Lung-protective ventilation saves lives in acute respiratory distress syndrome, and its central rule is simple: set tidal volume on ideal body weight, not actual weight. This calculator sizes the tidal volume at the ARDSNet target and offers sensible initial ventilator parameters for both paediatric and adult patients, computed locally in your browser.
How it works
For adults, ideal body weight (IBW) comes from the Devine formula, then tidal volume is the mL/kg target times IBW:
IBW male = 50 + 2.3 × (height_inches − 60)
IBW female = 45.5 + 2.3 × (height_inches − 60)
tidal volume = mL/kg × IBW (target 6, range 4–8)For children, ideal body weight is not derived from height the same way, so the tool takes the measured or estimated ideal weight you enter and multiplies it by the mL/kg target directly.
Why lung size correlates with height, not weight
The physiological basis for using IBW rather than actual weight is that lung size scales with frame size, which is better predicted by height. A patient who weighs 120 kg because of obesity does not have lungs twice the size of a patient who weighs 60 kg — their lungs are sized for a person of their height. If tidal volume is set on actual weight for an obese patient, the lungs are over-distended with each breath, causing ventilator-induced lung injury (VILI), the mechanism that the ARDSNet protocol was specifically designed to prevent.
Illustrative worked examples
Adult male, 175 cm (5 ft 9 in):
- Height in inches = 68.9 in
- IBW = 50 + 2.3 × (68.9 − 60) = 50 + 20.5 = 70.5 kg
- Target TV at 6 mL/kg = 70.5 × 6 = 423 mL
- Protective range (4–8 mL/kg) = 282–564 mL
Adult female, 160 cm (5 ft 3 in):
- Height in inches = 63.0 in
- IBW = 45.5 + 2.3 × (63.0 − 60) = 45.5 + 6.9 = 52.4 kg
- Target TV at 6 mL/kg = 52.4 × 6 = 314 mL
- Protective range = 210–419 mL
Paediatric patient, 20 kg ideal weight:
- Target TV at 6 mL/kg = 20 × 6 = 120 mL
- Protective range (4–8 mL/kg) = 80–160 mL
The plateau pressure check
Tidal volume alone is not sufficient to protect the lungs — plateau pressure (Pplat) must be monitored alongside it. The ARDSNet protocol targets Pplat below 30 cmH₂O. If your initial tidal volume results in Pplat above this threshold, reduce the tidal volume in 1 mL/kg steps toward 4 mL/kg until Pplat is controlled, accepting a lower pH if necessary (permissive hypercapnia). Never accept high plateau pressure to maintain a “target” tidal volume.
Initial ventilator settings: context
The calculator provides a tidal volume target and a suggested initial respiratory rate range. These are starting points, not a complete ventilator prescription. After setting initial parameters:
- Obtain an arterial blood gas within 30–60 minutes.
- Titrate rate to achieve target pH (goal typically 7.30–7.45 in ARDS management).
- Check plateau pressure with an inspiratory hold and adjust tidal volume if Pplat exceeds 30 cmH₂O.
- Titrate FiO₂ and PEEP to oxygenation targets per your unit’s protocol.
- Reassess every 4–6 hours and following any clinical change.
This is an educational tool. Ventilator management requires qualified clinical assessment and must not be based on a calculator alone.