Acute Respiratory Distress Syndrome

Acute Respiratory Distress Syndrome

Acute Respiratory Distress Syndrome

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Acute Respiratory Distress Syndrome - Spotting the Storm

  • Acute, diffuse, inflammatory lung injury → severe hypoxemia & bilateral radiographic opacities.
    • Edema origin: Respiratory failure not fully explained by cardiac failure or fluid overload (objective assessment if no risk factors present). Chest X-ray: Bilateral diffuse opacities in ARDS
  • Berlin Definition (Key Criteria):
    • Timing: Within 1 week of a known clinical insult or new/worsening respiratory symptoms.
    • Chest Imaging (X-ray/CT): Bilateral opacities not fully explained by effusions, lobar/lung collapse, or nodules.
    • Oxygenation (on PEEP/CPAP ≥ 5 cmH₂O):
      Severity$PaO_2/FiO_2$ (mmHg)
      Mild>200 to ≤300
      Moderate>100 to ≤200
      Severe100

⭐ The Berlin Definition requires symptoms to have started within 1 week of a known clinical insult or new/worsening respiratory symptoms.

Acute Respiratory Distress Syndrome - Lung Under Siege

Alveolar-capillary membrane damage in ARDS and VALI

  • Acute, diffuse inflammatory lung injury: ↑alveolar-capillary permeability, protein-rich non-cardiogenic edema, severe hypoxemia.
  • Berlin Definition Key Criteria:
    • Timing: Acute onset (within 1 week of insult).
    • Chest Imaging: Bilateral opacities (non-cardiac).
    • Origin of Edema: Non-cardiac origin.
    • Oxygenation ($P_aO_2/F_iO_2$ ratio with PEEP $\geq$5 cmH2O):
      • Mild: >200 to $\leq$300 mmHg
      • Moderate: >100 to $\leq$200 mmHg
      • Severe: $\leq$100 mmHg

⭐ Diffuse alveolar damage (DAD) with hyaline membrane formation is the characteristic histopathological finding in ARDS.

  • Management: Lung-protective ventilation (LPV): low tidal volumes (4-6 mL/kg predicted body weight), optimal PEEP.

Acute Respiratory Distress Syndrome - The Usual Suspects

ARDS: Triggered by direct or indirect lung injury.

  • Direct Lung Injury (Insult directly to lungs):
    • Pneumonia: Severe bacterial, viral, or fungal infection.
    • Aspiration: Inhalation of gastric contents; near-drowning.
    • Pulmonary Contusion: Bruising of lung from trauma.
    • Fat Embolism Syndrome: After long bone fractures.
    • Inhalational Injury: From smoke, toxic gases, chemical irritants.
  • Indirect Lung Injury (Systemic process affecting lungs):
    • Sepsis: Widespread infection; most common overall ARDS cause.
    • Severe Trauma/Shock: Often with multiple transfusions (TRALI).
    • Acute Pancreatitis: Severe pancreatic inflammation.
    • Drug Overdose: E.g., salicylates, opioids, TCAs.
    • Major Burns: Extensive thermal injury, systemic inflammation.

⭐ Sepsis (especially pulmonary) and pneumonia are the most common causes of ARDS.

📌 "P-SST" for Pneumonia, Sepsis, ASpiration, Trauma.

Acute Respiratory Distress Syndrome - Breathing Battles

  • Key Management Strategies:
    • Lung Protective Ventilation (LPV): Tidal Volume (Vt) 4-6 mL/kg Predicted Body Weight (PBW), Plateau Pressure (Pplat) <30 cmH2O, Driving Pressure ($\Delta$P = Pplat - PEEP) <15 cmH2O; Permissive Hypercapnia (pH >7.20).
    • PEEP: Titrate for optimal oxygenation (e.g., $P_aO_2$ 55-80 mmHg or $S_pO_2$ 88-95%) and compliance.
    • Prone Positioning: If $P_aO_2/F_iO_2$ < 150 mmHg, for 12-16 hours/day.
    • Neuromuscular Blocking Agents (NMBAs): Consider early, short course for severe ARDS ($P_aO_2/F_iO_2$ < 150 mmHg).
    • Fluid Management: Conservative strategy.
    • ECMO (Extracorporeal Membrane Oxygenation): For refractory hypoxemia despite maximal conventional therapy.

⭐ Lung-protective ventilation using low tidal volumes (around 6 mL/kg predicted body weight) is a cornerstone of ARDS management and improves survival.

High‑Yield Points - ⚡ Biggest Takeaways

  • Berlin Definition: Acute onset, bilateral opacities, hypoxemia (PaO2/FiO2 ≤300), non-cardiac origin.
  • PaO2/FiO2 severity (PEEP ≥5): Mild (201-300), Moderate (101-200), Severe (≤100).
  • Pathophysiology: Diffuse Alveolar Damage (DAD), ↑ permeability edema.
  • Lung Protective Ventilation: Low tidal volumes (4-6 mL/kg PBW), Plateau pressure <30.
  • Prone positioning (PaO2/FiO2 <150) for moderate-severe ARDS improves mortality.
  • Common causes: Sepsis, pneumonia, aspiration.
  • Treat underlying cause, supportive care; no specific drug improves survival.

Practice Questions: Acute Respiratory Distress Syndrome

Test your understanding with these related questions

In acute respiratory distress syndrome (ARDS), which type of cell is primarily damaged?

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Flashcards: Acute Respiratory Distress Syndrome

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In abdominal compartment syndrome, peak inspiratory pressure _____, leading to hypoxia

TAP TO REVEAL ANSWER

In abdominal compartment syndrome, peak inspiratory pressure _____, leading to hypoxia

increases

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