Extradural morphine gives better pain relief than patient-controlled i.v. morphine after hysterectomy

We examined if patient-controlled analgesia (PCA) with i.v. morphine provided comparable postoperative analgesia after hysterectomy as extradural morphine, without increasing the incidence of side effects. The study (n = 40) was randomized and double-blind. An extradural catheter was inserted before surgery and anaesthesia was standardized. The extradural group received extradural morphine 0.06 mg kg-1 by the end of surgery and a second dose 6 h later. The i.v. group received an i.v. infusion of morphine 0.2 mg kg-1 after surgery. PCA with morphine 0.04 mg kg-1 i.v. was used in both groups. Pain relief (VAS), side effects and cognitive functions were evaluated for 18 h. Plasma samples were obtained for analysis of morphine concentrations. Mean consumption of PCA morphine was 2.4 mg h-1 for the i.v. group and 1 mg h-1 for the extradural group. Despite unlimited access to morphine, the i.v. group had higher VAS scores as the extradural group (P < 0.001). Plasma concentrations of morphine varied 8-10-fold in both groups. In the i.v. group itching, tiredness, blurred vision and vertigo correlated with cumulative consumption of i.v. morphine whereas in the extradural group this correlation existed only for tiredness. Both groups showed reduced ability to perform tests of cognitive function, indicating a central effect of both i.v. and extradural morphine, despite markedly lower plasma morphine concentrations in the extradural group.