Master Respiratory System
for PLAB 1

What the PLAB 1 Tests in Respiratory System

PLAB 1 tests your ability to diagnose and manage common respiratory conditions in acute, chronic, and emergency settings. You must interpret clinical presentations (e.g., breathlessness, cough, wheeze, haemoptysis) and select appropriate investigations (e.g., spirometry, CXR, ABG, CT pulmonary angiogram) and first-line treatments. Key decisions include when to admit, when to use non-invasive ventilation, and when to escalate to intensive care. You need to know British Thoracic Society (BTS) guidelines for asthma, COPD, pneumonia, pulmonary embolism, and pleural disease. Also tested: interpretation of oxygen saturation, peak expiratory flow rate (PEFR), and ABG results. Candidates must demonstrate safe prescribing (e.g., oxygen targets, inhaler step-up, antibiotics) and recognition of red flags (e.g., stridor, silent chest, tension pneumothorax).

High-Yield Concepts

• Asthma: acute severe vs life-threatening: Acute severe: PEFR 33-50% best/predicted, SpO2 ≥92%, can't complete sentences. Life-threatening: PEFR <33%, SpO2 <92%, silent chest, cyanosis, bradycardia, exhaustion, confusion. First-line: high-flow O2 (target SpO2 94-98%), salbutamol 5 mg nebulised, prednisolone 40-50 mg PO (or IV hydrocortisone 100 mg if very ill). Consider IV magnesium sulfate 1.2-2 g if poor response.
• COPD: NICE/BTS criteria for exacerbation and LTOT: Exacerbation: increased sputum purulence/volume, worsened breathlessness. First-line: amoxicillin 500 mg TDS 5 days (or doxycycline 200 mg stat then 100 mg OD) plus prednisolone 30 mg OD 5 days. Long-term oxygen therapy (LTOT) if PaO2 <7.3 kPa (or <8 kPa with polycythaemia, pulmonary hypertension, or cor pulmonale) when clinically stable. Target SpO2 88-92%.
• Community-acquired pneumonia (CAP): CURB-65 severity score: CURB-65: Confusion (new, AMTS ≤8), Urea >7 mmol/L, Respiratory rate ≥30/min, BP <90 systolic or ≤60 diastolic, age ≥65. Score 0-1: treat at home (amoxicillin 500 mg TDS 5 days). Score 2: hospitalise (amoxicillin + clarithromycin 500 mg BD). Score ≥3: severe, consider IV co-amoxiclav 1.2 g TDS + clarithromycin 500 mg BD, or levofloxacin 500 mg BD.
• Pulmonary embolism (PE): Wells' score and management: Wells' score: clinical signs of DVT (3 pts), PE as likely as alternative (3 pts), heart rate >100 (1.5), immobilisation/surgery within 4 weeks (1.5), previous DVT/PE (1.5), haemoptysis (1), cancer (1). Score >4: likely PE → d-dimer (if low probability) or CT pulmonary angiogram. Anticoagulation: low-molecular-weight heparin (e.g., enoxaparin 1.5 mg/kg OD) or rivaroxaban 15 mg BD for 21 days then 20 mg OD.
• Pleural effusion: Light's criteria for exudate vs transudate: Exudate if any of: pleural fluid protein/serum protein >0.5, pleural fluid LDH/serum LDH >0.6, pleural fluid LDH >2/3 upper limit of normal serum LDH. Common causes: transudate (heart failure, cirrhosis, nephrotic syndrome), exudate (pneumonia, malignancy, TB, PE). Diagnostic tap: send for protein, LDH, pH, glucose, cytology, culture, and if TB suspected, ADA and GeneXpert.
• Pneumothorax: tension vs simple, management thresholds: Tension pneumothorax: tracheal deviation away, distended neck veins, hypotension, hyperresonance, absent breath sounds → immediate needle decompression (2nd intercostal space, midclavicular line, 14G cannula). Simple pneumothorax: if <2 cm rim on CXR and no breathlessness → conservative or aspiration; if >2 cm or symptomatic → chest drain (4th/5th intercostal space, mid-axillary line, size 16-24 Fr).
• Bronchiectasis: diagnosis and exacerbation management: Diagnosis: high-resolution CT chest (bronchial dilation, tram-track opacities). Exacerbation: increased cough, purulent sputum, haemoptysis. First-line antibiotics: amoxicillin 500 mg TDS 5-7 days or doxycycline 200 mg stat then 100 mg OD. If Pseudomonas suspected or known: ciprofloxacin 500-750 mg BD (monitor tendonitis). Chest physiotherapy and postural drainage essential.
• Tuberculosis: diagnosis and treatment regimen: Diagnosis: CXR (apical infiltrates/cavitation), sputum smear (ZN stain), GeneXpert, culture (gold standard). Treatment: 2 months of rifampicin, isoniazid, pyrazinamide, ethambutol (RIPE), then 4 months of rifampicin and isoniazid. Monitor LFTs (isoniazid/rifampicin hepatotoxicity). Directly observed therapy (DOT) recommended. Notify public health.

Common Traps in Respiratory System Questions

• Confusing asthma and COPD: asthma is variable obstruction with reversibility (PEFR variability >20%), COPD is fixed obstruction (FEV1/FVC <0.7) with minimal reversibility.
• Forgetting oxygen targets: in COPD, target SpO2 88-92% (not 94-98%) to avoid hypercapnic respiratory failure.
• Using CURB-65 alone for pneumonia in young adults: if CURB-65 is 0 but patient is hypoxic (SpO2 <92%) or has sepsis, still admit.
• Missing tension pneumothorax in a shocked patient with tracheal deviation: immediate needle decompression before CXR.
• Assuming all wheeze is asthma: consider anaphylaxis, foreign body, vocal cord dysfunction, or heart failure (cardiac asthma).
• Not checking for contraindications to rivaroxaban (e.g., severe renal impairment CrCl <15 mL/min, active bleeding) before prescribing for PE.

How to Revise Respiratory System for the PLAB 1

Prioritise acute presentations: acute asthma, COPD exacerbation, pneumonia, PE, and pneumothorax. Questions often present a clinical scenario with vital signs, ABG, and CXR findings; you must choose the next best step (investigation or management). Practise interpreting PEFR, SpO2, and ABG results (especially type 1 vs type 2 respiratory failure). Know the BTS/SIGN asthma guideline step-up and the NICE COPD exacerbation pathway. Memorise CURB-65 scoring, Wells' criteria, and Light's criteria. Questions commonly test safe oxygen prescribing and when to use non-invasive ventilation (e.g., for COPD with pH 7.25-7.35). Focus on first-line antibiotics and their durations. Review CXR signs: consolidation, effusion, pneumothorax, hilar lymphadenopathy (TB/sarcoidosis). Do not over-interpret spirometry—know the difference between obstructive and restrictive patterns.

Practise it: MedLumen has 35 Respiratory System questions for the PLAB 1, each with a full explanation and references.