physics

Positive end-expiratory pressure

Positive end-expiratory pressure is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Positive end-expiratory pressure rather than just read about it. In short: Positive end-expiratory pressure (PEEP) is the pressure in the lungs (alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration. The two types of PEEP are extrinsic PEEP (applied by a ventilator) and intrinsic PEEP (caused by an incomplete exhalation).

Key takeaways

Positive end-expiratory pressure belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Positive end-expiratory pressure to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Positive end-expiratory pressure from memory before moving on to harder problems.

Reference excerpt

Positive end-expiratory pressure (PEEP) is the pressure in the lungs (alveolar pressure) above atmospheric pressure (the pressure outside of the body) that exists at the end of expiration. The two types of PEEP are extrinsic PEEP (applied by a ventilator) and intrinsic PEEP (caused by an incomplete exhalation). Pressure that is applied or increased during an inspiration is termed pressure support. PEEP is a therapeutic parameter set in the ventilator (extrinsic PEEP), or a complication of mechanical ventilation with air trapping (auto-PEEP).

Intrinsic (auto-) PEEP Auto-PEEP is an incomplete expiration prior to the initiation of the next breath causes progressive air trapping (hyperinflation). This accumulation of air increases alveolar pressure at the end of expiration, which is referred to as auto-PEEP. Auto-PEEP develops commonly in high minute ventilation (hyperventilation), expiratory flow limitation (obstructed airway) and expiratory resistance (narrow airway). Once auto-PEEP is identified, steps should be taken to stop or reduce the pressure build-up. When auto-PEEP persists despite management of its underlying cause, applied PEEP may be helpful if the patient has an expiratory flow limitation (obstruction).

Extrinsic (applied) PEEP Applied PEEP is usually one of the first ventilator settings chosen when mechanical ventilation is initiated. It is set directly on the ventilator. A small amount of applied PEEP (4 to 5 cmH2O) is used in most mechanically ventilated patients to mitigate end-expiratory alveolar collapse. A higher level of applied PEEP (>5 cmH2O) is sometimes used to improve hypoxemia or reduce ventilator-associated lung injury in patients with acute lung injury, acute respiratory distress syndrome, or other types of hypoxemic respiratory failure.

Complications and effects Positive end-expiratory pressure can contribute to:

Decrease in systemic venous return, cardiac output, cardiac index pulmonary capillary wedge pressure (PCWP), preload, arterial blood pressure Increase in: Intrathoracic pressure, RV afterload (CVP and PAP) lung functional residual capacity Pulmonary barotrauma can be caused. Pulmonary barotrauma is lung injury that results from the hyperinflation of alveoli past the rupture point. The effects of PEEP on intracranial pressure (ICP) have been studied. Although PEEP is hypothesized to increase ICP due to impedance of cerebral blood flow, it has been shown that high PEEP does not increase ICP. Renal functions and electrolyte imbalances, due to decreased venous return metabolism of certain drugs are altered and acid-base balance is impeded.

History John Scott Inkster, an English anaesthetist and physician, is credited with discovering PEEP. When his discovery was published in the proceedings of the World Congress of Anaesthesia in 1968, Inkster called it Residual Positive Pressure.

See also Continuous positive airway pressure – Ventilator which applies mild air pressure continuously to keep airways open (CPAP) Positive airway pressure – Mechanical ventilation in which airway pressure is always above atmospheric pressure

References

Illustrations

Worked examples

Example 1 — a first encounter with Positive end-expiratory pressure

Start with the simplest possible case. Write down what Positive end-expiratory pressure claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Positive end-expiratory pressure before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Positive end-expiratory pressure ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Positive end-expiratory pressure

In research: Positive end-expiratory pressure appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Positive end-expiratory pressure in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Positive end-expiratory pressure is common in secondary-school and first-year university syllabi. It links to neighbouring topics Intensive care medicine, Modes of mechanical ventilation, Respiratory system procedures, so understanding it makes those chapters shorter.
In everyday life: Look for Positive end-expiratory pressure outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Positive end-expiratory pressure in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Positive end-expiratory pressure means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Positive end-expiratory pressure out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Positive end-expiratory pressure in simple terms?

Why does Positive end-expiratory pressure matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Positive end-expiratory pressure?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Positive end-expiratory pressure.