THE CIRCULATING RED CELL AND PLASMA VOLUME AND THE DISTRIBUTION OF BLOOD IN LARGE AND MINUTE VESSELS IN EXPERIMENTAL SHOCK IN DOGS, MEASURED BY RADIOACTIVE ISOTOPES OF IRON AND IODINE 1

Abstract

Measurements of the total circulating red cell and plasma volume, and of the distribution of blood in large and minute vessels were made in dogs in experimental shock, by means of techniques employing Evans blue, 2 isotopes of radioactive Fe, and radioactive I. The following characteristics of the circulation in shock have been demonstrated. There is always a greater reduction in circulating red cells and plasma than can be accounted for by measured external blood loss. A part of this discrepancy in blood vol. may be lost into damaged areas or by intestinal bleeding in certain types of shock. Regardless of etiology, there is a. widespread trapping of red cells within the minute vessels of all the organs in the body. The effect of this trapping is a reduction in capillary blood flow through all organs. Since the normal capillary blood content is less than 20% of the total vol., the trapping of even a small portion thereof may result in a fatal reduction in capillary flow. There is an abnormal distribution of whole blood between large and minute vessels which is not reflected by changes in the arterial hematocrit. There are marked deviations from normal in the hematocrit of large and small vessel blood, and these are directly related to changes in the arterial hematocrit. The degree of red cell trapping present does not parallel the reduction in total blood vol., but is related to the reduction in mean arterial pressure. However, this correlation between trapping and arterial pressure may not apply when the hematocrit is abnormally high. The findings indicate that the therapy of shock should be directed not only towards restoration of total blood vol., but also towards the resumption and maintenance of normal capillary flow.