Determination of Cell Volume in Massive Transfusions Using Fe⁵⁹ and Cr⁵¹

¹ From the Departments of Physiology and Pharmacology, University of Texas Dental School, and Baylor University College of Medicine, Houston, Texas

When dogs are injected with either or both Fe⁵⁹ and Cr⁵¹-labeled cells (initial tag) prior to a series of transfusions (up to 20.0–25.0 cc % body weight) the measured blood and cell volume closely approach and may exceed the expected. After the series of transfusions are completed, if an additional isotope (final tag) is injected the blood and cell volumes are much less than the expected. The difference between the blood and cell volumes determined by the initial and final tag can be explained by the ‘trapping’ of red blood cells. The volume of red blood cells ‘trapped’ after multiple transfusion (up to 10.0–14.9% body weight) can equal or exceed the added cell volume.