Vascular resistance and the efficacy of red cell substitutes in a rat hemorrhage model

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Abstract
We have compared polyethylene glycol-modified bovine hemoglobin (PEG-Hb; high O2affinity, high viscosity, high oncotic pressure) and human hemoglobin cross-linked between the α-chains (αα-Hb; low O2affinity, low viscosity, low oncotic pressure) with a non-O2-carrying plasma expander (pentastarch, high viscosity and oncotic pressure) after a 50% (by volume) exchange transfusion followed by a severe (60% of blood volume) hemorrhage. Mean arterial pressure and systemic vascular resistance rose significantly in the αα-Hb but not in the PEG-Hb animals. Two-hour survival was greater in the PEG-Hb animals (93%) than in control (35%), pentastarch (8%), or αα-Hb (6%) animals. In the PEG-Hb animals, there was no disturbance of acid-base balance, significantly less accumulation of lactic acid, and higher cardiac output than in the other groups. The data suggest that the rise in vascular resistance that follows αα-Hb exchange transfusion offsets the additional O2transport provided by the cell-free hemoglobin. When resistance does not rise, as with PEG-Hb, even relatively small amounts of cell-free hemoglobin appear to be a very effective blood replacement.