[The place for using erythrocyte substitutes in hemodilution: fluosol-DA and polymerized pyridoxylated hemoglobin]

In conditions of limited haemodilution (haematocrit 0.25), an improvement in the rheological properties of blood and an increase in cardiac output allow increased perfusion of capillaries and maintenance of tissue oxygenation so long as normal circulating volume is maintained. However, some authors have suggested that blood substitutes enabling oxygen transport are necessary. The suitability of such substitutes depends on their physicochemical properties and, until now, only the use of haemoglobin solutions and fluorocarbon emulsions has been. The use of fluorocarbons requires respiration under hyperoxia or pure oxygen, which is a major limitation. Haemoglobin solutions suffer from inadequate concentration, short vascular persistence and too high an affinity for oxygen, but these deficiencies disappear with polymerized pyridoxylated haemoglobin. Though both types of preparation can keep animals alive with zero haematocrit for some time, their contribution to oxygenation goes down as the haematocrit goes up. According to Zander and Makowski [40]. the minimum acceptable amount of oxygen in the blood is reached with a haemoglobin concentration of 4.4 g X 100 ml-1 with a Po2 of 90 mmHg (12 kPa), and of 3.3 g X 100 ml-1 with a Po2 of 550 mmHg (73 kPa); these values correspond to a haematocrit close to 0.10. At this haematocrit and with a Po2 of 90 mmHg, a 70 g X l-1 haemoglobin solution contributes for 28% to the consumption of oxygen in baboons, while Fluosol DA 20, used at Po2 550 mmHg, takes care of 55% of this consumption. At higher haematocrits, it is not certain that these substitutions have a real advantage over the usual plasma expanders at normovolaemic haemodilution.(ABSTRACT TRUNCATED AT 250 WORDS)