Noninvasive ventilation through a helmet in postextubation hypoxemic patients: Physiologic comparison between neurally adjusted ventilatory assist and pressure support ventilation

Purpose: Neurally adjusted ventilatory assist (NAVA) has been shown to improve patient-ventilator interaction and reduce asynchronies in intubated patients, as opposed to pressure support ventilation (PSV). This is a short-term head-to-head physiologic comparison between PSV and NAVA in delivering noninvasive ventilation through a helmet (h-NIV), in patients with postextubation hypoxemic acute respiratory failure. Methods: Ten patients underwent three 20-min trials of h-NIV in PSV, NAVA, and PSV again. Arterial blood gases (ABGs) were assessed at the end of each trial. Diaphragm electrical activity (EAdi) and airway pressure (P _aw) were recorded to derive neural and mechanical respiratory rate and timing, inspiratory (delay _TR-insp) and expiratory trigger delays (delay _TR-exp), time of synchrony between diaphragm contraction and ventilator assistance (time _synch), and the asynchrony index (AI). Results: ABGs, peak EAdi, peak P _aw, respiratory rate, either neural or mechanical, neural timing, and delay _TR-exp were not different between trials. Compared with PSV, with NAVA the mechanical expiratory time was significantly shorter, while the inspiratory time and duty cycle were greater. Time _synch was 0.79 ± 0.35 s in NAVA versus 0.60 ± 0.30 s and 0.55 ± 0.29 s during the PSV trials (p < 0.01 for both). AI exceeded 10% during both PSV trials, while not in NAVA (p < 0.001). Conclusions: Compared with PSV, NAVA improves patient-ventilator interaction and synchrony, with no difference in gas exchange, respiratory rate, and neural drive and timing.