THE SUBJECTIVE, BEHAVIORAL AND COGNITIVE EFFECTS OF SUBANESTHETIC CONCENTRATIONS OF ISOFLURANE AND NITROUS-OXIDE IN HEALTHY-VOLUNTEERS

A prospective, crossover, double-blind trial was conducted in nine hea lthy volunteers in which the subjective, psychomotor and memory effect s of isoflurane (0.0, 0.3 and 0.6%) and nitrous oxide (N2O) (0, 20 and 40%) were examined. Dependent measures included visual analog scales and a standardized drug effects inventory (subjective effects), reacti on time and eye-hand coordination (e.g., psychomotor performance), and immediate and delayed free recall (memory). There were some similarit ies in subjective effects between the two inhaled drugs (e.g., increas ed ratings of ''drunk'' and ''spaced out''), but isoflurane had effect s which N2O did not have. Isoflurane but not N2O increased visual anal og scale ratings of ''confused,'' ''sedated,'' and ''carefree,'' and d ecreased ratings of ''in control of thoughts'' and ''in control of bod y.'' An odor was detected with isoflurane and it was disliked. Psychom otor performance was more grossly impaired during isoflurane inhalatio n than during N2O inhalation. Psychomotor recovery from both agents wa s rapid and complete so that 5 min after the inhalation period had cea sed, performance had returned to baseline levels. Both isoflurane and nitrous oxide impaired immediate and delayed free recall. The feasibil ity of using isoflurane in conscious sedation procedures is discussed.