Prediction of static compliance of the respiratory system based on anthropometric measurements in patients on mechanical ventilation: a cross-sectional pragmatic study

Introduction

Standard values for static compliance of the respiratory system (Crs) ranging from 50 to 70 ml/cmH₂O lack population-specific data and may be influenced by anthropometry.

Objective

Describe Crs in ICU patients, evaluate its relationship with predicted body weight (PBW), and develop a predictive model for individualized Crs reference values based on anthropometric variables.

Methods

A multicenter cross-sectional study was conducted across Brazil, involving mechanically ventilated patients. Individuals with hemodynamic instability, chest wall deformities, or intrathoracic limitations were excluded. Data collected included PBW, plateau pressure, Crs, and Driving Pressure (DP). Patients were categorized into high Crs (≥0.60 ml/cmH₂O/kg) and low Crs (<0.60 ml/cmH₂O/kg).

Results

The study included 147 patients with mean values of Crs (38.0 ± 11.2 ml/cmH₂O), DP (10.0[8.0–11.2] cmH2O), and Crs/PBW (0.62 ± 0.1 ml/cmH₂O/kg). Between high and low Crs groups has observed statistically differences in Crs and DP values. Additionally, Crs also showed correlation with the variables age, height, PBW, Ppeak, and Pplat. Thus, it can be understood that height directly influences Crs, especially in patients with high Crs lungs. A multiple linear regression model using height, age, and sex as predictors was fitted to estimate Crs in patients with high Crs lungs, yielding an R² of 0.567 with p < 0,01.

Conclusion

Our study indicated that Crs in mechanically ventilated patients with near-normal elastance is associated with anthropometric data, particularly height and sex. A Crs/PBW cutoff of 0.6 ml/cmH2O/kg was established. The study also presents a preliminary model for Crs prediction.