Respiratory depression with patient-controlled analgesia.

The increased interest in pain management by physicians in general and anaesthetists in particular over the last two decades, along with advances in our knowledge of nociceptive mechanisms, has led to the introduction of acute pain services. Many are based primarily on patientcontrolled analgesia (PCA), which has been shown to provide superior analgesia than conventional intramuscular opioid analgesia, and is perceived as being safer with fewer logistic problems in monitoring and general patient management than techniques based on intraspinal opioids. Mishaps associated with PCA have been reported occasionally, but their relative infrequency tends to reinforce this perception of the safety of the technique. The cases reported by Etches in this issue of the Journal draw attention to the occurrence of respiratory depression in patients receiving PCA, and he suggests some factors which may increase patient susceptibility to this problem. The reported incidence of' respiratory depression with opioids administered by various routes depends on the definition of the problem. Only a small percentage, 0.25-0.4%, of patients receiving epidural morphine in a survey of Swedish practice required naloxone, t while with other routes of opioid administration 2,3 an incidence of 0.2-0.9% has been reported. Mild CO 2 retention has occurred with both epidural and PCA morphine, 4 while oxygen desaturation was similar (though more marked with PCA) in patients receiving epidural morphine or PCA meperidine, s While the above reports of lifethreatening events may underestimate the true incidence, available data would suggest that the overall risk of severe respiratory depression from appropriate doses of opioids is similar (< 1%) regardless of the route of administration. The factors increasing the potential for respiratory depression can be divided into "patient related" and "technique related." The former are relevant regardless of route of administration and include advanced age, head injury, sleep apnoea syndrome, obesity, respiratory failure, con-