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COPD for USMLE Step 3

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Chronic obstructive pulmonary disease for the USMLE Step 3 Exam
Pathophysiology
  • Chronic Inflammation:
    • COPD results from prolonged inflammation of the airways and lung parenchyma, triggered by exposure to irritants like cigarette smoke.
    • Neutrophils, macrophages, and CD8+ T cells predominate, causing destruction of alveoli and narrowing of the small airways.
  • Airflow Limitation:
    • Airflow obstruction in COPD is due to:
    • Small Airway Disease: Inflammation and fibrosis of the bronchioles.
Small airway disease COPD
    • Emphysema: Destruction of alveoli leads to loss of elastic recoil and air trapping.
  • Protease-Antiprotease Imbalance:
    • Increased protease activity (e.g., neutrophil elastase) breaks down lung tissue, while decreased antiprotease activity (e.g., alpha-1 antitrypsin) fails to protect against this damage, leading to emphysema.
  • Oxidative Stress:
    • Oxidants from cigarette smoke and inflammatory cells contribute to further lung injury and amplification of inflammation.
Clinical Features
  • Chronic Cough and Sputum Production:
    • Often an early manifestation, with increased sputum production during exacerbations.
  • Dyspnea:
    • Progressive shortness of breath, particularly with exertion, is the primary symptom of COPD.
  • Wheezing and Chest Tightness:
    • These symptoms may be present and worsen during exacerbations.
  • Exacerbations:
    • Sudden worsening of symptoms, often triggered by respiratory infections, pollution, or other irritants.
Diagnosis
  • Spirometry:
    • Diagnostic tool for COPD:
    • FEV1/FVC <0.70: Confirms airflow limitation post-bronchodilator.
    • FEV1: Degree of reduction correlates with severity.
  • Chest X-ray:
    • Findings may include hyperinflation, flattened diaphragms, and increased lung radiolucency in advanced COPD.
  • Arterial Blood Gas (ABG):
    • In severe cases or exacerbations, ABGs may show hypoxemia and hypercapnia, indicating respiratory failure.
Management
  • Smoking Cessation:
    • The most effective intervention to slow disease progression and improve long-term outcomes.
  • Bronchodilators:
    • Short-acting beta-agonists (SABAs): Used as needed for symptom relief during exacerbations.
    • Long-acting bronchodilators (LABAs and LAMAs): Maintenance therapy to improve lung function and reduce exacerbation frequency.
  • Inhaled Corticosteroids (ICS):
    • Used in combination with bronchodilators (LABA/ICS) in patients with severe COPD or frequent exacerbations.
  • Phosphodiesterase-4 Inhibitors (PDE-4 inhibitors):
    • Roflumilast can be added in patients with severe COPD and chronic bronchitis to reduce exacerbations.
  • Oxygen Therapy:
    • Long-term oxygen therapy is recommended for patients with severe hypoxemia (PaO2 ≤55 mmHg or SaO2 ≤88%).
  • Pulmonary Rehabilitation:
    • Exercise programs combined with education, especially beneficial for moderate-to-severe COPD.
Exacerbations
  • Management of Exacerbations:
    • Bronchodilators: SABAs with or without short-acting anticholinergics (e.g., ipratropium) are first-line therapy.
    • Systemic Corticosteroids: Short courses of prednisone (e.g., 40 mg daily for 5 days) help improve recovery.
    • Antibiotics: Prescribed if there is increased sputum purulence or evidence of bacterial infection.
Complications
  • Pulmonary Hypertension and Cor Pulmonale:
    • Chronic hypoxia can lead to pulmonary hypertension, causing right heart failure (cor pulmonale).
  • Acute Respiratory Failure:
    • Severe exacerbations can result in acute respiratory failure, requiring mechanical ventilation or non-invasive positive pressure ventilation (NIPPV).
Key Points
  • COPD is a progressive disease characterized by chronic inflammation, airflow limitation, and alveolar destruction, mainly caused by smoking.
  • Spirometry (FEV1/FVC <0.70) confirms the diagnosis, and chest X-rays support findings in advanced cases.
  • Smoking cessation is the most critical intervention to slow disease progression.
  • Maintenance treatment includes long-acting bronchodilators (LABAs and LAMAs), with inhaled corticosteroids added for severe disease.
  • Exacerbations are managed with bronchodilators, systemic corticosteroids, and antibiotics when needed.
  • Complications include pulmonary hypertension, cor pulmonale, and acute respiratory failure, which may require advanced respiratory support.

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