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IBW for Ventilation Calculator

Enter sex and height to get the predicted body weight and tidal volume targets.

How it is calculated

The tool computes predicted body weight (PBW) from height in centimetres: PBW = 50 + 0.91 × (height − 152.4) kg for males and PBW = 45.5 + 0.91 × (height − 152.4) kg for females. Here 152.4 cm is 60 inches, and 0.91 kg per cm is the metric form of the usual 2.3 kg per inch. The tidal volume targets are then PBW × 6 and PBW × 8 mL, rounded to whole millilitres. Actual body weight is not used at all, only height and sex. Heights of zero or below, or so short that PBW falls to zero or less, give no result. This is a calculation aid for teaching and checking, not a substitute for the clinician's order.

Worked example

A male patient is 175 cm tall. Height above 152.4 cm: 175 − 152.4 = 22.6 cm. PBW = 50 + 0.91 × 22.6 = 50 + 20.57 = 70.57 kg. Low target: 70.57 × 6 = 423 mL. High target: 70.57 × 8 = 565 mL. So the 6 to 8 mL/kg range is about 423 to 565 mL, whatever the patient's actual weight.

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Common mistakes

  • Entering height in metres or inches. The field is in centimetres, so 1.75 or 69 gives no result or a wrong weight; type 175.
  • Using the patient's actual weight with 6 to 8 mL/kg. The targets are based on predicted weight from height, which is the whole point of the formula in obese or oedematous patients.
  • Picking the wrong sex. The female baseline is 4.5 kg lower, which lowers the volume range by roughly 27 to 36 mL at the same height.
  • Reading the 8 mL/kg value as a goal. The two figures are the ends of a range; the volume actually set depends on the clinical picture and local protocol.

Sources

About this calculator

The ARDSnet formula calculates predicted (ideal) body weight from height and sex — Male: 50 + 2.3 × (height in inches − 60) kg; Female: 45.5 + 2.3 × (height in inches − 60) kg, applied here in the equivalent metric form 50 (or 45.5) + 0.91 × (height in cm − 152.4) — because lung size correlates with height, not actual weight, which is unreliable in edematous or obese patients. Multiplying that predicted weight by 6–8 mL/kg gives the lung-protective tidal volume range established by the landmark ARDSnet trial.

Intensivists and respiratory therapists set mechanical ventilator tidal volumes from this calculation for every ventilated patient, since ventilating to actual body weight in an overweight or fluid-overloaded patient can badly overinflate the lungs and cause ventilator-induced lung injury — a low tidal volume strategy has been shown to reduce mortality in ARDS.

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