RELATIONSHIP OF THE PLASMA VOLUME AND THE CELL PLASMA RATIO TO THE TOTAL RED CELL VOLUME

Abstract

Six bleeding expts. were performed on four splenectomized, unanesthetized dogs. The plasma vol. and hematocrit reading were detd. before hemorrhage. After the removal of a known quantity of red cells, the plasma vol. and hematocrit reading were again detd. The red cell vol. before hemorrhage was calculated from the prehemorrhage plasma vol. and hematocrit reading, and from the sum of the post-hemorrhage red cell vol. (plasma vol. and hematocrit reading) and the vol. of red cells removed. Evidence is presented to show that the calculation of the red cell vol. from the sum of the post-hemorrhage red cell vol. and vol. of red cells removed represents approx. the true red cell vol. When the hematocrit reading is approx. 50, the red cell vol. as calculated from the plasma vol. and hematocrit reading is approx. 25% higher than the true red cell vol. This error occurs because the cell plasma ratio of blood removed from the body is higher than that of the entire circulating blood. The Hb conc. of blood removed from the body is higher than the Hb conc. of the entire circulating blood. When the hematocrit reading is approx 50, the total circulating Hb is approx. 25% higher than the true total circulating Hb. As the Hb conc. and the cell plasma ratio of blood removed from the body are not representative of all the blood in the vascular system, it is not possible to accurately quantitate changes in plasma vol. from changes in either the Hb conc. or hematocrit reading.