|Classification and external resources|
Respiratory failure is inadequate gas exchange by the respiratory system, with the result that levels of arterial oxygen, carbon dioxide or both 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 greater than 80 mmHg (11 kPa), and carbon dioxide PaCO2 less than 45 mmHg (6.0 kPa). Classification into type I or type II relates to the absence or presence of hypercapnia respectively.
Type 1 respiratory failure is defined as hypoxia 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 (< 60 mmHg (8.0 kPa)) PaCO2 normal or low (<50 mmHg (6.7 kPa)) PA-aO2 increased
This type of respiratory failure is caused by conditions that affect oxygenation such as:
- Parenchymal disease (V/Q mismatch)
- Diseases of vasculature and shunts: right-to-left shunt, pulmonary embolism
- Interstitial lung diseases: ARDS, [pneumonia].
Hypoxia (PaO2 <8kPa) with Hypercapnia (PaCO2 >6.0kPa).
The basic defect in type 2 respiratory failure is characterized by:
PaO2 decreased (< 60 mmHg (8.0 kPa)) PaCO2 increased (> 50 mmHg (6.7 kPa)) PA-aO2 normal pH decreased
Type 2 respiratory failure is caused by inadequate ventilation; 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:
- Increased airways resistance (chronic obstructive pulmonary disease, asthma, suffocation)
- Reduced breathing effort (drug effects, brain stem lesion, extreme obesity)
- A decrease in the area of the lung available for gas exchange (such as in chronic bronchitis).
- Neuromuscular problems (GB syndrome., myasthenia gravis, motor neurone disease)
- Deformed (kyphoscoliosis), rigid (ankylosing spondylitis), or flail chest.
- Pulmonary dysfunction
- Cardiac dysfunction
Emergency treatment follows the principles of cardiopulmonary resuscitation. Treatment of the underlying cause is required. Endotracheal intubation and mechanical ventilation in severe respiratory failure ( PaO2 less than 50 mmHg ) 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.
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