New setting of neurally adjusted ventilatory assist for noninvasive ventilation by facial mask: a physiologic study

BACKGROUND: Noninvasive ventilation (NIV) is generally delivered using pneumatically-triggered and cycled-off pressure support (PS(P)) through a mask. Neurally adjusted ventilatory assist (NAVA) is the only ventilatory mode that uses a non-pneumatic signal, i.e., diaphragm electrical activity (EAdi), to trigger and drive ventilator assistance. A specific setting to generate neurally controlled pressure support (PS(N)) was recently proposed for delivering NIV by helmet. We compared PS(N) with PS(P) and NAVA during NIV using a facial mask, with respect to patient comfort, gas exchange, and patient-ventilator interaction and synchrony. METHODS: Three 30-minute trials of NIV were randomly delivered to 14 patients immediately after extubation to prevent post-extubation respiratory failure: (1) PS(P), with an inspiratory support ≥8 cmH(2)O; (2) NAVA, adjusting the NAVA level to achieve a comparable peak EAdi (EAdi(peak)) as during PS(P); and (3) PS(N), setting the NAVA level at 15 cmH(2)O/μV with an upper airway pressure (Paw) limit to obtain the same overall Paw applied during PS(P). We assessed patient comfort, peak inspiratory flow (PIF), time to reach PIF (PIF(time)), EAdi(peak), arterial blood gases, pressure-time product of the first 300 ms (PTP(300-index)) and 500 ms (PTP(500-index)) after initiation of patient effort, inspiratory trigger delay (Delay(TR-insp)), and rate of asynchrony, determined as asynchrony index (AI%). The categorical variables were compared using the McNemar test, and continuous variables by the Friedman test followed by the Wilcoxon test with Bonferroni correction for multiple comparisons (p < 0.017). RESULTS: PS(N) significantly improved patient comfort, compared to both PS(P) (p = 0.001) and NAVA (p = 0.002), without differences between the two latter (p = 0.08). PIF (p = 0.109), EAdi(peak) (p = 0.931) and gas exchange were similar between modes. Compared to PS(P) and NAVA, PS(N) reduced PIF(time) (p < 0.001), and increased PTP(300-index) (p = 0.004) and PTP(500-index) (p = 0.001). NAVA and PS(N) significantly reduced Delay(TR-insp), as opposed to PS(P) (p < 0.001). During both NAVA and PS(N), AI% was <10% in all patients, while AI% was ≥10% in 7 patients (50%) with PS(P) (p = 0.023 compared with both NAVA and PS(N)). CONCLUSIONS: Compared to both PS(P) and NAVA, PS(N) improved comfort and patient-ventilator interaction during NIV by facial mask. PS(N) also improved synchrony, as opposed to PS(P) only. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03041402. Registered (retrospectively) on 2 February 2017.