A Novel Cooling Method and Comparison of Active Rewarming of Mildly Hypothermic Subjects

• Published in: Wilderness & environmental medicine Vol. 28; no. 2; pp. 108 - 115
• Main Authors: Christensen, Mark L., DO, Lipman, Grant S., MD, Grahn, Dennis A., PhD, Shea, Kate M., MD, Einhorn, Joseph, MD, Heller, H. Craig, PhD
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA Elsevier Inc 01.06.2017; SAGE Publications
• Subjects: Administration, Intravenous; Adult; afterdrop; Arteriovenous Anastomosis; Convection; Emergency; Female; glabrous skin; Humans; hypothermia; Hypothermia - etiology; Hypothermia - therapy; Immersion - adverse effects; Male; Middle Aged; rewarming; Rewarming - methods; Shivering - physiology; arteriovenous anastomosis; afterdrop; hypothermia; glabrous skin; rewarming
• ISSN: 1080-6032; 1545-1534
• DOI: 10.1016/j.wem.2017.02.009

Objective To compare the effectiveness of arteriovenous anastomosis (AVA) vs heated intravenous fluid (IVF) rewarming in hypothermic subjects. Additionally, we sought to develop a novel method of hypothermia induction. Methods Eight subjects underwent 3 cooling trials each to a mean core temperature of 34.8±0.6 (32.7 to 36.3°C) by 14°C water immersion for 30 minutes, followed by walking on a treadmill for 5 minutes. Core temperatures (Δtes) and rates of cooling (°C/h) were measured. Participants were then rewarmed by 1) control: shivering only in a sleeping bag; 2) IVF: shivering in sleeping bag and infusion of 2 L normal saline warmed to 42°C at 77 mL/min; and 3) AVA: shivering in sleeping bag and circulation of 45°C warmed fluid through neoprene pads affixed to the palms and soles of the feet. Results Cold water immersion resulted in a decrease of 0.5±0.5°C Δtes and 1±0.3°C with exercise ( P < .01); with an immersion cooling rate of 0.9±0.8°C/h vs 12.6±3.2°C/h with exercise ( P < .001). Temperature nadir reached 35.0±0.5°C. There were no significant differences in rewarming rates between the 3 conditions (shivering: 1.3±0.7°C/h, R 2 = 0.683; IVF 1.3±0.7 ° C/h, R 2 = 0.863; and AVA 1.4 ± 0.6°C/h, R 2 = 0.853; P = .58). Shivering inhibition was greater with AVA but was not significantly different ( P = .07). Conclusions This study developed a novel and efficient model of hypothermia induction through exercise-induced convective afterdrop. Although there was not a clear benefit in either of the 2 active rewarming methods, AVA rewarming showed a nonsignificant trend toward greater shivering inhibition, which may be optimized by an improved interface.