Which statement defines respiratory failure?

• A. Not breathing spontaneously.
• B. Hyperventilation with acidosis.
• C. Patient can compensate with no hypoxia.
• D. Patient can no longer compensate; hypoxia and/or CO2 retention occur.

Answer: (D)

Respiratory failure occurs when the respiratory system can no longer maintain adequate gas exchange, so the patient cannot compensate and ends up with low oxygen (hypoxia) and/or high carbon dioxide (CO2 retention, hypercapnia).

That’s why the correct statement fits: the patient can no longer compensate, and hypoxia and/or CO2 retention occur.

Not breathing spontaneously isn’t the defining feature—some patients with respiratory failure may still breathe spontaneously with support. Hyperventilation with acidosis is physiologically unlikely (hyperventilation lowers CO2, causing alkalosis, not acidosis). And if the patient can compensate with no hypoxia, gas exchange is still adequate, which means it isn’t respiratory failure.