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

Abstract

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. © Springer-Verlag 2004.