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 (PSP ) 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 (PSN ) was recently proposed for delivering NIV by helmet. We compared PSN with PSP 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) PSP , with an inspiratory support ≥8 cmH2 O; (2) NAVA, adjusting the NAVA level to achieve a comparable peak EAdi (EAdipeak ) as during PSP ; and (3) PSN , setting the NAVA level at 15 cmH2 O/μV with an upper airway pressure (Paw) limit to obtain the same overall Paw applied during PSP . We assessed patient comfort, peak inspiratory flow (PIF), time to reach PIF (PIFtime ), EAdipeak , arterial blood gases, pressure-time product of the first 300 ms (PTP300-index ) and 500 ms (PTP500-index ) after initiation of patient effort, inspiratory trigger delay (DelayTR-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: PSN significantly improved patient comfort, compared to both PSP (p = 0.001) and NAVA (p = 0.002), without differences between the two latter (p = 0.08). PIF (p = 0.109), EAdipeak (p = 0.931) and gas exchange were similar between modes. Compared to PSP and NAVA, PSN reduced PIFtime (p < 0.001), and increased PTP300-index (p = 0.004) and PTP500-index (p = 0.001). NAVA and PSN significantly reduced DelayTR-insp , as opposed to PSP (p < 0.001). During both NAVA and PSN , AI% was <10% in all patients, while AI% was ≥10% in 7 patients (50%) with PSP (p = 0.023 compared with both NAVA and PSN ).

CONCLUSIONS: Compared to both PSP and NAVA, PSN improved comfort and patient-ventilator interaction during NIV by facial mask. PSN also improved synchrony, as opposed to PSP only.

TRIAL REGISTRATION: ClinicalTrials.gov, NCT03041402 . Registered (retrospectively) on 2 February 2017.