Sevoflurane usage and fresh gas flows in Maquet anaesthetic machines at an academic hospital

Abstract

Background Low-flow anaesthesia (LFA) is an important tool to combat the rising healthcare costs and the global threat of climate change. This study aimed to prospectively analyse the conduct of inhalational anaesthesia at Charlotte Maxeke Johannesburg Academic Hospital to determine fresh gas flows (FGF) and the liquid agent consumption (LAC) at different stages of anaesthesia. Methods A prospective, contextual research design was followed. Consecutive convenience sampling was done across ten theatres equipped with Maquet Flow-i® anaesthetic machines. The study included 137 eligible cases. Data were downloaded from the anaesthetic machines and formula-based calculations of LAC were compared to the measured LAC displayed by the anaesthetic machines. Result The average FGF during induction, maintenance and time-weighted case average were 7.07, 1.41 and 1.73 l/min respectively. The average end-tidal sevoflurane concentration during maintenance was 2.40%, whilst the average minimum alveolar concentration was 0.90±0.10. The calculated average LAC for induction, maintenance and case were 7.74, 28.01 and 36.84 ml respectively, whilst the hourly LAC was 16.71 ml/h. The calculated case average LAC overestimated the measured values by 4.14±4.86 ml (12.98%), with 98.5% of values being within ±1.96 SD. Despite its brevity (4.6% of total case duration), the induction phase accounted for 21% of the predicted LAC. The predicted liquid agent expenditure over time was ZAR 54.32±23.55/h. Case average FGF had a very high positive correlation with the predicted cost of sevoflurane, r = 0.86, p < 0.001. Conclusion The study demonstrated that anaesthetists at CMJAH conducted medium flow anaesthesia, which correlated with increased sevoflurane consumption. With the average FGF induction of 7.07 l/min, the first strategy in achieving LFA would be to encourage anaesthetists to lower this value to the optimal FGF of 4 l/min when sevoflurane is introduced during induction