Analyzing Volatile Anesthetic Consumption by Auditing Fresh Gas Flow: An Observational Study at an Academic Hospital.

Abstract

Background: In a climate of cost containment, it is critical to analyze and optimize all perioperative variable costs. Fresh gas flow is one important variable that determines utilization of inhalational agents and can be tightly controlled by the anesthesia provider. Manufacturers of inhalational agents have recommendations for minimum gas flow for their respective agents. Any gas flow above these recommendations is considered misuse and leads to unnecessary expense. The purpose of this study was to characterize and quantify the excess use of inhalational agents by analyzing fresh gas flow rates for long duration cases.

Methods: Over a span of three months, operating room records were analyzed for all procedures lasting greater than 4 hours. End tidal inhalation agent percentage for Sevoflurane and Isoflurane and fresh gas flows were analyzed. 303 unique patients with at least 4 hours of anesthesia time were included. Analysis excluded the first and last 30 minutes of all anesthetics to account for need for higher gas flows during induction/emergence of anesthesia. 152 patients received sevoflurane alone. 33 patients received isoflurane alone. 107 patients received both isoflurane and sevoflurane and were included in sevoflurane group given the higher gas flow needs of sevoflurane. 11 patients received neither agent and were excluded from analysis. We proceed with n = 292 unique patients. (259 in Sevo, 33 in iso) We used the two-sided one sample t-test setting 2 ml/min as the null for sevo and 1 ml/min as the null for iso; we ran analysis using a nonparametric test that didn't require the fresh gas flow to be normally distributed - the two-sided one-sample Wilcoxon rank-sum test: p value = < 0.0001.

Results: The results of our study revealed a sevoflurane (n = 259) mean fresh gas flow (L/min) 2.55 (95% CI, 2.45-2.66) - significantly different from null of 2 ml/min (p < 0.0001). Isoflurane (n = 33) mean fresh gas flows (L/min) 2.33 (95% CI, 2.00-2.66) - significantly different from null of 1 l/min (p < 0.0001).

Conclusion: Manufacturer recommendation for sevoflurane is to maintain gas flows 1-2 l/min and Isoflurane at above 1 l/min. Given these recommendations, the anesthesia providers delivered fresh gas flows at least 28% higher than necessary for sevoflurane and at least 130% greater than necessary for isoflurane anesthetics that lasted greater than 4 hours. This is an area where cost reduction can be readily achieved. Future plans to realize a reduction in inhalational agent utilization include education of the benefits of fresh gas flow and instituting a low fresh gas flow policy.