A knowledge of the rate of fluid loss from the body is a useful aid in planning treatment of patients with severe burns. Different methods for obtaining this data have been investigated. Evaporation rates recorded from a probe evaporimeter have been compared with gravimetric measurements. The evaporimeter underestimated evaporation, especially at high levels, but could be calibrated against known evaporation rates. Estimates of whole-body fluid loss have been made from calibrated evaporimeter data and results compared with measurements of fluid loss by weight change for three patients. Problems with assessing whole-body evaporation rates in the clinical environment are highlighted. Weight change gives a more accurate assessment of total body fluid loss, but considerable effort is necessary to record all relevant information. Probe evaporimeter measurements are simple to perform and allow local evaporation rates to be estimated, but results should be treated with caution. Evaporation rates from wounds of 17 patients with severe burns have been evaluated in terms of surface diffusion resistances. The diffusion resistances of some burn wounds increased with time, but many did not change significantly during the first ten days after injury, and there was considerable variation with burn type and severity.
The influence of the thermal environment on heat losses from patients with severe burns has been studied. Burn wounds were several degrees cooler than intact skin when patients were admitted to hospital. Wound temperatures gradually increased, becoming similar to those of intact skin by three days after injury. Temperatures of intact skin in peripheral regions of burned patients were raised. Evaporation of fluid from wounds of patients with 15-36% burns increased heat loss by 50-120 W, but sweating could increase heat losses by several hundred watts. Patients with large percentage burns tended to sweat less than others with smaller burns, under the same conditions. Patients with over 30% burns could be treated at air temperatures up to 35 degrees C without inducing sweating in the Intensive Care Room, which had forced airflow and good temperature control. Patients treated in standard wards where it was difficult to maintain a constant air temperature were more likely to sweat.
Heat losses from burned patients need to be reduced to avoid placing unnecessary demands on body metabolism. In order to allow more accurate assessments of heat loss, heat transfer has been studied in a clean air unit used for intensive care of burned patients. Evaporation rates have been measured from a phantom representing a recumbent human torso with burn wounds simulated by moist lint strips mounted on the surface. Heat transfer is determined by a complex interaction of free and forced convection, with evaporation rate being greatest on the side of the abdomen in free convection and towards the top in the forced case. Air diffusion resistances have been derived to describe evaporative heat transfer from different parts of a body. Equations have been fitted to data obtained under a wide range of conditions, and will be used to evaluate heat losses from burned patients in order to improve treatment conditions.
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