Master Respiratory System
for PLAB 1

Core Concepts

The respiratory system facilitates gas exchange (O2 in, CO2 out). Key physiological concepts include ventilation, perfusion, and diffusion. Common conditions frequently encountered in PLAB 1 include:

• Obstructive Lung Diseases: Characterised by airflow limitation, especially during expiration (e.g., Asthma, COPD, Bronchiectasis, Cystic Fibrosis). Spirometry shows FEV1/FVC ratio < 0.7.
• Restrictive Lung Diseases: Characterised by reduced lung volumes (e.g., Interstitial Lung Disease, Pulmonary Fibrosis, chest wall deformities). Spirometry shows reduced FVC, FEV1, and TLC with preserved or increased FEV1/FVC ratio.
• Infections: Pneumonia, Bronchitis, Tuberculosis.
• Vascular: Pulmonary Embolism (PE), Pulmonary Hypertension.
• Malignancy: Lung Cancer.
• Pleural Diseases: Pneumothorax, Pleural Effusion, Mesothelioma.
• Acute Respiratory Failure: Type I (hypoxaemic) and Type II (hypercapnic).

Clinical Presentation

• Dyspnoea (SOB): Commonest symptom. Acute (PE, pneumothorax, acute asthma) vs. chronic (COPD, CHF, interstitial lung disease).
• Cough: Productive (sputum - infection, bronchiectasis) vs. non-productive (asthma, GERD, ACE inhibitors, interstitial lung disease, tumour). Acute (<3 weeks) vs. chronic (>8 weeks).
• Wheeze: Expiratory whistling sound, characteristic of airway narrowing (asthma, COPD, bronchiectasis).
• Stridor: High-pitched inspiratory sound indicating upper airway obstruction (epiglottitis, foreign body, laryngeal oedema).
• Chest Pain: Pleuritic (sharp, worse on inspiration/cough - pneumonia, PE, pneumothorax) vs. non-pleuritic (angina, musculoskeletal).
• Haemoptysis: Coughing up blood (bronchitis, bronchiectasis, TB, lung cancer, PE).
• Cyanosis: Bluish discolouration of skin/mucosa due to deoxygenated haemoglobin.
• Clubbing: Swelling of fingertips (lung cancer, bronchiectasis, CF, IPF, cyanotic heart disease).
• Fever & Chills: Suggestive of infection (pneumonia, TB).
• Weight Loss & Night Sweats: Malignancy or chronic infection (TB).

Diagnosis (Gold Standard)

• Asthma: Spirometry with significant bronchodilator reversibility (FEV1 increase >12% and >200ml) or positive direct bronchial challenge test (e.g., methacholine).
• COPD: Spirometry showing persistent airflow obstruction (post-bronchodilator FEV1/FVC <0.7).
• Pneumonia: Chest X-ray (CXR) showing new focal consolidation. Sputum culture for pathogen identification.
• Pulmonary Embolism (PE): CT Pulmonary Angiogram (CTPA). V/Q scan if CTPA contraindicated (e.g., renal impairment, contrast allergy).
• Pneumothorax: CXR showing visceral pleural line and absence of lung markings peripheral to it.
• Pleural Effusion: CXR (blunting of costophrenic angle), Ultrasound (USS) for localisation, diagnostic pleural fluid aspiration with analysis (Lights' criteria, cytology).
• Lung Cancer: Histological or cytological biopsy (bronchoscopy, CT-guided biopsy, EBUS, pleural fluid cytology).
• Tuberculosis (TB): Isolation of *Mycobacterium tuberculosis* from culture (sputum, bronchoalveolar lavage, tissue). Ziehl-Neelsen stain for acid-fast bacilli (AFB).
• Cystic Fibrosis (CF): Sweat chloride test (>60 mmol/L). Genetic testing for CFTR mutations.
• Bronchiectasis: High-Resolution CT (HRCT) chest showing bronchial dilatation and lack of tapering.

Management (First Line)

• Asthma:
  • Reliever: Short-acting beta-2 agonist (SABA, e.g., Salbutamol).
  • Controller: Inhaled corticosteroids (ICS). Step-up approach (add LABA, LTRA, etc.).
  • Acute Exacerbation: O2, high-dose SABA, Ipratropium bromide, systemic corticosteroids.
• COPD:
  • Smoking Cessation (most crucial).
  • Bronchodilators: SAMA/SABA as needed. Regular LAMA (e.g., Tiotropium) and/or LABA (e.g., Salmeterol, Formoterol). ICS for frequent exacerbations with high eosinophils.
  • Pulmonary Rehabilitation. Oxygen therapy if chronic hypoxaemia.
  • Acute Exacerbation: O2, bronchodilators, systemic steroids, antibiotics if purulent sputum (CURB-65 for severity).
• Pneumonia:
  • Community-Acquired: Amoxicillin or Macrolide (e.g., Clarithromycin) for mild-moderate. Dual therapy (e.g., Amoxicillin + Clarithromycin) for severe.
  • Hospital-Acquired: Local guidelines, often broad-spectrum (e.g., Piperacillin/Tazobactam).
  • Supportive care: Oxygen, fluids, analgesia. CURB-65 for severity assessment and site of care.
• Pulmonary Embolism (PE): Anticoagulation (Low Molecular Weight Heparin bridging to DOACs/Warfarin). Thrombolysis for massive PE (haemodynamic instability).
• Pneumothorax:
  • Small (<2cm): O2, conservative management (if asymptomatic).
  • Large (>2cm) or symptomatic: Aspiration or chest drain insertion.
  • Tension Pneumothorax: Immediate needle decompression (2nd ICS mid-clavicular line) followed by chest drain.
• Tuberculosis (TB): Multi-drug regimen (RIPE: Rifampicin, Isoniazid, Pyrazinamide, Ethambutol) for 6 months (longer for extrapulmonary TB). Directly Observed Therapy (DOT).
• Lung Cancer: Multi-Disciplinary Team (MDT) discussion for treatment plan (surgery, radiotherapy, chemotherapy, immunotherapy).

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