Neurally adjusted ventilatory assist vs pressure support ventilation during noninvasive mechanical ventilation: another physiologic evaluation to consider?

Neurally adjusted ventilatory assist (NAVA) is an original approach to noninvasive ventilation that can improve patient-ventilator interaction and may infl uence physiologic outcomes 1 3 because the electrical activity of the diaphragm, a pneumatically independent signal, is used to control the timing and level of assist provided, regardless of the interface used. In a recent issue of CHEST (January 2013), Bertrand et al 4 compared patient-ventilator interaction during pressure support ventilation (PSV) and NAVA applied noninvasively and showed reductions in all of the following with NAVA: ineffective efforts, trigger and cycling-off delays, and inspiratory times. This, thus, demonstrated a lower “severe asynchrony” (“severe” defi ned by an asynchrony index . 10%), but despite these positive fi ndings in patient-ventilator interaction, the clinical impact was not so clear and deserves comment. First, there were no signifi cant changes in the oxygenation index when patient-ventilator synchrony improved with NAVA. This fi nding is relevant because it is not in accordance with the fi ndings of previous studies. 1 , 3 It could be hypothesized that the restoration of diaphragmatic activity contributes to a recruitment of poorly ventilated areas. In this study, were the selected positive endexpiratory pressures too low and were the observation periods too short? Furthermore, in terms of practical implications, is the expected oxygenation improvement correlated to a reduced patient-ventilator asynchrony index or to independent factors? 4 , 5