Introduction
No current technique has been established to effectively rewarm hypothermic victims in the prehospital environment, and testing treatments with established cooling models is suboptimal.
Objectives
To compare the effectiveness of arteriovenous anastomosis (AVA) vs heated intravenous fluid (IVF) rewarming in hypothermic subjects. Additionally, to develop a novel method of inducing mild hypothermia.
Methods
Eight subjects underwent 3 cooling trials each to a mean core temperature of <35°C by 14°C water immersion for 30 minutes, followed by walking on a treadmill for 5 minutes for convective “afterdrop” cooling. Core temperatures changes (Δtes) and rates of cooling (°C/h) were measured by continuous esophageal measurements. Participants were then rewarmed by 1) control: shivering 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; 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 0.5°C ± 0.5 Δ tes and 1°C ± 0.3 Δ tes with afterdrop (P < .01); with an immersion cooling rate of 0.9°C/h ± 0.8 vs 12.6°C/h ± 3.2 with afterdrop (P < .001). After cooling, core temperatures reached a nadir of 35.0°C ± 0.5°C. There were no significant differences in rewarming rates between the 3 conditions (shivering: 1.3°C/h ± 0.7, R2 = 0.683; IVF: 1.3°C/h ± 0.7, R 2 = 0.863; and AVA: 1.4°C/h ± 0.6, R 2 = 0.853; P = .58). Shivering inhibition was greater with AVA, but not significantly different (P = .07).
Conclusion
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 trend toward greater shivering inhibition, which may be optimized by an improved interface.