Dead Space Fraction (VD/VT, Bohr & Enghoff) | Online Free Tool | Elysia Tools
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Dead Space Fraction (VD/VT, Bohr & Enghoff)
Calculate VD/VT using both the Bohr equation (PACO₂-based) and the Enghoff modification (PaCO₂-based). Normal ~0.20–0.40; >0.60 signals severe dead space in ARDS/PE. Derived from Bohr 1891, Enghoff 1938, Tusman 2012, LITFL, StatPearls. Not medical advice.
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Key facts
Category
Health
Input types
number
Output type
json
Sample coverage
4
API ready
Yes
Overview
Calculate the dead space fraction (VD/VT) with both the Bohr equation and the Enghoff modification. Enter mixed expired CO₂ and arterial PaCO₂, and optionally provide alveolar or end-tidal PACO₂ for the Bohr calculation. The result includes fractions, percentages, and a reference category; it is not medical advice.
When to use
Estimate physiological dead space from mixed expired CO₂ and arterial blood gas values.
Compare Bohr and Enghoff VD/VT when alveolar or end-tidal PACO₂ is available.
Review dead space values in critical care, anesthesiology, ARDS, or pulmonary embolism assessment.
How it works
1Enter mixed expired CO₂ (PĒCO₂) and arterial PaCO₂ in mmHg.
2Optionally enter alveolar or end-tidal PACO₂ for the Bohr calculation; if omitted, PaCO₂ is used as an approximation.
4The JSON result reports both fractions and percentages, along with a reference category and the selected decimal precision.
Use cases
Critical care teams can compare Enghoff and Bohr estimates when evaluating impaired gas exchange.
Anesthesiology workflows can use end-tidal PACO₂ with mixed expired CO₂ to estimate Bohr dead space.
Clinical education and research can demonstrate how different CO₂ measurements change VD/VT results.
Examples
1. Normal adult dead space estimate
Respiratory therapist
Background
A respiratory therapist reviews mixed expired CO₂ and arterial blood gas values from an adult patient.
Problem
Calculate VD/VT and check whether the result falls within the commonly referenced normal adult range.
How to use
Enter PĒCO₂ as 28 mmHg, PaCO₂ as 40 mmHg, leave PACO₂ blank, and set decimal places to 2.
{"peco2":28,"paco2":40,"decimalPlaces":2}
Outcome
Both Bohr and Enghoff are calculated as 0.30, or 30%, and the result is categorized as normal dead space fraction.
2. ARDS assessment with separate end-tidal PACO₂
Critical care clinician
Background
A critical care clinician has mixed expired CO₂, arterial PaCO₂, and an end-tidal PACO₂ value that differ from one another.
Problem
Compare the Bohr estimate using end-tidal PACO₂ with the Enghoff estimate using arterial PaCO₂.
How to use
Enter PĒCO₂ as 18 mmHg, PaCO₂ as 48 mmHg, PACO₂ as 35 mmHg, and set decimal places to 2.
FAQ
What does VD/VT measure?
VD/VT is the fraction of each breath that does not participate effectively in CO₂ exchange, expressed as a ratio or percentage.
What is the difference between Bohr and Enghoff?
Bohr uses alveolar PACO₂, while Enghoff uses arterial PaCO₂ and may also reflect shunt and ventilation-perfusion mismatch.
What happens if PACO₂ is not entered?
The calculator uses arterial PaCO₂ as an approximation for PACO₂ in the Bohr calculation.
What is a typical adult VD/VT range?
A commonly referenced normal adult range is approximately 0.20–0.40, or 20–40%.
What does a value above 0.60 indicate?
A value above 0.60 is considered severely elevated and may be associated with severe dead space, including in ARDS or pulmonary embolism. Interpret it clinically.