Three main requirements influence the control of the temperatures of operating suites: (1) avoid humidities which contribute to the risks of anaesthetic explosions; (2) promote the comfort and working efficiency of the staff; and (3) conserve the patient's resources.
In the United States, an air temperature of 70 to 75°F. (21 to 24°C.) with 50 to 60% relative humidity provides a compromise between the requirements of the patients and those of the operators. In Britain, a temperature of 65 to 70°F. (18 to 21°C.) and a relative humidity of 50% is “well tolerated for many hours”. In the U.S.S.R., air-conditioning should provide in summer an air temperature of 68 to 72·5°F. (20 to 22°C.) and in winter 66 to 68°F. (19 to 20°C.) with a relative humidity of 55%.
According to the American Society of Heating, Refrigeration and Air-conditioning Engineers (1961) Guide “little is known about optimum air conditions for maintaining normal body temperatures during anaesthesia and the immediate post-operative period”. Clarke and his colleagues' observation in New York City that the patient's temperature begins to rise when the wet-bulb temperature exceeds 75°F.s (23·8°C.) fills one important gap. But this finding may not apply to other populations. Deaths from heat stress have occurred in Britain with wet-bulb temperatures of this order; and in the tropics surgeons operate successfully without air-conditioning where the ambient wet-bulb temperature rarely falls much below 75°F. (23·8°C.). When temperature control is available, it is not only at high temperatures that trouble arises. Excessive cooling of the patient leads to cardiac arrhythmias.
The patient's position is more hazardous than that of those exposed to climatic extremes in industry or in the armed forces. He is not only unconscious but his responses may be poikilothermic in character because shivering is abolished and there is peripheral vasodilatation. When he is exposed to levels of warmth at which he might not maintain thermal equilibrium, his body temperature should be recorded continuously during the period of anaesthesia in the theatre and in the ward.
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