VASCULAR-RESISTANCE AND THE EFFICACY OF RED-CELL SUBSTITUTES IN A RATHEMORRHAGE MODEL

We have compared polyethylene glycol-modified bovine hemoglobin (PEG-H b; high O-2 affinity, high viscosity, high oncotic pressure) and human hemoglobin cross-linked between the alpha-chains (alpha alpha-Hb; low O-2 affinity, low viscosity, low oncotic pressure) with a non-O-2-car rying plasma expander (pentastarch, high viscosity and oncotic pressur e) after a 50% (by volume) exchange transfusion followed by a severe ( 60% of blood volume) hemorrhage. Mean arterial pressure and systemic v ascular resistance rose significantly in the alpha alpha-Hb but not in the PEG-Hb animals. Two-hour survival was greater in the PEG-Hb anima ls (93%) than in control (35%), pentastarch (8%), or alpha alpha-Hb (6 %) animals. In the PEG-Hb animals, there was no disturbance of acid-ba se balance, significantly less accumulation of lactic acid, and higher cardiac output than in the other groups. The data suggest that the ri se in vascular resistance that follows alpha alpha-Hb exchange transfu sion offsets the additional O-2 transport provided by the cell-free he moglobin. When resistance does not rise, as with PEG-Hb, even relative ly small amounts of cell-free hemoglobin appear to be a very effective blood replacement.