Induced low P50 in anesthetized rats: blood gas, circulatory and metabolic adjustments

In anesthetized, normoxic or hypoxic rats the hemodynamic, metabolic and O2 transport characteristics following exchange transfusion with human erythrocytes containing a high O2 affinity hemoglobin (Hemoglobin Creteil, beta 89 Ser----Asp) have been studied. The in vivo oxygen partial pressure at 50% oxygen hemoglobin saturation (P50) decreased from 37.4 +/- 2.1 to 12.7 +/- 0.7 mm Hg; the arterial oxygen tension was reduced significantly from 109.9 +/- 7.7 to 87.3 +/- 12.0 mm Hg. There was a decrease in right ventricular partial pressure of oxygen (PvO2), (P less than 0.001), oxygen consumption (VO2), (P less than 0.001), arterio-venous difference, (P less than 0.001), and peripheral vascular resistance index, (P less than 0.01). Exchange transfusion with normal rat blood (P50 = 37.2 +/- 2.4 mm Hg) or with 2,3-diphosphoglycerate-enriched human red blood cells (P50 = 34.7 +/- 2.2 mm Hg), did not modify these variables in normoxic rats. In hypoxia, the reduction in P50 was associated with a further decrease in PvO2 an increase in serum lactate concentration and a VO2 decrease.