COMPARISON OF ACID-BASE STATUS IN CONSCIOUS AND ANESTHETIZED RATS DURING ACUTE HYPOTHERMIA

Acute hypothermia was surface-induced in unrestrained conscious rats a t two different levels, moderate (30-degrees-C T(B)) and severe (20-de grees-C T(B)). Data reflecting the acid/base status were determined. T he values obtained for moderate hypothermia were compared with the aci d/base pattern observed during hypothermia induced by two different an aesthetics, sodium pentobarbital and urethane, at room temperature. Co nscious, hypothermic animals developed an apparent respiratory alkalos is, with an increase in pH(a) (from 7.476 to 7.546 in moderate hypothe rmia and from 7.484 to 7.563 in severe hypothermia) correlated with a decrease in arterial bicarbonate levels (from 22.9 to 16.8 mmol l-1 an d from 20.7 to 14.9 mmol l-1 respectively). Lactate increased slightly in conscious, severely hypothermic rats (1.02 mmol l-1). This acid/ba se pattern was clearly different from that seen in sodium pentobarbita l (mild respiratory acidosis) and urethane-induced hypothermia (metabo lic acidosis). These results suggest that conscious rats follow a patt ern closer to that underlying the relative alkalinity shown by many po ikilotherms than to that underlying the constant pH shown in hibernati ng mammals. This latter pattern, nevertheless, approaches that observe d during moderate pentobarbital hypothermia and the acid/base pattern during shallow hypothermia in birds. Anaesthesia may interfere with th e development of the processes that lead to the acid/base pattern obse rved in conscious animals.