Dead space fraction, VD/VT ratio, and bedside Bohr-style workflow
Dead Space Calculator (VD/VT)
Calculate physiologic dead space and the VD/VT ratio using PaCO₂, ETCO₂, and tidal volume. This helps assess ventilation efficiency, understand why CO₂ clearance may be impaired, and connect bedside capnography to ABG physiology.
Use this alongside our Minute & Alveolar Ventilation calculator, Desired VE tool, ABG Analyzer, and our Mastering ABG Analysis guide to interpret ventilation inefficiency in a broader acid-base and gas-exchange context.
Calculator inputs
What this calculator helps you understand
Dead space fraction
The VD/VT ratio estimates how much of each breath is not participating in gas exchange.
CO₂ clearance efficiency
Higher dead space means more wasted ventilation and can help explain why a patient may retain CO₂ despite seemingly adequate ventilation.
Results
Why dead space matters
Dead space is the portion of each breath that does not participate in gas exchange. When dead space rises, a larger percentage of ventilation becomes wasted ventilation, which means the patient may need more total ventilation to clear the same amount of CO₂.
This is one reason dead space helps explain why two patients can have similar minute ventilation but very different PaCO₂ values.
How this fits into the PulmTools ventilation cluster
- • Use this page to estimate wasted ventilation
- • Use Minute & Alveolar Ventilation to understand effective ventilation more broadly
- • Use Desired VE when targeting a new PaCO₂
- • Use ABG Analyzer to interpret CO₂ and acid-base effects in context
- • Review Mastering ABG Analysis to connect the physiology to bedside decision-making