THE EFFECT OF GENERAL ANESTHESIA ON THE CHEMICAL COMPOSITION OF BLOOD PLASMA OF NORMAL RABBITS

¹ Department of Ophthalmology Research, College of Physicians and Surgeons, Columbia University, New York, New York

Changes in the chemical composition of blood plasma of rabbits during anesthesia induced with pentobarbital, urethane and halothane were studied. Anesthesia with each of these agents reduced blood plasma [K⁺], elevated plasma [Mg⁺⁺] and did not alter plasma [Na⁺]. Anesthesia with urethane and halothane but not pentobarbital resulted in pronounced hyperglycemia and depression of plasma [Ca⁺⁺]. The PO₂ was slightly depressed under pentobarbital and urethane anesthesia and was elevated during administration of the halothane-O₂ mixture. Halothane and, to a lesser extent, pentobarbital, but not urethane, anesthesia increased the pCO₂ in blood and resulted in acidosis. Maintained alkalosis under pentobarbital anesthesia did not affect the anesthesia-induced changes in [K⁺] and [Mg⁺⁺]. The extent and time course of these electrolyte changes suggest that they could not be accounted for by changes in the rate of urinary excretion alone. These results, together with the results on curarized, unanesthetized animals, suggest a relationship between the depression of plasma [K⁺] and decreased muscle activity. The mechanism of the increased plasma [Mg⁺⁺] is obscure, but it appears to be related to the state of anesthesia. These results indicate that general anesthesia induced with any agent is likely to result in significant changes in the chemical composition of blood plasma, and such effects should be taken into consideration in the evaluation of experimental results obtained in anesthetized animals.