Distribution of Red Cells and Plasma in the Dog

Abstract

Two questions are examined: a) is the venous hematocrit a representative sample of the percentage of red cells to plasma in the circulation, and b) does the distribution of red cells and plasma remain constant with changes in blood volume? The dogs were anesthetized with a morphine-pentobarbital combination. Red cell volume was measured with either radioactive Cr⁵¹ or Fe⁵⁹ and plasma volume with Evans blue or radioactive I¹³¹. The distribution of cells was expressed by the ratio BH/VH and of plasma by (100-BH)/(100-VH). The body hematocrit (BH) was significantly less than the venous hematocrit (VH) for 60 control dogs, and the distribution of red cells, expressed by the ratio BH/VH, was 0.90 and for the plasma 1.09. Transfusion of blood (100– 149 cc/kg, group III) was followed by a significant shift from the control value in the distribution of plasma but not of red cells. Neither hemorrhage of 15% of the estimated blood volume, reinfusion of the blood nor successive transfusion into group III was followed by a significant change in the distribution of red cells and plasma from the control distribution. With a large hemorrhage 58% of the measured blood volume and shock there was a significant shift in the distribution of red cells (0.795) from the control value. Since changes in blood volume may accompany a shift in the cell-plasma distribution, the cell or plasma volume, venous hematocrit, and a factor cannot be used for measuring blood volume unless the factor is determined for the circulatory condition being studied. Following this work we reconsidered the effect of these data on previously published work from this laboratory. Some of the absolute values were significantly altered but not the direction or percentage change.