Changes in end-expiratory lung volume on induction of anaesthesia with thiopentone or propofol.

ABSTRACT

To determine the effects of induction agent and obesity on the change in functional residual capacity caused by induction of anaesthesia, we measured the change in end-expiratory respiratory volume (EERV) during induction of anaesthesia with either thiopentone or propofol. Female patients breathed via a face mask from a closed circle system connected to a water spirometer. The spirometer tracing was used to measure the decrease in EERV. The median decrease was 200 (95% confidence limits 90-280) ml after thiopentone and 285 (200-425) ml after propofol. The decrease in each group was significant (P < 0.01) but there was no difference between the two groups. The change in EERV, expressed as a proportion of the predicted functional residual capacity, was not related to obesity (estimated as the ratio of actual to predicted body weight).