Editing Respiratory failure (section)

===Type 1===
Type 1 respiratory failure is characterized by a [[Hypoxemia|low level of oxygen in the blood (hypoxemia)]] (PaO2) < 60 mmHg with a normal (normocapnia) or low (hypocapnia) level of carbon dioxide (PaCO2) in the blood.<ref name=mirabile/>

The fundamental defect in type 1 respiratory failure is a failure of oxygenation characterized by:

:::{| class="wikitable"
|P<sub>a</sub>O<sub>2</sub> || decreased (< {{convert|60|mmHg|kPa|abbr=on}})
|-
| P<sub>a</sub>CO<sub>2</sub> || normal or decreased (<{{convert|50|mmHg|kPa|abbr=on}})
|-
| P<sub>A-a</sub>O<sub>2</sub> || increased
|}

Type I respiratory failure is caused by conditions that affect [[Oxygenation (medical)|oxygenation]] and therefore lead to lower-than-normal oxygen in the blood. These include:

* Low ambient oxygen (e.g. at high altitude).<ref name=mirabile/>
* [[Ventilation-perfusion mismatch]] (parts of the lung receive oxygen but not enough blood to absorb it, e.g. [[pulmonary embolism]], [[Acute respiratory distress syndrome]], [[Chronic obstructive pulmonary disease]], [[Heart failure|Congestive heart failure]].<ref name=mirabile/>
* Alveolar hypoventilation (decreased [[Respiratory minute volume|minute volume]] due to reduced respiratory muscle activity, e.g. in acute [[neuromuscular disease]]); this form can also cause type 2 respiratory failure if severe.
* Diffusion problem (oxygen cannot enter the capillaries due to parenchymal disease, e.g. in [[pneumonia]] or [[Acute respiratory distress syndrome|ARDS]]).
* [[Right-to-left shunt]] (oxygenated blood mixes with non-oxygenated blood from the [[venous system]], e.g. [[Arteriovenous malformation]], Complete [[atelectasis]], Severe pneumonia, Severe pulmonary edema).