Isovolemic hemodilution with a bovine hemoglobin-based oxygen carrier: Effects on hemodynamics and oxygen transport in comparison with a nonoxygen-carrying volume substitute

Abstract

Objective : Stroma-free hemoglobin solutions have been shown to maintain oxygen transport in the absence of red blood cells. This study was designed to investigate the impact of such solutions on hemodynamics and oxygen transport during progressive isovolemic hemodilution within and even beyond a clinically relevant range of hematocrit values. Design : Prospective, randomized experimental study comparing a bovine hemoglobin-based oxygen carrier (bHBOC) with a conventional nonoxygen-carrying volume substitute (hydroxyethyl starch [HES]). Setting : Animal laboratory of a university cardiovascular research center. Participants : Splenectomized full-grown foxhounds, anesthetized with pentobarbital and piritramid. Interventions : Twelve splecnectomized foxhounds were anesthetized and mechanically ventilated. Catheters were placed for hemodilution, arterial and venous blood sampling, and hemodynamic measurements. The baseline hematocrit (Hct) value was adjused to 0.35 by an initial isovolemic exchange of blood for identical volumes of HES (10% HES 200/0.5). Thereafter, the hematocrit was progressively reduced by isovolemic hemodilution using either HES ( n = 6) or bHBOC ( n = 6). Measurements and Main Results : Hemodynamic and laboratory parameters of oxygen transport were measured at Hct values of 0.30, 0.20, and 0.10. Oxygen content was directly estiamted using an oxygen-specific fuel cell. Arterial oxygen content at an Hct value of 0.10 nearly doubled in bHBOC-treated dogs as compared with HES-diluted animals ( p < 0.001). This gain in oxygen-carrying capacity was completely negated by a decrase in cardiac output (−32% Hct 0.35 v Hct 0.30; p < 0.001) immediately on the first infusion of bovine hemoglobin. Thus, oxygen delivery was significantly lower as compared with HES-treated dogs at Hct 0.30 and 0.20, but remained stable at a level of 60% of baseline until Hct was 0.10. Both the pulmonary and the systemic vascular resistances increased. Conclusions : Isovolemic hemodilution with bHBOC did not improve systemic oxygen delivery in comparison with a nonoxygen-carrying diluent (HES) in a range of Hct values down to 0.10. Unchanged mixed venous lactate levels and stable oxygen consumption indicate sufficiently maintained oxygen delivery. This might become advantageous in patients who are unable to adequately increase cardiac output during hemodilution.