IM28.11-14 | Obstructive Airway Disease Functional and Imaging Tests — Summary & Reflection

KEY TAKEAWAYS

Investigations in obstructive airway disease confirm diagnosis, grade severity, identify complications, and guide management.

Spirometry is the gold standard: FEV1/FVC < 0.70 post-bronchodilator = COPD (GOLD 1–4 by FEV1 % predicted); ≥12% AND ≥200 mL FEV1 rise post-BD = significant reversibility (asthma). Flow-volume loop: scooped expiratory limb = obstruction; narrow loop = restriction.

PEFR: three attempts, highest recorded; compare to personal best. Asthma severity: <33% = life-threatening; 33–50% = severe; 50–75% = moderate; ≥75% = mild. Diurnal variability >20% on most days = confirms variable airflow limitation.

ABG (indications: SpO₂ <92%, known CO₂ retainer, severe/life-threatening exacerbation): PaCO₂ low + pH high = resp. alkalosis (hyperventilation); PaCO₂ high + pH low = resp. acidosis (type-2 RF); HCO₃⁻ elevated = chronic compensation (chronic CO₂ retainer → target SpO₂ 88–92%). Normal PaCO₂ in breathless asthmatic = near-fatal sign.

CXR: hyperinflation (flat diaphragms, horizontal ribs) + oligaemia = COPD/emphysema; consolidation (air bronchogram) = pneumonia; pleural line = pneumothorax; blunted angle = effusion; upper lobe nodule in smoker = cancer until proven otherwise. CXR in uncomplicated asthma = normal.

REFLECT

Return to the opening vignette: the 48-year-old smoker with a normal examination and GOLD 2 COPD on spirometry. Without spirometry, this patient would have left the clinic without a diagnosis, without smoking cessation counselling, without a GOLD-guided treatment plan, and without a prognosis. Reflect on this: at what point in the natural history of COPD is the disease still modifiable? What is the single investigation that, performed in a primary care clinic on every symptomatic smoker over 40, would have the largest population-level impact on COPD mortality? And how does the answer inform your commitment to performing spirometry routinely — not just when patients are severely breathless?