Respiratory Medicine
Airflow obstruction
Spirometry defines disease: asthma shows reversibility (FEV1 rise >12% and >200 mL), while COPD shows a post-bronchodilator FEV1/FVC below 0.70. Recognise life-threatening asthma: silent chest, exhaustion, cyanosis, PEF under 33%, normal or rising PaCO2 in a breathless patient. Treat with oxygen targeted at 94–98%, nebulised salbutamol and ipratropium, systemic steroids, and intravenous magnesium in severe cases. High-dose beta-agonists cause hypokalaemia and lactic acidosis.
Gas exchange
Type 1 failure is PaO2 below 8 kPa with normal or low PaCO2; type 2 adds PaCO2 above 6 kPa. In COPD with a risk of hypercapnia, target SpO2 88–92% with controlled oxygen and recheck gases; use non-invasive ventilation for persistent hypercapnic acidosis (pH <7.35). An apparently normal PaCO2 in an acutely breathless patient is abnormal.
Infection, effusion and embolism
CURB-65 stratifies pneumonia. Use Light's criteria to separate exudative from transudative effusions. For suspected pulmonary embolism, apply Wells or PERC and request CTPA (V/Q if contrast is contraindicated). Tuberculosis typically cavitates at the apices; isolate and use IGRA plus culture.
Traps: calling every wheeze asthma (consider cardiac failure, PE, anaphylaxis, foreign body); expecting clubbing in COPD, which does not cause it - think lung cancer, bronchiectasis, empyema, fibrosis.
Worked example: pleural fluid protein 38 g/L with serum protein 65 g/L gives a ratio of 0.58, above 0.5, so the effusion is an exudate; combined with a low glucose and low pH, think infection or malignancy rather than heart failure.