Hemoglobin Is a Vital Determinant of Arterial Oxygen Content in Hypoxemic Patients with Pulmonary Arteriovenous Malformations
Symbol and Symbol are commonly measured in respiratory practice, but arterial oxygen content (Symbol) refers to the volume of oxygen delivered to the tissues per unit blood volume. Symbol is calculated from Symbol and the hemoglobin concentration in blood, recognizing that each gram of hemoglobin can transport approximately 1.34 ml of oxygen when fully saturated.Objectives:
To prospectively evaluate serial changes in Symbol in humans, incorporating and excluding dynamic changes to oxygenation and hemoglobin parameters that may occur during life.Methods:
A cohort of 497 consecutive patients at risk of both hypoxemia and anemia were recruited. The patients had radiologically proven pulmonary arteriovenous malformations (PAVMs), which result in hypoxemia due to right-to-left shunting, and concurrent hereditary hemorrhagic telangiectasia, which placed them at risk of iron deficiency anemia due to recurrent hemorrhagic iron losses. Presentation Symbol (breathing room air, by pulse oximetry), hemoglobin, red cell and iron indices were measured, and Symbol calculated as Symbol × hemoglobin × 1.34 ml/g. Serial measurements were evaluated in 100 cases spanning up to 32.1 (median, 10.5) years.Results:
Presentation Symbol ranged from 7.6 to 27.5 (median, 17.6) ml/dl. Symbol did not change appreciably across the Symbol quartiles. In contrast, hemoglobin ranged from 5.9 to 21.8 g/dl (median, 14.1 g/dl), with a linear increase in Symbol across hemoglobin quartiles. After PAVM embolization and an immediate increase in Symbol, hemoglobin fell and Symbol was unchanged 1.6-12 (median, 4) months later. When hemoglobin fell because of iron deficiency, there was no change in Symbol. Similarly, when hemoglobin rose after iron treatment, there was no change in Symbol, and the expected Symbol increment was observed. These relationships were not evident during pregnancy when hemoglobin fell, and PAVMs usually deteriorated: in pregnancy Symbol commonly increased, and serial Symbol values (incorporating hemodilution/anemia) more accurately reflected deteriorating PAVM status. An apparent fall in Symbol with age in females was attributable to the development of iron deficiency. There was an unexplained increase in Symbol with age in follow-up of males after embolization.Conclusions:
Hemoglobin/Symbol should be further incorporated into oxygenation considerations. More attention should be given to modest changes in hemoglobin that substantially modify Symbol.