Effect of mild hypothermia on the coefficient of oxygen delivery in hypoxemic dogs.

Hypothermia is one of therapeutic options in patients with severe acute respiratory failure. This study was designed to determine the optimum core temperature during hypoxemia by analyzing oxygen delivery (DO2) and consumption (VO2). Six dogs were ventilated using a mixed gas of N2 and air (fractional concn of O2 in inspired gas = 0.12) with total muscle relaxation under general anesthesia. Hypoxia (arterial PO2 approximately 35 Torr) was maintained during the experimental period. The core temperature was reduced progressively from 37 to 30 degrees C by surface cooling. The coefficient of oxygen delivery was defined as DO2 divided by VO2. In each animal, the DO2/VO2 was calculated by altering the core temperature by 1 degrees C, and its relative value was a third-order polynomial function of core temperature having a maximum value at a core temperature of 32.1 +/- 0.46 degrees C. At a core temperature of 32 degrees C, the blood lactate level was significantly lower than that at a core temperature of 37 degrees C (6.3 +/- 1.3 vs. 12.2 +/- 1.6 mg/dl; P < 0.05). The relative value of the DO2/VO2 was highest with limited lactate elevation at a core temperature approximately 32 degrees C. Under the condition of hypoxia, mild hypothermia approximately 32 degrees C may be optimal to improve oxygen demand-supply balance.