Heat loss in humans covered with cotton hospital blankets

We evaluated mean skin temperature, cutaneous heat loss, and perceived warmth in six volunteers covered with one or three cotton hospital blankets, warmed or unwarmed. Mean skin temperatures were significantly higher during each treatment than during the control periods preceding each blanket application. Total cutaneous heat loss during the control period was 81 +/- 11 watts. Covering the volunteers with a single warmed or unwarmed blanket for 60 min reduced heat loss 33% +/- 5%; when they were covered with three warmed or unwarmed blankets, heat loss was reduced an additional 18% +/- 6%. Warmed blankets reduced heat loss 9-16 watts more than unwarmed ones, but the benefit dissipated in approximately 10 min. The volunteers' perception of warmth was similar when they were covered with three warmed or unwarmed blankets; it also was similar when they were covered with a single warmed or unwarmed blanket. These data indicate that increasing the number of covering blankets from one to three decreases heat loss only slightly. Similarly, warming the blankets is relatively ineffective and the benefit short-lived. The reduction in heat loss, even by three warmed blankets replaced at 10-min intervals, was small compared to that provided by available active warming systems.