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.
Shaikh et al. (Mon,) studied this question.