Low output syndrome is a common complication in patients undergoing cardiac surgery. Its incidence was reported to be 2 to 6%. Morbidity and mortality of low output syndrome is high and the costs for treating the disease are immense.Natriuretic propeptide Type B (NT-proBNP) is a biological marker for the diagnosis, prognosis and therapy of cardiac failure after cardiac surgery.

Cardiac index and NT-proBNP will be correlated with morbidity and mortality. A critical threshold value for intraoperative cardiac index and NT-proBNP will be calculated.

Low output syndrome is a common complication in patients undergoing cardiac surgery. Its incidence was reported to be 2 to 6% [1]. In patients suffering from low output syndrome cardiac output is severely reduced due to myocardial failure. Among other reasons for myocardial failure, ischemia, insufficient myocardial protection during aortic cross-clamping, and severely reduced ventricular function prior surgery are the most common risk factors for low output syndrome. Low output syndrome is treated with positive inotropic drugs and mechanical assist devices [2]. Morbidity and mortality of low output syndrome is high and the costs for treating the disease are immense.

If cardiac output cannot be increased cardiac failure persist and vital organs are hypoperfused. Critical and prolonged hypoperfusion results in single and multi organ failure. Until today a definite threshold for a critically reduced cardiac output or cardiac index requiring immediate therapy is not completely known. Cardiogenic shock is diagnosed by clinical signs and it is not diagnosed by cardiac output or cardiac index. The critical value for a severely reduces cardiac index was reported to be in a range of 1.75 to 2.5L/min/m² [3-5].

Natriuretic propeptide Type B (NT-proBNP) is a biological marker for the diagnosis, prognosis and therapy of cardiac failure after cardiac surgery [6,7].

The primary objective of this prospective observational study in 150 patients undergoing cardiac surgery with an intraoperative measured cardiac output <2L/min/m² is to monitor NT-proBNP for 7 days. Cardiac index and NT-proBNP will be correlated with morbidity and mortality [8]. A critical threshold value for intraoperative cardiac index and NT-proBNP will be calculated.

Inclusion Criteria:

• Adult patient undergoing cardiac surgery
• Written informed consent
• Cardiac index before cardiopulmonary bypass <2L/min/m²

Exclusion Criteria:

• Missing consent
• Serum creatinine >1.5mg/dL [>123µmol/L]

150 patients undergoing cardiac surgery, being monitored with a Swan-Ganz catheter and an intraoperatively before cardiopulmonary bypass measured cardiac index <2L/min/m².