The effect of back-up rate during non-invasive ventilation in young patients with cystic fibrosis

Objective The aim of the study was to evaluate the effect of the back-up rate on respiratory effort during non-invasive mechanical ventilation.Design An in vitro study evaluated the inspiratory trigger in seven domiciliary ventilators. Then, a prospective, randomized, crossover trial compared the effect on respiratory effort of three different back-up rates during pressure support (PS) and assist-control/volume-targeted (AC/VT) ventilation.Setting A research unit and a tertiary referral pediatric center.Patients Ten patients with cystic fibrosis (CF).Interventions During the in vivo study, the back-up rate was progressively increased to the maximum that patients could tolerate (Fmax) and respiratory effort, as judged by pressure/time product of the diaphragm (PTPdi/min), was compared between the two ventilatory modes.Results Differences were observed between trigger pressure, trigger time delay, trigger pressure/time product and the slope between flow and pressure in the seven ventilators. PS and AC/VT ventilation were associated with a decrease in respiratory effort (PTPdi/min was 518±172, 271±119 and 291±138 cmH₂O . s^–1 . min^-1, for spontaneous breathing, PS and AC/VT ventilation, respectively, p=0.05). During the two modes, increasing the back-up rate to Fmax resulted in a greater reduction in PTPdi/min (p=0.001), which was more pronounced during AC/VT ventilation, due to the automatic adjustment of the inspiratory/expiratory time ratio.Conclusions Increasing the back-up rate during PS and AC/VT ventilation decreases respiratory effort in young patients with CF, but this effect was more marked with AC/VT ventilation.Electronic Supplementary Material Supplementary material is available in the online version of this article at This study was supported with grants from Vaincre la Mucoviscidose (VLM), the Comité National contre les Maladies Respiratoires (CNMR) and the Société de Pneumologie de Langue Française (SPLF).