Use of crystalline hemoglobin as replacement of RBC mass

Replacement of a circulatory RBC mass was performed isovolemically in experimental dogs using either 7% crystalline hemoglobin solution with a low P50 (the oxygen tension necessary to produce 50% saturation of hemoglobin at pH 7.4 and 37 degrees C) or with an albumin solution. Progressive RBC depletion caused increased cardiac output in both groups. Oxygen delivery was better preserved after using the crystalline hemoglobin solution, and, under conditions of extreme anemia, oxygen transport using this solution enabled dogs to survive the otherwise lethal insult. Although administration of crystalline hemoglobin preserved oxygen transport, oxygen off-loading was at a lower tension because of the lower P50. Decreased mixed venous oxygen tension, which presumably reflects lower tissue oxygen tension, was associated with systemic vasoconstriction. The administration of oxygen-carrying solutions with low P50 values results in a relatively vasoconstricted state. This vascular response is mediated by changes in tissue oxygen tension, rather than by impaired tissue oxygen consumption.