How do peak airway pressure and plateau pressure differ, and what does a large difference indicate?

• A. Peak pressure reflects alveolar pressure; plateau reflects airway resistance
• B. Peak pressure equals plateau pressure in all cases
• C. A large difference indicates low airway resistance
• D. Peak pressure includes airway resistance; plateau reflects alveolar pressure; a large difference indicates high airway resistance or secretions

Answer: (D)

The key idea is how peak airway pressure vs plateau pressure separate the effects of airway resistance from the lungs’ elastic recoil. Peak airway pressure is what you measure during actual inspiration and it includes the pressure needed to overcome both the elastic recoil of the lungs and chest wall and the resistance of the conducting airways. Plateau pressure, measured during an inspiratory hold when there’s no flow, reflects the elastic recoil alone because the resistive component disappears when flow is zero.

A large difference between peak and plateau pressures means most of the pressure is being lost to airway resistance rather than to expanding the lung tissue. That points to high airway resistance or obstructions in the airway, such as bronchospasm, mucus plugging, or a kinked or secretions-filled endotracheal tube. If the plateau pressure were also high with a small difference, that would suggest decreased compliance (stiffer lungs) rather than increased airway resistance.