This is a single-blind randomized clinical trial. Patients undergoing abdominal tumor surgery were recruited to participate in the study. Apart from routine treatment in the surgical intensive care unit, the subjects were randomly divided into two groups: Propofol group (Group P) and Dexmedetomidine group (Group D) and received continuous intravenous infusion of Propofol (infusion dosage range: 0.3 ~ 1.6 mg/kg/h) or Dexmedetomidine (infusion dosage range: 0.1 ~ 0.7 mcg/kg/h) according to their assigned group. Patients' hemodynamic status was monitored using a chest Bioreactance technique, Continuous Non-Invasive Cardiac Output and Hemodynamic Monitor at preset time points (time of recruitment [0h], 2, 4, 6, 12h and 24h). Clinical data such as vital signs, hemodynamic parameters, laboratory results, fluid volume and drugs used were also recorded.

Inclusion Criteria:

• non-emergent major abdominal tumor surgery with ICU admission
• the need of sedation during ICU stay

Exclusion Criteria:

• age older than 99 years
• age younger than 20 years
• refractory arrhythmias
• refractory shock status after resuscitation
• new onset of myocardial infarction
• severe heart failure or NYHA 4
• APACHE score > 30 when recruiting
• severe liver cirrhosis or CHILD B or C
• organ transplantation within one year
• pregnancy
• allergic to propofol or dexmedetomidine