Calculator Inputs
Use the form below to estimate adult tidal volume from predicted body weight and ventilation targets.
Example Data Table
| Case | Sex | Height | PBW | Target | Estimated VT | Rate | Minute Ventilation |
|---|---|---|---|---|---|---|---|
| Adult A | Male | 178 cm | 73.3 kg | 6.0 mL/kg | 440 mL | 14 | 6.16 L/min |
| Adult B | Female | 162 cm | 54.2 kg | 5.5 mL/kg | 298 mL | 18 | 5.36 L/min |
| Adult C | Male | 170 cm | 66.0 kg | 7.0 mL/kg | 462 mL | 12 | 5.54 L/min |
Formula Used
Predicted Body Weight for males: PBW = 50 + 0.91 × (height in cm − 152.4)
Predicted Body Weight for females: PBW = 45.5 + 0.91 × (height in cm − 152.4)
Tidal Volume: VT = PBW × selected mL/kg target
Minute Ventilation: VE = VT × respiratory rate ÷ 1000
Estimated Dead Space: VD = PBW × dead space factor
Alveolar Ventilation: VA = (VT − VD) × respiratory rate ÷ 1000
Cycle Time: 60 ÷ respiratory rate
Expiratory Time: cycle time − inspiratory time
I:E Ratio: inspiratory time : expiratory time
How to Use This Calculator
- Choose sex because the predicted body weight equation changes.
- Enter height and select centimeters or inches.
- Set the target tidal volume in mL/kg PBW.
- Enter respiratory rate, inspiratory time, and dead space factor.
- Add actual weight if you want a comparison with PBW.
- Press the calculate button to show results above the form.
- Review the estimate, range, minute ventilation, and interpretation notes.
- Use the CSV or PDF buttons to save the result summary.
FAQs
1. What is tidal volume?
Tidal volume is the amount of air delivered with each breath. In ventilated adults, clinicians often estimate a starting value from predicted body weight instead of actual weight.
2. Why does the calculator use predicted body weight?
Predicted body weight is based on height and sex. It better reflects lung size than actual body weight, especially when body mass is very high or very low.
3. What is a common protective target?
Many adult ventilation strategies begin around 4 to 6 mL/kg predicted body weight. Exact targets depend on lung mechanics, gas exchange, diagnosis, and local protocol.
4. What does minute ventilation show?
Minute ventilation estimates total air moved each minute. It combines tidal volume and respiratory rate, helping you compare how changes in settings affect overall ventilation.
5. What does alveolar ventilation mean?
Alveolar ventilation estimates the portion of ventilation reaching gas exchange areas after subtracting dead space. It is useful for understanding effective ventilation, not just total delivered volume.
6. Can I use this for children?
No. This version is designed for adult estimation. Pediatric ventilation requires age-specific assessment, smaller ranges, and different clinical considerations.
7. Why is the I:E ratio marked not feasible?
That happens when inspiratory time is too long for the chosen respiratory rate. There is no remaining expiratory time, so the combination should be reviewed.
8. Is this calculator medical advice?
No. This calculator is for education and estimation only. Final ventilator settings should always follow clinician judgment, patient response, and institutional guidance.