Use of a BoussignacTM continuous positive airway pressure mask to improve postoperative pulmonary function in morbidly obese patients

To the Editor, In a randomized controlled trial in morbidly obese patients undergoing bariatric surgery, Wong et al. compared the Boussignac continuous positive airway pressure (CPAP) mask with a venturi mask and showed that the Boussignac CPAP mask can improve early postoperative oxygenation as measured by the PaO2/FIO2 ratio. These results make a valuable contribution to the treatment of postoperative respiratory insufficiency following bariatric surgery, which is a major concern for morbidly obese patients. However, in our view, there are two issues related to this study that warrant cautious interpretation of the results. First, the patient position during the early postoperative period is not clearly documented. Considering the potentially deleterious effects of supine positioning on pulmonary function in morbidly obese patients, these patients are more optimally managed in a non-supine position. During the first 48 postoperative hours after abdominal surgery, it has been shown that arterial oxygenation in morbidly obese patients is better maintained in the semi-recumbent position rather than in the supine position. Furthermore, morbidly obese patients placed in a reverse Trendelenburg position have improved pulmonary compliance and increased functional residual capacity, which improves oxygenation relative to the supine position. In our view, an important variable to consider is whether Wong et al. maintained identical positioning in all patients when evaluating the effects of the two respiratory treatments on postoperative pulmonary function. Second, although pain scores were reported to have been similar in the two groups at all time points, the article did not specify the postoperative analgesic protocol used in the two groups. This makes it difficult to assess whether all patients were ensured adequate postoperative analgesia. Following bariatric surgery, pain is recognized as being the most frequent postoperative problem, even for surgery that is performed laparoscopically. Inadequate postoperative analgesia results in splinting with rapid and shallow breathing. Furthermore, in morbidly obese patients, intensity of postoperative pain influences the extent of postoperative atelectasis 24 hr after tracheal extubation. Thus, ensuring optimal analgesia for morbidly obese patients in the postoperative period is of great importance, not only for patient comfort but also for improvement of pulmonary function and a reduction in the risk of respiratory complications. We recognize that providing optimal postoperative pain relief for morbidly obese patients remains a major challenge for modern anesthetic practice. For example, use of opioids is often inevitable to achieve satisfactory postoperative pain control, especially when regional anesthetic techniques are either difficult or impossible for anatomical reasons. Morbidly obese patients are at a very high risk for postoperative exacerbation of respiratory depression, with further depression with the administration of opioids. For this reason, standardization of the postoperative analgesic protocol should be an important element of the study design when evaluating effects of different treatments on He Ping Liu and Fu Shan Xue contributed equally to this work.