To the Editor:
This is an interesting article and we congratulate the authors on the elegant prospective randomized study design. The essence of the reported findings was a lower arterial oxygen level in patients with chronic obstructive pulmonary disease at 60 min after extubation within the 100% oxygen group.1 However, there are no data about other factors that would influence this finding. We would like to know if the authors considered any potential confounding variables. Rose et al.2 elaborated on such potential factors. It is worthy to note that their study included many different surgeries as well as patients who did not have chronic obstructive pulmonary disease. However, they did report that perioperative risk factors associated with critical respiratory events (hypoxemia, hypoventilation, and/or airway obstruction) in postanesthesia care unit (PACU) include age more than 60, male sex, diabetes mellitus, and obesity. Anesthetic risk factors included opioid or sedative premedication and fentanyl as the sole opioid greater than 2 μg kg−1 h−1. Their study concluded that critical respiratory events are relatively rare and there are multiple factors that influence their incidence. Did Kleinsasser et al.1 account for any of these possible factors? It is worthwhile to investigate the causative factors, because critical respiratory events have been associated with longer PACU stays, a higher incidence of cardiac complications while in PACU, and increased frequency of unanticipated intensive care unit admissions; therefore, we commend the authors for investigating this issue within this subset of patients.
Perhaps it is understandable that the type of surgery (carotid artery stenosis) has a low incidence of postoperative pain, but there should be some information for the reader to evaluate whether respiratory depression due to opioid administration was present in one or both arms of the study. We would be interested to know how many patients received opioids in the PACU, as we feel that is a key piece of information to know prior to drawing any valid conclusions. The oxygen partial pressures for the 100% oxygen group were reduced at 15 and 60 min and carbon dioxide partial pressures at 5 and 15 min were shown to be marginally elevated as compared to the 30% oxygen group; however this was not statistically significant. Therefore, inclusion of opioid PACU consumption until 60 min would be helpful in excluding respiratory depression due to opioids as a cause for PACU desaturations. We would also like to know if any of the patients received blocks or local anesthesia infiltration.
Although the authors demonstrated that the demographic variables between the two groups were similar, there was no mention made of comorbidities such as obstructive sleep apnea, which could influence PACU desaturations.3 We would be interested to learn from the authors if comorbidities were considered in the study design. The authors noted that 76 patients were screened and 53 enrolled; however, it appears that the exclusion criteria was based solely on pulmonary function testing and did not take into account comorbid conditions that could potentially confound the results. If obstructive sleep apnea was screened for and those patients excluded, would the results be the same? We would be interested to know if the authors considered any other factors that could have contributed to the results they reported.
The authors declare no competing interests.