 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 more than , and carbon dioxide paco2 lesser than . classification into type i or type ii relates to the absence or presence of hypercapnia respectively. ==types== ===type 1=== type 1 respiratory failure is defined as hypoxemia 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: :::{| class="wikitable" border="1" |pao2 || decreased (< ) |- | paco2 || normal or decreased (<) |- | pa-ao2 || increased |} this type of respiratory failure is caused by conditions that affect oxygenation such as: * low ambient oxygen (e.g. at high altitude) * ventilation-perfusion mismatch (parts of the lung receive oxygen but not enough blood to absorb it, e.g. pulmonary embolism) * alveolar hypoventilation (decreased 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 ards) * shunt (oxygenated blood mixes with non-oxygenated blood from the venous system, e.g. right-to-left shunt) ===type 2=== hypoxemia (pao2 6.0kpa). the basic defect in type 2 respiratory failure is characterized by: :::{| class="wikitable" border="1" |pao2 || decreased (< ) |- | paco2 || increased (> ) |- | pa-ao2 || normal |- |ph || decreased |} type 2 respiratory failure is caused by inadequate alveolar 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 but cannot be eliminated. the underlying causes include: * increased airways resistance (chronic obstructive pulmonary disease, asthma, s
Causes_of_death Intensive_care_medicine Medical_emergencies Organ_failure Respiratory_diseases