[Haemodynamic effects of acute intra-operative haemodilution in open heart surgery (author's transl)]

Haemodynamic measurements were made in 80 patients who underwent acute haemodilution (up to 40 ml/kg blood withdrawal) before cardiopulmonary bypass. Measurements of cardiac output, pulmonary arterial pressures including wedge pressure were made. Cardiac index, stroke volume and total peripheral resistance were calculated. Oxygen studies included: arterial and central venous partial pressures and saturations. Haemoglobin content, haematocrit and blood gas determinations were made during haemodilution and bypass. There was a direct relationship between haemodilution and stroke volume (stroke volume increase of 8,5% with 9,4 ml/kg and 25% increase with 40 ml/kg blood withdrawal). No change was found in mean pulmonary artery or wedge pressures. Central venous oxygen saturation remained constant during haemodilution which indicates that oxygen supply was adequate. Haemodilution should be avoided in patients with less than 35% haematocrit, with more than two vessel coronary artery disease and Class IV N.Y.H.A. because of the risk of possible impaired cardiac output compensation. During bypass, a haematocrit of 20% and 6 g% provides greater perfusion and optimal microcirculation. The problems of large volume homologous blood transfusion, hepatitis risk and loss of clotting factors can be lessened with haemodilution.