The most common cause of acute alveolar hyperventilation is:

a. hypoxemia.
b. metabolic alkalosis.
c. tachycardia.
d. supplemental oxygen administration.

A
The most common cause of acute alveolar hyperventilation is hypoxemia. The decreased PaO2 seen during acute alveolar hyperventilation usually develops from a decreased ventilation-perfusion ratio, capillary shunting, or venous admixture associated with a pulmonary disorder. The PaO2 continues to drop as the pathologic effects of the disease intensify. Eventually the PaO2 may decline to a point low enough (a PaO2 of about 60 mm Hg) to significantly stimulate the peripheral chemoreceptors, which in turn causes the ventilatory rate to increase. The increased ventilatory response in turn causes the PaCO2 to decrease and the pH to increase.