Cortical CO2 and O2 at high pressures of argon, nitrogen, helium, and oxygen

In 37 chloralosed cats (45–50 mg/kg) exposed to increased pressures of argon, nitrogen, or helium between 8.67 and 10.8 atm abs in the presence of either 0.2 or 2.34 atm abs oxygen or oxygen alone, the cortical carbon dioxide was measured with a modified Severinghaus electrode and the cortical oxygen polarographically. In mixtures with an oxygen partial pressure of 2.34 atm abs, the cortical oxygen increased above controls. The greater the density of the mixture then, the less was the increase. The cortical carbon dioxide also increased, but conversely, the greater the density of the mixture the greater the increase in carbon dioxide. In mixtures of low oxygen partial pressures, the cortical oxygen was below control values whereas the carbon dioxide showed little change except for a slight increase with the heavier argon mixture. Inert gas narcosis, as indicated by depression of auditory induced cortical spikes, did not correlate with the changes in cortical carbon dioxide but with the inert gas itself. Increasing the oxygen partial pressure and the density of the mixture respired caused retention of brain carbon dioxide, which synergistically potentiated the narcosis. nitrogen narcosis; inert gases; depth intoxication; tissue carbon dioxide; tissue oxygen; brain Submitted on August 10, 1964