Propofol Concentration Measurements: Blood samples (1.0 ml) will be collected from an indwelling line in oxalate tubes. Samples will be collected at scheduled time points. The number of samples for subjects may vary depending on the amount of time subjects are in surgery. Samples may also be drawn at unscheduled time points if propofol dose adjustments are made during the surgical procedure. The total sample volume for propofol concentration measurements will not exceed 22ml.