Effect of Varying the Hematocrit Ratio on the Susceptibility to Hemorrhagic Shock

¹ From the Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson, Mississippi

By the use of a) acetyl phenylhydrazine, b) hemorrhage, c) transfusion, and d) natural variation, 67 dogs with hematocrit ratios varying from 12 to 56 were obtained. These dogs were subjected to hemorrhagic shock by lowering their arterial blood pressure to 30 mm Hg, and the time lapse between the initial production of hypotension and the beginning deterioration of the animal determined. This time lapse is a measure of the resistance of the animal to the development of irreversible shock. A graph of initial hematocrit versus the time required for the development of irreversible shock shows that an increase in the hematocrit ratio from 12 to 35 increases the resistance of the animals by a factor of approximately 5; however, increasing the hematocrit ratio above 35 decreases the resistance of the animal to the development of irreversible shock.