Which finding indicates an increase in airway resistance in a patient on mechanical ventilation with a constant tidal volume?

• A. Increased plateau pressure
• B. Decreased peak inspiratory pressure
• C. Decreased transairway pressure
• D. Increased peak inspiratory pressure (PIP) and transairway pressure (PTA)

Answer: (D)

When airway resistance increases, the pressure needed to push the same tidal volume through the airways goes up, but the pressure in the alveoli once flow stops (plateau pressure) stays the same if the lung and chest wall compliance haven’t changed. So the signal of higher resistance is a rise in peak inspiratory pressure, and the pressure drop across the airways—often called transairway pressure or the difference between peak and plateau pressures—also increases. That combination means the airway is offering more resistance to flow, not that the lung itself is stiffer. The result you’d see is both higher peak inspiratory pressure and a larger pressure drop across the airway, while plateau pressure remains unchanged.