[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anaesthesia and ICU](https://durgical.com/en/anaesthesia/) › [Critical care (ICU)](https://durgical.com/en/anaesthesia/areas/critical-care/) › Ventilating ARDS: low volumes, prone position and more

# Ventilating ARDS: low volumes, prone position and more

- Concept

How the ventilator and the patient's position are used to support badly inflamed lungs without injuring them further.

Updated Nov 13, 2026

## Key points

- Berlin criteria: onset within a week, bilateral opacities, not mainly cardiac or fluid overload, and a low PaO2/FiO2 ratio on PEEP.
- Severity by PaO2/FiO2: mild 201–300, moderate 101–200, severe 100 or less (mmHg).
- Low tidal volume by predicted body weight with a plateau ceiling is the intervention proven to lower mortality.
- Prone positioning for long daily sessions lowers mortality in moderate to severe ARDS (PaO2/FiO2 below about 150).
- Permissive hypercapnia is accepted to protect the lung, unless raised intracranial pressure or severe acidosis forbids it.

On this page

- The basics Key points
- What it is
- Key points
- Components
- How it works
- Berlin severity grades of ARDS (all on PEEP or CPAP)
- In practice
- Next step
- Elsewhere in DurgiPedia

- Study Test yourself

- Connections Connections

## What it is

Acute respiratory distress syndrome (ARDS) is an inflammatory injury of the alveolar-capillary membrane triggered by a direct insult (pneumonia, aspiration, inhalation injury, near-drowning) or an indirect one (sepsis, major trauma, pancreatitis, massive transfusion). Protein-rich fluid floods the alveoli, surfactant fails and the lung becomes heavy, stiff and patchy: dependent regions collapse while a small aerated region, the «baby lung», receives most of each breath. The Berlin definition requires onset within one week of a known insult, bilateral opacities not explained by effusion, collapse or nodules, respiratory failure not fully explained by heart failure or fluid overload, and hypoxaemia measured as the ratio of arterial oxygen to inspired oxygen fraction while on PEEP; the ratio grades it as mild, moderate or severe. A newer global definition also includes patients on high-flow oxygen and allows pulse oximetry and ultrasound. No drug cures ARDS: treatment is the cause plus supportive care that avoids further harm. The proven core is lung-protective ventilation, with a low tidal volume by predicted body weight, a plateau pressure kept below a ceiling, enough PEEP to keep the lung open and acceptance of a higher CO2 (permissive hypercapnia). For moderate to severe disease, prone positioning for long daily sessions lowers mortality. Other measures include a conservative fluid strategy once shock has resolved, short-term neuromuscular blockade for severe asynchrony or hypoxaemia, and referral for extracorporeal membrane oxygenation when all else fails.

## Key points

- Common causes: pneumonia, sepsis, aspiration of gastric contents, major trauma, pancreatitis, transfusion, inhalation injury.
- Pathology moves from an exudative phase (oedema, hyaline membranes) to a proliferative phase and, in some, fibrosis.
- Oxygen targets are moderate (SpO2 roughly in the high eighties to mid nineties); hyperoxia brings no benefit.
- Echocardiography helps exclude a cardiac cause and shows right ventricular strain from high pressures or hypercapnia.
- Survivors often have weakness, cognitive problems and reduced quality of life for months: plan rehabilitation.

## Components

- Lung-protective ventilation: low tidal volume by predicted body weight, plateau below the ceiling, driving pressure as low as possible.
- PEEP: higher levels in moderate to severe ARDS, guided by a PEEP–oxygen table, compliance or oxygenation response.
- Prone position: long daily sessions, started early, by a trained team with a checklist.
- Conservative fluids: avoid positive balance once shock is controlled; diuretics if needed.
- Rescue: neuromuscular blockade for refractory asynchrony, inhaled pulmonary vasodilators as a bridge, ECMO in a referral centre.

## How it works

- The aerated «baby lung» is small, so normal tidal volumes overstretch it: volumes must be matched to the open lung.
- PEEP keeps unstable units open and prevents cyclic collapse (atelectrauma).
- Prone position makes lung inflation more uniform, recruits the dorsal lung, improves drainage and unloads the heart's weight.
- Reducing lung stretch reduces the release of inflammatory mediators into the blood (biotrauma) and multiple organ failure.

## Berlin severity grades of ARDS (all on PEEP or CPAP)

| Grade | PaO2/FiO2 (mmHg) | Main additions to lung protection |
| --- | --- | --- |
| Mild | 201–300 | Lung-protective ventilation, treat the cause, conservative fluids |
| Moderate | 101–200 | Consider higher PEEP; prone position when the ratio stays low |
| Severe | 100 or less | Prone position, short-term neuromuscular blockade, early ECMO referral |

## In practice

- Treat the cause: antibiotics and source control for sepsis or pneumonia; ARDS is a syndrome, not a final diagnosis.
- Routine recruitment manoeuvres with sustained high pressures are not recommended; high-frequency oscillation is not used routinely.
- Corticosteroids have a role in specific causes (such as severe COVID-19 pneumonia); in other ARDS the evidence is mixed and practice varies.
- Inhaled vasodilators may improve oxygenation briefly but do not improve survival.
- Refer early for ECMO when severe hypoxaemia or acidosis persists despite optimal ventilation and proning.

## Next step

- Recheck blood gases after each change and the PaO2/FiO2 ratio daily; measure plateau and driving pressure.
- Plan proning with the whole team: eyes, face, pressure areas, lines and tube secured; watch for pressure injuries.
- Call a senior and the ECMO referral centre early if oxygenation or acidosis does not respond despite proning.
- Screen daily for lighter sedation and a spontaneous breathing trial as the lung recovers.
- After discharge, arrange follow-up for weakness, cognition, mood and lung function.

## Test yourself

Think of the answer, then tap the question to see it.

## What are the Berlin criteria for ARDS?

Onset within one week of an insult, bilateral opacities, respiratory failure not mainly from heart failure or fluids, and a low PaO2/FiO2 on PEEP.

## Which ventilation measure has been shown to lower mortality in ARDS?

Low tidal volume ventilation based on predicted body weight with plateau pressure kept below a ceiling.

## Why does prone positioning help in moderate to severe ARDS?

It makes lung inflation more uniform, recruits dorsal lung, improves ventilation-perfusion matching and reduces lung stress.

## What is permissive hypercapnia?

Accepting a higher PaCO2 and lower pH to keep tidal volumes and pressures low, unless raised intracranial pressure or severe acidosis forbids it.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anaesthesia/ventilating-ards-low-volumes-prone-position-and-more/)

## Elsewhere in DurgiPedia

- [Lung and chest wall compliance](https://durgical.com/en/physiology/lung-and-chest-wall-compliance/)
- [Hypoxemic and hypercapnic respiratory failure](https://durgical.com/en/physiology/hypoxemic-and-hypercapnic-respiratory-failure/)
- [Surface tension, surfactant and Laplace's law](https://durgical.com/en/physiology/surface-tension-surfactant-and-laplace-s-law/)
- [Reading an arterial blood gas step by step](https://durgical.com/en/physiology/reading-an-arterial-blood-gas-step-by-step/)
- [Patient positions: Fowler, supine, lateral, prone and others](https://durgical.com/en/nursing/patient-positions-fowler-supine-lateral-prone-and-others/)

## Connections

## Related 7

- [PEEP, plateau pressure and lung protection](https://durgical.com/en/anaesthesia/peep-plateau-pressure-and-lung-protection/)
- [Mechanical ventilation modes: volume, pressure and support](https://durgical.com/en/anaesthesia/mechanical-ventilation-modes-volume-pressure-and-support/)
- [NIV and high-flow nasal oxygen in the ICU](https://durgical.com/en/anaesthesia/niv-and-high-flow-nasal-oxygen-in-the-icu/)
- [Analgesia and sedation in the ICU: targets and scales](https://durgical.com/en/anaesthesia/analgesia-and-sedation-in-the-icu-targets-and-scales/)
- [Fluid responsiveness: when more fluid helps](https://durgical.com/en/anaesthesia/fluid-responsiveness-when-more-fluid-helps/)
- [Shock: a bedside approach by type](https://durgical.com/en/anaesthesia/shock-a-bedside-approach-by-type/)
- [Weaning and the spontaneous breathing trial](https://durgical.com/en/anaesthesia/weaning-and-the-spontaneous-breathing-trial/)

## Related conditions 5

- [Acute respiratory distress syndrome (ARDS)](https://durgical.com/en/conditions/acute-respiratory-distress-syndrome/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- [Aspiration pneumonia and pneumonitis](https://durgical.com/en/conditions/aspiration-pneumonia-and-pneumonitis/)
- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)
- [Acute respiratory failure (hypoxaemic and hypercapnic)](https://durgical.com/en/conditions/acute-respiratory-failure/)

## In Pharmacology 4

- [Neuromuscular blockers](https://durgical.com/en/pharmacology/classes/neuromuscular-blockers/)
- [Cisatracurium](https://durgical.com/en/pharmacology/cisatracurium/)
- [Corticosteroids (glucocorticoids)](https://durgical.com/en/pharmacology/classes/corticosteroids/)
- [Nitric oxide (inhaled)](https://durgical.com/en/pharmacology/nitric-oxide/)

[← All of anaesthesia](https://durgical.com/en/anaesthesia/)

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: [Acute Respiratory Distress Syndrome](https://www.ncbi.nlm.nih.gov/books/NBK436002/) (StatPearls (NCBI Bookshelf), 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anaesthesia/ventilating-ards-low-volumes-prone-position-and-more/