Comparison the Hemodynamics Effects Between Dexmedetomidine and Propofol in Major Abdominal Surgical Patients

The alpha2 agonist dexmedetomidine is a new sedative agent combined with the analgesic qualities and lack of respiratory depression. Patients sedated with dexmedetomidine could be easily roused, these advances shows dexmedetomidine may be a effective and safe sedative agent. But some studies showed some adversely effects of dexmedetomidine on haemodynamics (such as bradycardia, hypotension), the investigators want to further research the effects of dexmedetomidine on haemodynamics, such as Cardiac Output (CO), Systemic Venous Resistance Index(SVRI), and so on. Propofol is widely used sedative agent in ICU, it also has adversely effects like bradycardia and hypotension, so the investigators want to compare the effect of dexmedetomidine with propofol on haemodynamics after major abdominal surgery. Expect to further research the mechanism of haemodynamics of dexmedetomidine.