Evidence‑Based Management of Acute Respiratory Distress Syndrome (ARDS)

Diagnostic Criteria

• PaO₂/FiO₂ ≤ 300 mmHg measured with a minimum PEEP of 5 cmH₂O is required for ARDS diagnosis, together with acute onset (≤ 1 week), bilateral opacities, and exclusion of cardiac edema. Society of Critical Care Medicine 1
• Severity classification (Berlin Definition) – Mild: 200 < PaO₂/FiO₂ ≤ 300 mmHg; Moderate: 100 < PaO₂/FiO₂ ≤ 200 mmHg; Severe: PaO₂/FiO₂ ≤ 100 mmHg, all assessed at PEEP ≥ 5 cmH₂O. Society of Critical Care Medicine 1
• Differential diagnoses (“ARDS mimics”) include diffuse interstitial lung disease, extensive pulmonary infection, and drug‑induced lung injury, which require alternative management. European Respiratory Society 2

Epidemiology

• Incidence – Approximately 10 % of all ICU admissions and 25 % of patients receiving invasive mechanical ventilation develop ARDS. Society of Critical Care Medicine 1

Mechanical Ventilation Strategies

Lung‑Protective Ventilation (Strong Recommendation)

• Low tidal volume of 4–8 mL/kg predicted body weight (PBW) with plateau pressure ≤ 30 cmH₂O is mandatory for all ARDS patients. American Thoracic Society 3
• Permissive hypercapnia (allowing modest PaCO₂ rise) is acceptable to maintain lung‑protective parameters. Society of Critical Care Medicine 1

Positive End‑Expiratory Pressure (PEEP)

• Higher PEEP is conditionally recommended for moderate‑to‑severe ARDS to improve oxygenation and alveolar recruitment. American Thoracic Society 3
• PEEP titration should consider gas exchange, hemodynamics, lung recruitability, end‑expiratory transpulmonary pressure, and driving pressure. Society of Critical Care Medicine 1
• Esophageal pressure monitoring may be used to estimate transpulmonary pressure and guide individualized PEEP settings. Society of Critical Care Medicine 1

Recruitment Maneuvers

• Conditional use of brief recruitment maneuvers in moderate‑severe ARDS is permitted, but prolonged maneuvers should be avoided. Evidence quality is low. American Thoracic Society 3

Oxygenation Targets

• Target PaO₂ of 70–90 mmHg and SpO₂ of 92–97 % while avoiding hyperoxia, which can exacerbate lung injury. Society of Critical Care Medicine 1

Adjunctive Therapies

Prone Positioning (Strong Recommendation)

• Prone positioning for ≥ 12 hours daily is mandatory in severe ARDS (PaO₂/FiO₂ < 150 mmHg) and is associated with a significant mortality reduction. American Thoracic Society 3
• Recommended duration is 12–18 hours per day. Society of Critical Care Medicine and American Thoracic Society [1][3]

High‑Frequency Oscillatory Ventilation (Strong Recommendation Against)

• Routine use of HFOV in moderate‑to‑severe ARDS is strongly discouraged; high‑quality trials show no benefit and possible harm. American Thoracic Society 3

Follow‑Up Imaging

• Chest radiograph should be repeated at 6 weeks in patients with persistent respiratory symptoms or who are high‑risk (e.g., smokers, age > 50 years). British Thoracic Society 4
• If the follow‑up radiograph remains abnormal, CT thorax and bronchoscopy are recommended for further evaluation. British Thoracic Society 4

Heterogeneity and Precision‑Medicine Considerations

• ARDS exhibits aetiological, physiological, and biological heterogeneity (different causes, lung recruitability, and inflammatory phenotypes) that influence response to therapies. European Respiratory Society 2 and European Respiratory Society 5
• Emerging data identify two biological subphenotypes (hyper‑inflammatory vs. hypo‑inflammatory) with differential responses to PEEP levels, fluid strategies, and pharmacologic agents. European Respiratory Society 2 and European Respiratory Society 5
• Historical failures of anti‑inflammatory, anticoagulant, and antioxidant trials are attributed to treating heterogeneous populations without phenotype‑specific targeting. European Respiratory Society 2 and European Respiratory Society 5
• Future precision‑medicine approaches that stratify patients by treatable traits and endotypes are expected to improve therapeutic success. European Respiratory Society 2 and European Respiratory Society 5

Acute Respiratory Distress Syndrome Management

Definition and Diagnostic Criteria

• The European Respiratory Society defines ARDS as the presence within 1 week of a known clinical insult of acute arterial hypoxemia (PaO₂/FiO₂ ≤ 300 mmHg) with minimum PEEP of 5 cmH₂O, plus bilateral radiographic opacities not entirely explained by cardiac failure or fluid overload 6, 7
• ARDS is classified based on severity of hypoxemia, with mild being 200 < PaO₂/FiO₂ ≤ 300 mmHg, moderate being 100 < PaO₂/FiO₂ ≤ 200 mmHg, and severe being PaO₂/FiO₂ ≤ 100 mmHg 6, 7, 8

Pathophysiology

• ARDS involves alveolar epithelial inflammation, airspace flooding with plasma proteins, surfactant depletion, and loss of normal endothelial reactivity, leading to extensive right-to-left intrapulmonary shunting and hypoxemia 7
• The inflammatory response includes neutrophil activation, cytokine release, and oxidant stress 7
• In CVICU patients, ARDS may be complicated by right ventricular dysfunction due to increased pulmonary vascular resistance and the effects of positive pressure ventilation 9

Treatment Approach

Ventilation Strategies

• The American Thoracic Society recommends implementing lung-protective ventilation with low tidal volumes (4-8 ml/kg predicted body weight) and limiting plateau pressures (<30 cmH₂O) 7, 8
• Higher PEEP should be used in moderate to severe ARDS without prolonged recruitment maneuvers 8
• The target PaO₂ should be 70-90 mmHg or SaO₂ 92-97% 10
• Esophageal pressure measurement should be considered to guide PEEP selection 10
• Driving pressure (plateau pressure minus PEEP) should be monitored and minimized 9

Positioning and Adjunctive Therapies

• Prone positioning should be implemented for >12 hours daily in severe ARDS (PaO₂/FiO₂ <100 mmHg) 10, 8
• Neuromuscular blocking agents (cisatracurium) should be considered for 48 hours in early severe ARDS 8
• Corticosteroids should be considered in selected patients with ARDS, particularly when initiated early 8
• Venovenous ECMO should be considered as rescue therapy for very severe ARDS failing conventional management 10

Hemodynamic Management in CVICU

• Adequate intravascular volume should be ensured while avoiding fluid overload, which can worsen pulmonary edema 8
• A conservative fluid management strategy should be implemented once shock is resolved 9
• Right ventricular function should be monitored with echocardiography to detect acute cor pulmonale 8
• RV function should be optimized by reducing unnecessary systemic oxygen demand, maintaining oxygenation, avoiding acidosis, and using appropriate lung recruitment and prone positioning 9

CVICU-Specific Considerations

• The interaction between mechanical ventilation and right ventricular function should be closely monitored 9
• High airway pressures can adversely alter venous return, distend the "baby lung," and raise ejection impedance of the afterload-sensitive right ventricle 9
• Monitoring signals linked to the tidal cycle and ventricular loading should be used to help predict preload and afterload dependence of the right ventricle 9
• In patients receiving ECMO, volume replacement and vasopressor use should be carefully balanced to avoid venous collapse during extracorporeal blood extraction while preventing volume overload 9