Protection Against Cold in Prehospital Care—Thermal Insulation Properties of Blankets and Rescue Bags in Different Wind Conditions

INTRODUCTION In a cold, wet, or windy environment, cold exposure can be considerable for an injured or ill person. The subsequent autonomous stress response initially will increase circulatory and respiratory demands, and as body core temperature declines, the patient's condition might deteriorate. Therefore, the application of adequate insulation to reduce cold exposure and prevent body core cooling is an important part of prehospital primary care, but recommendations for what should be used in the field mostly depend on tradition and experience, not on scientific evidence. OBJECTIVE The objective of this study was to evaluate the thermal insulation properties in different wind conditions of 12 different blankets and rescue bags commonly used by prehospital rescue and ambulance services. METHODS The thermal manikin and the selected insulation ensembles were setup inside a climatic chamber in accordance to the modified European Standard for assessing requirements of sleeping bags. Fans were adjusted to provide low (< 0.5 m/s), moderate (2-3 m/s) and high (8-9 m/s) wind conditions. During steady state thermal transfer, the total resultant insulation value, Itr (m2 C/Wclo; where C = degrees Celcius, and W = watts), was calculated from ambient air temperature (C), manikin surface temperature (C), and heat flux (W/m2). RESULTS In the low wind condition, thermal insulation of the evaluated ensembles correlated to thickness of the ensembles, ranging from 2.0 to 6.0 clo (1 clo = 0.155 m2 C/W), except for the reflective metallic foil blankets that had higher values than expected. In moderate and high wind conditions, thermal insulation was best preserved for ensembles that were windproof and resistant to the compressive effect of the wind, with insulation reductions down to about 60-80% of the original insulation capacity, whereas wind permeable and/or lighter materials were reduced down to about 30-50% of original insulation capacity. CONCLUSIONS The evaluated insulation ensembles might all be used for prehospital protection against cold, either as single blankets or in multiple layer combinations, depending on ambient temperatures. However, with extended outdoor, on-scene durations, such as during prolonged extrications or in multiple casualty situations, the results of this study emphasize the importance of using a windproof and compression resistant outer ensemble to maintain adequate insulation capacity.