An early study showed that patients receiving a single dose of epidural pethidine at the end of major surgery had a longer period before further analgesics were required than patients receiving equipotent doses of morphine or pethidine. Blake15 compared patient-controlled epidural pethidine (PCEA) with intravenous patient-controlled analgesia (PCA) pethidine following abdominal aortic surgery, where all patients also received epidural bupivicaine. The PCEA group had lower pain scores, despite having lower plasma pethidine concentrations, confirming the central action of epidural pethidine. In a similar study, Chen16 compared epidural and PCA pethidine in 37 patients following gastrectomy. Pain and satisfaction scores were similar, but the epidural group had lower plasma concentrations of pethidine and norpethidine.