Plasma volume expansion with solutions of hemoglobin, albumin and Ringer's lactate in sheep

Introduction: Hemoglobin based blood substitutes have been well studied with respect to oxygen carrying and vascular effects, but little is known about their volume expansion properties. Methods: In the present study we measured plasma volume expansion (Evans blue and hematocrit changes) and hemodynamic responses in conscious hemorrhaged (mean arterial pressure = 50 mmHg for 2 hrs) and normovolemic splenectomized sheep, after a 30-min infusion of either 20ml/kg 10% diaspirin cross-linked hemoglobin (DCLHb), 20ml/kg 8% human albumin (Alb) or 60ml/kg of a solution of Ringer's lactate (RL). Results: All regimens expanded blood volume, and increased blood pressure and cardiac output after hemorrhage. However, only 15±3% of the infused volume of RL were evident as intravascular expansion 10-min post-infusion, compared to 67±16% and 139±139% for Alb and DCLHb, respectively. DCLHb infusions were associated with higher blood pressures and lower cardiac outputs compared to RL and Alb, but the increased O₂ content of blood with DCLHb resulted in similar systemic delivery of oxygen. These differences in hemodynamics and vascular volume continued for 2-hrs, after 24-hrs vascular volume and all hemodynamics were similar in all three groups. The better volume expansion with DCLHb may be due to greater mobilization of endogenous interstitial protein or reduced transcapillary loss as total intravascular endogenous plasma protein increased after infusion of DCLHb, while after infusions of Alb and RL there was an apparent loss of endogenous intravascular protein. Vasoconstriction by DCLHb could lower blood-to-tissue transport of fluid and protein. Conclusions: In addition to oxygen carrying and vasoactivity, DCLHb is associated with volume expansion properties out of proportion to its colloid osmotic pressure.