A Mechanistic Analysis of Possible Blood Transfusion Failure to Increase Circulatory Oxygen Delivery in Anemic Patients.

ABSTRACT

The effects of changing hematocrit (Hct) on the rate of circulatory oxygen ([Formula see text]) delivery were modeled analytically to describe transfusion of 0.5-3.0 units of packed red blood cells (pRBC, 300 mL/unit, 60% Hct) to anemic patients. In our model, Hct affects [Formula see text] delivery to the microcirculation by changing blood [Formula see text] carrying capacity and blood viscosity, which in turn affects blood flow velocity and, therefore, [Formula see text] delivery. Changing blood velocity impacts the [Formula see text] delivery by affecting the oxygen diffusive losses as blood transits through the arteriolar vasculature. An increase in Hct has two opposite effects it increases the blood [Formula see text] carrying capacity and decreases the flow velocity. This suggests the existence of an optimal Hct that maximizes [Formula see text] delivery. Our results show that maximal [Formula see text] delivery occurs in the anemic range, where [Formula see text]%. Optimal blood management is associated with transfusing enough units up to reaching maximal [Formula see text] delivery. Although somewhat complex to implement, this practice would result in both substantial blood savings and improved [Formula see text] delivery.