Hemodynamic effects of exchange transfusions with liposome-encapsulated hemoglobin.

The ability of liposome-encapsulated hemoglobin (LEH) to sustain life in rats at hematocrits 45% below lethal levels was demonstrated by virtually total exchange transfusions. All control animals (transfused with 7% albumin in Erilyte) died at a mean hematocrit of 5.35%, with corresponding oxygen-carrying capacity of 2.65 ml/100 ml. All LEH animals survived with a final RBC hematocrit of 2.96% and an oxygen-carrying capacity of 7.05 ml/100 ml. LEH animals maintained normal blood pressures and essentially normal cardiac output, while control animals failed to do so. Systemic vascular resistance of control animals at 78% exchange was reduced to 33% of baseline, while of LEH animals at 92% exchange, to 80% of baseline. In-vitro measurements were made of LEH and RBC suspension viscosity as a function of shear rate, suspension concentration, and lipid membrane composition. The viscous behavior of the LEH suspensions was non-Newtonian and nearly the same as suspensions of natural RBC prepared similarly, though LEH suspensions had slightly higher viscosity.