ARTERIAL WASHIN OF HALOTHANE AND ISOFLURANE IN YOUNG AND ELDERLY ADULT PATIENTS

We have studied the effect of age on washin of isoflurane and halothane by comparing end - tidal ( P E') and arterial ( P a) partial pressures of the agents in young (18–32 yr) and elderly (63–82 yr) healthy patients for 20 min after introduction of the agents, before surgery. P E' was measured by infra - red analysis and P a by gas chromatography. Washin of isoflurane occurred at the same rate in the young and elderly, with no significant difference between young and elderly in P E' or Pa as proportions of the inspired partial pressure ( P I). After 20 min of isoflurane administration, mean P a/ P l in the young was 0.57 (95% confidence limit (CL) 0.53–0.62) and 0.55 in the elderly (95% CL 0.51–0.59). Washin of halothane was slower in the elderly than in the young, with P a/ P l significantly less in the elderly from 10 min after introduction of halothane. The difference between age groups, however, was small: mean P a/ P l after 20 min of halothane administration 0.45 (95% CL 0.41–0.49) in the young and 0.38 (95% CL 0.35–0.41) in the elderly. Washin of isoflurane was significantly faster than that of halothane in both young and elderly subjects. For isoflurane, the P E'- P a gradient was small relative to P a and did not differ significantly between young and elderly. For halothane, P E'- P a in the young did not differ significantly from that for isoflurane. In the elderly, P E'- P a for halothane was significantly greater than in the young and than P E'- P a for isoflurane.