Respiratory depression after low-dose caudal morphine

Abstract

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

Clinical features: 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.

Conclusion: 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.