Estimation of Transpulmonary Driving Pressure, Strain, and Lung-Specific Elastance Using Volumetric Methods in Invasively Ventilated Children—A Feasibility Study

OBJECTIVES: To study the feasibility of integrating the nitrogen multiple breath wash-in/washout (NMBW) technique with the positive end-expiratory pressure-step (PEEP-step) method to estimate transpulmonary driving pressure (DP TP ), strain, and lung-specific elastance ( k ). DESIGN: Prospective feasibility physiology study. SETTING: National board-affiliated 30-bed quaternary care hospital PICU. PATIENTS: Invasively ventilated children from 2 months to 16 years old between December 1, 2021, and August 30, 2022. INTERVENTIONS: In volume-control mode, functional residual capacity (FRC) was measured using the NMBW technique at zero end-expiratory pressure (ZEEP), and end-expiratory lung volume was measured during the PEEP-step method. MEASUREMENTS AND RESULTS: Data from 33 of 63 eligible subjects were analyzed, of whom 18 of 33 had pediatric acute respiratory distress syndrome (PARDS). Median (interquartile range [IQR]) FRC normalized to body weight was 15.1 mL/kg (IQR, 10.6-20.4 mL/kg). A correlation was found between FRC and respiratory compliance at ZEEP (rho = 0.775; p < 0.001). Strain demonstrated a positive correlation with both the DP TP (rho = 0.55; p < 0.001) and plateau pressure (rho = 0.72; p < 0.001) at ZEEP. Median k was lower in PARDS than non-PARDS subjects (16.1 cm H 2 O [IQR, 10.8-18.6 cm H 2 O] vs. 19.84 cm H 2 O [IQR, 18.50-23.93 cm H 2 O]; p = 0.045), but this difference was not present when k was normalized to body weight and height. CONCLUSIONS: Despite technical limitations, it appears possible to estimate DP TP , strain, and k by integrating the PEEP-step and NMBW methods. Validation against the gold standard esophageal pressure manometry is warranted.