Abstract

1. Dogs in light thiopental sodium anesthesia were subjected to 45 minutes of inhalation of 10, 20, 30 and 40 per cent CO2 in O2. A series of ten dogs was employed for each of the CO2 in O2 mixtures studied.

2. An underlying light thiopental sodium anesthesia protects the dog from convulsions and tachycardia during 45 minutes of exposure to 10, 20, 30 and 40 per cent CO2 in O2. Thiopental sodium anesthesia offers the further advantage that the distress associated with the inhalation of C2 by the unanesthetized subject is avoided.

3. A disadvantage to the use of thiopental sodium anesthesia to facilitate the administration of CO2 is the associated greater risk of respiratory arrest when CO2 in high concentrations is administered for prolonged periods.

4. When concentrations of 10, 20 and 30 per cent CO2in O2 were administered to the dog, the depression of the venous blood pH was roughly proportional to the concentration of CO2 administered and approximated twotenths (0.2) of a unit for each increment of 10 per cent in the CO2 concentration. The depression in the pH produced by the inhalation of 40 per cent CO2 in O2 was, however, only four-hundredths (0.04) greater than that produced by 30 per cent.

5. A marked increase in the amplitude of the T wave occurred during the inhalation of each of the CO₂ in O₂ mixtures studied. There was no correlation between the amount of the elevation of the T wave and the concentration of CO₂ inhaled.

6. Of the 40 dogs subjected to inhalation of CO₂, 39 made a rapid and complete recovery. The remaining animal exhibited symptoms indicative of injury to the central nervous system and on post mortem examination was demonstrated to have toxoplasmosis accompanied by a widely disseminated chronic meningoencephalitis.