[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.