ARDS Quiz

Understanding Acute Respiratory Distress Syndrome (ARDS)

Acute Respiratory Distress Syndrome (ARDS) is a life-threatening form of respiratory failure characterized by widespread inflammation in the lungs. This guide provides an overview for students and healthcare professionals preparing for exams or seeking to refresh their knowledge on this critical care topic.

What are the Berlin Criteria for ARDS?

The Berlin Definition, established in 2012, provides a standardized framework for diagnosing and stratifying ARDS. The key criteria are:

• Timing: Onset within one week of a known clinical insult or new/worsening respiratory symptoms.
• Chest Imaging: Bilateral opacities on chest radiograph or CT scan, not fully explained by effusions, lobar/lung collapse, or nodules.
• Origin of Edema: Respiratory failure not fully explained by cardiac failure or fluid overload. An objective assessment (e.g., echocardiography) is needed to exclude hydrostatic edema if no risk factor is present.
• Oxygenation: Impairment of oxygenation, classified by the PaO2/FiO2 ratio on at least 5 cmH2O of PEEP:
  • Mild ARDS: 201-300 mmHg
  • Moderate ARDS: 101-200 mmHg
  • Severe ARDS: ≤ 100 mmHg

Key Management Principles: Lung-Protective Ventilation

The cornerstone of ARDS management is mechanical ventilation using a lung-protective strategy. The goal is to maintain gas exchange while minimizing ventilator-induced lung injury (VILI).

• Low Tidal Volume (LTVV): Tidal volumes are targeted at 4-6 mL/kg of predicted body weight (PBW), not actual body weight. This prevents overdistension of alveoli (volutrauma).
• Plateau Pressure (Pplat): The goal is to keep Pplat below 30 cmH2O. Pplat reflects the pressure in the alveoli at the end of inspiration and is a key indicator of lung stress.
• Positive End-Expiratory Pressure (PEEP): Adequate PEEP is applied to prevent alveolar collapse at the end of expiration (atelectrauma) and improve oxygenation by recruiting collapsed lung units.
• Driving Pressure (ΔP): Calculated as Pplat – PEEP, driving pressure represents the “tidal stress” on the lung. A target of < 15 cmH2O is associated with improved survival.

Adjunctive Therapies in Severe ARDS

For patients with moderate to severe ARDS, additional therapies may be considered:

• Prone Positioning: Placing the patient face down for >16 hours per day can improve oxygenation and has been shown to reduce mortality in severe ARDS. It helps by recruiting dorsal lung regions, improving V/Q matching, and making chest wall mechanics more uniform.
• Neuromuscular Blockade: A continuous infusion of a neuromuscular blocking agent (e.g., cisatracurium) for up to 48 hours may be used in early, severe ARDS to improve patient-ventilator synchrony and reduce lung inflammation.
• Conservative Fluid Management: After initial resuscitation, a strategy of conservative fluid management (diuresis or fluid restriction) to achieve a neutral or negative fluid balance improves lung function and shortens the duration of mechanical ventilation.

Common Causes and Risk Factors

ARDS can be triggered by direct or indirect lung injury.

Direct Lung Injury

• Pneumonia (bacterial, viral)
• Aspiration of gastric contents
• Pulmonary contusion
• Near-drowning
• Inhalational injury

Indirect Lung Injury

• Sepsis (most common cause)
• Severe trauma with shock and multiple transfusions
• Pancreatitis
• Drug overdose
• Burns

This content is for educational and informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional for diagnosis and treatment.