Pulmonary hypertension and systemic vasoconstriction may offset the benefits of acellular hemoglobin blood substitutes

Objective: We tested the hypothesis that the pharmacologic properties of a small volume of αα-cross-linked hemoglobin (ααHb) could effectively resuscitate pigs subjected to hemorrhage. Methods: Fourteen pigs hemorrhaged to a mean arterial pressure (MAP) of 40 mm Hg for 60 minutes were treated with a 4-mL/kg 2-minute infusion of 10 g/dL ααHb or 7 g/dL human serum albumin, an oncotically matched control solution. Results: The removal of blood (17 ± 1.5 mL/kg) caused the typical physiologic responses to hemorrhagic hypovolemia. Infusion of ααHb restored mean arterial pressure and coronary perfusion pressure, but cardiac output and mixed venous O₂ saturation did not improve significantly. Pulmonary arterial pressure and pulmonary vascular resistance increased markedly and were higher than baseline levels after ααHb. Infusion of human serum albumin produced only minor hemodynamic changes. Brain blood flow did improve to baseline values after ααHb, but was the only tissue to do so. In the human serum albumin group, superior mesenteric artery blood flow recovered to baseline values, whereas brain blood flow did not. Blood flows to other tissues were similar in both groups. Conclusion: Small-volume infusion of ααHb restored mean arterial pressure and brain blood flow, but pulmonary hypertension and low peripheral perfusion may offset benefits for trauma patients.