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A 68-year-old man, a heavy smoker (50 pack-years), presents to the emergency department with a 3-day history of worsening dyspnoea, increased yellow-green sputum volume, and wheeze. He has known COPD (baseline post-bronchodilator FEV1 45 percent predicted). On examination he is cyanosed, using accessory muscles, respiratory rate 28/min, SpO2 86 percent on air, and produces purulent sputum. Arterial blood gas on air: pH 7.31, PaCO2 68 mmHg (9.1 kPa), PaO2 52 mmHg (6.9 kPa), bicarbonate 32 mmol/L.
Questions
a) What is the most likely diagnosis and the underlying pathophysiological disturbance on the blood gas? (2 marks)
Acute exacerbation of COPD complicated by acute-on-chronic type-2 (hypercapnic) respiratory failure — a partially compensated acute respiratory acidosis (low pH with raised PaCO2 and raised bicarbonate showing chronic renal compensation).
b) List three immediate first-line management steps. (3 marks)
- Controlled oxygen via nasal cannulae 1 to 2 L/min or Venturi 24 to 28 percent, target SpO2 88 to 92 percent — to correct hypoxaemia without precipitating CO2 narcosis (V/Q redistribution and Haldane effect).
- Nebulised bronchodilators (driven with air) — salbutamol 5 mg + ipratropium 500 mcg every 4 to 6 hours.
- Systemic corticosteroid — prednisolone 40 mg orally once daily for 5 days (REDUCE trial).
c) When and how would you start non-invasive ventilation? (2 marks)
Start NIV (BiPAP) within 60 minutes because the pH is below 7.35 with PaCO2 at least 45 mmHg, i.e. acute hypercapnic respiratory failure despite standard therapy. Settings: IPAP 10 to 15 cmH2O, EPAP 4 to 5 cmH2O, FiO2 titrated to SpO2 88 to 92 percent, with a full-face mask; repeat ABG at 1 hour looking for a rising pH and falling PaCO2.
d) Would you give antibiotics, and which? Give one indication and a first-line agent with dose. (2 marks)
Yes — he meets Anthonisen Type 1 criteria (all three: increased dyspnoea, increased sputum volume, increased sputum purulence), which carries the strongest evidence for antibiotic benefit. First-line oral amoxicillin-clavulanate 500/125 mg three times daily for 5 to 7 days; alternatives doxycycline 100 mg twice daily or azithromycin 500 mg once daily.
e) Name one complication of this admission and one measure that improves long-term survival. (1 mark)
Complication: CO2 narcosis from over-oxygenation (or pneumothorax, pneumonia, cor pulmonale). Long-term survival: smoking cessation or long-term oxygen therapy (at least 15 h/day) for chronic hypoxaemia (NOTT/MRC trials).