Free · Pulmonary calculators 💨

Bohr Dead Space from Mixed Expired Carbon Dioxide

Use mixed expired carbon dioxide, not end-tidal carbon dioxide, in the expired control.

  • Formula & worked example
  • Private in your browser
  • No signup
Go to tool

Calculator inputs

Loading calculator…

How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Health results are educational estimates, not a diagnosis or treatment recommendation. A qualified clinician can interpret measurements in the context of your health.

Formula and method

Alveolar CO₂ 40 mmHg, mixed expired CO₂ 28 mmHg and tidal volume 500 mL give dead space 150 mL.

Dead-space volume = tidal volume × (alveolar CO₂ − mixed expired CO₂) / alveolar CO₂.

Worked example

Enter these known values and leave the other values blank.

Alveolar CO₂ pressure
40 mmHg
Mixed expired CO₂ pressure
28 mmHg
Tidal volume
500 mL
Bohr dead-space volume
150 mL

Assumptions and limitations

  • Use mixed expired carbon dioxide, not end-tidal carbon dioxide, in the expired control. Both pressures require matching units. Replacing alveolar with arterial CO₂ gives the Enghoff modification, whose physiological interpretation differs.
  • Arithmetic inverses use independent observations. Clear the unknown control before entering the remaining measurements.
  • This measurement calculation does not determine a diagnosis or treatment.

Common questions

How is this result calculated?

Dead-space volume = tidal volume × (alveolar CO₂ − mixed expired CO₂) / alveolar CO₂.

Which measurements and units should I use?

Use mixed expired carbon dioxide, not end-tidal carbon dioxide, in the expired control. Both pressures require matching units. Replacing alveolar with arterial CO₂ gives the Enghoff modification, whose physiological interpretation differs.

References

Bookify adds independently reviewed bounds for dead-space: alveolar_CO2_concentration > 0; expiratory_CO2_concentration >= 0; expiratory_CO2_concentration <= alveolar_CO2_concentration; tidal_volume > 0; physiological_deadspace >= 0; physiological_deadspace <= tidal_volume. The Bohr mass-balance endpoints of zero and full dead space are retained.

Explore pulmonary calculators 💨 or browse all health calculators.