Discussion
desaturation, hypoventilation, apnea, hypoxemia, depression, respiratory depression, postoperative respiratory depression
HYPOVENTILATION, RESPIRATORY DEPRESSION
This post-hoc analysis estimated that compared with when patients were on RA, SO was associated with a 2- to threefold increase in the rates of apnea and respiratory rate depression episodes. The design of PRODIGY trial, as well as the lack of strict protocolized criteria for the initiation of SO, do not allow for any safe conclusions regarding the nature of the association between SO and respiratory depression. Even though we cannot exclude a potential role for SO in promoting respiratory depression, the most parsimonious explanation for the observed association is that patients who were at higher risk for respiratory depression were also more likely to receive SO. According to this explanation, the decision of healthcare providers for SO treatment is primarily based on diagnoses and patient-related factors that are widely perceived to heighten the risk for postoperative respiratory depression. However, this is not supported by our findings, since, as shown in Table Most observational studies that have examined the use of SO in postoperative patients have focused on its efficacy in preventing or treating hypoxemia and provided variable results, with some supporting a beneficial effect [We postulate that in our cohort, although healthcare providers might have initiated SO based on the criteria discussed above, SO maintenance and intermittent monitoring of oxygenation via pulse oximetry spot-checks, may have precipitated apnea and respiratory depression by concealing hypoventilation in well-saturated patients. Importantly, the majority of the overall 46% incidence of OIRD was determined by capnography, and only a small portion (8%) of it constituted arterial desaturation episodes (i.e., SpODecreased wakefulness is an important contributory characteristic of pharmacologically induced respiratory depression in postoperative patients [