Seeking Optimal Relation Between Oxygen Saturation and Hemoglobin Concentration in Adults With Cyanosis from Congenital Heart Disease

In patients with cyanosis from congenital heart disease, erythropoiesis is governed by many factors that may alter the expected relation between oxygen saturation (O2sat) and hemoglobin concentration. We sought to define the relation between O2sat and hemoglobin in such patients and to predict an ideal hemoglobin concentration for a given O2sat. Adults with congenital heart defects and cyanosis were studied prospectively with blood tests and exercise testing. Non-optimal hemoglobin was defined as any evidence of inadequate erythropoiesis; namely iron, folate, or B12 deficiency, raised erythropoietin, reticulocytosis, or a right-shifted oxygen-hemoglobin curve. For patients without these factors, a linear regression equation of hemoglobin vs.O2sat was used to predict the optimal hemoglobin for all patients. Of 65 patients studied, 21 met all pre-study criteria for optimal hemoglobin. For all patients there was no correlation between O2sat and hemoglobin (r=-0.24), whereas there was a strong linear correlation for those meeting criteria for optimal hemoglobin (r=-0.888, p<0.001). The optimal hemoglobin regression equation was hemoglobin = 60.5- (0.474 x O2sat). A negative correlation was found between the hemoglobin difference (predicted minus measured) and exercise duration on cardiopulmonary exercise testing (R = -0.402, p=0.007) and 6-minute walk distance (R=-0.478, p<0.001). In conclusion, a strong relation between O2sat and hemoglobin concentration can be shown in stable cyanotic patients and used to predict an optimal hemoglobin. This relation may be useful in defining a functional anemia in this group