Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Anesthesia/OR Economics
Introduction: Strategies to lower anesthetic drug costs are becoming increasingly important. A potential saving is to reduce the fresh gas flow (FGF) during maintenance anesthesia. For low solubility volatile agents (sevoflurane, desflurane), equilibration between inspired and expired gas concentrations is rapid. Thus, a high FGF is not needed to maintain the inspired concentration in the anesthesia circuit. This study was designed to measure gas flows and concentrations during general anesthesia (GA) and to calculate the potential savings from a reduction in FGF to 2 L/min during maintenance.
Methods: The study was conducted at HUMC with IRB approval and patient consent. During GA, FGF and agent concentrations were continuously measured using a flow transducer inserted between the common gas outlet of the anesthesia machine and the anesthesia circuit. The data were continuously measured and recorded to disk. Anesthesia personnel knew that their cases were being monitored and were asked to follow their usual practices; they were blinded to the values recorded by the computer. The maintenance anesthesia interval was defined as 15 min after initiation of the volatile agent until the FGF was increased and the volatile agent discontinued at the end of the case. Maintenance gas flows and delivered concentrations were compared among the volatile agents using analysis of variance. The volatile agent cost was calculated by converting the total anesthetic gas volume delivered to ml of liquid agent using the following prices per liquid ml: sevoflurane $0.72, isoflurane $0.28, desflurane $0.31. P<0.05 was required to claim statistical significance. Data are presented as the mean +/- SD.
Results: 44 general anesthetics were monitored (Table 1). There were no significant differences among maintenance gas flows. The delivered MAC-adjusted desflurane concentration was significantly lower than that of either sevoflurane or isoflurane. Based on the concentrations and flows used, the greatest savings from flow reduction would occur for sevoflurane.
Discussion: Excessive gas flows were administered during maintenance anesthesia. Why practitioners delivered a lower MAC-adjusted desflurane concentration is unclear, but possibly reflects concern about provoking excessive sympathetic responses at higher concentrations  and the subsequent administration of adjuvant drugs. Cost of volatile agent delivery during maintenance anesthesia could be reduced by [approximate]50% at HUMC if practitioners reduced fresh gas flows from their current levels to 2 L/min. This FGF is consistent with the current labeling guidelines for sevoflurane. It should be appreciated that if anesthetic concentrations need to be acutely increased or decreased, fresh gas flows should be increased temporarily to more rapidly change the concentration in the anesthesia circuit. Although anesthetic drug costs represent a small percentage of the overall cost of perioperative health care, important savings can be realized due to the high volume of cases.
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