The effect of hypothermia on gas exchange in anaesthetized rats in a confined atmosphere.

Both hypothermia and anaesthesia are known to prolong hypoxic survival. The combined effect of anaesthesia and hypothermia on survival in a confined atmosphere was studied in rats whose O2 consumption (VO2) produced hypoxia. Blood gases and respiratory parameters were measured in either ambient temperature TA = 30 degrees C (final body temperature TB = 36 degrees C) or initial TA = 30 degrees C followed by TA = 0 degree C below 100 torr inspired O2 (final TB = 19 degrees C). Oxygen consumption, breathing frequency and heart frequency decreased in hypoxic hypothermia compared to hypoxic normothermia. Hypothermia did not affect blood pressure, blood gas tension of pH. Hypothermia in hypoxia: 1) reduced the demand for oxygen with respect to O2 transport; 2) abolished the normothermic elevation of lactate in the blood, and 3) maintained high arterial saturation of oxygen. In contrast with awake rats (our previous study), there was no difference in the terminal inspired PO2 and survival time for normothermia and hypothermia in the anaesthetized rat, but survival time was doubled by anaesthesia as compared to awake rats due to reduced VO2.