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Complete respiratory failure, also called '''hypercapnic respiratory failure''' or type II respiratory failure, is characterised by both hypoxaemia and hypercapnia. This is more severe and also causes [[respiratory acidosis]].
Complete respiratory failure, also called '''hypercapnic respiratory failure''' or type II respiratory failure, is characterised by both hypoxaemia and hypercapnia. This is more severe and also causes [[respiratory acidosis]].
Respiratory can develop acutely or chronically, depending on whether the etiology is acute or chronic.


== Etiology ==
== Etiology ==
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=== Hypercapnic respiratory failure ===
=== Hypercapnic respiratory failure ===
Hypercapnic respiratory failure may occur due to (alveolar) [[hypoventilation]] or due to severe lung disease or increased dead space.
Hypercapnic respiratory failure may occur due to (alveolar) [[hypoventilation]] or due to increased dead space.
==== Hypoventilation ====
==== Hypoventilation ====
{{#lst:Hypoventilation|etiology}}
{{#lst:Hypoventilation|etiology}}
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Increased dead spacing occurs when there is a ventilation/perfusion mismatch (V/Q mismatch) where regions of the lung are not perfused. When a part of the lung receives no perfusion, the alveoli in the area effectively become dead space (due to not having blood to exchange gas to). This can occur in case of:
Increased dead spacing occurs when there is a ventilation/perfusion mismatch (V/Q mismatch) where regions of the lung are not perfused. When a part of the lung receives no perfusion, the alveoli in the area effectively become dead space (due to not having blood to exchange gas to). This can occur in case of:


* Pulmonary embolism (severe)
* [[Pulmonary embolism]] (severe)
* Interstitial lung disease (severe)
* [[Interstitial lung disease]] (severe)
 
== Pathophysiology ==
 
=== Hypoxaemia ===
Oxygen is essential for the body, and so hypoxaemia may cause a variety of complications, the severity of which depend on the severity of the hypoxaemia, the current oxygen requirement of the organs, and the patients habitual blood oxygen level.


==== Severe lung disease ====
=== Hypercapnia ===
CO2 diffuses easily across the respiratory membrane. Even so, severe lung disease can impair the respiratory membrane such that even CO2 diffusion is impaired.
Hypercapnia is problematic mainly because it causes respiratory acidosis and because it affects the brain. CO<sub>2</sub> increases glutamine and GABA transmission, depressing consciousness. Carbon dioxide is also a cerebral vasodilator, increasing cerebral blood flow and potentially increasing intracranial pressure. The depressive effects of CO<sub>2</sub> on the brain can cause so-called ''CO<sub>2</sub> narcosis''.  


== Clinical features ==
== Clinical features ==


Hypoxaemia causes symptoms of respiratory distress, including dyspnoea, tachypnoea, and anxiety. A compensatory tachycardia may occur. Severe hypoxaemia causes cyanosis, initially on the lips and tips of the body, called acrocyanosis. Eventually, altered mental status, confusion, and restlessness can occur.
Hypercapnia causes depressed consciousness, which may range from sluggishness to somnolence to coma.


Hypercapnia causes depressed consciousness.
== Compensatory mechanisms ==
Symptoms are less severe for chronic than for acute respiratory failure. In chronic cases, compensatory mechanisms like polyglobulia for hypoxaemia and increased bicarbonate reabsorption in the kidney for respiratory acidosis decreases the physiological impacts of respiratory failure.
[[Category:Pathophysiology]]