Bohr Equation
normal range: 0.25-0.35 ml
The Bohr equation quantifies physiological dead space by comparing exhaled CO₂ to arterial or alveolar CO₂ to determine the fraction of ventilation that does not participate in gas exchange.
사용 적응증
Used to quantify physiologic dead space (VD/VT) from PaCO2 and mixed‑expired CO2, mainly in ventilation–perfusion assessment. Clinically useful for evaluating impaired ventilation in ARDS, sepsis, COPD, heart failure, and during exercise testing. Helps identify ventilatory inefficiency, guide mechanical ventilation adjustments, and stratify mortality risk in ARDS (higher VD/VT correlates with higher mortality 1 [Level II evidence]).
통찰 및 주의사항
Reflects how much each breath is wasted ventilation; rises with V/Q mismatch. Insights: useful for tracking ventilatory inefficiency and disease severity. Cautions: end‑tidal CO₂ often underestimates alveolar CO₂ in lung or cardiac disease, leading to erroneous dead‑space estimates; shunt and V/Q heterogeneity distort values; Enghoff modification reflects global gas‑exchange defects, not pure dead space. Volumetric capnography provides more accurate PACO₂ than PETCO₂.