To the Editor,

Tabing et al. studied changes in costs and workflow at Vanderbilt University Medical Center when desflurane vaporizers were removed from anesthesia machines in the operating rooms (ORs).1 They studied cases that took ≥ 15 min from the end of the case until the OR exit. In contrast, observational and randomized studies of prolonged times to tracheal extubation have used ≥ 15 min from the time of finishing applying the surgical dressing on the patient (or its functional equivalent) to tracheal extubation.2-4 There is excellent reliability for the dressing on until extubation period (Krippendorff’s alpha = 0.989).3 Furthermore, prolonged (≥ 15 min) times for that period are associated with longer times to OR exit.2-6 From Table 4 of reference 6, among cases with prolonged times to tracheal extubation, the mean time from end of surgery to OR exit was 28 min. Therefore, among the authors’ cases with tracheal intubation and extubation in the OR, what percentage of cases in the before and after periods had times ≥ 28 min from the end of surgery to OR exit (i.e., as previously studied) or, alternatively, ≥ 30 min (i.e., what an organization might monitor), and what was the corresponding relative risk and confidence interval?

For sevoflurane, using an approximate Canadian acquisition price ($200/250 mL), fresh gas flow (2 L·min−1), average vaporizer concentration (2%), and OR temperature (20°C) and pressure (760 mmHg), administration costs are approximately $11.05 per hour during anesthesia maintenance. Even though, in the US, sevoflurane acquisition costs are about half of that in Canada, the authors report in their Table 5 that the cost of sevoflurane was $0.63 per case. This apparent discrepancy would require explanation and redo of the cost analysis, as necessary. In comparison, the authors’ values in Table 5 for isoflurane and desflurane seem reasonable based on typical fresh gas flows (i.e., without feedback to providers).7,8