Dynaic changes in acid base balance during heatstroke in dogs

The dynamic changes in acid base balance and respiratory metabolism during the development of heatstroke in dogs were studied. Three groups of five unanesthetized dogs each were exposed to different climatic conditions while at rest: A) 24° C, 50% relative humidity (RH); B) 35° C, 35% RH, and C) 45° C, 25% RH, These conditions were maintained for 4 h or until the dogs collapsed. The heatstroke dogs were cooled in tap water bathes and were observed for another 4 h. Dogs of groups A and B did not show any notable changes in rectal temperature (T_re) and acid base balance. All dogs in group C developed heatstroke. Their peak mean T_re (44.1° C) was reached after a mean of 111 min of exposure, with respiratory alkalosis followed by increasingly severe metabolic acidosis above T_re of 42° C. At peak T_re mean arterial pH was 7.26. Acidosis increased (pHa=7.17) following cooling, as panting subsided. At T_re above 42° C blood lactate increased and bicarbonate decreased significantly, attaining mean values of 58 mg% and 8 mEq/l, respectively. Bicarbonate changes correlated linearly with lactate changes. During recovery lactate decreased and blood pH increased approximating normal by the end of the experiment. The results illustrate the body's ability to spontaneously correct arterial pH without therapeutic means.