<qa>  What was the purpose of the study?This study was originally undertaken to evaluate the analgesic efficacy of an intravenously administered dose of ketorolac compared with intravenous morphine in the relief of acute, postoperative pain in children admitted to the Intensive Care Unit. Using the urine and plasma samples originally collected from patients in the morphine treatment group and which were never analyzed, this proposal seeks to study the pharmacokinetics and metabolism of intravenous morphine in critically-ill children along with its concentration-related efficacy using prior measures of pain. 