Influence of cell-free Hb on local tissue perfusion and oxygenation in acute anemia after isovolemic hemodilution

BACKGROUND: Oxygen-carrying solutions are intended to eliminate the blood transfusion trigger. Their ability to maintain microvascular perfusion and to deliver oxygen to tissue when they replace the RBCs as oxygen carriers has not been directly measured. STUDY. DESIGN AND METHODS: Microvascular response to exchange transfusion with a polymerized bovine cell-free Hb (PBH) solution after acute isovolemic hemodilution with a plasma expander was investigated by using the hamster window model. In vivo functional capillary density (FCD), blood flow, and high-resolution oxygen distribution In microvascular networks were measured by noninvasive methods. RESULTS: Exchange transfusion of PBH solution after a 60-percent isovolemic hemodilution with dextran 70 (MW, 70 kDa) resulted in a Hct of 11 percent and a Hb content of 6.7 g per dL. FCD was 0.37 of baseline. Interstitial pO(2) was reduced from 21.0 mm Hg to 0.3 mmHg. Arteriolar and venular blood flows were ratios of 0.75 and 0.76 relative to baseline. In a previous study, tissue PO2 after hemodilution to 5.6 g of Hb per dL with dextran 70 was 23.0 mmHg. Hypervolemic injection of PBH solution increased blood pressure and caused vasoconstriction. CONCLUSION: Using PBH solution to replace RBC oxygen-carrying capacity during low Hb content conditions (< 50%) causes abnormally low tissue oxygenation and FCD, while the same level of hemodilution with dextran maintains normal microvascular conditions.