The low-down on fresh gas flows (2016)

Type of publication:
Conference abstract

*Keogh T., *Elcock D.

Anaesthesia, June 2016, vol./is. 71, Supplement 3, p. 26

Inhalational anaesthetic agents are minimally metabolised and mostly exhaled unchanged; using a closed breathing system with CO<inf>2</inf> absorption, reduces waste of volatiles and permits the reduction of fresh gas flow (FGF) to providing only the patient's metabolic requirements [1]. In addition to reducing wastage of volatiles, low FGF benefits the environment and improves cost effectiveness with a potentially advantageous impact on care. We looked at practice in a typical district general hospital (The Royal Shrewsbury Hospital), with the aim of identifying potential cost savings; we surveyed FGF and investigated whether our volatile costs were influenced by use of the relatively expensive sevoflurane. Methods Theatre lists were inspected to identify cases anticipated to last > 60 min, and were then audited by going into theatre and recording data. A maximum of one case was analysed from each list per day so as to avoid bias by targeting a particular anaesthetist and to avoid influences on an individual's practice once they realised they were being surveyed. A range of specialities was audited and data were collected after at least 30 min on table to allow time for the anaesthetist to modify flows. Results Median flow rates (n = 49) were found to be 0.95 l.min<sup>-1</sup> with an interquartile range of between 0.70 l.min<sup>-1</sup> and 1.10 l.min<sup>-1</sup> (Fig. 1). While these are low flows compared with those required by non-circle systems, they are not basal flow rates and therefore an estimated saving of around 50% could be made if typical flows were < 0.5 l.min<sup>-1</sup> (roughly equal to 70 000/pa in the Trust). Based on our pharmacy costs, we estimate equivalent doses of sevoflurane to be roughly 14x the cost of isoflurane, suggesting a saving of up to 93% per case if only the latter were used. However we acknowledge that this is simplistic and may not offset the disadvantages of isoflurane. Discussion We may have underestimated FGF being used; it is probable that people do not use low-flows in the anaesthetic room, at the beginning of cases, or possibly at all in shorter cases. Results have shown a generally responsible use of FGF rates, and perhaps limiting the type of volatiles used would not be as cost-effective as may have been thought, but rather encouraging the use of 'minimal flows'(< 500 ml) may be more promising. The introduction of self-adjusting low FGF on newer anaesthetic machines will also weaken any case for preferring isoflurane on grounds of cost alone – indeed manufacturers may argue the cost of this type of technology is quickly offset by the savings made in volatile costs. We think that rather than trying to reduce costs by limiting use of sevoflurane, there is more to gain by promoting the use of 'minimal flow'. (Figure Presented) .

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