PEEP, plateau pressure and lung protection
- Concept
PEEP keeps small air sacs open at the end of each breath; plateau pressure shows how hard the lung is being stretched.
What it is
Positive end-expiratory pressure (PEEP) is the pressure kept in the airways at the end of expiration. By stopping alveoli from collapsing it increases functional residual capacity, recruits lung units, reduces shunt and improves oxygenation, and it limits the injury caused by alveoli opening and closing with every breath. Its costs are real: it raises intrathoracic pressure and can reduce venous return and cardiac output, it can overdistend healthy lung regions, and it can raise intracranial pressure. On a volume-controlled breath, the peak inspiratory pressure reflects both airway resistance and the stiffness of the lungs and chest wall. A short inspiratory pause stops flow, so the resistive part disappears and the pressure left, the plateau pressure, approximates the pressure inside the alveoli. Subtracting PEEP from the plateau gives the driving pressure, which equals tidal volume divided by respiratory system compliance and shows how much the breath stretches the lung that is actually open. Lung protection means a low tidal volume by predicted body weight, a plateau pressure kept below an accepted ceiling, a driving pressure kept as low as possible and enough PEEP to keep the lung open without overstretching it. An expiratory pause measures intrinsic PEEP, the trapped pressure left when expiration is too short.
Key points
- Static compliance = tidal volume ÷ (plateau minus PEEP); falling compliance signals stiffer lungs or chest wall.
- Plateau pressure is measured on a passive patient with an inspiratory pause; active breathing makes the reading unreliable.
- Ventilator-induced lung injury: volutrauma (overstretch), barotrauma (air leak), atelectrauma (cyclic opening and closing) and biotrauma (inflammation).
- A stiff chest wall (obesity, raised abdominal pressure) raises plateau pressure without the same stress on the lung itself.
Components
- Extrinsic PEEP: set on the ventilator.
- Intrinsic PEEP: trapped gas from incomplete expiration, found with an expiratory hold.
- Total PEEP: extrinsic plus intrinsic, the true end-expiratory alveolar pressure.
- Peak pressure, plateau pressure and driving pressure: the three numbers read on every volume-controlled breath.
How it works
- PEEP keeps alveoli open, so less blood passes through unventilated lung (less shunt) and oxygenation improves.
- Recruited lung shares each breath, so a recruitable lung becomes less stiff and driving pressure may fall.
- In a lung that does not recruit, extra PEEP only overstretches open regions and raises dead space.
- Higher intrathoracic pressure lowers the gradient for venous return and raises right ventricular afterload.
Reading the airway pressures on a volume-controlled breath
| Pattern | What it means | Common causes |
|---|---|---|
| Peak up, plateau unchanged | Higher airway resistance | Kinked or bitten tube, secretions, bronchospasm |
| Peak up, plateau up | Lower compliance | Pneumothorax, mainstem intubation, pulmonary oedema, ARDS, abdominal distension, auto-PEEP |
| Peak down, volumes down | Leak or disconnection | Cuff leak, circuit disconnection, chest drain air leak |
| Expiratory flow not reaching zero | Gas trapping | Obstructive disease, high rate, short expiration |
In practice
- Use predicted body weight from height and sex to choose tidal volume; actual weight overestimates lung size in obesity.
- If PEEP rises and oxygenation, compliance and blood pressure all improve or stay stable, the lung was recruitable.
- Hypotension after raising PEEP suggests reduced venous return: check fluid responsiveness and step back if needed.
- In asthma or COPD on the ventilator, rising plateau with gas trapping needs a lower rate and longer expiration, not more PEEP by reflex.
- Raised intracranial pressure and unilateral lung disease call for careful PEEP titration with close monitoring.
Next step
- Measure plateau and driving pressure after each change of tidal volume or PEEP, and at least daily.
- After raising PEEP, recheck blood pressure, oxygenation and compliance; obtain a blood gas.
- A sudden rise in plateau pressure needs a chest examination and X-ray or lung ultrasound for pneumothorax or tube displacement.
- Call a senior if plateau pressure stays above the accepted ceiling despite low tidal volumes, or oxygenation keeps falling.
Test yourself
Think of the answer, then tap the question to see it.
What does a high peak pressure with a normal plateau pressure suggest?
Raised airway resistance, for example a kinked or bitten tube, secretions or bronchospasm, rather than stiffer lungs.
How is driving pressure calculated and why does it matter?
Plateau pressure minus PEEP, equal to tidal volume divided by compliance; lower driving pressure is linked to better survival in ARDS.
How does PEEP improve oxygenation?
It keeps alveoli open at end-expiration, raising functional residual capacity and reducing shunt through collapsed lung.
Which manoeuvre detects intrinsic PEEP?
An end-expiratory hold: the pressure measured above the set PEEP is the trapped intrinsic PEEP.
Elsewhere in DurgiPedia
- Lung and chest wall compliance
- Mechanics of breathing: pressures and muscles
- Surface tension, surfactant and Laplace's law
- Ventilation–perfusion matching and West zones
Connections
Educational content; it does not replace supervised training, your institution's protocols or the anaesthetist's or intensivist's decision. It contains no doses and no ventilator or infusion settings.
Sources: Positive End-Expiratory Pressure (StatPearls (NCBI Bookshelf), 2025); Invasive Mechanical Ventilation (StatPearls (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.