Efficacy of a low-dose spinal morphine with bupivacaine for postoperative analgesia in children undergoing hypospadias repair

Background:  Children undergoing hypospadias repair need to be protected from highly unpleasant sensory and emotional experiences during and after surgery. We designed a double-blinded, randomized, and placebo-controlled study to compare the efficacy of a low-dose (2 μg·kg⁻¹) of intrathecal morphine with placebo for postoperative pain control of children undergoing repair of hypospadias surgery with spinal anesthesia.
Methods:  Fifty-four children were randomly assigned to one of two spinal anesthesia groups. Group M ( n  = 27) received hyperbaric bupivacaine plus 2 μg·kg⁻¹ of preservative-free morphine and group P ( n  = 27) received hyperbaric bupivacaine plus 0.9% NaCl (placebo) under inhalation anesthesia. General anesthetics were discontinued subsequent to the block. The primary outcome was the presence of pain-requiring analgesics during the first 12 h after the spinal block. Side effects were also recorded. The analgesic effects were evaluated by using the Children's Hospital of Eastern Ontario Pain Scale.
Results:  Forty-nine patients completed the trial. Fifteen patients (60%) in group P received supplementary analgesics within the first 12 h compared to only four patients (16.7%) in group M ( P  = 0.005). Mean duration of analgesia was 480 ± 209 and 720 ± 190 min in group P and group M respectively ( P  = 0.009). The groups were similar in postoperative side effects.
Conclusion:  Spinal anesthesia provided by hyperbaric bupivacaine is adequate for distal hypospadias repair in children, but adding 2 μg·kg⁻¹ intrathecal morphine provides better postoperative pain control when compared to placebo in these children.