Preoperative haemodilution.

In preoperative haemodilution, blood is withdrawn before surgery while normovolaemia is maintained by infusion of cell free fluid. A surgical bleeding then entails a smaller loss of red cells. Reinfusion of the saved blood maintains normovolaemia, raises hematocrit and decreases the need for donor blood. Dilutional anaemia may endanger the oxygenation of the tissues. Tissue oxygenation can be upheld by an augmented and redistributed cardiac output and by a raised oxygen extraction. These compensatory mechanisms are less efficient in the presence of vascular stenosis, in particular in the myocardium which relies virtually exclusively on coronary vasodilatation. Major contraindications to preoperative haemodilution are, apart from coronary insufficiency, ventricular failure and valvular disease. Deleterious increases in cardiac oxygen consumption and/or heart rate may result from e.g. hypovolaemia, arterial desaturation and painful stimuli. The haemodilution procedure requires knowledge and vigilance in all involved personnel and gives best results if combined with other blood saving measures, like blood predeposit and intraoperative red blood cell salvage.