Prospective, Observational Study in Cardiac Surgery: How Much Cardiac Output is Enough?

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].

The primary objective of this prospective observational study in 600 patients undergoing cardiac surgery is to try to define a threshold for a critically reduced cardiac output or cardiac index requiring immediate therapy.

If cardiac output and cardiac index are not reduced below a critical threshold, morbidity, mortality, and length of stay in the intensive care unit and in the hospital are reduced [6].