Combined monitoring of functional residual capacity and compliance may avoid hyperinflation and cardiac depression in ARDS

Introduction

Combined monitoring of functional residual capacity (FRC) and compliance of the respiratory system (C_rs) at the bedside may allow alveolar recruitment and detect hyperinflation [1]. The aims of this study were to evaluate the FRC by a modified nitrogen multiple washout technique (NMBW) combined with the study of C_rs, to set best PEEP on data of FRC and Crs, and to evaluate by echocardiography study the cardiac response to different levels of PEEP.

Methods

Thirty patients with ALI/ARDS were ventilated with an Engstrom carestation ventilator (GE Healthcare, Helsinki, Finland) in accordance with the ARDS net guidelines. FRC measurement was carried out with the COVX module integrated within the ventilator (GE Healthcare) by the NMBW technique. Every patient had a basal FRC measurement and then three measurements at PEEP 15/10/5 cm H₂O during a de-recruiting maneuver. At every step we studied the changes of FRC, C_rs, PaO₂/FIO₂ ratio and performed a transthoracic echocardiography (Agilent 5500; Hewlett and Packard) to evaluate the integral of velocity time of left ventricular outflow tract (LVOT VTI). All data are reported as mean ± SD. ANOVA was used to compare changes during the time.

Results

Table 1 presents the main results of the study. Best PEEP was set at 10 cmH₂O, at which level the decrease of FRC and improvement of C_rs indicates the start of de-recruitment and end of overdistention.

Table 1

Conclusions

Increased levels of PEEP improve FRC. Combined monitoring of FRC and C_rs may detect hyperinflation. Hyperinflation impairs LV systolic function.