Choice reaction time. A method of measuring postoperative psychomotor performance decrements.

Postoperative psychomotor performance changes were measured in three groups of thirteen subjects using a portable serial four-choice reaction time apparatus. Anaesthesia consisted of either thiopentone, nitrous oxide and halothane (thiopentone subjects) or methohexitone and fentanyl/nitrous oxide and incremental methohexitone (methohexitone subjects). Tests were performed on the day before operation and after 2, 4, 6, 8 and approximately 24 hours recovery on both groups of patients and at approximately the same times on nonoperated control patients. Control subjects' mean four-choice reaction time decreased steadily with practice such that the difference between first and last tests was statistically significant. Mean four-choice reaction times of thiopentone and methohexitone subjects increased from 515 to 550 ms and 552 to 600 ms respectively after 2 hours recovery. Subsequently four-choice reaction times decreased in both groups although methohexitone subjects were still significantly slower than controls after 6 hours. Thiopentone subjects were slower than controls at 2, 4 and 8 hours recovery. There was no difference between the three groups of subjects after 24 hours recovery.