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CARDIOVASCULAR ANESTHESIA

Prediction of the Effect of Acute Normovolemic Hemodilution on the Hematological Constituents of Sequestered Autologous Whole Blood

Paul G. Loubser, MD^*, and Anthony Chan, PhD

*Research Division, Hematicus Limited Partnership, Sugar Land; and Department of Physics and Astronomy, Rice University, Houston, Texas

Address correspondence and reprint requests to Paul G. Loubser, MD, Director of Research, Hematicus Limited Partnership, 302 Lake Glen Court, Sugar Land, TX 77478. Address e-mail to pgl{at}hematicus.com.

During acute normovolemic hemodilution (ANH), autologous whole blood is collected in a series of collection bags containing anticoagulant. The effect of hemodilution on the actual hematological constituents of this sequestered whole blood product has never been examined. We developed a mathematical model that predicts how whole blood bag constituents change during ANH to elucidate the theoretical basis for ANH efficacy. Formulas were derived to calculate the effect of ANH on [X], the blood constituent of interest. An exponential envelope was defined so that the projected impact of ANH on each constituent could be computed while initial blood volume and whole blood bag volume (WB_ANH) were manipulated. Equivalency of autologous whole blood hemoglobin, platelets, and fibrinogen were determined by comparison with standard allogeneic blood products. We determined that the concentration of blood constituent X in a particular unit of collected blood ([X]_n) is provided as a fraction of the initial concentration ([X]₀). As WB_ANH increases relative to estimated blood volume, the decrement in [X]_n increases in successive blood collection bags. Irrespective of initial blood volume, the equivalence of a 450-mL autologous whole blood bag to 1 U of packed red cells and 1 U of whole blood-derived platelet concentrate is 13.3 g/dL and 123 x 10³/µL, respectively. The impact of ANH on autologous whole blood constituents may be accurately predicted using this model. Conversion of WB_ANH into equivalent allogeneic blood products could provide a useful method of comparing outcome in various ANH studies. The exponential envelope may be used to assess the actual ANH technique performed by the anesthesiologist, which in turn may impact quality assurance standards.