BACKGROUND:  Transfusions are intended to augment oxygen‐carrying capacity. The ability of fresh and stored red blood cells (RBCs) to maintain microvascular perfusion and oxygen delivery to the tissue has not been directly measured.

STUDY DESIGN AND METHODS:  Microvascular responses to exchange transfusion with fresh and stored RBCs after acute isovolemic hemodilution with a plasma expander were investigated with the hamster window chamber 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 with an RBC suspension after a 60 percent isovolemic hemodilution with dextran 70 (6% MW = 70 kDa) resulted in a hematocrit of 18 percent (5.6 ± 0.2 g/dL hemoglobin [Hb]). All other systemic variables were unchanged. Stored RBCs (28 days in citrate‐phosphate‐dextrose‐adenine‐1) resuspended in fresh frozen plasma matched to the Hct and Hb concentration were exchange transfused until 25 percent of the circulating RBCs were stored RBCs. Stored RBCs reduced microvascular flow and FCD by 63 and 54 percent, respectively, of the level achieved when fresh RBCs were exchange transfused. Microvascular oxygen extraction by the stored RBC was 54 percent lower than that of the fresh RBCs. The tissue oxygen levels were 3.5 and 14.4 mmHg for the stored and fresh RBCs, respectively.

CONCLUSION:  Circulation of stored RBCs in a hemodiluted animal resulted in significantly malperfused and underoxygenated microvasculature that was not detectable at the systemic level.