Acute non-cardiogenic pulmonary edema with diffuse alveolar damage and severe hypoxemia.
Also known as: ARDS, acute respiratory distress syndrome, noncardiogenic pulmonary edema, Berlin criteria
Overview
Acute, diffuse inflammatory lung injury causing increased pulmonary vascular permeability and alveolar edema, leading to hypoxemic respiratory failure not fully explained by cardiac failure or volume overload. Defined by the Berlin criteria (2012) and updated by the global definition (2023).
Epidemiology
Affects ~10% of ICU patients and ~25% of mechanically ventilated patients (LUNG SAFE study). Mortality 35-46% depending on severity. Common in sepsis, pneumonia (including SARS-CoV-2), and trauma populations.
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Question 1PulmonaryMedium
A 45-year-old man develops acute dyspnea, bilateral pulmonary infiltrates, and hypoxemia (PaO₂/FiO₂ ratio 180) within 4 hours of a packed red blood cell transfusion. He is normotensive, BNP is normal, and there is no jugular venous distention or peripheral edema. Which of the following is the most likely diagnosis?
AAcute septic transfusion reaction
BAcute hemolytic transfusion reaction
CTransfusion-related acute lung injury
DTransfusion-associated circulatory overload
EAcute anaphylactic transfusion reaction
Reveal answer & full explanation
Correct answer: C — Transfusion-related acute lung injury
AAcute septic transfusion reaction
BAcute hemolytic transfusion reaction
CTransfusion-related acute lung injury✓
DTransfusion-associated circulatory overload
EAcute anaphylactic transfusion reaction
Why Transfusion-related acute lung injury is correct
TRALI is non-cardiogenic pulmonary edema that begins during or within 6 hours of a transfusion, fitting onset 4 hours after transfusion here
Donor anti-leukocyte (anti-HLA/anti-HNA) antibodies activate recipient neutrophils, causing pulmonary capillary leak with bilateral infiltrates and hypoxemia
The normal BNP, normotension, and absence of jugular venous distention or peripheral edema confirm a non-cardiogenic, non-overload process
Management is supportive (oxygen, lung-protective ventilation if needed); diuretics and steroids are not indicated
Why the others are wrong
Acute anaphylactic transfusion reaction — produces urticaria, bronchospasm, angioedema, and hypotension within minutes, not bilateral infiltrates with hypoxemia (buzzword-matching "transfusion reaction")
Transfusion-associated circulatory overload — also causes dyspnea after transfusion but is cardiogenic, with hypertension, elevated BNP, and edema that are absent here (premature closure on the most common transfusion pulmonary reaction)
Acute septic transfusion reaction — bacterial contamination of the unit causes high fever, rigors, and hypotension progressing to shock, not a normotensive picture of isolated hypoxemia with bilateral infiltrates (buzzword-matching another acute transfusion complication)
Acute hemolytic transfusion reaction — intravascular hemolysis from ABO-incompatible blood causes fever, chills, flank or back pain, hypotension, and hemoglobinuria, often progressing to DIC and acute kidney injury, not a normotensive picture of bilateral infiltrates with isolated hypoxemia (assuming every acute transfusion reaction is hemolytic)
Question 2PulmonaryMedium
A 38-year-old female who is 32 weeks pregnant develops acute severe dyspnea and hypoxemia (SpO2 84%) requiring intubation. Her chest X-ray shows bilateral alveolar infiltrates. Echo shows no cardiac pathology. She had no prior lung disease. Her PaO2/FiO2 ratio is 98. She received a blood transfusion 4 hours ago for placenta previa. Which of the following is the most likely diagnosis?
ATransfusion-related acute lung injury
BAnaphylactic transfusion reaction
CAmniotic fluid embolism
DAcute pulmonary embolism
ECommunity-acquired pneumonia
Reveal answer & full explanation
Correct answer: A — Transfusion-related acute lung injury
ATransfusion-related acute lung injury✓
BAnaphylactic transfusion reaction
CAmniotic fluid embolism
DAcute pulmonary embolism
ECommunity-acquired pneumonia
Why transfusion-related acute lung injury is correct
All diagnostic criteria are met: acute onset within 6 hours of transfusion (symptoms began 4 hours after transfusion)
Bilateral radiographic infiltrates are present
Hypoxemia is confirmed by a PaO2/FiO2 ratio of 98 (below 300) and SpO2 of 84% (below 90%)
There was no pre-existing acute lung injury before transfusion and no evidence of circulatory overload
Two-hit model: pregnancy and surgery prime the pulmonary endothelium, then donor anti-HLA or anti-HNA antibodies activate primed neutrophils, causing non-cardiogenic edema
It is the most common cause of transfusion-associated mortality
Why the others are wrong
Acute pulmonary embolism — right-concept-wrong-radiograph; pregnancy is a hypercoagulable state, but PE characteristically leaves the chest film clear or shows only focal atelectasis rather than bilateral alveolar infiltrates, and it has no temporal link to the transfusion
Community-acquired pneumonia — anchoring on bilateral infiltrates; it would not arise within hours of transfusion and no fever prodrome is described
Amniotic fluid embolism — right-concept-wrong-setting; it occurs during or immediately after delivery or amniocentesis, not 4 hours after a blood transfusion
Anaphylactic transfusion reaction — right-trigger-wrong-reaction; the recent transfusion and the need for intubation suggest an allergic reaction, but transfusion anaphylaxis (classically an IgA-deficient recipient with anti-IgA antibodies) begins within minutes of starting the transfusion with hypotension, bronchospasm, urticaria, or angioedema, not as bilateral alveolar infiltrates with severe hypoxemia 4 hours later
Additional high-yield points
Treatment is supportive: lung-protective ventilation and avoidance of diuretics
Most patients recover within 48–96 hours
Distinguish from transfusion-associated circulatory overload (TACO), which is cardiogenic edema that responds to diuretics; TRALI does not
High-risk donors are multiparous women sensitized to HLA antigens, now excluded from donating plasma
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Hypersensitivity pneumonitis (acute) — Exposure history (birds, mold); resolves with antigen avoidance and steroids
Diagnostic workup
Diagnostic criteria
Berlin Criteria (2012): (1) acute onset ≤1 week of insult or new symptoms, (2) bilateral opacities on chest imaging, (3) respiratory failure not fully explained by cardiac failure/fluid overload, (4) impaired oxygenation with PEEP ≥5 cm H2O — mild PaO2/FiO2 >200 to ≤300, moderate >100 to ≤200, severe ≤100. 2023 global definition extends to high-flow nasal O2 ≥30 L/min, accepts SpO2/FiO2 ≤315 (if SpO2 ≤97%) and lung ultrasound, and adapts criteria for resource-limited settings.
Labs
ABG — severe hypoxemia, often with respiratory alkalosis (early) progressing to acidosis
CBC, BMP, LFTs, lactate, lipase, blood and urine cultures
BNP and echocardiography to exclude cardiogenic edema
Berlin definition severity stratification of ARDS and associated mortality (Ranieri 2012).
Treatment
First-line
Treat underlying cause (source control, antibiotics for sepsis, supportive care)
Lung-protective mechanical ventilation (ARDSnet protocol, ARMA trial), which lowers mortality by limiting overdistension and cyclic stretch of the small aerated 'baby lung' (less ventilator-induced lung injury), not by improving oxygenation:
Low tidal volume 6 mL/kg ideal body weight (start 8 then titrate down)
Plateau pressure ≤30 cm H2O
PEEP titrated to maintain oxygenation (lower or higher PEEP-FiO2 tables); PEEP and proning, not low tidal volume, recruit collapsed alveoli
Neuromuscular blockade (cisatracurium) — selective use in early severe ARDS (ACURASYS supported; ROSE was negative; reserve for severe dyssynchrony)
Adjuncts for refractory hypoxemia: inhaled pulmonary vasodilators (nitric oxide, epoprostenol) — improve oxygenation but no mortality benefit
Second-line / adjunct
Veno-venous ECMO for severe ARDS with refractory hypoxemia/hypercapnia despite optimization (EOLIA, post-hoc Bayesian analysis suggests benefit) — refer to experienced center
Corticosteroids: dexamethasone 20 mg/day × 5 d then 10 mg × 5 d in moderate-severe ARDS (DEXA-ARDS); 6 mg/day in COVID-19 ARDS (RECOVERY trial)
Avoid: routine high-dose steroids late (>14 days), beta-2 agonists, statins, surfactant — none have improved outcomes in adult ARDS
Early mobilization, daily SBT and sedation interruption to limit ICU complications
Pulmonary fibrosis (fibrotic ARDS) with chronic pulmonary dysfunction
Ventilator-associated pneumonia, line infections
PANCE pearls
ARDSnet low-tidal-volume (6 mL/kg IBW) ventilation is the only proven mortality-reducing intervention besides prone positioning and dexamethasone (COVID-ARDS).
PaO2/FiO2 ratios are measured on PEEP ≥5 — without PEEP, severity grading does not apply.
Steroids are useful in COVID-19 ARDS (RECOVERY) and may benefit other moderate-severe ARDS (DEXA-ARDS); avoid in influenza ARDS unless other indication.
ECMO is rescue therapy for refractory hypoxemia — early referral to ECMO centers improves outcomes.
References
ARMA / ARDSnet — Ventilation with Lower Tidal Volumes for ARDS (ARDS Network, NEJM 2000)
PROSEVA — Prone Positioning in Severe Acute Respiratory Distress Syndrome (Guérin et al., NEJM 2013)
Berlin Definition — Acute Respiratory Distress Syndrome: The Berlin Definition (Ranieri et al., JAMA 2012)
RECOVERY — Dexamethasone in Hospitalized Patients with COVID-19 (Horby et al., NEJM 2021)
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