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BJA Advance Access published online on April 19, 2004
British Journal of Anaesthesia, doi:10.1093/bja/aeh156
© 2004 by The Board of Management and Trustees of the British Journal of Anaesthesia
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Accepted February 1, 2004

Clinical Investigation

Perioperative thermal insulation: minimal clinically important differences?

A. Bräuer 1*, T. Perl 1, Z. Uyanik 1, M. J. M. English 2, W. Weyland 3, U. Braun 1

1 Department of Anesthesiology, Emergency and Intensive Care Medicine, University of Göttingen, Robert-Koch-Str. 40, D-37075 Göttingen, Germany
2 Department of Anaesthesia, Montreal General Hospital and McGill University, Montreal, Canada
3 Department of Anaesthesia and Intensive Care Medicine, Evangelisches Bethesda-Krankenhaus, Essen, Germany

* To whom correspondence should be addressed. E-mail: abraeue{at}gwdg.de.


  Abstract

Background. Reduction of heat losses from the skin by thermal insulation is used to avoid perioperative hypothermia. However, there is little information about the physical properties of various insulating materials used in the operating room.

Methods. The following insulation materials were tested using a validated manikin: cotton surgical drape tested in two and four layers; Allegiance drape; 3M Steri-Drape; metallized plastic sheet; ThermadrapeTM; Barkey thermcare 1 tested in one and two layers; hospital duvet tested in one and two layers. Heat loss from the surface of the manikin can be described as: Q·=h·{Delta}T·A where Q· is heat flux, h is the heat exchange coefficient, {Delta}T is the temperature gradient between the environment and surface and A is the area covered. The heat flux per unit area (Q·A-1) and surface temperature were measured with nine calibrated heat-flux transducers. The environmental temperature was measured using a thermoanemometer. {Delta}T was varied and h was determined by linear regression analysis as the slope of {Delta}T vs Q·A-1. The reciprocal of h defines the insulation.

Results. The insulation value of air was 0.61 Clo. The insulation values of the materials varied between 0.17 Clo (two layers of cotton surgical drapes) to 2.79 Clo (two layers of hospital duvet).

Conclusions. There are relevant differences between various insulating materials. The best commercially available material designed for use in the operating room (Barkey thermcare 1) can reduce heat loss from the covered area by 45% when used in two layers. Given the range of insulating materials available for outdoor activities, significant improvement in insulation of patients in the operating room is both possible and desirable.

Keywords: Keywords: complications, hypothermia; equipment, insulation; equipment, manikin; heat loss; measurement, heat flux


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