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 quantita tive analysis was applied as a complementary approach to determine the relative contributions of several non-respiratory components to the a rterial acid-base response. Acute decrease in body temperature (TB) lo wered 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 [A(tot)], although both tot al phosphorus [PT] and inorganic phosphate [Pi] increased. The acid-ba se changes found were intermediate between those predicted by alpha-st at and pH-stat hypotheses. Deviation from the regulative alpha-imidazo le strategy was more apparent in the plasma than in the intraerythrocy te compartment. We conclude that blood pH changes observed were mainly caused by increased relative ventilation (lung ventilation per unit o f CO2 removed) and by resulting changes in P-CO2, with a minor metabol ic component but without significant contribution from ionic shifts or changes in plasma protein concentration.