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{{Hypoxemia}}
{{CMG}}


{{SK}} Hypoxia, desaturation
'''For patient information, click [[Hypoxemia (patient information)|here]]'''


==Pathophysiology==
{{Hypoxemia}}


Causes are classified into 5 groups:
{{CMG}}; {{AE}}


*Low inspired fractional concentration of oxygen (low FiO<sub>2</sub>)
{{SK}} Hypoxia, desaturation
*Alveolar hypoventilation
*Impairment of diffusion across blood-gas membrane
*Shunt
*Ventilation-perfusion inequality


Conditions that result in hypoxemia act via one or more of these primary causes.
== [[Hypoxemia overview|Overview]] ==


===Low inspired oxygen fraction (low FiO<sub>2</sub>)===
== [[Hypoxemia historical perspective|Historical Perspective]] ==
See also: [[FiO2|FiO<sub>2</sub>]] <br />
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).


===Alveolar hypoventilation===
== [[Hypoxemia classification|Classification]] ==


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 pathophysiology|Pathophysiology]] ==


===Impaired diffusion===
== [[Hypoxemia causes|Causes]] ==


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 differential diagnosis|Differentiating Hypoxemia from other Diseases]] ==


===Shunt===
== [[Hypoxemia risk factors|Risk Factors]] ==
[[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.


===Ventilation-perfusion inequality===  
== [[Hypoxemia screening|Screening]] ==


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).
== [[Hypoxemia natural history, complications and prognosis|Natural History, Complications and Prognosis]] ==


==Causes==
== Diagnosis ==


=== Causes in Alphabetical Order ===
[[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]]


* 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>
== Treatment ==
* [[ARDS]] ('''A'''cute '''R'''espiratory '''D'''istress '''S'''yndrome)
* [[Atelectasis]]
* [[Bronchial Asthma]]
* Bronchial mucus obstruction
* [[Congestive heart failure]]
* [[Emphysema]]
* [[Hamman-Rich Syndrome]]
* [[High altitude sickness]]
* Lung compression due to [[Pleural Effusions|pleural effusions]]/[[tumor]]
* Lymphangitic metastases
* [[Mechanical ventilation]]
* [[Neoplastic]]
* [[Pneumoconiosis]]
* [[Pneumonia]]
* [[Pneumothorax]]
* [[Pulmonary edema]]
* [[Pulmonary embolism]]
* [[Right to left shunt]]
* [[Sarcoidosis]]
* Thoracic deformity


== Physical Examination ==
[[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]]


===Skin===
== Case Studies ==
[[Cyanosis]] may be present


[[Hypoxemia case study one|Case #1]]


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Latest revision as of 18:57, 1 February 2018


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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Synonyms and keywords: Hypoxia, desaturation

Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Hypoxemia from other Diseases

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Study of Choice |History and Symptoms | Physical Examination | Laboratory Findings | Electrocardiogram | Chest X Ray | Echocardiography or Ultrasound | CT | MRI | Other Imaging Findings | Other Diagnostic Studies

Treatment

Medical Therapy | Surgery | Primary Prevention | Secondary Prevention | Cost-Effectiveness of Therapy | Future or Investigational Therapies

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Case #1

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