Because of problems associated with finding compatible donors and disease transmission by transfusion, the search for a red cell substitute has been ongoing for more than 50 years. An ideal substitute would carry and deliver oxygen like red cells, be easy to produce in large quantities, be non-antigenic, and persist in the circulation at least long enough for resuscitation.
One hemoglobin-based oxygen carrier of bovine origin was previously licensed for use in dogs but is no longer available. Because the cost of hemoglobin solution was higher, and duration of effect shorter than that of blood, its main value was in emergency situations when blood was not immediately available. Volume overload was a potential risk, as was vasoconstriction caused by removal of nitric oxide, thus decreasing oxygen delivery to ischemic tissues. Human clinical trials are ongoing, so a safer product may become available.