BACKGROUND: Mechanical ventilation is frequently used in the intensive care unit. Sedation is usually required to tolerate the presence of a tracheal tube and other unpleasant stimulus during mechanical ventilation. The ideal regimen for sedation has not yet been determined. This study was designed to compare the characteristics of safety and effectiveness of propofol to those of midazolam for sedation in patients undergoing mechanical ventilation in surgical intensive care unit. METHODS: 44 mechanically ventilated patients were randomized to receive either propofol (loading dose 20~40 mg, followed by 10~50 microgram/kg/min) or midazolam (loading dose 1~2 mg, followed by 0.2~0.8 microgram/kg/min). Infusion rates were titrated to 3~5 points of Ramsay scale. All patients also received morphine 0.5 microgram/kg/24 h without any muscle relaxants. Hemo-dynamic changes (SBP, DBP, HR), ventilatory parameters and recovery time were evaluated. Hepatic and renal functions were measured before start of infusion and after discontinuation of both drugs. RESULTS: The mean initial loading and maintenance dose were 0.35 mg/kg and 1.5 mg/kg/hr for the propofol, 29.2 microgram/kg and 29.1 microgram/kg/h for midazolam group, respectively. There was no difference between the two groups regarding the sedation score evaluated by Ramsay scale. Patients receiving propofol recovered more rapidly than those receiving midazolam (40.5+/-20.1 min vs. 88.2+/-29.5 min respectively; P<.05). No one in either group showed marked hemodynamic(>30% of pre-injection value) or hepatic or renal function changes. CONCLUSIONS: Propofol is a sedative agent with shorter awakening time than midazolam but with the same safety and clinical effectiveness for the continuous sedation of mechanically ventilated patients.