Epidural and intrathecal opioids.

Small doses of epidural and intrathecal opioids produce effective and prolonged analgesia postoperatively, although the quality of analgesia does not differ from when conventional routes are used. The different opioids differ only in the speed of onset and duration of action, and in the incidence of side-effects. 'Minor' complications such as nausea, vomiting, pruritus and retention of urine are relatively common. There is a small incidence of respiratory depression which is delayed for several hours after drug administration and which may be prolonged. It is commoner after morphine and after intrathecal administration, and is also associated with advanced age, concomitant use of other central depressant drugs, respiratory disease and large doses. Because of the potentially lethal nature of this complication, it is recommended that the epidural and intrathecal routes of administration are used only when patients can be closely and constantly observed postoperatively.