Static compliance measures how easily the lungs and chest wall expand, isolating lung stiffness by using the plateau pressure held at end-inspiration.
Normal lung/chest-wall compliance.
Mildly reduced — early stiffening.
Moderately reduced — significant stiff lung.
Severely reduced — e.g. severe ARDS or fibrosis.
Given: Vt 500 mL, plateau 20, PEEP 5 cmH₂O.
15 cmH₂OCompliance is the volume gained per unit of driving pressure.
Roughly 50–100 mL/cmH₂O in healthy lungs. It falls in stiff-lung conditions like ARDS, pulmonary fibrosis, and pulmonary edema.
Plateau pressure (measured during an inspiratory hold with no airflow) reflects lung and chest-wall stiffness alone. Peak pressure also includes airway resistance, which static compliance deliberately excludes.
The lungs are getting stiffer — worsening ARDS, developing edema or pneumothorax, or abdominal distension pressing on the diaphragm. It's a key trend to watch.
Driving pressure (plateau − PEEP) is tidal volume divided by compliance. Lower compliance means a given tidal volume needs a higher driving pressure, which is itself linked to worse ARDS outcomes.