Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide or both cannot be kept at normal levels. A drop in the oxygen carried in blood is known as hypoxemia; a rise in arterial carbon dioxide levels is called hypercapnia. Respiratory failure is classified as either Type 1 or Type 2, based on whether there is a high carbon dioxide level, and can be either acute or chronic.
Several types of condition can potentially result in respiratory failure: Conditions which reduce the flow of air into and out of the lungs, including physical obstruction by foreign bodies or masses, and reduced breathing ability due to drugs or changes to the chest. Conditions which impair the lungs’ blood supply. These include thromboembolic conditions and conditions which reduce the output of the right heart, such as right heart failure and some myocardial infarctions. Conditions which limit the ability of the lung tissue to exchange oxygen and carbon dioxide between the blood and the air within the lungs. Any disease which can damage the lung tissue can fit into this category. The most common causes are (in no particular order) infections, interstitial lung disease, and pulmonary oedema.
Type of respiratory failure
respiratory failure is defined as a low level of oxygen in the blood (hypoxemia) with either a normal (normocapnia) or low (hypocapnia) level of carbon dioxide (PaCO2) but not an increased level (hypercapnia). 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||decreased (< 60 mmHg (8.0 kPa))|
|PaCO2||normal or decreased (<50 mmHg (6.7 kPa))|
Hypoxemia (PaO2 <8kPa or normal) with hypercapnia (PaCO2 >6.0kPa). The basic defect in type 2 respiratory failure is characterized by:
|PaO2||decreased (< 60 mmHg (8.0 kPa))or normal|
|PaCO2||increased (> 50 mmHg (6.7 kPa))|
Type 2 respiratory failure is caused by inadequate alveolar ventilation; both oxygen and carbon dioxide are affected. Defined as the buildup of carbon dioxide levels (PaCO2) that has been generated by the body but cannot be eliminated. 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 (Guillain–Barré syndrome, motor neuron disease)
- Deformed (kyphoscoliosis), rigid