Defining and quantifying oxygen delivery potency of blood products

Transfusion is intended to correct anemia when it is believed to either impair adequate oxygen (O₂) delivery or when the resulting compensatory cardiovascular workload poses clinical risk. Dosing is typically based on hemoglobin (Hb) levels, without consideration of differences in red blood cell (RBC) or Hb-based blood substitute O₂ delivery potential. Such consideration requires quantified assessment of O₂ delivery potency, for which there is no accepted metric. We developed an in vitro metric to predict the O₂ delivery potency for various "Hb formulations" (fresh and stored whole blood [sWB]), stored RBC concentrate (sRBCc), and artificial WB analogs (WBAs) composed with different Hb-based O₂ carriers. O₂ uptake and delivery were modeled across physiologic O₂ gradients by integrating data from matched O₂ association (high pH; ie, in the lungs) and dissociation curves (low pH; ie, in tissues). These data were used to compute a novel O₂ delivery potency metric, lung-to-tissue O₂ flux (L-TOF). Using L-TOF, we quantified O₂ delivery potency of sRBCc (additive solution 1) and determined that equipotent transfusion at day 0 and day 42 would require an increase in "dose" of 158% (476 ± 21.6 mL of day 42 sRBCc was equipotent to 300 ± 0.0 mL of fresh RBCs). Employing a novel in vitro model of massive transfusion, L-TOF was used to quantify transfusion effectiveness by examining change in recipient blood L-TOF after receipt of either crystalloid (normal saline), sWB (citrate phosphate dextrose adenine-1), or WBAs. L-TOF enables direct comparison of O₂ delivery potency between different blood products, offering a predictive readout of transfusion quality.