Differentiating Lung From Chest Wall Mechanics Is Difficult Without Esophageal Manometry in Children With Acute Respiratory Distress Syndrome.

Objectives: Pediatric acute respiratory distress syndrome (PARDS) guidelines recommend limiting airway plateau pressure (Pplat) to 28 cm H2O, allowing for higher limits when chest wall compliance (CCW) is poor since less of the pressure is transmitted to lung (transpulmonary pressure). Transpulmonary pressure depends on Pplat and the ratio of lung elastance to respiratory system elastance (EL/ERS). EL/ERS measurement requires esophageal manometry, although it is not routinely available. We sought to determine if routinely available clinical data could reliably predict EL/ERS or changes in EL/ERS, to understand when Pplat greater than 28 cm H2O could be acceptable.

Design: Secondary analysis of randomized controlled trial with esophageal manometry monitoring.

Setting: Quaternary PICU.

Patients: Mechanically ventilated children with PARDS.

Interventions: None.

Measurements and main results: Two hundred seven patients and 750 patient days were included. Using the first day per patient, median EL/ERS was 0.83 (interquartile range, 0.72-0.87), with a weak negative correlation with respiratory system compliance (CRS) (r = -0.26; p < 0.001). CRS was strongly correlated with lung compliance (Cl) (r = 0.94; p < 0.001) and moderately correlated with CCW (r = 0.53; p < 0.001). Multivariable analysis identified that higher CRS, younger age and peripheral neuromuscular disease were associated with higher CCW, while higher CRS was the only variable independently associated with higher Cl (all p < 0.01). When trying to predict high (> 0.9) or low (< 0.7) EL/ERS, CRS was the only variable retaining an independent association: lower CRS (CRS × 10 [mL/cm H2O/kg × 1/10]) with high EL/ERS (odds ratio [OR], 0.70; 95% CI, 0.54-0.86; p = 0.002; area under the receiver operating characteristic curve [AUC], 0.73) and higher CRS (CRS × 10 [mL/cm H2O/kg × 1/10]) with low EL/ERS (OR, 1.14; 95% CI, 1.02-1.28; p = 0.017; AUC, 0.60). Change in EL/ERS from day to day was not predictable.

Conclusions: In PARDS, CRS is more strongly tied to Cl than CCW. While EL/ERS is not easily predictable from clinical variables, when CRS is low, EL/ERS is generally high. Therefore, increasing Pplat above the suggested thresholds when CRS is impaired may be inappropriate without measuring esophageal pressure.