COMPONENTS OF THE BLOOD ACID-BASE DISTURBANCE THAT ACCOMPANIES URETHANE ANESTHESIA IN RATS DURING NORMOTHERMIA AND HYPOTHERMIA

1. We have studied the components of the metabolic acidosis that accom panies urethane anaesthesia in rats, both with and without the hypothe rmia that results from this anaesthesia. 2. Acid-base disturbances wer e analysed with an approach based on Stewart's analysis of acid-base c hemistry. 3. The pH fall in the blood of normothermic anaesthetized ra ts (body temperature T-b) = 37 degrees C) was related to increases in plasma anions (lactate and [Cl-]), which decreased the strong ion diff erence ([SID]), as well as to increase the weak acid buffers due to in creases in albumin. 4. A stronger metabolic acidosis was found in the blood of rats with hypothermia induced by urethane (T-b=32 degrees C). Although plasma lactate was unchanged in hypothermic rats, [SID] decr eased due to alterations in the plasma ionic balance, The metabolic ac idosis found in hypothermia was also associated with increased weak ac id buffers due to increases in albumin and inorganic phosphate. Furthe r to hyperphosphataemia, signs of acute renal disfunction, such as inc reases in plasma [Mg2+] and blood urea nitrogen were found. Plasma ret ention of endogenous acids together with the retention of acid endprod ucts of the metabolism of urethane because of acute renal failure may have contributed to strengthening the fall in pH and [HCO3-] found in urethane-induced hypothermic rats.