[Theoretical, experimental and clinical effects of variations in hematocrit during hemodilution]

By decreasing both viscosity and maximum oxygen capacity, a fall in hematocrit has two opposing effects on oxygen transport. The resultant of these effects was studied using a mathematical model representing the circulatory system and the oxygen transport system. This simulation showed that hemodilution decreased mean aortic pressure, increased central venous pressure and cardiac output. Oxygen supply to the tissues was maximum at a hematocrit of 30 p. cent. Blood volume was an essential parameter. These theoretical concepts of an optimum hematocrit of 30 p. cent were confirmed in the isolated rat heart perfused by blood with varying hematocrits. A clinical study in general surgery involving 307 patients where the hematocrit was reduced to below 32 p. cent by replacing blood loss by Ringer lactate or a fluid gelatin type solution, showed the good tolerance of normovolaemic hemodilution when used carefully, and its value in the prevention of post-operative thrombo-embolic disease.