Capnography Monitoring Enhances Safety of Postoperative Patient-Controlled Analgesia

Background: Patient-controlled analgesia is associated with potentially fatal opioid-related respiratory depression. Opioids are a well-recognized cause of respiratory depression. However, in the postoperative patient, unrecognized pulmonary disease may lead to retention of carbon dioxide, which is further antagonized by opioids and may lead to lifethreatening respiratory depression. Therefore, using a method that would provide earlier warnings for respiratory problems could improve patient outcomes. Objective: To assess the efficacy of monitoring postoperative patients who were receiving patient-controlled opioid therapy with capnography modules in addition to the routine use of pulse oximetry to monitor ventilatory status and generate alerts when respiratory parameters exceed hospital-established limits. Method: Postoperative patients receiving patient-controlled analgesia were compared in relation to the use of pulse oximetry and capnography modules and their ability to generate alerts about abnormal respiratory parameters. A total of 634 patients receiving patient-controlled analgesia therapy were studied, of whom 239 (38%) received hydromorphone, 297 (47%) received morphine, and 98 (15%) received fentanyl. All 9 patients experiencing respiratory depression received supplemental oxygen. Results: Of the 634 patients studied, 9 (1.4%) experienced respiratory depression by bradypnea (< 6 breaths per minute). Six (67%) events were related to hydromorphone and 3 (33%) were related to morphine. In 7 (78%) events, there was no basal infusion rate and the saturation of peripheral oxygen was > 92%. All respiratory depression events occurred within the first 24 hours of patient-controlled analgesia therapy. In all cases, capnography, but not pulse oximetry, alerted the nurse to impending respiratory depression. Conclusions: Capnography was more effective than pulse oximetry in providing early warning of respiratory depression in patients receiving supplemental oxygen. Capnographic monitoring and automatic pausing of patient-controlled analgesia improved postoperative outcomes in situations that could have otherwise been fatal. Use of capnography improved clinician confidence that opioid dosing could be safely continued in postoperative patients for more effective pain management.