However, in patients with ARDS, the relationship among IBW, lung volume, and height is almost lost compared with subjects with healthy lungs.4,5 Figure 1 shows such a relationship in 41 normal subjects and 66 patients with ARDS. IBW was computed according to the following formulas1: 50 +0.91 × (centimeters of height −152.4) for men and 45.5 + 0.91 × (centimeters of height −152.4) for women. Accordingly, the relationship found in subjects with healthy lungs was gas volume = −3,128 +114 × IBW (R2 =0.54, P < .0001), whereas in patients with ARDS, gas volume =253 +38 × IBW (R2 =0.16, P = .0008). The mean gas volume in subjects with healthy lungs was 3,977.6 ±1,387 mL and in patients with ARDS, 2,646.1 ±924.86 mL. As shown, IBW hardly can be considered an acceptable surrogate for the lung volume in patients with ARDS. Therefore, the same Vt/IBW may lead to a completely different strain, depending on the “baby lung”6,7 volume (ie, the ventilatable lung volume still open to ventilation).8 For example, if, in a 70-kg patient with ARDS, the baby lung is 300 mL, 6 mL/kg Vt/IBW would induce a strain of 420/300 or 1.4; whereas, if the baby lung is 800 mL, the induced strain would be 420/800 or 0.52. Establishing that the same Vt/IBW in the individual patient may lead to an extremely variable degree of strain, we must ask ourselves whether there is a strain threshold that may induce lung injury or whether the lung injury is proportional to the strain applied in a sort of continuum. If so, in practice, how should the ventilation be set in ARDS?