Master Respiratory
for PLAB 1

What the PLAB 1 Tests in Respiratory

Respiratory in PLAB 1 tests your ability to manage common acute and chronic presentations: breathlessness, cough, wheeze, haemoptysis, and chest pain. You must differentiate asthma from COPD using spirometry (post-bronchodilator FEV1/FVC <0.7 for COPD), apply CURB-65 (≥2 scores = hospital admission) for community-acquired pneumonia, and recognise when to suspect pulmonary embolism (Wells score, D-dimer, CT pulmonary angiogram). Knowledge of first-line antibiotics (amoxicillin 500mg TDS for CAP, co-amoxiclav for HAP), inhaler step-up for asthma (BTS/SIGN guidelines: SABA then ICS/LABA), and oxygen targets (SpO2 94-98%, 88-92% in COPD with hypercapnia) is essential. You are expected to interpret chest X-rays for pneumothorax, pleural effusion, and consolidation, and select appropriate investigations (sputum cultures, pleural fluid analysis, bronchoscopy).

High-Yield Concepts

• Community-Acquired Pneumonia (CAP) Severity Assessment: Use CURB-65: Confusion (AMTS ≤8), Urea >7 mmol/L, Respiratory rate ≥30/min, BP systolic <90 or diastolic ≤60, age ≥65. Score 0-1: treat at home with oral amoxicillin 500mg TDS (or doxycycline if penicillin-allergic). Score ≥2: admit for IV antibiotics (co-amoxiclav 1.2g TDS plus clarithromycin 500mg BD).
• COPD Diagnosis and Exacerbation Management: Diagnosis: post-bronchodilator FEV1/FVC <0.7. Exacerbation: increase in breathlessness, sputum volume, or purulence. First-line: increase bronchodilator (SABA via spacer), prednisolone 30mg PO OD for 5 days, antibiotics (amoxicillin or doxycycline) if purulent sputum. Oxygen target SpO2 88-92% to avoid hypercapnic respiratory failure.
• Asthma Stepwise Management (BTS/SIGN 2024): Step 1: SABA as needed. Step 2: add ICS (e.g., beclometasone 200-400mcg/day) or LTRA. Step 3: ICS/LABA combination (e.g., Symbicort SMART regimen). Step 4: increase ICS to high dose (beclometasone >800mcg/day) plus LABA. Step 5: add oral prednisolone, consider biologic (omalizumab for allergic asthma).
• Pulmonary Embolism (PE) Diagnostic Pathway: Assess pre-test probability with Wells score: clinical signs of DVT (3 pts), PE as likely as other diagnosis (3), HR >100 (1.5), immobilisation/surgery within 4 weeks (1.5), previous DVT/PE (1.5), haemoptysis (1), cancer (1). Score >4: arrange CTPA. Score ≤4: do D-dimer; if positive, CTPA. Start LMWH (e.g., enoxaparin 1.5mg/kg OD) while awaiting results.
• Pleural Effusion: Light's Criteria for Exudate: Effusion is exudative if any of: pleural fluid protein/serum protein >0.5, pleural fluid LDH/serum LDH >0.6, or pleural fluid LDH >2/3 upper limit of normal serum LDH. Transudate (e.g., heart failure): treat cause. Exudate: send for cytology, culture, and consider TB (ADA >40 U/L suggests TB).
• Tension Pneumothorax: Immediate Decompression: Clinical: tracheal deviation away, hyperresonance, absent breath sounds, distended neck veins, hypotension. Do not wait for X-ray. Insert large-bore cannula (14G) in 2nd intercostal space, midclavicular line. Then insert chest drain (28-32Fr) in 5th intercostal space, anterior axillary line (triangle of safety).
• Tuberculosis: Diagnosis and First-Line Treatment: Suspect: persistent cough >3 weeks, night sweats, weight loss, haemoptysis. Sputum for AFB smear and GeneXpert. Start RIPE regimen: rifampicin 600mg, isoniazid 300mg, pyrazinamide 1.5-2g, ethambutol 15mg/kg for 2 months, then rifampicin+isoniazid for 4 months. Check LFTs at baseline and monthly.
• Oxygen Therapy and Hypercapnic Respiratory Failure: Aim SpO2 94-98% for most patients. For COPD with known hypercapnia (or at risk): use Venturi mask 24% or 28% to target SpO2 88-92%. Check ABG after 30-60 min. If pH <7.25 despite optimal therapy, consider NIV (BiPAP). Criteria for NIV: respiratory acidosis (pH 7.25-7.35), tachypnoea, accessory muscle use.

Common Traps in Respiratory Questions

• Confusing asthma and COPD: COPD has fixed airflow obstruction (post-bronchodilator FEV1/FVC <0.7) with little reversibility; asthma is variable and reversible.
• Giving high-flow oxygen to COPD patients without targeting SpO2 88-92% — this can suppress hypoxic drive and cause hypercapnic respiratory arrest.
• Forgetting to calculate CURB-65 before deciding home vs. hospital for CAP — a score of 2 or more mandates admission regardless of clinical gestalt.
• Ordering a D-dimer in a high-probability PE patient (Wells >4) — this is inappropriate; go straight to CTPA to avoid false negatives.
• Missing tension pneumothorax because you waited for a chest X-ray in a haemodynamically unstable patient — decompress immediately.
• Assuming a pleural effusion in heart failure is always transudate — check Light's criteria; if exudative, investigate for infection or malignancy.

How to Revise Respiratory for the PLAB 1

Prioritise acute management algorithms: CURB-65, Wells score, and asthma step-up. Questions often present a clinical scenario with ABG, spirometry, or chest X-ray findings — practise interpreting these quickly. Focus on distinguishing CAP from exacerbation of COPD or asthma. Know the exact antibiotic choices and doses, as well as oxygen targets. Traps often involve missing key signs (e.g., tracheal deviation in tension pneumothorax) or misapplying severity scores. Revise the BTS guidelines for pleural procedures and NIV criteria. Use question banks that mimic the time pressure; aim to answer each respiratory question in under 90 seconds by memorising cut-offs and first-line drugs.

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