In Response

We are grateful to Drs Dexter and Epstein1 for their letter to the editor regarding our recent brief report,2 in particular for their finding of our denominator error, which reflected a percent change increase when it should have been a decrease. Desflurane purchasing was cut roughly in half, reflecting a 55% decrease. Our use of the wrong denominator (113 instead of 252) is verified by Dexter and Epstein1 when they asked: “Were the intended values 55.2% for desflurane (ie, [252–113]/252) and 16.4% for sevoflurane (ie, [305–263]/262)?” This formula is correct, but their calculation also contains a small error: 262 bottles of sevoflurane is correct, not 263. It is easy to see how such errors can happen, and this is quite embarrassing to us. We appreciate their observations and effort to point this out. The appropriate corrections have been made for the print version of this article due to their catch in the electronic publication. Regarding the financial impact of this, Dexter and Epstein1 also correctly state that our article did not account for operating room turnover times. Our institution’s measured turnover times over time support the overall assertion of cost savings. The Figure in this response shows that our inpatient operating room turnover times have actually decreased since the start of education initiatives about carbon dioxide emissions associated with various agents. This reduction in turnover time is a simple 10% (4 minutes) over the 3-year period. Coincidentally there has been a 10% increase in the number of cases over the same period. Clinical locations shown in the Figure are for inpatient operating rooms, with outpatient and children’s hospital operating rooms included for comparison. Historically, there had been a 1:1 ratio of desflurane vaporizers to anesthesia machines at our institution; today this ratio is 1 desflurane vaporizer to 3.8 anesthesia machines for all locations.Figure.: Turnover times in minutes for inpatient, outpatient, and children’s hospital operating rooms.Notably, time to extubation studies comparing sevoflurane with desflurane referenced by the authors are not studies of turnover time. Time to extubation studies are of limited relevance to the actual costs of running an operating room for a number of reasons, including the unusual nature of the timing of the discontinuation of the volatile anesthetic and the critical importance of the scheduling and economic characteristics of the operating room that the data are applied to, as the authors themselves point out in their reference.3 It is also correct that turnover time influences are multifactorial (patient transport, cleaning, equipment setup, etc). Our decrease in turnover time institution may yield an even greater cost saving than initially reported. This interesting finding has led us to pursue a follow-up project. Regarding the Consolidated Health Economic Evaluation Reporting Standards checklist mentioned, this was indeed uploaded on submission of our work. A brief report is intended for preliminary data reporting and therefore naturally limited in comparison with the scope of a full research article. We sincerely thank the letter writers for their input. We are committed to economical and ecological studies around anesthesiology. Economic impact aside, the environmental impact of our initiative cannot be ignored, because it equates to a reduction of 2865 tons of carbon dioxide emissions annually.2 Finally, we would like to respectfully emphasize that our authors report no conflicts of interest, whereas Dr Dexter did appropriately disclose that the Department of Anesthesia at University of Iowa “performed relevant studies for Baxter and Merck.” Specifically note that Baxter is the maker of desflurane. Karin L. Zuegge, MDDepartment of AnesthesiologyUniversity of WisconsinMadison, Wisconsin[email protected] Shannon K. Bunsen, BSUW Health Sustainability ProgramUniversity of WisconsinMadison, Wisconsin Christopher R. Turner, MD, PhD, MBADepartment of AnesthesiologyUniversity of WisconsinMadison, Wisconsin Russell C. Ward, ACEUW Health Clinical EngineeringUniversity of WisconsinMadison, Wisconsin Deborah A. Rusy, MD, MBADepartment of AnesthesiologyUniversity of WisconsinMadison, Wisconsin