Enghoff Equation
normal: <20%
The Enghoff equation estimates total physiologic dead space using the arterial–expired CO₂ difference to reflect both ventilation–perfusion mismatch and true dead space.
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사용 적응증
Assesses physiologic dead space (VD/VT) when alveolar–arterial gas exchange is impaired, chiefly to quantify V/Q mismatch and shunt in ARDS, COPD, hypoxemic respiratory failure, and mechanically ventilated patients. Provides a global estimate of gas exchange inefficiency because PaCO₂ replaces PACO₂, capturing both dead space and venous admixture—useful for severity assessment and ventilatory titration (e.g., in ARDS) 1 [Level II evidence].
통찰 및 주의사항
Overestimates dead space because it replaces alveolar PCO₂ with arterial PCO₂, making it sensitive to all V/Q mismatch rather than true dead space 1. Useful for detecting global gas‑exchange impairment, but nonspecific, inflated by shunt and diffusion defects (V/Q inequality is the dominant cause of AaDO₂ widening 2). Avoid overinterpreting as pure dead‑space physiology; changes may not reflect true ventilation efficiency.