Samples were collected in ethylenediaminetetraacetic acid (EDTA) tube and centrifuged for 10 min at 3,500rpm. Plasma was stored at -70°C until assay. Arterial blood samples (4 ml) were taken at preset intervals: 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 15, 20, 30, 40, 50, 58, 60, 62, 66, 70, 80, 90, 120 and 150 min after administration of propofol. Venous blood samples (4ml) were taken at preset intervals: 180, 240, 300, 600, 720 and 1,200 min after administration of propofol. In addition, arterial samples were drawn when LOC (loss of consciousness) and ROC (recovery of consciousness) were observed.