Personalizing Perioperative Analgesia in Children

Measures and Procedures: Participants will receive standard care, standard anesthetic and an intraoperative dose of morphine per the clinical team. Research procedures will include: 1. Blood draws for genotyping candidate genes and exploratory genes 2. Standardized PACU (post anesthesia care unit) Protocol: Subjective pain assessments: Numerical Rating Scale (NRS) 0 to 10. Objective assessment with FLACC (facial expression; leg movement; activity; cry; and consolability) scale, 0-10. 3. Significant postoperative pain will be managed in the PACU with rescue doses of morphine and opioids by the clinical team. Analgesic interventions and morphine requirements are collected 4. Effects of opioids on pupil measures 5. Respiratory response to 5% carbon dioxide preoperatively and postoperatively (first 350 patients only). Another measure of end tidal carbon dioxide will be implemented when the device is clinically available. 6. Serial blood draws for morphine pharmacokinetic modeling (through subject #351). 7. Opioid adverse effects in PACU and at home.