In Reply

Thank you for giving us the opportunity to answer the questions raised by Drs. Ifeanyi and Van Meter. In essence, Ifeanyi and Van Meter ask for confounding factors that may have affected the results of our recently published study.¹ 

Issue: Opioid use in the postanesthesia care unit. No opioids were given in the postanesthesia care unit, however, pirtramide 0.1 mg/kg was administered before emergence. Piritramide (not used in the United States) has a slightly lower analgesic potency than morphine, but is less respiratory depressing. We wish to thank Ifeanyi and Van Meter for raising this important point, because the piritramide was not mentioned in the article.

Issue: Comorbidities as obstructive sleep apnea (OSA). No, we did not scan for OSA or other comorbidities and we did not form subgroups since this would have resulted in a substantially higher number of subjects needed—but in a similar answer to our scientific question. If one wanted to find out if a chronic obstructive pulmonary disease patient with OSA displays more profound postoperative desaturations than simple chronic obstructive pulmonary disease patients do—then a specific study could be set up. In our study, we examined oxygen breathing during emergence in chronic obstructive pulmonary disease patients¹ —that is: we looked at a physiological function in a certain population rather than examining the population itself. For the latter, a different paradigm and a different standpoint are required.

Issue: Screening for and excluding OSA patients, would the result be the same? Well, we do not know for certain, but an educated guess is yes, the result would be the same. First, the patients we examined had a body mass index of 25 to 26, but OSA patients are typically more obese. Second, there were no differences in arterial partial pressures of carbon dioxide at the individual time points indicating comparable ventilatory efficiency, or in an another word: homogeneity. Also, because all SDs with carbon dioxide were rather small, single patients with airway obstruction and apnea did not seem to play a role in our study.

Again, we would like to thank you for the opportunity to respond to the letter of Drs. Ifeanyi and Van Meter.