Drug preparation, blinding, and randomization
Thiopental sodium (500 mg), diluted with 20 ml of normal saline at a concentration of 25 mg/mL, was prepared in a 20-ml syringe. Twenty milliliters of propofol (1%) was prepared in a 20-mL syringe. Remifentanil (1 mg) was diluted with normal saline to a concentration of 50 ug/mL (final volume, 20 ml). To maintain blinding of the outcome assessor (an experienced anesthesiologist, Y. J. Oh), syringe contents (thiopental, propofol and remifentanil) were concealed with an opaque syringe and giving sets. All anesthetic drug infusions during the intervention were blinded to both the patient and outcome assessor, and all drugs used for the intervention were prepared by a single anesthetic nurse. Randomization was performed using computer-generated random numbers by an anesthesiologist who was not involved in the anesthetic intervention and data collection.