In the immediate postoperative period following cardiac surgery, many patients require short-term sedation until cardiovascular and respiratory stability has been achieved and weaning from artificial ventilation can be started. For these patients, current guideline recommended propofol over benzodiazepine, mainly because of the short elimination half life of propofol. However, hypotension, a very common side effect of propofol, may impose restrictions on its use in some cardiac surgery patients. Remimazolam besylate is a novel, ultra-short-acting benzodiazepine that undergoes organ-independent metabolism by tissue esterases into an inactive metabolite. In other words, remimazolam has both the property of quick offset of effect like propofol and the stable hemodynamic effect like midazolam, making it favorable for use as a sedative in cardiac surgery patients. The aim of this study is to evaluate the hemodynamic effect of remimazolam besylate versus propofol in patients undergoing cardiac surgery.

Inclusion Criteria:

• Sign the informed consent form voluntarily and follow the plan requirements;
• age over 60 years old;
• post coronary artery bypass surgery;
• anticipated mechanical ventilation duration >8 hours
• admission to the cardiac surgery intensive care unit of Zhongshan hospital, Fudan University

Exclusion Criteria:

• delirium before surgery
• severe cognitive dysfunction before surgery
• patients with over degree II A-V block or consistent bradycardia
• patients who are still not awake 12 hours after surgery
• patients who are agitated or cannot follow command
• patients with mechanical circulatory support (ECMO, IABP)
• patients who are allergy to propofol or remimazolam
• BMI≥30kg/m2
• patients with much drainage, the surgery ask for blood pressure control or reopen the chest