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| {{Hypoxemia}}
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| {{CMG}}
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| {{SK}} Hypoxia, desaturation
| | '''For patient information, click [[Hypoxemia (patient information)|here]]''' |
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| ==Overview==
| | {{Hypoxemia}} |
| '''Hypoxemia''' (or hypoxaemia) is an abnormal deficiency in the concentration of [[oxygen]] in [[arterial]] blood (Mosby's Medical Dictionary). A frequent error is made when the term is used to describe poor tissue diffusion as in hypoxia. It is possible to have a low oxygen content (e.g. due to anemia) but a high PO<sub>2</sub> in arterial blood so incorrect use can lead to confusion.
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| Hypoxemia is different from [[hypoxia]], which is an abnormally low oxygen availability to the body or an individual tissue or organ.
| | {{CMG}}; {{AE}} |
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| The type of hypoxia that is caused by hypoxemia is referred to as ''hypoxemic hypoxia''. Because of the frequent incorrect use of hypoxemia, this is sometimes erroneously stated as ''hypoxic hypoxia''.
| | {{SK}} Hypoxia, desaturation |
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| ==Pathophysiology== | | == [[Hypoxemia overview|Overview]] == |
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| Causes are classified into 5 groups:
| | == [[Hypoxemia historical perspective|Historical Perspective]] == |
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| *Low inspired fractional concentration of oxygen (low FiO<sub>2</sub>)
| | == [[Hypoxemia classification|Classification]] == |
| *Alveolar hypoventilation
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| *Impairment of diffusion across blood-gas membrane
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| *Shunt
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| *Ventilation-perfusion inequality
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| Conditions that result in hypoxemia act via one or more of these primary causes.
| | == [[Hypoxemia pathophysiology|Pathophysiology]] == |
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| ===Low inspired oxygen fraction (low FiO<sub>2</sub>)=== | | == [[Hypoxemia causes|Causes]] == |
| See also: [[FiO2|FiO<sub>2</sub>]] <br />
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| If the concentration of oxygen in the inspired gas is low, then a reduced amount of oxygen is delivered to the gas exchanging parts (alveoli) of the [[lung]] each minute. This can result in hypoxemia even if the lungs are normal. It is the ''inspired'' oxygen concentration that is important rather than the ''atmospheric'' concentration as the person may not be breathing atmospheric gas (eg during an anesthetic).
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| ===Alveolar hypoventilation=== | | == [[Hypoxemia differential diagnosis|Differentiating Hypoxemia from other Diseases]] == |
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| If the [[Pulmonary alveolus|alveolar]] ventilation is low, there may be insufficient oxygen delivered to the alveoli each minute. This can cause hypoxemia even if the lungs are normal, as the cause may be outside the lungs (eg airway obstruction, depression of the brain's respiratory center, or muscular weakness).
| | == [[Hypoxemia risk factors|Risk Factors]] == |
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| ===Impaired diffusion=== | | == [[Hypoxemia screening|Screening]] == |
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| Impaired diffusion across the blood-gas membrane in the lung can cause hypoxemia. However this is a very rare cause as it is only in extremely unusual circumstances that actually does cause a problem. Most of the past cases once thought to be due to a diffusion problem are now recognised as being due to ventilation-perfusion inequality.
| | == [[Hypoxemia natural history, complications and prognosis|Natural History, Complications and Prognosis]] == |
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| ===Shunt=== | | == Diagnosis == |
| [[Shunt (medical)|Shunt]] of blood from the right side to the left side of the circulation (right-to-left shunt) is a powerful cause of hypoxemia. The shunt may be intracardiac or may be intrapulmonary. This cause can be readily distinguished from the others as it is the only cause that cannot be corrected by the administration of 100% oxygen.
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| ===Ventilation-perfusion inequality===
| | [[Hypoxemia diagnostic study of choice|Diagnostic Study of Choice]] |[[Hypoxemia history and symptoms|History and Symptoms]] | [[Hypoxemia physical examination|Physical Examination]] | [[Hypoxemia laboratory findings|Laboratory Findings]] | [[Hypoxemia electrocardiogram|Electrocardiogram]] | [[Hypoxemia chest x ray|Chest X Ray]] | [[Hypoxemia echocardiography or ultrasound|Echocardiography or Ultrasound]] | [[Hypoxemia CT|CT]] | [[Hypoxemia MRI|MRI]] | [[Hypoxemia other imaging finidings|Other Imaging Findings]] | [[Hypoxemia other diagnostic studies|Other Diagnostic Studies]] |
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| Ventilation-perfusion inequality (or ''ventilation perfusion mismatch'') is a common cause of hypoxaemia in people with lung disease. It is the areas of the lung with V/Q ratios that are less than one (but not zero) that cause hypoxaemia by this mechanism. (A V/Q ratio of zero is actually shunt so does not contribute to this cause).
| | == Treatment == |
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| ==Causes==
| | [[Hypoxemia medical therapy|Medical Therapy]] | [[Hypoxemia surgery|Surgery]] | [[Hypoxemia primary prevention|Primary Prevention]] | [[Hypoxemia secondary prevention|Secondary Prevention]] | [[Hypoxemia cost-effectiveness of therapy|Cost-Effectiveness of Therapy]] | [[Hypoxemia future or investigational therapies|Future or Investigational Therapies]] |
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| === Causes in Alphabetical Order === | | == Case Studies == |
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| * After pulmonary resection<ref>Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:77 ISBN 1591032016</ref> <ref>Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:68 ISBN 140510368X</ref>
| | [[Hypoxemia case study one|Case #1]] |
| * [[ARDS]] ('''A'''cute '''R'''espiratory '''D'''istress '''S'''yndrome)
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| * [[Atelectasis]]
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| * [[Bronchial Asthma]]
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| * Bronchial mucus obstruction
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| * [[Congestive heart failure]]
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| * [[Emphysema]]
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| * [[Hamman-Rich Syndrome]]
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| * [[High altitude sickness]]
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| * Lung compression due to [[Pleural Effusions|pleural effusions]]/[[tumor]]
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| * Lymphangitic metastases
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| * [[Mechanical ventilation]]
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| * [[Neoplastic]]
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| * [[Pneumoconiosis]]
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| * [[Pneumonia]]
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| * [[Pneumothorax]]
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| * [[Pulmonary edema]]
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| * [[Pulmonary embolism]]
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| * [[Right to left shunt]]
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| * [[Sarcoidosis]]
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| * Thoracic deformity
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| == Physical Examination ==
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| ===Skin===
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| [[Cyanosis]] may be present
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| {{WH}}
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| {{WS}} | | {{WS}} |
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