Vasoplegic syndrome is a common complication after cardiac surgery. Low dose vasopressin can up-regulate blood pressure and improve clinical outcomes compared with norepinephrine (mainly acute kidney injury Anesthesiology 2017; 126:85-93). Pituitrin is used as a substitute for vasopressin in our center, which contains both vasopressin and oxytocin. Oxytocin may alleviate inflammatory process-associated kidney injury (Peptides 2006;27:2249-57). Therefore, the investigators hypothesize Pituitrin may be preferable to norepinephrine in the renal protection of patients with vasoplegic syndrome after cardiac surgery. Moreover, the serum levels of vasopressin, catecholamine, corticosteroid and corticotropin-releasing hormone will be measured.

Inclusion Criteria:

1. Patients diagnosed as vasoplegic syndrome(defined as mean arterial pressure less than 65 mmHg resistant to fluid challenge and cardiac index greater than 2.2 L/min · m2) within 24 hours after cardiac surgery.

Exclusion Criteria:

1. Age < 18 and > 75 years.
2. Received renal replacement therapy before cardiac surgery.
3. Diagnosed as endocrine disease before cardiac surgery.
4. Diagnosed as sever peripheral vascular disease before cardiac surgery.
5. Extracorporeal membrane oxygenation support before admission.
6. To receive heart transplantation.
7. Infection on admission.
8. Pregnant or maternal patients.
9. Refusal of consent