Fig. 5. Mean blood concentrations of thiopental enantiomers and propofol from site-directed left main coronary arterial infusions of  rac -,  R -, and  S -thiopental. Individual enantiomer concentrations were determined by chiral separation after administration of  rac -thiopental. The  horizontal bar on the time axis indicates the period of drug infusion. Error bars for change have not been shown for clarity of display. Note time scale expansion.