Thirty human subjects were exposed for four hours to 500 ppm N-2O and 15 ppm enflurane in air and then, within five minutes, given a 35-minute battery of psychological tests. Performance of a divided-attention audiovisual task and a digit-span memory test were significantly decreased compared with control data following exposure to air. A tachistoscopic task, four tests from the Wechsler memory scale, and five others from the Wechsler Adult Intelligence Scale were unaffected. Thirty subjects exposed to 500 ppm N-2-O in air only scored significantly lower on the digit-span test only.
The principal findings of this study were that enflurane affected performance on these tests in a manner qualitatively similar to, though quantitatively different from, halothane. Since the minimum alveolar concentration (MAC), an index of anesthetic potency, is about twice as high for enflurane as for halothane, comparison of the same trace amounts of each agent would be expected to show a smaller effect of enflurane. This was found in these studies. In addition, the end-expired concentration of enflurane following cessation of anesthetic administration decreases at approximately twice the rate of halothane in the amount of time taken for these tests.3 Despite these limitations, statistically significant impairment of performance of subjects was produced by enflurane, as well as by 500 ppm N2O when given as the only anesthetic. These findings confirm the previous conclusion that trace anesthetic concentrations in amounts found in operating rooms not specially equipped for elimination of overflow anesthetic gases may interfere with optimum performance on psychological tests measuring perceptual, cognitive and motor skills. The anesthetics were being cleared from the subjects even as they were being tested, so if they had been tested while being exposed, performance decrements would probably have been even greater.
1. Bruce DL, Bach MJ, Arbit J: Trace anesthetic effects on perceptual~ cognitive and motor skills. Anesthesiology 40:453-458, 1974.
2. Batson HC: An Introduction to Statistics in the Medical Sciences. Minneapolis. Burgess. 1956, p 22.
3. Torri G, Oamia G. Fabiani ML. et al: Uptake and elimination of enflurane in man. Br J Anaesth 44:789-794, 1972.
*Study available online at https://pubs.asahq.org/anesthesiology/article/42/2/194/22661/Psychological-Studies-of-Human-Performance-as