Physiologic VD/VT Calculator

Calculates physiologic deadspace-to-tidal-volume ratio from arterial and mixed expired carbon dioxide.

Inputs

Color mode links each input to the matching equation term and solving arithmetic.

Equation and Work

Equation:
Solving steps:
VD/VT
—
ratio
VD/VT
—
percent
Reference status
—
Normal/reference: 20–40% in spontaneously breathing patients; 40–60% in intubated patients receiving mechanical ventilation.

Clinical Significance

Physiologic deadspace-to-tidal-volume ratio from arterial and mixed expired carbon dioxide.

This calculator expands that idea by identifying the relevant measured values, substituting the selected inputs, and carrying the arithmetic through in the solving steps.

Reflects the portion of tidal volume not participating in gas exchange; higher values suggest wasted ventilation or ventilation in excess of perfusion.

Requires a correctly collected mixed expired gas sample at the same time as the arterial sample.

References (APA 7th Edition)

  1. Chang, D. W. (2020). Respiratory Care Calculations (Revised 4th ed.). Jones & Bartlett Learning. Formula content adapted from the uploaded text/reference packet.