To the Editor
Zuegge et al1 reported that their department’s “tracking of anesthetic volatile agent purchasing show[ed] a >100% reduction (from 252 to 113 bottles/month) in desflurane usage and a 14% increase (from 262 to 305 bottles/month) in sevoflurane usage over this period, while isoflurane usage remained steady. This change in purchasing trend [over the period of 5 years] led to a savings estimate of $25,000 per month.”
Purchasing reductions mathematically cannot exceed 100%. Were the intended values ≅55.2% for desflurane (ie, [252–113]/252) and ≅16.4% for sevoflurane (ie, [305–263]/262)?
Anesthesia & Analgesia editorial policy requires that brief reports follow the relevant Enhancing the QUAlity and Trans parency Of health Research guideline, which for economic end points is the Consolidated Health Economic Evaluation Reporting Standard. Such requirements are designed to help ensure that research methodologies are valid. The authors’ analysis of “savings” failed to consider the following items, listed in sequence of the Consolidated Health Economic Evaluation Reporting Standard statement: cost savings perspective (eg, societal), resource use associated with the intervention, valuation of each resource changed, listing of cost model assumptions, incremental secondary costs, and estimation of outcomes of interest expected to differ.
Valid economic analyses of anesthetic drugs must include effects on personnel and workflow costs, including nonoperative time. There are slower emergence times (end surgery to extubation) and turnover times with sevoflurane compared to desflurane.2 Differences in times for tracheal extubation can be quantified accurately using either prospective observational studies or randomized clinical trials.3 Time reductions in proportional scales are relatively homogeneous among studies, making meta-analyses useful and their findings easily applied to cost modeling.2 The values of the cost reductions are highly heterogeneous among operating rooms of the same hospital and among hospitals (eg, based on workday duration and personnel compensation).4 These economic relationships are well understood.2,4 When these factors are ignored, such as in the authors’ study, findings do not produce generalizable economic science.
For example, suppose that 85% of the authors’ 2648 general anesthesia cases per month in fiscal year 2015 were performed principally in operating rooms with >8 hours of cases, averaging 3 cases per operating room per day.1,2,4 Suppose the mean time to extubations was 9.2 minutes.2 Then, the authors likely added a mean of 3.3 minutes per case because of the shift from desflurane to sevoflurane, including both extra emergence time in the operating room and delay in starting next cases, where 3.3 = 25% × 9.2 minutes + 0.5 minutes × 2. Using a cost of $3.44 per minute of operating room time, based on May 2016 Bureau of Labor Statistics Occupational Employment Statistics survey (Accessed: Thursday, December 14, 2017), this extra time may have increased hospital costs by $25,550 per month. Compared with the reported $25,000 reduction in purchasing costs,1 no substantive savings likely accrued. Note that if the hospitals’ public accounting reports were used, because costs per minute for operating room time are generally much larger than $3.44, the hospital’s net costs would have increased. Regardless of the details of our example, the authors overestimated the savings from their vaporizer labeling and education initiative.
Franklin Dexter, MD, PhD, FASA
Department of Anesthesia, University of Iowa
Iowa City, Iowa
Richard H. Epstein, MD
Department of Anesthesiology, Perioperative Medicine and Pain Management
University of Miami
Coral Gables, Florida
Department of Anesthesiology
Sidney Kimmel Medical College
Thomas Jefferson University
1. Zuegge KL, Bunsen SK, Volz LM, et al. Provider education and vaporizer labeling lead to reduced anesthetic agent purchasing with cost savings and reduced greenhouse gas emissions. Anesth Analg. 2019;128:e97–e99.
2. Dexter F, Bayman EO, Epstein RH. Statistical modeling of average and variability of time to extubation for meta-analysis comparing desflurane to sevoflurane. Anesth Analg. 2010;110:570–580.
3. Masursky D, Dexter F, Kwakye MO, Smallman B. Measure to quantify the influence of time from end of surgery to tracheal extubation on operating room workflow. Anesth Analg. 2012;115:402–406.
4. Epstein RH, Dexter F, Brull SJ. Cohort study of cases with prolonged tracheal extubation times to examine the relationship with duration of workday. Can J Anesth. 2013;60:1070–1076.