Drug concentration measurements
Arterial blood samples for drug concentration analysis in plasma were drawn at baseline and at 20, 30, 40, and 50 min after the start of the administration of the intravenous anesthetics. High-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS) was used for dexmedetomidine and S-ketamine. Propofol concentrations were measured with HPLC and fluorescence detection. Interassay coefficients of variation in the relevant concentration ranges were 1.2–2.9%, 3.7–8.0%, and 0.7–2.2%, respectively (