The effect of fresh gas flow during induction of anaesthesia on sevoflurane usage: a quality improvement study

Abstract

Reducing fresh gas flow during inhalational anaesthesia results in cost savings and decreases environmental impact. We are interested in the influence of fresh gas flow on the early (induction) phase of overall fresh gas flow and vapour consumption. This stage is often excluded in studies of fresh gas flow. Data were collected from 3199 sevoflurane anaesthetics over an 11-month period in four operating theatres. We determined fresh gas flow at different stages of anaesthesia, and developed an explanatory model for the influence of the 'induction' period. Following a three-month collection of baseline data we emphasised the importance of the early phase to our department repeatedly over a two-week period. We explored the relationship between fresh gas flow and total vapour usage, and used a simple mathematical model to explore the effect of changes in the fresh gas flow and duration of the 'induction' phase. Mean fresh gas flow was 1.15 l.min À1 in the baseline period and 0.91 l.min À1 in the two months following our educational effort (p = 0.0005). In the following six months, mean fresh gas flow was 1.17 l.min À1 (p = 0.7726 compared with baseline). These results were driven by changes in both fresh gas flow and duration of the initial high-flow period. We found some correlation (R 2 = 0.85) between overall fresh gas flow and vapour consumption; a 1 l.min À1 increase in fresh gas flow consumes an additional 18 ml.hr À1 of liquid sevoflurane. This preliminary study demonstrates that an episode of high fresh gas flow at the start of anaesthesia has a large and modifiable effect on overall fresh gas flow and vapour consumption. We also confirmed the linear relationship between fresh gas flow and vapour usage.

Are high fresh gas flow rates necessary during the wash‐in period in low‐flow anesthesia?

“…The role of high FGF during the wash‐in period on consumption has not been studied much. In a current study, Kennedy et al 14 collected data from 3199 sevoflurane anesthetics and investigated the impact of FGF in the wash‐in period of anesthesia on the volatile agent consumption. They concluded that changing FGF in the early phase can make a large difference on vapor consumption.…”

Seeing the wood for the trees: Insights into reducing inhalational agent consumption

“…We 5 recently demonstrated that the length of time spent at an initial high flow rate is a major contributor to overall vapour consumption and that vapour consumption essentially matches the area under the flow rate/time curve. Based on this work the difference in desflurane consumption between machines is likely due to the higher flow rates seen in the Flow‐i over the first 5‐8 min.…”

“…Our work suggests that the minimum FGF used during maintenance is only one of many factors contributing to total vapour consumption 5 . We frequently encounter users who claim they have no need for automated systems or to modify their practice stating “I always use a flow rate of 300 ml (or 200 ml).” These individuals are invariably only referring to the middle of the maintenance phase and such claims need to be met with request for actual data, such as that provided by Mostad et al Our data suggests that, broadly speaking, the minimum FGF used during maintenance is a relatively unimportant factor in reducing total vapour consumption.…”

An audit of inhalational anaesthetic agent usage in paediatric anaesthesia

“…The environmental impacts of inhaled anaesthetic agents are well described [1]. Our group has a long interest in reducing fresh gas flow (FGF) rates to reduce economic and environmental costs associated with volatile anaesthesia [2].…”