['The most serious complication of patient-controlled analgesia (PCA) is respiratory depression (RD). The incidence of RD in the literature is derived from intermittent sampling of pulse oximetry (Spo(2)) and respiratory rate and defined as a deviation below an arbitrary threshold.', 'We monitored postsurgical patients in a hospital ward receiving morphine or meperidine PCA with continuous oximetry and capnography. Nurses responding to audible monitor bedside alarms documented respiratory status and interventions.', 'A total of 178 patients were included in the analysis, 12% and 41% of whom had episodes of desaturation (Spo(2) <90%) and bradypnea (respiratory rate <10) lasting 3 min or more. One patient required "rescue" with positive pressure ventilation, and none required naloxone. Patients over 65 years of age and the morbidly obese were at greater risk for desaturation. Patients over 65 years of age were also more likely to have bradypnea, whereas the morbidly obese and patients receiving continuous infusions were less likely to have bradypnea.'] Does continuous oximetry/capnometry monitoring reveal frequent desaturation and bradypnea during patient-controlled analgesia?