Question
How can identical tidal volumes lead to different outcomes in ARDS patients with the same predicted body weight?
Answer
Even when ARDS patients share the same predicted body weight and receive identical tidal volumes, the impact of ventilation can vary significantly due to differences in functional lung volume. In some patients, much of the lung may be consolidated or collapsed, leaving only a small portion—the so-called “baby lung”—available for ventilation. Delivering standard tidal volumes in these cases results in higher stress and strain per unit of lung tissue, increasing the risk of ventilator-induced lung injury.
This heterogeneity emphasizes the need for individualized ventilator strategies. Clinicians must go beyond predictive formulas and assess each patient’s functional lung capacity through imaging, compliance trends, and clinical response. Recognizing that not all lungs of the same size behave the same way is essential to avoid overdistension, minimize injury, and improve outcomes in patients with severe respiratory failure.
This Ask the Expert is an edited excerpt from the course, Mechanical Power at a Glance, presented by Keith Lamb, RRT, RRT-ACCS, FAARC, FCCM.
