Heat transfer capabilities of surface cooling systems for inducing therapeutic hypothermia

Abstract

Therapeutic Hypothermia has emerged as a strong neuroprotective treatment for ischemic patients after myocardial infarction and stroke. Body surface cooling systems allow for a simple non-invasive method to induce therapeutic hypothermia in ischemic patients. The performance of three body surface cooling systems were compared in this study. They were 1) Arctic Sun with ArcticGel pads (AS); 2) Blanketrol III with Maxi-Therm Lite blankets (BL); and 3) Blanketrol III with Kool Kit (KK). The purpose of this study was to test the hypothesis that the Blanketrol III with the Kool Kit provides the most heat transfer due to its tighter fit and increased surface area in highly perfused areas of the body (e.g., the torso) compared to the other two systems. Eight participants were enrolled and cooled on three separate occasions (one for each condition). Shivering was not inhibited. Participants were cooled until either: 1) core temperature (Tco) reached 35°C; 2) 120 minutes elapsed; or 3) the participant or researcher wished to stop for any reason. Heat loss was the main performance measure. Heat loss was transiently highest with AS at the start of cooling, but there were no differences between systems at the end of cooling. AS also produced a significant reduction in ΔTco in comparison to the KK condition from 30 to 60 minutes of cooling (p < 0.05) and the BL condition from 60 to 120 minutes (p < 0.05). Results suggest that each of the cooling systems had its own benefits and limitations. Heat transfer capabilities of each system is dependent on the cooling pump unit and the design of the water-perfused covers. Both cooling pump units in this study had similar performances in their ability to reduce water temperature (output temperature was 4°C). However, the Blanketrol III unit likely had a greater flow rate and therefore may have more cooling power. AS had an early transient advantage in heat removal, but this effect decreased over the course of cooling and may represent a minimal advantage in longer periods of cooling that are recommended in guidelines.