Mild hypothermia alters the oxygen consumption/delivery relationship by decreasing the slope of the supply-dependent line.

Abstract

To evaluate the effect of mild hypothermia on the relationship between systemic oxygen consumption and oxygen delivery. Prospective animal study. University research laboratory. Anesthetized and ventilated rabbits. Rabbits were subjected to stepwise cardiac tamponade to reduce oxygen delivery while body temperature was maintained at 34 degrees C (group H, n = 8) or 39 degrees C (group N, n = 8). The oxygen consumption/oxygen delivery relationship was analyzed by the dual-line method. The slope of the supply-dependent line was significantly decreased in group H (y = 0.57x + 1.3) compared with that in group N (y = 0.72x + 1.7), indicating that the ability of tissues to extract oxygen was impaired during hypothermia. Consequently, the proportion of the supply-independent area over the entire range of oxygen delivery was decreased in response to hypothermia. The potential for tissue hypoxia is likely to be increased during hypothermia when the circulation becomes unstable and oxygen delivery decreases.