Observational Study of Anaesthetists’ Fresh Gas Flow Rates during Anaesthesia with Desflurane, Isoflurane and Sevoflurane

Abstract

Reducing excessive fresh gas flow rates (FGF) is an established and simple strategy to reduce the administration of volatile anaesthetic agents. We studied clinicians’ FGF use to understand better why two previous clinical trials achieved significant reductions in FGF by using feedback to anaesthetists. Anaesthesia information management system data from a US academic medical centre were analysed retrospectively. One year of data starting from July 2008 had 11,170 cases. Fresh gas flow rates were measured each minute during cases. Anaesthetists were more likely to choose FGF of multiples of 1 l/minute and 0.5 l/minute than random. However, the pattern was too inconsistent to be of economic or psychological importance and thus is not needed when describing a target FGF. Cumulative distributions of FGF were shifted to the left for desflurane and isoflurane compared to sevoflurane (i.e. cost comparisons among agents may need to use different target FGF). Variation in mean FGF among anaesthetists was small. Even if all anaesthetists had identical mean FGF, the standard deviation of FGF among cases would be reduced by less than 0.1 l/minute for all agents. Most of the achievable reductions in FGF were small reductions in FGF for the many cases with <3 l/minute. These results show that departments choosing to use inexpensive automatic email feedback on FGF should target all anaesthetists and focus on variation in FGF among anaesthetists’ cases.