Type one Acutr hypoxemic respiratory failure

From Egan's Eighth Edition
Page 914
The primary cause of hypoxemia are the following:
*Ventilation/perfusion mismatch
*Shunt
*Alveolar hypoventilation
*Perfusion/diffusion impairment
*Decrease inspiratoy oxygen

*Ventilation/perfusion mismatch
in healthy lung
high ventilation/perfusion ratio at the apex of the lungs and a low ration at the bases.
Pathologic V/Q mismatch : Obstructive lung disease are frequent causes.bronchospasm, mucus plugging, inflammation, premature airway closure(asthmatic or emphysematous)

*Shunt
Shunt is an extreme version of V/Q mismatch inwhich there is no ventilation to match perfusion(V/Q=0).
Common etiologies may be atelectasis, pulmonary edema,pneumonia.
Does not respond to supplemental oxygen because the gas exchange unit( the alveolus) is not open.
ARDS

*Alveolar Hypoventilation
This cause of hypoxemia will be discussed under the section Acute hypercapnic Respiratory Failure.

*Diffusion Impairment
diffusion refers to movement of gas across the alveolar-capillary membrance due to a pressure gradient.
The most common presentation is in patients with interstitial lung disease (e.g., pulmonary fibrosis, asbestosis, sarcoidosis)

*Perfusion/Diffusion Impairment
is a rare cause of hypoxemia found in individuals with liver disease complicated by the hepatopulmonary syndrome.
clubbing can be found in the hepatopulmonary syndrome.

*Decreased Inspired Oxygen
high altitude, airlines account