemic limbs has been shown to have a significant protective benefit for durations up to 4 hours. It was hypothesized that this benefit could be extended to 8hours. Six swine were anesthetized and instrumented, then underwent a 25% total blood volume hemorrhage. Animals were randomized to hypothermia or normothermia followed by 8hours of Zone 3 resuscitative endovascular balloon occlusion of the aorta, then resuscitation with shed blood, warming, and 3hours of critical care. Physiologic parameters were continuously recorded, and laboratory specimens were obtained at regular intervals. There 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]=15,206U/mL [12,476-19,987] vs 23,027U/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 8hours (7,345ng/mL [5,082-10,732] vs 5,126ng/mL [4,720-5,298]; P=0.28). No histologic differences were observed in hind limb skeletal muscle. While 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 8hours, the benefit from hypothermia decreases.