What is a normal Vd/Vt ratio?

Normal Vd/Vt is 0.20–0.35 (20–35%). Values above 0.6 are associated with significantly increased mortality in ARDS, while acute increases suggest pulmonary embolism or reduced pulmonary blood flow.

How is Vd/Vt used clinically?

Elevated Vd/Vt requires compensatory increases in minute ventilation to maintain normocapnia and can predict difficulty weaning from mechanical ventilation; serial measurements guide management.

Dead Space Fraction (Vd/Vt) — Ventilation Efficiency

Calculate the dead space fraction (Vd/Vt) using the Bohr-Enghoff equation: Vd/Vt = (PaCO2 − PETCO2) / PaCO2 to assess ventilation efficiency and pulmonary embolism risk.

Use the full interactive calculator below, or

Dead Space Fraction (Vd/Vt) — Ventilation Efficiency

Frequently Asked Questions

What is a normal Vd/Vt ratio?

How is Vd/Vt used clinically?