Differential effects of hypothermia upon blood acid-base state and blood gases in sodium pentobarbital and urethane anaesthetised rats.

1. The effects of two anaesthetics, sodium pentobarbital and urethane, and the effects of anaesthesia-associated hypothermia on acid-base status and blood gases were studied in rats without assisted ventilation. 2. Manipulation of conscious rats produces a progressive increase in arterial lactate associated with slight hyperventilation. 3. Sodium pentobarbital anaesthesia produces mild respiratory acidosis accompanied by increase in lactate arterial values. Urethane anaesthesia leads to partially compensated metabolic acidosis. 4. Hypothermia reduces metabolic acidosis and hypercapnia induced by sodium pentobarbital anaesthesia. No difference between hypothermic and normothermic values was observed in urethane anaesthesia.