Pathomorphologic and histochemical changes in the liver during hemodilution

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In preoperative haemodilution, blood is withdrawn before surgery while normovolaemia is maintained by infusion of cell free fluid.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.

[Hemodilution and tissue oxygenation]

In a healthy person, when the haematocrit decreases in acute moderate haemodilution, oxygen delivery and oxygen pressures are preserved or improved by increasing the cardiac output. With a haematocrit of about 0.32, oxygen transport is maximum if the patient's heart function is normal, with no coronary heart disease. If the haematocrit falls below 0.25, there is a risk of anoxic anaemia, by splanchnic and cutaneous vasoconstriction and by a limitation of coronary blood flow adaptation to an increase in cardiac output. If oxygen requirements are increased by muscle exercise, fever, other stresses or when respiratory hypoxaemia occurs, extreme haemodilution is rapidly responsible for an oxygen debt. In all situations, the tissue oxygenation is compromised in the case of hypovolaemia.

Hemodilution -- new clothes for an anemic emperor

This review deals with the rationale for the use of hemodilution in patients not subjected to open heart surgery. The claim for an optimum of circulatory oxygen transport at 30% hematocrit has been disproved; hemodilution thus simply means acute normovolemic anemia. Accordingly, it generates a cardiovascular strain and particularly jeopardizes cerebral and myocardial oxygen supply. Potentially serious clinical side effects have been reported. Hemodilution should therefore not be carried beyong the lower normal range for the hemoglobin or hematocrit level, i.e. 12--12.5 g% or 35--36%.

Moderate and extreme haemodilution in open-heart surgery: evaluation of haemolysis, cell damage and protein changes

Clinical chemical data from patients operated upon in moderate and extreme haemodilution have been compared. Haemolysis was more pronounced during and after moderate dilution that in extreme dilution. A slight liver damage was found post-operatively after moderate dilution. Several changes were of about the same magnitude in both groups: Serum CK increased, reaching maximal activity 3-18 h after operation. An acute phase reaction of plasma proteins took place post-operatively, except that the concentration of complement C-3 dropped during the first days after operation. The serum levels of phosphate were positively correlated to several of the acute phase proteins.