200 patients who are scheduled for craniotomy surgery under general anesthesia at 3 major children's hospitals will be eligible. Potential patients include those undergoing brain surgery for cancer, epilepsy, vascular malformations, and craniofacial reconstructive surgery. Following surgery, patients will receive routine postoperative management and treated for pain based on institutional routine. We will follow patients for the first 5 post-operative days or until discharge, whichever comes first.