Althesin, ketamine and methohexitone at pressure--duration of action of a single i.v. dose.

General anaesthesia for emergency surgery in a pressurized habitat is likely to involve the use of i.v. agents. The anaesthetic property of such agents is known to be antagonized by pressure, but the effect on their duration of action is not easily predicted. The recovery of mice from a single i.v. dose of Althesin, ketamine or methohexitone was estimated by their ability to remain upright in a rotating drum. At 35 atm abs. duration of action was significantly reduced: P less than 0.05 for Althesin; P less than 0.01 for ketamine and methohexitone. A number of animals in each group, however, displayed recovery times that were comparable to control. The convulsion rate with methohexitone was 60% at 35 atm abs., whereas at 1 atm abs. it was 20%. The clinical implications of these findings are discussed.