This is an open label study that will be conducted in infants and children presenting for procedures (eg., surgery or cardiac catheterization) at Stanford and Lucile Packard Children's hospital in California and at The Children's Hospital in Denver, CO. Patients with abnormal kidney or liver functions will be excluded from the study as the dysfunction in these organs affects the clearance of medications from the body and affects dosing. Preterm neonates will also be excluded. All patients will be premedicated and anesthetised at the discretion of the anesthesia faculty providing clinical care for the child. Once the patient's procedure is underway, a 0.5 cc blood sample will be drawn from an intravenous line. This is the preload blood sample (T0). Following this a 2mg/kg intravenous bolus of Ketamine will be administered over 5 minutes (this is the usual dose and manner in which ketamine is administered). Five minutes after the bolus, timed blood samples will be drawn at the following intervals: 5, 10, 15, 20, 30, 45, 60, 120, 180, 240, 300, 360 and 720 minutes after bolus. (Total 14 blood samples; total blood required is 7 mls for the entire study). When the procedure is completed the anesthesiologist will awaken the patient as per their usual practice. Blood samples that still need drawing will be done in the post-anesthesia recovery room or intensive care or ward-any location where the patient is likely to remain after the surgery.