Physiologic dead space - definition and determinants
Core concept
- Dead space = ventilated but not perfused (or under-perfused) -> wasted ventilation
- Physiological dead space = anatomical + alveolar dead space
- Anatomical: conducting airways (mouth to terminal bronchioles), ~150 mL/2 mL per kg
- Alveolar: ventilated alveoli with absent/reduced perfusion (V/Q mismatch)
- Bohr equation: Vd/Vt = (PaCO2 - PECO2) / PaCO2
- PECO2 = mixed expired CO2; relies on PaCO2 as surrogate for ideal alveolar PCO2
3 more sections, plus exam facts
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