ACUTE RESPIRATORY DISTRESS SYNDROME

✓ Medically ReviewedDISEASEID: MDBT0064🚨 TRIAGE: EMERGENCYICD-10: J80

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Definition

CLINICAL DEFINITION

Acute respiratory distress syndrome is sudden inflammatory lung failure with permeability oedema (fluid leak into air sacs). It starts within one week of a known trigger such as sepsis (body-wide infection response). Triggers include pneumonia (lung infection) and aspiration (inhaled stomach contents). Berlin criteria need bilateral opacities (cloudy areas on imaging) not fully explained by cardiac failure. They need low oxygen despite support on PEEP (lung pressure) of 5 or more.

IN PLAIN ENGLISH

The lungs suddenly fill with fluid and cannot pass oxygen well. This follows infection, inhaled vomit, injury or major inflammation. Both lungs look white on X-ray from fluid. The person feels very breathless and needs hospital oxygen. Many need a breathing machine in intensive care.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Acute respiratory distress syndrome is not heart failure oedema (fluid from weak pump) alone. It is not simple pneumonia (single lung infection) without widespread leak and low oxygen ratio. It is not atelectasis (flat air sacs) that opens fast with suction and physio (chest treatment). It is not chronic fibrosis (long term scarring) that builds over months without acute trigger.

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Word Breakdown

syndr-

=run together

-ome

=mass or group forming a condition

Literal Meaning: group of sudden breathing difficulty signs running together

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Abbreviations

ARDS=Acute respiratory distress syndrome - sudden leaky lung failure with low oxygen

PEEP=Positive end-expiratory pressure - pressure kept in lungs to hold sacs open

FiO2=Fraction of inspired oxygen - oxygen share in inhaled gas

PaO2=Arterial oxygen pressure - oxygen level in artery blood

PBW=Predicted body weight - size estimate used to set ventilator breath size

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Synonyms & Variants

Shock lung›Diffuse alveolar damage syndrome›Acute hypoxaemic respiratory failure from permeability oedema›

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Category-Specific Context

Acute respiratory distress syndrome is a Disease because it is a defined failure syndrome (linked set of findings) with causes and course. It sits within respiratory failure (breathing system failure) and critical illness. It is not a Symptom (patient complaint) or Sign (exam finding) alone. Care pairs cause treatment with oxygen and ventilation support.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency DepartmentIntensive Care UnitHigh Dependency UnitTrauma UnitPostoperative Recovery Unit

USAGE & DOCUMENTATION NOTES

Use the term only when Berlin criteria (timing, imaging and oxygen rules) are met. Record onset trigger, PaO2 to FiO2 ratio (blood oxygen over inhaled oxygen) and PEEP (lung pressure) level. State severity as mild, moderate or severe. Exclude cardiac oedema (heart fluid) with echo (heart ultrasound) at diagnosis.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Injury harms alveolar-capillary lining (tiny sac and vessel wall). Permeability (leakiness) rises and protein-rich oedema (fluid leak) floods sacs. Surfactant (lung coating) is lost and sacs collapse. Blood passes without oxygen pickup causing shunt (blood bypassing air). Stiff lungs lower compliance (stretch ability) and raise breathing work.

PRIMARY CAUSES

Pneumonia

Direct germ invasion injures sac lining and triggers inflammation that impairs oxygen transfer

Non-pulmonary sepsis

Body-wide inflammation injures vessel lining and raises leak across lung vessels

Aspiration of gastric contents

Acid and particles burn airways and sacs and trigger intense inflammation

Major trauma and pulmonary contusion (bruised lung)

Direct impact plus body-wide inflammation damage vessels and sacs together

Transfusion-related acute lung injury

Donor antibodies activate white cells that injure lung capillaries and cause leak

Acute pancreatitis

Pancreatic enzymes and blood signals spread and injure lung vessels from afar

Near drowning and smoke inhalation

Direct chemical and particle injury strips lining and floods sacs with fluid

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Epidemiology

Prevalence:Acute respiratory distress syndrome is common in ventilated intensive care cohorts worldwide. It follows pneumonia (lung infection), sepsis (infection response) and aspiration (inhaled contents) most often. Risk rises after trauma, transfusion and major surgery. Counts vary by Berlin use and case finding.

Age Group:All ages can be affected from children to older adults. Risk and death rise with older age and frailty (low reserve). Young patients more often follow trauma, drowning or infection. Older patients more often follow sepsis and pneumonia.

Geographic Distribution:Acute respiratory distress syndrome occurs worldwide in all health systems. Case mix follows sepsis, pneumonia and trauma burdens. Detection and survival track access to oxygen monitoring, ventilation and intensive care.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 EMERGENCY

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Cardiogenic oedema needing diuretics not just ventilation
Tension pneumothorax under PEEP
Untreated sepsis source
Pulmonary embolism
Diffuse alveolar haemorrhage

URGENT EVALUATION TRIGGERS

Worsening low oxygen despite oxygen support
New low pressure or shock signs
Severe breathlessness with confusion
High airway pressures with one-sided chest signs
No improvement after initial resuscitation

Contraindications & Precautions

CONTRAINDICATIONS

Do not use large tidal volumes (big machine breaths) in ARDS lungs
Do not delay lung-protective ventilation while awaiting full workup
Do not give large fluid boluses without lung and volume checks

SPECIAL PRECAUTIONS

Monitor plateau pressure (lung stretch pressure) and driving pressure each shift
Watch for pneumothorax under PEEP with high airway pressures
Screen daily for sepsis source and ventilator pneumonia
Plan prolonged recovery with weakness and scarring review

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Ventilator-induced lung injury
Barotrauma with pneumothorax (pressure lung injury with collapsed lung)
Ventilator-associated pneumonia
Pulmonary fibrosis with lasting breathlessness
Critical illness weakness
Acute kidney injury with multiorgan failure
Delirium with long term cognitive fog

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Reference Ranges

CRITICAL (PANIC) VALUEPaO2 to FiO2 ratio (blood oxygen over inhaled oxygen) at or below 300 on PEEP 5 or more marks ARDS. Ratio 100 or less marks severe disease. Falling ratio with rising pressures or new shock signals emergency.

UNIT OF MEASUREMENTmmHg for PaO2 with kPa in brackets; percent for FiO2 (inhaled oxygen share).

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

RDS of the newborn

Shares letters but is surfactant (lung coating) lack in newborns, not adult permeability leak

SARS

Shares letters and lung failure but SARS is a viral infection that can cause ARDS, not ARDS itself

Cardiogenic pulmonary oedema

Looks similar on imaging but is pressure overload from heart failure, not permeability leak

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Cardiogenic pulmonary oedema

Key Distinguishing Feature: Eases with diuretics (fluid removers) with heart strain on echo and enlarged heart shadow

Bilateral pneumonia

Key Distinguishing Feature: Fever with raised white cells and lobar consolidation without Berlin timing and PEEP rule

Pulmonary embolism

Key Distinguishing Feature: Sharp chest pain with clear lungs and clot on CT angiography (vessel imaging)

Diffuse alveolar haemorrhage

Key Distinguishing Feature: Bloody sputum with falling haemoglobin and red cells on lavage (lung wash)

Acute interstitial pneumonia

Key Distinguishing Feature: No trigger found with rapid fibrosis pattern rather than oedema with acute onset

Atelectasis

Key Distinguishing Feature: Re-expands with recruitment and bronchoscopy without refractory low oxygen

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Clinical Pearls

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Use low tidal volumes (small breaths) of 6 mL per kg predicted weight from the start. This limits stretch injury more than chasing normal gases.

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Keep plateau pressure (stretch pressure) below 30 and review driving pressure each shift. Lower pressures beat larger breaths when lungs are stiff.

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Prone (face-down) severe cases early for 12 or more hours per day per protocol. Proning improves oxygen and survival in refractory low oxygen.

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Treat the trigger in parallel with ventilation such as antibiotics and source control. Ventilation buys time but does not cure sepsis or aspiration.

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Screen daily for ventilator pneumonia (machine lung infection) and barotrauma (pressure injury). Fever may be masked by sedation and cooling.

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Example Usage & SOAP

CLINICAL SENTENCE

""64-year-old woman with sepsis developed ARDS with bilateral opacities and low oxygen on PEEP 10.""

IN A SOAP NOTE

S: 64-year-old with pneumonia and worse breathlessness for 2 days, dry cough. O: Temp 38.2C, HR 112, BP 98/62, RR 30, SpO2 87 percent on high oxygen, crackles both lungs, drowsy but rousable. Gases show low oxygen ratio. A: Severe ARDS with sepsis and low oxygen. P: Intensive care admit, broad antibiotics, lung-protective ventilation, prone plan, echo to exclude cardiac oedema.

DIFFERENTIAL DIAGNOSIS CONTEXT

White lungs both sides with low oxygen suggests ARDS when Berlin timing and PEEP rules fit. Heart strain on echo with leg swelling favours cardiac oedema (heart fluid). Sharp pain with clear lungs favours embolism (lung clot). Bloody sputum with anaemia (low red cells) favours haemorrhage (lung bleeding).

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Classifications & Scoring

GRADING SYSTEM

Berlin Definition of ARDS

2012 consensus grading ARDS as mild with ratio 200 to 300, moderate 100 to 200, severe 100 or less, all on PEEP 5 or more with acute onset and bilateral opacities

SCORING TOOL

SOFA Score

Tracks organ failure across lungs, circulation, liver, kidney, brain and clotting to follow critical illness

SCORING TOOL

APACHE II Score

Estimates intensive care death risk from physiology, age and chronic health on admission

SCORING TOOL

Murray Lung Injury Score

Lung score using X-ray spread, low oxygen level, PEEP need and compliance to grade injury

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Prognosis

SHORT-TERM OUTCOME

Short term course depends on cause, severity and organ failures. Low oxygen and shock can worsen within days. Many need prolonged ventilation (machine breathing) and intensive care stay. Death risk climbs with moderate to severe grades.

LONG-TERM PROGNOSIS

Survivors often face breathlessness, weakness and exercise limits for months. Some develop fibrosis (lung scarring) and need oxygen or rehab (recovery programme). Anxiety, depression and thinking fog are common after intensive care. Follow-up imaging and lung tests guide recovery.

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References & Coding

ICD-10 DIAGNOSTIC CODE

J80

LITERATURE CITATIONS & GUIDELINES

[1]Ranieri et al Berlin Definition of ARDS JAMA 2012

[2]National Heart Lung and Blood Institute ARDSNet guidance

[3]Harrison's Principles of Internal Medicine

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.

ACUTE RESPIRATORY DISTRESS SYNDROME

Definition

Word Breakdown

Abbreviations

Synonyms & Variants

Category-Specific Context

Clinical Context & Usage

Primary Causes & Pathophysiology

Epidemiology

Red Flags & Triage ★

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

URGENT EVALUATION TRIGGERS

Contraindications & Precautions

CONTRAINDICATIONS

SPECIAL PRECAUTIONS

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Reference Ranges

Confused With (LASA & DDx) ★

Clinical Pearls

Example Usage & SOAP

Classifications & Scoring

Berlin Definition of ARDS

SOFA Score

APACHE II Score

Murray Lung Injury Score

Prognosis

SHORT-TERM OUTCOME

LONG-TERM PROGNOSIS

Related Terms

References & Coding