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  • Physician

Acute respiratory distress syndrome

Summary

Acute respiratory distress syndrome (ARDS) is a severe inflammatory reaction of the lungs to pulmonary damage. Sepsis is the most common cause, but a variety of systemic and pulmonary factors (e.g., pneumonia, aspiration) can lead to ARDS. Affected individuals initially present with acute onset cyanosis, dyspnea, and tachypnea. Most patients will improve significantly in the weeks following the initial presentation, but some cases progress to pulmonary fibrosis, which prolongs hospital stay and delays the resolution of symptoms. The chief finding in ARDS is hypoxemic respiratory failure with decreased arterial oxygen pressure, which usually progresses to hypercapnic respiratory failure. Chest x-ray typically shows diffuse bilateral infiltrates (butterfly pattern). Management of ARDS focuses on maintaining adequate oxygenation, which often requires intubation and (lung protective) mechanical ventilation because nasal prongs and/or mask ventilation are insufficient. Moreover, any treatable causes of ARDS should be addressed. Even if adequate treatment is initiated, ARDS remains an acutely life-threatening disease with a high mortality rate.

Etiology

Systemic causes

Primary damage to the lungs

Sepsis is the most common cause of ARDS!

References:[1][2][3][4]

Pathophysiology

References:[5][3][6][7]

Clinical features

References:[8][9][10]

Diagnostics

ARDS is a likely diagnosis in the presence of both typical causes and therapy-resistant hypoxemia. The diagnosis is further supported by characteristic findings on chest x-ray that are not explained by underlying cardiac disease.

References:[1][11][9]

Differential diagnoses

References:[9][1][12]

The differential diagnoses listed here are not exhaustive.

Treatment

Approach

Lung protective ventilation

  • Description: Pressure-controlled ventilation with a low tidal volume and low peak inspiratory pressure to avoid further pulmonary damage. However, increasing the positive end-expiratory pressure (PEEP) is often necessary during treatment. With this type of ventilation, higher levels of CO2 can be tolerated (permissive hypercapnia).
  • Settings
    • Standard tidal volume ≅ 6 mL/kg body weight
    • FiO2 < 0.5 (< 50% in the gas mixture) to avoid oxygen toxicity
    • PEEP and FiO2 can be adjusted to recruit collapsed alveoli and guarantee sufficient oxygen saturation.
  • Goal: SaO2 > 90% (or PaO2 > 55 mm Hg)

A high respiratory rate and a low tidal volume are the principles of lung protective ventilation!

Extracorporeal life support (ECMO)

References:[1][13][14][15][16][17][18][19]

Acute management checklist

All patients with ARDS

  • Quantify hypoxemia: Use the P/F ratio to evaluate ARDS severity. [11]
    • Mild: P/F 200–300 mm Hg
    • Moderate: P/F 100–200 mm Hg
    • Severe: P/F < 100 mm Hg
  • Start lung protective ventilation strategy [20][21][22]
  • Identify and treat the underlying cause.
  • Ensure euvolemia.
  • Hemodynamic monitoring
  • Pain management and sedation
  • Consider further diagnostics.
    • CT scan of the chest
    • Consider bronchoscopy if the etiology remains unclear.
  • ICU admission
  • Consider transfer to ARDS/ECMO center of care.

Moderate or severe ARDS

  • Prone positioning for > 12 hours/day [21]
  • Higher PEEP (use incremental FiO2-PEEP combinations according to local protocols)
  • Airway recruitment maneuvers
  • Neuromuscular blockade in the first 48 h [23]

Severe ARDS with persistent hypoxemia

Prognosis

References:[5][26]