Additional laboratory data obtained in our patient include hematocrit, 54%; hemoglobin, 18 grams per 100 milliliters of blood; cutaneous oxygen saturation with the patient at rest, 83%.
For a normal adult male at sea level these values would be hematocrit, 45%; hemoglobin, 15 grams per 100 milliliters of blood; and cutaneous oxygen saturation, 100%.
Chronic hypoxemia
Chronic hypoxemia resulting from a right-to-left shunt through the ventricular septal defect causes a decrease in systemic arterial oxygen tension, or pO2. This is reflected by the decrease in cutaneous oxygen saturation to 83%. Decreased arterial pO2 stimulates the kidneys to increase production of erythropoetin. This, in turn, stimulates the bone marrow to increase red blood cell production, resulting in an increase in hematocrit and hemoglobin.