The aim of the study is to describe the effects of hypertonic saline/hydroxyethylstarch solution in comparison to saline solution for 25 + 25 patients undergoing coronary bypass grafting surgery (CABG) using CPB. The study fluid will be given into the venous reservoir of the CPB circuit after aortic declamping. Primary endpoints are the changes in body weight and extracellular water from baseline to the first postoperative morning.

Cardiac surgery and cardiopulmonary bypass (CPB) cause fluid retention in the body. Both dilution of serum proteins and destruction of vascular endothelial glycocalyx cause extravasation of the fluids. We cannot avoid this phenomenon but we can try to restore the excess fluid into the intravascular space where it can be excreted via the kidneys.

Hypertonic saline (HS) creates an osmotic gradient across the cellular membrane, causing a fluid shift from the intracellular space into the extracellular space and from the extravascular space into the intravascular space. The intravascular hypertonic benefit is short-lasting as a result of redistribution of fluid between the intravascular and interstitial spaces. The effect can be lengthened by adding colloid component into the solution.

The aim of the study is to describe the effects of hypertonic saline/hydroxyethylstarch solution in comparison to saline solution for 25 + 25 patients undergoing coronary bypass grafting surgery (CABG) using CPB. The study fluid will be given into the venous reservoir of the CPB circuit after aortic declamping. Primary endpoints are the changes in body weight and extracellular water from baseline to the first postoperative morning. Secondary endpoints are the need of fluids and diuretic medication during the perioperative period.

Inclusion Criteria:

• male gender and no need for pulmonary artery catheter (pulmonary hypertension or left ventricular ejection fraction < 40%).

Exclusion Criteria:

• chronic hyponatremia and significant renal dysfunction.