Dead Space Fraction (VD/VT, Bohr & Enghoff)

Dead Space Fraction (VD/VT, Bohr & Enghoff) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

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.
3The calculator applies Bohr: (PACO₂ − PĒCO₂) / PACO₂, and Enghoff: (PaCO₂ − PĒCO₂) / PaCO₂.
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.

{"peco2":18,"paco2":48,"paco2Alveolar":35,"decimalPlaces":2}

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Normal adult dead space estimate

2. ARDS assessment with separate end-tidal PACO₂

FAQ

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