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Respiratory failure
Classification and external resources
ICD-10 J96.
ICD-9 518.81
DiseasesDB 6623
eMedicine med/2011
MeSH D012131

The term respiratory failure, in medicine, is used to describe inadequate gas exchange by the respiratory system, with the result that arterial oxygen and/or carbon dioxide levels cannot be maintained within their normal ranges. A drop in blood oxygenation is known as hypoxemia; a rise in arterial carbon dioxide levels is called hypercapnia. The normal reference values are: oxygen PaO2 > 60 mmHg, and carbon dioxide PaCO2 < 45 mmHg (values in kPa being PO2 below 8kPA and PCO2 above 6.7 kPa). Classification into type I or type II relates to the absence or presence of hypercapnia respectively.




Type 1

Type 1 respiratory failure is defined as hypoxaemia without hypercapnia, and indeed the PaCO2 may be normal or low. It is typically caused by a ventilation/perfusion (V/Q) mismatch; the volume of air flowing in and out of the lungs is not matched with the flow of blood to the lungs. The basic defect in type 1 respiratory failure is failure of oxygenation characterized by:

PaO2 low (< 60mmHg)
PaCO2 normal or low (≤ 49mmHg)
PA-aO2 increased

This type of respiratory failure is caused by conditions that affect oxygenation such as:

Type 2

Type 2 respiratory failure is caused by increased airway resistance; both oxygen and carbon dioxide are affected. Defined as the build up of carbon dioxide levels (PaCO2) that has been generated by the body. The underlying causes include:

  • Reduced breathing effort (in the fatigued patient)
  • Increased resistance to breathing (such as in asthma)
  • A decrease in the area of the lung available for gas exchange (such as in emphysema).

The basic defect in type 2 respiratory failure is characterized by:

PaO2 decreased
PaCO2 increased
PA-aO2 normal
pH decreased


Chest X-ray showing ARDS


Mechanical Ventilator

Emergency treatment follows the principles of cardiopulmonary resuscitation. Treatment of the underlying cause is required. Endotracheal intubation and mechanical ventilation may be required. Respiratory stimulants such as doxapram may be used, and if the respiratory failure resulted from an overdose of sedative drugs such as opioids or benzodiazepines, then the appropriate antidote such as naloxone or flumazenil will be given.

See also


  1. ^ Johnson SB (2008). "Tracheobronchial injury". Seminars in Thoracic and Cardiovascular Surgery 20 (1): 52–57. doi:10.1053/j.semtcvs.2007.09.001. PMID 18420127.  


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