Urinary morphine excretion during and after morphine anaesthesia for open-heart surgery in children

The urine of 20 children undergoing complete correction of atrial septal defect (ASD) or tetralogy of Fallot (TF) were analyzed for morphine and its glucuronide conjugation product before and after induction of morphine anaesthesia, throughout the operation and for two hours post-operatively. Children with ASD had a higher, mean urine flow rate during anesthetic induction and during the entire operation than those with TF (P less than 0.01). ASD children excreted a greater percentage of the administered morphine by the time they reached the recovery room and after two hours in the recovery room than those with TF. Urinary morphine in the glucuronide form increased progressively from anaesthetic induction until the post-operative period in both groups and was more than 93% after two hours in the recovery room. Fifty-five per cent of ASD patients had respiratory dynamics that enabled them to be extubated within six hours of the end of their operation. Those that could be extubated after six hours had excreted a significantly greater percentage of morphine than those that couldn't (P less than 0.025). None of the children with TF could be extubated until the day after operation. These data demonstrate that the ability to maintain adequate spontaneous respiration after morphine anaesthesia is directly related to urinary output during anaesthesia and operation.