I often care for postoperative patients receiving patient-controlled analgesia (PCA). Some recent research suggests that capnography is an effective way to monitor the respiratory status of patients on PCA-yet this technology isn't used in my hospital, which is considered one of the best in the area. What gives? -D. S., MASS.

Capnography, a standard monitoring technique for endotracheally intubated patients in the OR and ED, is a relatively new option for postoperative patients in medical/surgical units. But advances in technology, such as small portable devices and sampling devices on oxygen masks and cannulas, make it increasingly practical in nursing units. As The Joint Commission places more emphasis on preventing complications associated with PCA, expect this trend to continue.

Capnography and Spo₂ are both used to monitor patients on PCA for signs of opioid-induced respiratory depression. But Spo₂, which measures arterial oxygen saturation in peripheral blood, can be misleading if the patient is receiving supplemental oxygen because oxygen saturation values won't necessarily fall significantly with hypoventilation.

Capnography, which measures CO₂ levels during expiration, is emerging as a more reliable indicator of respiratory depression. A patient who's oversedated will retain CO₂ regardless of supplemental oxygen. Using capnography and Spo₂ together gives you a more accurate picture of his respiratory status than either tool used alone.