Abstract
Thermal blankets which are mats with warm water circulation are often used to prevent body temperatures of anesthetized patients from decreasing in the operating room. Although the water temperature is controlled within an appropriate temperature range, burn injuries are sometimes found on the patient parts contacting the mat. The purpose of this study is to give some experimental evidence to clarify the mechanism of burn injuries found at pressurized parts under a normal temperature environment. The effects of the local pressure on temperature distribution and physiological activities in an anesthetized pig's haunch on a warm water mat were experimentally investigated. The local pressure on the haunch was found to cause (1) a decrease of blood perfusion rate, (2) a decrease of cooling rate due to blood flow, (3) an increase of local temperatures, (4) a decrease of tissue pH, and (5) a decrease of tissue oxygen saturation. These results agree with the phenomena induced by the decrease of blood flow rate. In addition, the ratio of the metabolic heat production rate under pressure to that without pressure was compared with the ratio of the blood flow rate under pressure to that without pressure. Experimental data were used for this analysis by a simplified heat transfer model. The former ratio was found to range three to four times the latter ratio for the conditions in this report. This means that the pressurized parts reach higher equilibrium temperatures than those without pressure. Finally, the effect of pressure on burn injuries at normal temperatures is discussed.
