Toxicity of human hemoglobin solution infused into rabbits

Aqueous human hemoglobin is being considered as an oxygen-transporting resuscitation solution. However, there are some indications that such solutions may be toxic. We report here that at a clinically significant dose (20% to 30% of the estimated blood volume) of hemoglobin solution (10 gm/dl), toxicity similar to that reported in humans is produced in rabbits. This toxicity is characterized by cardiac rhythm disturbances (25%) and coagulation abnormalities, manifested as intravascular thrombi. Hypoxia, tissue necrosis (brain 29%, liver 25%), and death (22%) were seen. Hypoxia appears to be the cause of death, because the arterial PO2 of rabbits that died was significantly lower (43 +/- 8 mm Hg) than that of rabbits that lived (80 +/- 12 mm Hg). We also report the effect of the method of preparation or degree of purity on the observed toxicity. Stroma-free red blood cell hemolysate, stroma-free hemoglobin, zinc-precipitated hemoglobin, and chromatographically purified hemoglobin were infused. Purification of these solutions ranged from removal of stroma to removal of all detectable nonhemoglobin protein components. In addition, the nonhemoglobin proteins were concentrated and infused into rabbits to compare their effects. All of these hemoglobin solutions induced similar toxicity for rabbits infused with stroma-free hemoglobin. The nonhemoglobin proteins, as well as human serum albumin, exhibited no toxicity. These results demonstrate that, at the clinically relevant dose, hemoglobin or something inherently associated with hemoglobin is toxic.