Factors influencing acid-base status during acute severe hypothermia in unanesthetized rats

Blood acid-base changes were studied during acute hypothermia (4-6 h) induced by cold exposure in the unanesthetized rat. Stewart's quantitative analysis was applied as a complementary approach to determine the relative contributions of several non-respiratory components to the arterial acid-base response. Acute decrease in body temperature (TB) lowered PaCO2 (32.5 to 14.5 mmHg) and [HCO3-]a(24.20 mEq/L to 17.56 mEq/L), increased pHa (7.481 to 7.608) and diminished the [OH-]/[H+] ratio, but had no significant effect on [SID] or [Atot], although both total phosphorus [PT] and inorganic phosphate [Pi] increased. The acid-base changes found were intermediate between those predicted by alpha-stat and pH-stat hypotheses. Deviation from the regulative alpha-imidazole strategy was more apparent in the plasma than in the intraerythrocyte compartment. We conclude that blood pH changes observed were mainly caused by increased relative ventilation (lung ventilation per unit of CO2 removed) and by resulting changes in PCO2, with a minor metabolic component but without significant contribution from ionic shifts or changes in plasma protein concentration.