Bench investigation of the accuracy of the dynamic approach in respiratory mechanics during noninvasive ventilation with different pressure support levels

Abstract

Background: Under the dynamic conditions of non-invasive mechanical ventilation, respiratory system mechanics parameters, including compliance (Crs) and airway resistance (Rrs), are affected by systemic and ventilator parameters. We evaluated the accuracy of respiratory mechanics in the dynamic approach in different lung disease models during pressure support ventilation (PSV).Methods: A Respironics V60 ventilator was connected to an active lung simulator for modeling four profiles of respiratory mechanics: normal, restrictive, obstructive and mixed obstructive/restrictive. PSV and positive end-expiration pressure (PEEP) were 2-25 cmH2O and 5 cmH2O, respectively. Measurements were performed with an air leak of 25-28 L/min. Ventilator performance and patient-ventilator asynchrony were evaluated by measuring flow, airway pressure, and volume. Crs and inspiratory/expiratory resistance (Rinsp/Rexp) were calculated by dynamic approach. Results: Crs was overestimated with pressure support (PS) at 5 cmH2O. Peak inspiratory/expiratory flow (PIF/PEF) and tidal volume (VT) was increased with PS level, while calculated Crs was decreased. At PS 10-15 cmH2O, the difference between calculated and preset Crs was ≤20% in higher resistance models (obstructive and mixed). In normal resistance conditions (restrictive and normal), the calculated Crs was always larger than the preset value significantly regardless of PS. Underestimations of Rinsp and Rexp were observed at PS 5-10 cmH2O. The calculation error might be controlled within 10% when PS above 15 cmH2O in higher resistance models. Conclusion: Higher gas flow is beneficial for Rrs estimation by using dynamic approach, whereas the calculation of Crs is always overestimated in normal resistance conditions.