Effects of reduction of carrier gas flow rate on sevoflurane and isoflurane consumption and costs

PurposeTo evaluate whether sevoflurane and isoflurane consumption would be actually halved by halving the carrier gas flow rate, as predicted by a theoretical model, we measured the consumed volume of liquid sevoflurane and isoflurane and total costs of anesthetic gas at carrier gas flow rates of 3 and 61·min−1.MethodsEighty patients of ASA physical status I or II were randomly assigned to one of four groups: sevoflurane at 3 or 61·min−1 and isoflurane at 3 or 61·min−1. Anesthesia was induced with thiamylal and maintained with sevoflurane or isoflurane, as well as with nitrous oxide in oxygen. The consumption of sevoflurane and isoflurane was measured by weighing the bottle of liquid agent, which was greater in the groups receiving 61·min−1 gas than in those receiving 31·min−1.ResultsHalving the carrier gas flow rate reduced the consumption of sevoflurane by 41.8% and that of isoflurane by 52.6%. It also reduced the total cost by 44.3% for sevoflurane and 49.2% for isoflurane.ConclusionHalving the carrier gas flow rates halved the consumption of isoflurane but not of sevoflurane, indicating that factors other than carrier gas flow rates are involved in determining consumption in the clinical setting.