Oxygenation and mechanisms of hypoxemia
- Arthur C Theodore, MD
Arthur C Theodore, MD
- Associate Professor of Medicine
- Boston University School of Medicine
The process of taking oxygen from the inspired air and using it to sustain aerobic cellular metabolism throughout the body can be conceptualized as having three steps:
●Oxygenation is the process of oxygen diffusing passively from the alveolus to the pulmonary capillary, where it binds to hemoglobin in red blood cells or dissolves into the plasma. Insufficient oxygenation is termed hypoxemia. This is to be differentiated from hypoxia, which is an abnormally low oxygen content in a tissue or organ.
●Oxygen delivery is the rate of oxygen transport from the lungs to the peripheral tissues.
●Oxygen consumption is the rate at which oxygen is removed from the blood for use by the tissues.
●Hypoxemia is defined as an abnormally low level of oxygen in the blood (ie, low partial oxygen tension).To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:
- American Thoracic Society, American College of Chest Physicians. ATS/ACCP Statement on cardiopulmonary exercise testing. Am J Respir Crit Care Med 2003; 167:211.
- O'Driscoll BR, Howard LS, Earis J, et al. BTS guideline for oxygen use in adults in healthcare and emergency settings. Thorax 2017; 72:ii1.
- Hansen JE, Sue DY, Wasserman K. Predicted values for clinical exercise testing. Am Rev Respir Dis 1984; 129:S49.
- Mellemgaard K. The alveolar-arterial oxygen difference: its size and components in normal man. Acta Physiol Scand 1966; 67:10.
- Kanber GJ, King FW, Eshchar YR, Sharp JT. The alveolar-arterial oxygen gradient in young and elderly men during air and oxygen breathing. Am Rev Respir Dis 1968; 97:376.
- Covelli HD, Nessan VJ, Tuttle WK 3rd. Oxygen derived variables in acute respiratory failure. Crit Care Med 1983; 11:646.
- Gilbert R, Keighley JF. The arterial-alveolar oxygen tension ratio. An index of gas exchange applicable to varying inspired oxygen concentrations. Am Rev Respir Dis 1974; 109:142.
- Peris LV, Boix JH, Salom JV, et al. Clinical use of the arterial/alveolar oxygen tension ratio. Crit Care Med 1983; 11:888.
- Trachsel D, McCrindle BW, Nakagawa S, Bohn D. Oxygenation index predicts outcome in children with acute hypoxemic respiratory failure. Am J Respir Crit Care Med 2005; 172:206.
- American Academy of Pediatrics. Committee on Fetus and Newborn. Use of inhaled nitric oxide. Pediatrics 2000; 106:344.
- Rodríguez-Roisin R, Roca J. Mechanisms of hypoxemia. Intensive Care Med 2005; 31:1017.
- Williams AJ. ABC of oxygen: assessing and interpreting arterial blood gases and acid-base balance. BMJ 1998; 317:1213.
- Gutierrez G. Cellular effects of hypoxemia and ischemia. In: The Lung: Scientific Foundations, 2nd ed, Crystal RG, West JB, Weibel ER, Barnes PJ (Eds), Lippincott-Raven Publishers, Philadelphia 1997. p.1969.
- Hornbein TF. Hypoxia and the brain. In: The Lung: Scientific Foundations, 2nd ed, Crystal RG, West JB, Weibel ER, Barnes PJ (Eds), Lippincott-Raven Publishers, Philadelphia 1997. p.1981.
- MEASURES OF OXYGENATION
- Arterial oxygen saturation (SaO2)
- Arterial oxygen tension (PaO2)
- A-a oxygen gradient
- PaO2/FiO2 ratio
- a-A oxygen ratio
- Oxygenation index
- MECHANISMS OF HYPOXEMIA
- V/Q mismatch
- Right-to-left shunt
- Diffusion limitation
- Reduced inspired oxygen tension
- EFFECTS OF HYPOXEMIA
- SUMMARY AND RECOMMENDATIONS