Changes in Cell and Plasma Volumes in the Dog Produced by Hemorrhage and Reinfusion

Abstract

Sixteen dogs were anesthetized with a combination of morphine and pentobarbital. They were bled slowly into a bottle until the mean blood pressure was 35.0 ± 2.0 mm Hg. Blood volume was determined by red cells tagged with radioactive Cr⁵¹ and injected at various times during the experiments. All figures are averages of the 16 dogs. At the end of the bleeding period 9.5 cc/kg of plasma was mobilized but 3.0 cc/kg of the original volume of red cells was trapped. On reinfusion the 9.5 cc/kg of plasma that had been mobilized and 8.2 cc/kg of the dog's original plasma were removed from the circulation or trapped. No more red cells were trapped, but those previously trapped were not released. The final blood volume after reinfusion (69.3 cc/kg) was therefore less than the control blood volume (81.4 cc/kg). Because of the ability of the circulation to adjust the circulating volume by trapping red cells and adding or removing plasma, it is essential to use additional injections of the material to be measured if a change in blood volume is suspected.