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Efficacy of forced-air warming systems with full body blankets

[Efficacité des systèmes de chauffage à air pulsé avec des couvertures à champ complet]

Anselm Bräuer, PhD^*, Michael J.M. English, FRCA, Nicolas Steinmetz^*, Nadja Lorenz, MD^*, Thorsten Perl, MD^*, Wolfgang Weyland, PhD and Michael Quintel, PhD^*

^* From the Department of Anesthesiology, Emergency and Intensive Care Medicine, University of Göttingen, Germany; the
Department of Anesthesia, Montreal General Hospital and McGill University, Montreal, Quebec, Canada; and the
Department of Anesthesia and Intensive Care Medicine, Evangelisches Bethesda-Krankenhaus Essen, Germany.

Address correspondence to: PD Dr. med. Anselm Bräuer, Department of Anesthesiology, Emergency and Intensive Care Medicine, University of Göttingen, Robert-Koch-Str. 40, D-37075 Göttingen, Germany. Phone: ++49-551-39-8826; Fax: ++49-551-39-8676; E-mail: abraeue{at}gwdg.de

Purpose: Postoperative hypothermia after cardiac surgery is still a common problem often treated with forced-air warming. This study was conducted to determine the heat transfer efficacy of 11 forced-air warming systems with full body blankets on a validated copper manikin.

Methods: The following systems were tested: 1) Bair Hugger® 505; 2) Bair Hugger® 750; 3) Life-Air 1000 S; 4) Snuggle Warm®; 5) Thermacare®; 6) Thermacare® with reusable Optisan® blanket; 7) WarmAir®; 8) Warm-Gard®; 9) Warm-Gard® and reusable blanket; 10) WarmTouch®; and 11) WarmTouch® and reusable blanket. Heat transfer of forced-air warmers can be described as follows: = h · T · A. Where = heat flux (W), h = heat exchange coefficient (W·m^–2·°C^–1), T = temperature gradient between blanket and manikin surface (°C), A = covered area (m²). Heat flux per unit area and surface temperature were measured with 16 heat flux transducers. Blanket temperature was measured using 16 thermocouples. The temperature gradient between blanket and surface (T) was varied and h was determined by linear regression analysis. Mean T was determined for surface temperatures between 32°C and 38°C. The covered area was estimated to be 1.21 m².

Results: For the 11 devices, heat transfers of 30.7 W to 77.3 W were observed for surface temperatures of 32°C, and between –8.8 W to 29.6 W for surface temperatures of 38°C.

Conclusion: There are clinically relevant differences between the tested forced-air warming systems with full body blankets. Several systems were unable to transfer heat to the manikin at a surface temperature of 38°C.