Dosing of medications is based on the plasma level achieved with a given dose and how long the medicine remains in the body. This study is called pharmacokinetics-that is, what the body does to the medication. Ketamine is an intravenous medication used for anesthesia and sedation in children. However the pharmacokinetics of Ketamine has not been systematically studied. We propose to study the pharmacokinetics of ketamine in different age groups of children ranging from infants to teenagers.