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

We have studied the effect of age on washin of isoflurane andhalothane by comparing end - tidal (PE') and arterial (Pa) partialpressures of the agents in young (18–32 yr) and elderly(63–82 yr) healthy patients for 20 min after introductionof the agents, before surgery. PE' was measured by infra - redanalysis and Pa by gas chromatography. Washin of isofluraneoccurred at the same rate in the young and elderly, with nosignificant difference between young and elderly in PE' or Paas proportions of the inspired partial pressure (PI). After20 min of isoflurane administration, mean Pa/Pl in the youngwas 0.57 (95% confidence limit (CL) 0.53–0.62) and 0.55in the elderly (95% CL 0.51–0.59). Washin of halothanewas slower in the elderly than in the young, with Pa/Pl significantlyless in the elderly from 10 min after introduction of halothane.The difference between age groups, however, was small: meanPa/Pl after 20 min of halothane administration 0.45 (95% CL0.41–0.49) in the young and 0.38 (95% CL 0.35–0.41)in the elderly. Washin of isoflurane was significantly fasterthan that of halothane in both young and elderly subjects. Forisoflurane, the PE'-Pa gradient was small relative to Pa anddid not differ significantly between young and elderly. Forhalothane, PE'-Pa in the young did not differ significantlyfrom that for isoflurane. In the elderly, PE'-Pa for halothanewas significantly greater than in the young and than PE'-Pafor isoflurane.