During apneic oxygenation in a patient who is not breathing, oxygen continues to be delivered to the alveoli. What is the primary mechanism?

• A Oxygen diffuses across the alveolar membrane due to concentration gradient
• B Oxygen is actively transported across the alveolar membrane
• C Residual diaphragmatic contractions create negative intrathoracic pressure
• D Negative pressure develops in alveoli as oxygen is absorbed, drawing oxygen down the airway ✓

Explanation

During apneic oxygenation, oxygen continues to be absorbed from the alveoli into the blood. This creates a negative pressure gradient in the alveoli, which draws oxygen down the airway from the pharynx. This is the basis for providing oxygen via nasal cannula during apnea, which can maintain oxygenation for extended periods. Active transport does not occur, and diaphragmatic contractions are absent during apnea.

Reference: Miller's Anesthesia, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.