Question
Why is the concept of the “baby lung” important when setting tidal volumes in ARDS patients?
Answer
The “baby lung” concept refers to the functional portion of aerated lung tissue in ARDS patients, which is often significantly reduced due to consolidation, collapse, or inflammation. Although clinical guidelines commonly recommend tidal volumes based on predicted body weight (e.g., 6 mL/kg), this approach assumes a normal lung volume, which may not apply in patients with ARDS. In reality, patients with similar body size may have vastly different volumes of functional lung tissue available for ventilation.
Delivering the same absolute tidal volume to two patients of the same height can result in very different mechanical stress profiles. A patient with a smaller "baby lung" will experience greater stress and strain per alveolus compared to a patient with a larger aerated lung volume. This increases the risk of ventilator-induced lung injury (VILI), making it critical to assess actual lung function, not just body size, when determining ventilator settings.
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.
