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Calculate ideal tidal volume based on ideal body weight (IBW)
For comparing TV/kg of actual vs ideal weight
ARDSNet Protocol (6 mL/kg IBW) - Low tidal volume for ARDS patients
Tidal volume (TV or VT) is the volume of air moved into or out of the lungs during a normal breath. In mechanical ventilation, setting the appropriate tidal volume is crucial for adequate oxygenation and ventilation while preventing ventilator-induced lung injury (VILI).
Tidal volume should be calculated based on ideal (predicted) body weight, not actual weight. Lung size correlates with height and sex, not with adipose tissue. Using actual weight in obese patients leads to overdistension and lung injury.
The landmark ARDSNet trial (2000) demonstrated that using 6 mL/kg IBW (vs. 12 mL/kg) in ARDS patients reduced mortality by 22%. This low tidal volume strategy is now standard of care for ARDS and increasingly used in all mechanically ventilated patients.
| Height (cm) | Height (ft/in) | Male IBW (kg) | Female IBW (kg) | TV @ 6mL/kg |
|---|---|---|---|---|
| 150 | 4'11" | 47.5 | 43.0 | 258-285 |
| 155 | 5'1" | 52.0 | 47.5 | 285-312 |
| 160 | 5'3" | 56.6 | 52.1 | 313-340 |
| 165 | 5'5" | 61.1 | 56.6 | 340-367 |
| 170 | 5'7" | 65.7 | 61.2 | 367-394 |
| 175 | 5'9" | 70.3 | 65.8 | 395-422 |
| 180 | 5'11" | 74.8 | 70.3 | 422-449 |
| 185 | 6'1" | 79.4 | 74.9 | 449-476 |
| 190 | 6'3" | 84.0 | 79.5 | 477-504 |
Males: IBW (kg) = 50 + 2.3 × (height in inches - 60)
Females: IBW (kg) = 45.5 + 2.3 × (height in inches - 60)
This formula estimates lean body mass based on height and is used for drug dosing and ventilator settings.
Lung size is determined by height, not weight. Using actual weight in obese patients would result in excessively high tidal volumes, leading to overdistension, volutrauma, and increased mortality. A 180 cm male who weighs 70 kg and one who weighs 120 kg have the same lung capacity.
For very short patients, the Devine formula may give unrealistically low IBW values. In practice, a minimum IBW of 35-40 kg is often used. Clinical judgment and monitoring of airway pressures should guide final settings.
The 6 mL/kg target from ARDSNet is specifically for ARDS patients. For patients with healthy lungs (e.g., during surgery), higher tidal volumes (8-10 mL/kg) may be appropriate. However, recent evidence suggests lung-protective ventilation benefits even non-ARDS patients.
Driving pressure = Plateau pressure - PEEP. It represents the pressure needed to deliver the tidal volume and correlates with survival in ARDS. A driving pressure <15 cm H₂O is associated with better outcomes.
If PaCO₂ is elevated, first try increasing respiratory rate (up to 30-35/min) while watching for auto-PEEP. If CO₂ remains high, permissive hypercapnia may be accepted (pH >7.20) rather than increasing tidal volume above lung-protective targets.
This calculator provides estimates for educational purposes. Actual ventilator settings must be individualized based on patient condition, underlying disease, airway pressures, blood gases, and clinical response. Always monitor plateau pressure (<30 cm H₂O) and driving pressure (<15 cm H₂O). Consult respiratory therapy and critical care specialists for ventilator management.