Fluid Management in Patients Undergoing Cardiac Surgery

Background: Currently used crystalloid solutes have a variable composition and may therefore influence acid-base status, intra- and extracellular water content and plasma electrolyte compositions and have a major impact on organ function and outcome. Despite continuing evaluation no superiority of one particular type of fluid has been reached so far. To the best of the investigators' knowledge no study in humans has ever assessed whether the type of crystalloid fluid given for fluid resuscitation in patients undergoing cardiac surgery has an impact on hemodynamic stability and cardiac function so far. Nonetheless in the animal model it was shown that the choice of crystalloid fluid may greatly influence cardiac performance Primary Aim: In this study the investigators want to clarify whether a balanced type acetate-buffered fluid solution in patients undergoing cardiac surgery is associated with better hemodynamic stability and cardiac function than a lactate-buffered crystalloid solute.