V/Q Mismatch — When Breathing Doesn’t Equal Oxygenation You’ve heard it before: Ventilation (V) and Perfusion (Q) have to match. When they don’t? That’s a V/Q mismatch — and that’s where things fall apart. • Shunt = Perfusion without ventilation Lungs are full of fluid? Collapsed? Air can’t get in. Blood flows anyway. (e.g. pneumonia, pulmonary oedema) • Dead Space = Ventilation without perfusion Air’s getting in — but blood isn’t. Blocked vessels, low flow. (e.g. PE, hypovolaemia) The result? H