Lung Compliance Calculator (Static & Dynamic Compliance, Driving Pressure)
Calculate static and dynamic respiratory system compliance on the ventilator from tidal volume, peak, plateau and PEEP pressures, plus driving pressure and the resistive pressure gap.
How it works
Static compliance Cstat = VT ÷ (Pplat − PEEP) · dynamic compliance Cdyn = VT ÷ (PIP − PEEP) · driving pressure ΔP = Pplat − PEEP = VT ÷ Cstat · resistive pressure = PIP − Pplat.
Compliance is the change in volume per unit change in pressure. Static compliance, measured with an end-inspiratory pause when there is no flow, reflects the elastic properties of the lungs and chest wall; dynamic compliance uses peak pressure and so also includes airway resistance. A fall in static compliance points to stiff lungs (ARDS, pulmonary edema, fibrosis, atelectasis, pneumothorax) or a stiff chest wall, while a widening PIP − Pplat gap with stable static compliance points to higher airway resistance (bronchospasm, secretions, a kinked tube). Amato and colleagues (NEJM 2015) showed that driving pressure — tidal volume scaled to compliance — was the ventilation variable most strongly linked to survival in ARDS, with risk rising above about 15 cmH₂O; ARDSNet keeps plateau pressure at 30 cmH₂O or less.
Worked example
A ventilated patient receives 450 mL with a PIP of 28 cmH₂O, a plateau pressure of 22 cmH₂O and PEEP of 8 cmH₂O. Static compliance = 450 ÷ (22 − 8) = 32.1 mL/cmH₂O (reduced), dynamic compliance = 450 ÷ (28 − 8) = 22.5 mL/cmH₂O, driving pressure = 14 cmH₂O (at or below 15) and the resistive gap is 6 cmH₂O.
Sources: Amato MBP et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med 2015;372:747–755 · ARDS Network. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and ARDS. N Engl J Med 2000;342:1301–1308
Frequently asked questions
What is a normal static compliance?
In ventilated adults with healthy lungs, respiratory system compliance is roughly 50–100 mL/cmH₂O. Values under about 40 are common in ARDS, and under 30 indicate very stiff lungs.
What is the difference between static and dynamic compliance?
Static compliance is measured during a no-flow inspiratory hold (plateau pressure) and reflects lung and chest wall stiffness. Dynamic compliance uses peak pressure during flow, so it also falls when airway resistance rises.
What is driving pressure?
Plateau pressure minus PEEP — the pressure that actually stretches the lung with each breath. Keeping it at or below about 15 cmH₂O is associated with better ARDS survival.
Why is my plateau pressure measurement unreliable?
The patient must be passive (no active breathing) and the hold long enough (about 0.5 s) for pressure to stabilize. Measure auto-PEEP with an expiratory hold and use total PEEP if it is present.
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Clinical decision tool for education and for use by trained clinicians alongside clinical judgement — not a diagnosis and not a substitute for medical assessment. Scores and cut-offs come from the cited validation studies and may not apply to every patient; follow local protocols.