The Efficacy of Adding a Continuous Intravenous Morphine Infusion to Patient-Controlled Analgesia (PCA) in Abdominal Surgery

Abstract

The effect of adding a continuous infusion of morphine 1 mg/hr to patient-controlled intravenous analgesia was studied in a randomized double-blind trial. Ninety-six patients scheduled for abdominal surgery were enrolled; 38 received PCA and continuous infusion (PCA + C), 45 received PCA alone and 13 were excluded because of protocol violations. PCA was delivered via an ABBOTT 4200 pump with settings of morphine 1 mg bolus and five-minute lockout in both groups. A separate pump delivered a continuous infusion of morphine 1 mg/ml (PCA + C) or 9% normal saline (PCA) at 1 ml/hr for three postoperative days. Pain was assessed by hourly verbal pain scores (VPS) and daily visual analog pain scores at rest and on movement (VASrest, VASmove). PCA delivered morphine and the demand to delivery ratio (D/D ratio) were used as indirect indicators of pain. These were assessed during daytime (0800–2200 hours), sleep (2200–0500 hours) and on first waking (0500–0800 hours). Patient demographics were similar. Patients receiving a continuous infusion had lower pain scores during the first 24 hours but not thereafter (VPS P=0.04, VASmove P=0.02). The PCA group delivered more PCA morphine during 0500–0800 hours and 0800–2200 hours on the first day only. There was no significant difference in the D/D ratio for any time period during the three days. Total morphine delivery was greater in the PCA + C group on the second and third postoperative days (P= 0.009 and P=0.0001 respectively). The incidence of respiratory depression and the total number of complications were significantly higher in those receiving continuous infusion (P=0.04 and P=0.011 respectively.) Adding a continuous morphine infusion of 1 mg/hr to the described PCA settings for three days following abdominal surgery improved analgesia during the first 24 hours but was associated with a greater incidence of complications.