Epidural and intravenous bolus morphine for postoperative analgesia in infants

To compare two doses of bolus epidural morphine with bolus iv morphine for postoperative pain after abdominal or genitourinary surgery in infants.

Eighteen infants were randomly assigned to bolus epidural morphine (0.025 mg.kg-1 or 0.050 mg.kg-1) or bolus iv morphine (0.050-0.150 mg.kg-1). Postoperative pain was assessed and analgesia provided, using a modified infant pain scale. Monitoring included continuous ECG, pulse oximetry, impedance and nasal thermistor pneumography. The CO2 response curves and serum morphine concentrations were measured postoperatively.

Postoperative analgesia was provided within five minutes by all treatment methods. Epidural groups required fewer morphine doses (3.8 +/- 0.8 for low dose [LE], 3.5 +/- 0.8 for high dose epidural [HE] vs. 6.7 +/- 1.6 for iv, P < 0.05) and less total morphine (0.11 +/- 0.04 mg.kg-1 for LE, 0.16 +/- 0.04 for HE vs 0.67 +/- 0.34 for iv, P < 0.05) on POD1. Dose changes were necessary in all groups for satisfactory pain scores. Pruritus, apnoea, and haemoglobin desaturation occurred in all groups. CO2 response curve slopes, similar preoperatively (range 36-41 ml.min-1.mmHg ETCO2-1.kg-1) were generally depressed (range, 16-27 ml.min-1.mmHg ETCO2-1.kg-1) on POD1. Serum morphine concentrations, negligible in LE (< 2 ng.ml-1), were similar in the HE and iv groups (peak 8.5 +/- 12.5 and 8.6 +/- 2.4 ng.ml-1, respectively).

Epidural and iv morphine provide infants effective postoperative analgesia, although side effects are common. Epidural morphine gives satisfactory analgesia with fewer doses (less total morphine); epidural morphine 0.025 mg.kg-1 is appropriate initially. Infants receiving epidural or iv morphine analgesia postoperatively need close observation in hospital with continuous pulse oximetry.