How do peak inspiratory pressure (PIP) and plateau pressure differ, and what does each indicate?

• A. PIP reflects airway resistance and compliance during dynamic flow; plateau pressure reflects alveolar pressure and lung compliance during an inspiratory hold; high PIP with normal plateau suggests airway resistance; high plateau indicates reduced compliance.
• B. PIP measures oxygenation; plateau measures carbon dioxide.
• C. PIP only reflects airway resistance; plateau pressure only reflects chest wall compliance.
• D. PIP and plateau always move together; either indicates high resistance.

Answer: (A)

Peak inspiratory pressure is the maximum pressure reached during active inspiration and reflects the combined effect of airway resistance and the lung/chest wall’s ability to expand while gas is flowing. Plateau pressure is measured with an inspiratory hold when there is no flow; it represents the pressure in the alveoli and, therefore, the static compliance of the lung (alveolar units) independent of airway resistance.

If peak pressure is high but plateau pressure is normal, the issue is increased airway resistance (think bronchospasm, mucus plugging, or a kinked tube) with relatively preserved alveolar compliance. If plateau pressure is high, the lungs are less compliant (stiff or edematous/ascinated by disease like ARDS, edema, or fibrosis), increasing the risk of barotrauma. Keeping plateau pressure under about 30 cm H2O is a common target to minimize lung injury.

So the best description is that PIP reflects dynamic factors—airway resistance and overall flow-related pressures—whereas plateau pressure reflects static lung compliance during an inspiratory hold.