Alveolar Ventilation Calculator
Calculate alveolar ventilation using respiratory rate, tidal volume, and dead space. Alveolar ventilation is the portion of ventilation that reaches gas-exchanging alveoli and is more directly related to PaCO₂ than total minute ventilation.
Calculate Alveolar Ventilation
Formula: VA = RR × (VT − VD). Enter VT and dead space in mL or L; the calculator reports VA in L/min.
Alveolar Ventilation Formula
Example: RR 12, VT 500 mL, VD 150 mL
VA = 12 × (500 − 150)
VA = 4200 mL/min = 4.2 L/min
Dead Space Comes Out Before You Multiply
Alveolar ventilation only counts the part of each breath that reaches gas-exchanging alveoli.
Subtract dead space from tidal volume first, then multiply by respiratory rate.
Why Alveolar Ventilation Matters
| Pattern | Meaning | Clinical Connection |
|---|---|---|
| Low VA | Less effective ventilation reaches alveoli | PaCO₂ may rise if CO₂ production is unchanged. |
| Normal/high VE but low VA | Dead space may be high | Total ventilation can look adequate while CO₂ clearance is poor. |
| High VA | More effective alveolar ventilation | PaCO₂ may fall if CO₂ production is unchanged. |
PaCO₂ Follows Alveolar Ventilation
PaCO₂ is inversely related to alveolar ventilation. If alveolar ventilation decreases, PaCO₂ tends to rise. If alveolar ventilation increases, PaCO₂ tends to fall, assuming CO₂ production remains stable.
CO₂ retention risk.
More ventilation is wasted and does not exchange gas.
Can reduce VA because more of each breath is dead space.
Look at ABGs, RR, VT, dead space, work of breathing, and disease process together.
Avoid These Errors
Minute ventilation includes dead space. Alveolar ventilation subtracts it.
Use RR × (VT − VD), not RR × VT − VD.
mL/min must be divided by 1000 to report L/min.
PE, emphysema, low perfusion, and high airway pressures can increase dead space.
Compare Minute Ventilation and Alveolar Ventilation
Minute ventilation shows total ventilation, but alveolar ventilation explains effective gas exchange and CO₂ clearance more directly.