title: Hemoglobin Is a Vital Determinant of Arterial Oxygen Content in Hypoxemic Patients with Pulmonary Arteriovenous Malformations.
abstract: BACKGROUND
  PaO2and SaO2are commonly measured in respiratory practice, but arterial oxygen content (CaO2) refers to the volume of oxygen delivered to the tissues per unit blood volume. CaO2is calculated from SaO2and the hemoglobin concentration in blood, recognizing that each gram of hemoglobin can transport approximately 1.34 ml of oxygen when fully saturated.
  
  
  OBJECTIVE
  To prospectively evaluate serial changes in CaO2in 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 SaO2(breathing room air, by pulse oximetry), hemoglobin, red cell and iron indices were measured, and CaO2calculated as SaO2× hemoglobin × 1.34 ml/g. Serial measurements were evaluated in 100 cases spanning up to 32.1 (median, 10.5) years.
  
  
  RESULTS
  Presentation CaO2ranged from 7.6 to 27.5 (median, 17.6) ml/dl. CaO2did not change appreciably across the SaO2quartiles. In contrast, hemoglobin ranged from 5.9 to 21.8 g/dl (median, 14.1 g/dl), with a linear increase in CaO2across hemoglobin quartiles. After PAVM embolization and an immediate increase in SaO2, hemoglobin fell and CaO2was unchanged 1.6-12 (median, 4) months later. When hemoglobin fell because of iron deficiency, there was no change in SaO2. Similarly, when hemoglobin rose after iron treatment, there was no change in SaO2, and the expected CaO2increment was observed. These relationships were not evident during pregnancy when hemoglobin fell, and PAVMs usually deteriorated: in pregnancy SaO2commonly increased, and serial CaO2values (incorporating hemodilution/anemia) more accurately reflected deteriorating PAVM status. An apparent fall in CaO2with age in females was attributable to the development of iron deficiency. There was an unexplained increase in CaO2with age in follow-up of males after embolization.
  
  
  CONCLUSIONS
  Hemoglobin/CaO2should be further incorporated into oxygenation considerations. More attention should be given to modest changes in hemoglobin that substantially modify CaO2.
authors.affiliation: 1 School of Medicine, Imperial College London.
authors.forename: Abeer
authors.initials: A
authors.lastname: Rizvi
authors.affiliation: 2 Respiratory Medicine, Imperial College Healthcare NHS Trust.
authors.forename: Patricia
authors.initials: P
authors.lastname: Macedo
authors.affiliation: 2 Respiratory Medicine, Imperial College Healthcare NHS Trust.
authors.forename: Lydia
authors.initials: L
authors.lastname: Babawale
authors.affiliation: 2 Respiratory Medicine, Imperial College Healthcare NHS Trust.
authors.forename: Hannah C
authors.initials: HC
authors.lastname: Tighe
authors.affiliation: 3 Respiratory Sciences, National Heart and Lung Institute, Imperial College London.
authors.forename: J Michael B
authors.initials: JMB
authors.lastname: Hughes
authors.affiliation: 4 Imaging, Imperial College Healthcare NHS Trust; and.
authors.forename: James E
authors.initials: JE
authors.lastname: Jackson
authors.affiliation: 5 Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, London, United Kingdom.
authors.forename: Claire L
authors.identifier: http://orcid.org/0000-0001-9007-5775
authors.initials: CL
authors.lastname: Shovlin
mesh_terms: D000328:Adult; D000740:Anemia / Q000097:blood*; D001165:Arteriovenous Malformations / Q000150:complications* / Q000628:therapy*; D001784:Blood Gas Analysis; D004621:Embolization, Therapeutic; D005260:Female; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D000860:Hypoxia / Q000097:blood*; D007501:Iron / Q000097:blood; D008131:London; D008168:Lung / Q000098:blood supply; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010092:Oximetry; D010100:Oxygen / Q000097:blood; D011247:Pregnancy; D011446:Prospective Studies; D011651:Pulmonary Artery / Q000002:abnormalities; D011667:Pulmonary Veins / Q000002:abnormalities; D012044:Regression Analysis
chemical_list: D006454:Hemoglobins; D007501:Iron; D010100:Oxygen
keywords: aging; anemia; hemorrhage; iron; pregnancy