Respiratory depression after low-dose caudal morphine

To report a case of respiratory depression after a small dose of caudal morphine administered to a 15-mo-old child.

A 15 mo, 9.8 kg boy underwent ureteral reimplantation with general endotracheal anaesthesia and 10 ml bupivacaine 0.25% (2.5 mg.kg-1). Ninety minutes after the bupivacaine, 0.4 mg (1 mg.ml-1, 0.4 ml, 0.04 mg.kg-1) preservative-free morphine was injected after negative aspiration. Slightly more than two hours after caudal morphine, the patient became lethargic and developed decreases in oxygen saturation (to 62%) without change in heart rate or respiratory rate. Intravenous naloxone 0.1 mg (0.01 mg.kg-1) markedly improved his level of consciousness. Racemic epinephrine was administered for treatment of coincident stridor. The patient required 11 hr continuous naloxone infusion (0.001-0.002 mg.kg-1.hr-1) in the intensive care unit. He was discharged on the second postopertive day without further complication.

Respiratory depression can occur in children greater than one year of age, even when small doses of caudal morphine are used. Decreased arterial oxygen saturation and lethargy are important heralds. A normal respiratory rate despite substantial hypoxaemia argues that pulse oximetry (without supplemental oxygen where possible) has a clear advantage over impedance pneumography for electronic monitoring.