Effects of reduction of the caudal morphine dose in paediatric circumcision on quality of postoperative analgesia and morphine-related side-effects

Abstract

This study compared the efficacy and adverse effects of three low doses of morphine (10, 15 and 30 μg.kg-1) for caudal epidural analgesia in children undergoing circumcision. A total of 135 boys undergoing out-patient circumcision were randomly assigned to receive 10, 15 or 30 μg.kg -1 of caudal morphine. Anaesthesia was induced and maintained with propofol. After induction, the morphine was added to 0.5 ml.kg-1 1% lignocaine solution with adrenaline 5 μg.ml-1 and injected caudally. Anaesthesia quality, postoperative pain and adverse events in a 24-hour period were evaluated. Paracetamol (20 mg.kg-1 orally) was used as rescue analgesia as required. No patient required paracetamol in the first eight hours after the caudal injections. In the first 24 hours postoperatively no further analgesia was required in 66.7%, 77.8% and 91.1% of the patients in the 10, 15 and 30 μg.kg-1 groups, respectively (P=0.01 for 10 vs. 30 groups). All patients had excellent analgesia. No respiratory complications were observed. Nausea-vomiting occurred in 13.3%, 20% and 46.7% of the patients in the 10, 15 and 30 μg.kg-1 groups (P=0.002 for 10 vs. 30 and 0.044 for 15 vs. 30). Pruritus occurred in 8.9%, 11% and 15.6% in the 10, 15 and 30 μg.kg-1 groups but was localised and did not require treatment. This study was not powered to assess concerns that low dose epidural morphine may rarely be associated with delayed apnoea and is therefore considered unsuitable for outpatient use in many centres. Increases in caudal morphine dose above 10 μg.kg-1 produce some 'paracetamol sparing' but no improvement in analgesia, some pruritus and a significant increase in nausea and vomiting.