Chest Medicine













Acute Respiratory Distress Syndrome (ARDS)
  • Acute lung injury caused by direct injury or secondary to systemic illness
  • Leads to release of inflammatory mediators → ↑ capillary permeability → non-cardiogenic pulmonary oedema

Aetiology
  • Direct cause: pneumonia, inhalation injury, gastric aspiration, contusion, vasculitis
  • Indirect cause: septicaemia, shock, haemorrhage, acute liver failure, pancreatitis, head injury, burns, drugs/toxins, obstetric emergencies

Signs and symptoms
  • Cyanosis, tachypnoea, tachycardia, peripheral vasodilation
  • Fine inspiratory crackles

Investigation
  • Basic bloods: CBC, electrolytes, LFT, CRP, clotting, ABG and blood culture (may add amylase if suspecting pancreatitis)
  • CXR: bilateral pulmonary infiltrates
  • Pulmonary artery catheter → measuring PCWP

Diagnostic criteria (need all 4)
  • A: Acute onset
  • R: Radiological abnormality (CXR showing bilateral infiltrates)
  • D: Dry (PCWP < 19 mmHg or lack of congestive cardiac failure)
  • S: Saturation low despite treatment (refractory hypoxaemia with PaO2:FiO2 < 200)

    • CXR showing ARDS (courtesy of James Heilman, MD, wikipedia.org)
    Note: bilateral pulmonary infiltrate (oedema) with a normal heart size and no pleural effusion (indicating no heart failure, but this CXR was taken in the AP projection - the patient was intubated and too unwell to stand - this may pool the effusion posteriorly, nullifying the costophrenic angle blunting effect)

Management
  • Admission to ICU
  • Respiratory support: CPAP with 40-60% oxygen or mechanical ventilation
  • Circulatory support: monitor PCWP, conservative fluid resuscitation, consider inotropes (dobutamine 2.5-10 mcg/kg/min infusion), vasodilators (nitric oxide 20-120 parts per million), and haemofiltration if renal failure
  • Treat the cause: e.g., IV antibiotics for sepsis

Reference: Oxford Handbook of Clinical Medicine (10th Edition)