There isn’t a consensus on whether capnography should be used in postoperative patients.

Eichhorn, John H. “Review article: practical current issues in perioperative patient safety.” Canadian journal of anesthesia 60.2 (2013):111-118.
The first paragraph of page 116 discusses the lack of consensus on how best to monitor postoperative patients for hypoventilation from postoperative pain medication.

Jarzyna, Donna, et al. “American Society for Pain Management Nursing guidelines on monitoring for opioid-induced sedation and respiratory depression.” Pain management nursing 12.3 (2011):118-145.e10.
Article states, “there is a paucity of information and no consensus about the benefits of technology supported monitoring, such as…capnography.”

Hutchison, Rob, and LesRodriguez. “Capnography and respiratory depression.” American journal of nursing 108.2 (2008):35-39.
This randomized prospective study of 54 postoperative orthopedic patients found a significantly higher rate of respiratory depression in the capnography group, concluding that “capnography may be more appropriate for use with postsurgical high-risk patients taking opioids” and “may have the added advantage of indicating those patients who may be at risk for obstructive sleep apnea.”