Respiratory

Acute Respiratory Distress Syndrome (ARDS)

ARDS is acute diffuse inflammatory injury of the alveolar-capillary barrier causing bilateral pulmonary opacities and severe hypoxaemic respiratory failure not fully explained by cardiac failure or fluid overload; treat the trigger while delivering lung-protective critical care and escalating early when oxygenation remains refractory.

In a nutshell

ARDS is acute inflammatory permeability oedema causing bilateral opacities and severe hypoxaemic respiratory failure not fully explained by cardiac failure or fluid overload. Treat the trigger in critical care, use lung-protective ventilation, prone appropriate moderate or severe disease and refer early for refractory respiratory failure or ECMO consideration.

Classic presentation

A patient with pneumonia or sepsis develops rapidly worsening hypoxaemia and bilateral infiltrates despite oxygen, with no single cardiac or fluid explanation for the respiratory failure.

Key points

ARDS is a syndrome caused by another illness, commonly pneumonia or sepsis, rather than a primary disease of unknown context.
The diagnostic pattern is acute hypoxaemic respiratory failure, bilateral opacities and no alternative explanation that fully accounts for the oedema.
Use predicted or ideal body weight for protective tidal-volume calculations, not actual body weight.
Protective ventilation limits tidal volume and plateau pressure; accept permissive hypercapnia when appropriate rather than causing ventilator-induced injury.
Prone moderate or severe ARDS early and for prolonged sessions with a trained ICU team.
Persistent severe gas-exchange failure needs early specialist respiratory-failure or ECMO-centre discussion.

First-line investigation

Arterial blood gas with a PaO2/FiO2 ratio and chest imaging, alongside clinical assessment of the trigger, cardiac function, volume status and other causes of acute hypoxaemia.

Management

Treat the cause and stabilise in critical care

Escalate early, stabilise airway and circulation, and treat sepsis, pneumonia, aspiration or another trigger without delaying time-critical support.^5,6,1

Protect the ventilated lung

Use predicted or ideal body weight to target tidal volume up to 6 mL/kg and keep plateau pressure at or below 30 cmH2O when mechanically ventilated.^1,3,2

Prone and optimise physiology

For moderate or severe ARDS, use trained-team prone positioning for prolonged sessions, consider higher PEEP and selected short-course neuromuscular blockade, and use conservative fluids once shock is corrected.^1,2,7

Refer refractory respiratory failure

Seek early severe-respiratory-failure or ECMO-centre advice when hypoxaemia or hypercapnia persists despite appropriate protective ventilation, proning, PEEP and treatment of the trigger.^1,2,3

Prevent ICU complications and reassess

Review gas exchange, compliance, haemodynamics, fluid balance and the underlying cause frequently; use appropriate ICU prevention, sedation, nutrition, mobilisation and weaning practices and discuss prognosis with the patient or representatives.^3,1

Exam traps

Use predicted or ideal body weight, not actual weight, for tidal volume.
ARDS is not diagnosed by hypoxaemia alone: bilateral opacities and exclusion of a complete cardiac or fluid explanation are part of the syndrome.
Do not increase tidal volume simply to normalise carbon dioxide if this breaches lung-protective targets.
Proning is a prolonged, trained-team ICU intervention with airway, line, pressure-area and haemodynamic risks.
Do not pursue conservative fluids through shock or hypoperfusion; reassess after initial resuscitation.
Routine high-frequency oscillation, inhaled nitric oxide and ECCO2R are not generic first-line ARDS treatments.

Illustrations

Bilateral opacities in severe ARDSA chest radiograph demonstrating widespread bilateral air-space opacities in severe ARDS, with a concise caption warning that imaging must be interpreted alongside cardiac, volume and clinical assessment.James Heilman, MD, Wikimedia Commons · CC-BY-SA-4.0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.