Derivation and Prospective Testing of a Two-step Sevoflurane-O₂-N₂O Low Fresh Gas Flow Sequence

Abstract

Simple vaporiser setting (F D ) and fresh gas flow (FGF) sequences make the practice of low-flow anaesthesia not only possible but also easy to achieve. We sought to derive a sevoflurane F D sequence that maintains the end-expired sevoflurane concentration (F A sevo) at 1.3% using the fewest possible number of F D adjustments with a previously described O 2 -N 2 O FGF sequence that allows early FGF reduction to 0.7 l.min -1 .

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

“…These results have been confirmed clinically . Other studies suggest that flow rates can be reduced to < 1 l.min −1 after 3 min while maintaining nitrous oxide sevoflurane and desflurane concentrations. Based on these studies and our observations, we suggest that no more than 3–5 min in the high FGF phase with FGF of 5 l.min −1 is a reasonable and attainable objective.…”

“…Other studies suggest that flow rates can be reduced to < 1 l.min −1 after 3 min while maintaining nitrous oxide sevoflurane and desflurane concentrations. Based on these studies and our observations, we suggest that no more than 3–5 min in the high FGF phase with FGF of 5 l.min −1 is a reasonable and attainable objective. Although higher FGF rates may be required for adequate pre‐oxygenation, we suggest that once vapour delivery commences, continued use of FGFs above 5 l.min −1 is only justified in specific situations such as bag‐mask ventilation with a large leak.…”

Low Flows Revisited

“…Future studies might look into the adjustments required for anaesthesia continuing past 45 minutes, as the study shows that F A N 2 O is climbing at this time at the expense of oxygen 1 . Another possible study might look at the option of switching from sevoflurane to isoflurane at the three-minute mark, to allow a further FGF reduction without contravening the Australian FGF recommendation for sevoflurane.…”

“…This issue of the Journal contains an article highlighting another simple technique to provide low-flow anaesthesia 1 . Since the symposium issue in August 1994 2 , the Journal has published only a few articles on low flow or closed-circuit anaesthesia [3][4][5][6][7] , suggesting that this form of general anaesthesia is still not very popular in this region, despite its well recognised financial and environmental advantages 8,9 .…”

“…This new article 1 by van Zundert and his group provides an easy 'rule-of-thumb' for administering sevoflurane at low flows. This article is similar to their previous article for desflurane using the same lowflow gas regimen 10 , though with differing vaporiser settings because of the different agents used.…”