The dose-effect relationship for morphine and vomiting after day-stay tonsillectomy in children

A dose-response curve for intravenous morphine and vomiting was investigate d in children having day-stay tonsillectomy. A retrospective chart review w as performed for the 164 children fulfilling the inclusion criteria. Morphi ne (mean 0.09 mg/kg SD 0.05) was used in 108 children in the perioperative period and a further 56 children were given no opioid Fifty-five of these 1 64 children vomited and 20 children required an overnight stay in hospital because of vomiting. The probability of vomiting or overnight stay in hospi tal was related to morphine dose (by logistic regression). The overall prob ability of vomiting after morphine 0.1 mg/kg was 50% and the probability of admission for vomiting with this dose was 10%. Pharmacodynamic parameter e stimates for postoperative vomiting were PO (the baseline probability of vo miting, with no opioid) 0.115 Pmax (the maximal probability of vomiting due to morphine) 0.997, ED50 (morphine dose that induces an effect equivalent to 50% of the legit Pmax) 0.18 mg/kg. Parameter estimates for overnight sta y because of vomiting after. morphine administration were PO 0.038 Pmax 0.9 99, ED50 0.369 mg/kg. Satisfactory postoperative analgesia in children has been reported with morphine 0.05 to 0.15 mg/kg. Doses above 0.1 mg/kg are a ssociated with a greater than 50% incidence of vomiting. Our data suggests that lower doses of morphine are associated with a decreased incidence of e mesis after tonsillectomy in children.