SIDE-EFFECTS DURING CONTINUOUS EPIDURAL INFUSION OF MORPHINE AND FENTANYL

Respiratory effects, nausea, somnolence, and pruritus were compared during a 48-hr period of continuous epidural morphine (n = 34) and fentanyl (n = 32) infusion in 66 patients following elective total replacement of the hip or knee joint. Respiratory effects were assessed by PaCO2. Side effects were assessed by visual analogue scale and considered to be present when the score was above 30. Assessment was made at preoperative visits then 3, 6, 12, 24, 36, and 48 hr after the epidural injection. The bolus dose and subsequent infusion rate were 3,900 +/- 1,300-mu-g and 42 7 +/- 213-mu-g . hr-1 for morphine, and 85 +/- 46-mu-g and 56 +/- 27-mu-g . hr-1 for fentanyl. Pain relief was similar in both groups. In the morphine group, PaCO2 elevation and nausea occurred over a period of more than 12 hr (P < 0.05). In the fentanyl group, there was no PaCO2 change, and nausea was confined to the first few hours. Nausea was more severe (P < 0.01 at six hours and more frequent (24 hr cumulative incidence, 53 vs 28%, P < 0.05) in the morphine group. Somnolence was prominent within several hours in two-thirds of patients in both groups. Somnolence continued to decline thereafter in the morphine group, but it was demonstrable in approximately half of the patients throughout the second day in the fentanyl group. The incidence was higher in the fentanyl group at the 48th hr (P < 0.05). There was a quadratic increase in pruritus over time (P < 0.001), and it was more severe in the morphine group (P < 0.001). Pruritus was generalized in the morphine group; but it was segmental in the fentanyl group. It remained the side effect of most clinical concern during the second day in both groups. The temporal course of respiratory effect and nausea were similar to that which follows a bolus epidural injection. Side effects were less during the second day of infusion in both groups with the notable exception of pruritus. Side effects were generally less in the fentanyl group. The continuous epidural infusion of opioids, after the initial bolus-related side effects, appears to be a safe technique for prolonged and steady pain relief with minimal side effects.