High pressure and intravenous steroid anesthesia in rats.

Anesthesia produced by the intravenous steroid agent, Althesin, was studied in Sprague-Dawley rats with and without high pressure of helium gas up to 100 atmospheres absolute (ATA). There were no cumulative or adaptive changes in Althesin requirement at normal pressures over 6-h periods. However, the apparent potency of the agent was reduced by 43% by the addition of 68 ATA helium. Subanesthetic doses of Althesin protected against the onset of convulsions and coarse tremors associated with the high pressure neurological syndrome. It is concluded that the steroid anesthetics may have a place in human diving technology and that the mechanisms associated with the anesthetic-pressure interactions are consistent with the critical volume or lipid bilayer fluidity hypothesis.