Static and Dynamic Compliance Calculator
Static and Dynamic Compliance Calculator
Static compliance uses the inspiratory-hold plateau and measures the respiratory system itself. Dynamic compliance uses the peak pressure and carries airway resistance inside it. The gap between them is the clinical point.
Static and dynamic compliance
Cstat, Cdyn and the resistive gapTidal volume 420 mL, peak 30 cmH₂O, plateau 24 cmH₂O, total PEEP 10 cmH₂O
Formula
Dynamic compliance = VT ÷ (Ppeak − PEEPtot)
Resistive pressure = Ppeak − Pplat = flow × airway resistance
- the plateau, not the peak
- during an end-inspiratory hold there is no flow, so no pressure is spent on airway resistance and what remains above PEEP is elastic recoil alone. A compliance computed from the PEAK and then called compliance is the error this page exists to prevent
- dynamic compliance
- tidal volume over peak minus PEEP, measured during flow, so it contains resistive as well as elastic pressure and is always the smaller whenever peak exceeds plateau. A trend and a signal of changing resistance, not a measure of the lung
- PEEPtot
- total PEEP: set plus intrinsic, from an expiratory hold. Giani, Bronco and Bellani state that all of these calculations should use total rather than set PEEP where the two differ
- units
- pressures in cmH₂O, volume in mL, compliance in mL/cmH₂O. Divide by predicted body weight for specific compliance in mL/cmH₂O/kg
Worked example
Tidal volume 420 mL, peak 30 cmH₂O, plateau 24 cmH₂O, total PEEP 10 cmH₂O
Static = 420 ÷ (24 − 10) = 30.0 mL/cmH₂O
Dynamic = 420 ÷ (30 − 10) = 21.0 mL/cmH₂O
Static exceeds dynamic by 9, because the 6 cmH₂O between peak and plateau is resistive, not elastic
Driving pressure = 24 − 10 = 14 cmH₂O, the same 420 ÷ 30.0 read the other way round
Set the plateau equal to the peak at 30 and both collapse to 21.0 — which is why computing compliance from the peak understates it by 30% here
Set the plateau to 11 and static compliance reads 420, a figure no adult produces: a plateau barely above PEEP almost always means no hold was held
What each compliance contains
| Static | Dynamic | |
|---|---|---|
| Pressure used | Plateau, no flow | Peak, during flow |
| Needs a manoeuvre | Yes, a 2 to 3 s hold | No |
| Contains airway resistance | No | Yes |
| What it measures | Elastic properties of lung plus chest wall | Elastic properties plus whatever the airway is doing |
| Relation to driving pressure | ΔP = tidal volume ÷ static compliance | None; it is not the pressure the lung sees |
Reference values, and where the sources disagree
| Quantity | Value | Source |
|---|---|---|
| Static compliance, passive, normal lungs | 50 to 60 mL/cmH₂O, or 0.7 to 1 per kg | Giani, Bronco and Bellani, 2019 |
| Static compliance, passive, normal lungs | 50 to 100 mL/cmH₂O | Critical-care compendium teaching value |
| Inspiratory resistance, normal lung with a tube | Rarely above 15 cmH₂O/L/s | Giani, Bronco and Bellani, 2019 |
| Plateau target in ARDS | Under 30 cmH₂O, with 4 to 8 mL/kg PBW | ESICM 2023 and ATS 2024 |
Why peak and plateau are not interchangeable
Every breath a ventilator delivers spends its pressure on two things: pushing gas through the airways against resistance, and stretching the lung and chest wall against elastance. The peak inspiratory pressure is the sum of both. The plateau, measured when an end-inspiratory hold has stopped all flow, is the elastic part alone. So tidal volume over plateau minus total PEEP measures the respiratory system, and tidal volume over peak minus total PEEP measures the respiratory system contaminated by whatever the airway was doing.
The two therefore answer different questions. Static compliance falls when the aerated lung shrinks or the chest wall stiffens: ARDS, oedema, effusion, abdominal distension, obesity. It is also the number driving pressure is built from, since driving pressure is tidal volume divided by static compliance. Dynamic compliance falls for all those reasons and also when resistance rises, so a dynamic value that drops while the static value holds steady is a resistance problem — bronchospasm, secretions, a partly obstructed tube — and not a lung problem. The peak-to-plateau difference is the cleanest way to see it: that gap is flow times resistance, and dividing it by the inspiratory flow in litres per second gives the resistance itself.
Two traps account for most wrong compliance values. The first is the plateau that was never measured: if the number typed in is really the peak, static compliance is understated, often by a third, and the understatement looks like worse disease. A plateau needs two to three seconds of hold and a flat trace, and effort during the hold invalidates it. The second is set PEEP used where total PEEP belongs. Intrinsic PEEP from incomplete emptying adds to the set value and only an expiratory hold reveals it, so using the set number where auto-PEEP exists inflates the pressure apparently available for inflation and inflates compliance with it.
This supports a clinician’s judgement rather than replacing it.
Frequently asked questions
What is the difference between static and dynamic compliance?
Static compliance is tidal volume divided by plateau minus total PEEP, measured with no flow, so it reflects the elastic properties of lung and chest wall. Dynamic compliance uses the peak pressure instead, measured during flow, so it also contains the pressure spent on airway resistance. Static is always the larger whenever the peak exceeds the plateau.
Which compliance should I use?
Static, for anything about the lung or chest wall — including driving pressure, which is tidal volume divided by static compliance. Dynamic compliance is a useful trend, but Hamilton Medical’s own clinical note states it cannot substitute for the static value, because it depends on the airway resistance.
What does a large gap between peak and plateau pressure mean?
Resistance. That gap is inspiratory flow multiplied by airway resistance, so a wide one points at bronchospasm, secretions, a kinked or narrow tube, or a high set flow. It says nothing about lung stiffness: the plateau is the number that reflects the respiratory system.
Can I measure compliance in a patient breathing spontaneously?
Not reliably. A plateau is valid only if the trace during the hold is flat, and inspiratory or expiratory effort makes it unusable; expiratory effort inflates it. On assisted breaths a readable plateau is still obtainable in over 90% of holds, but a low value is more trustworthy than a high one.
Should I use set PEEP or total PEEP?
Total PEEP, which is set PEEP plus any intrinsic PEEP, read off an expiratory hold. Giani, Bronco and Bellani state that every one of these calculations should use total rather than set PEEP where the two differ. Using set PEEP in a patient with air trapping overstates compliance.
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References
- Giani M, Bronco A, Bellani G. How to measure respiratory mechanics during controlled mechanical ventilation. AboutOpen. 2019;6(1). doi:10.33393/abtpn.2019.300
- Hamilton Medical Clinical Experts Group. Static compliance (Cstat) vs. dynamic compliance (Cdyn). Hamilton Medical knowledge base.
- Life in the Fast Lane Critical Care Compendium. Pulmonary mechanics. litfl.com
- Amato MBP, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015;372(8):747–55.
- Crítica e Ciências da Saúde / Critical Care Science. Application of new ARDS guidelines at the bedside. 2025. scielo.br
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/