New Setting of Neurally Adjusted Ventilatory Assist during Noninvasive Ventilation through a Helmet

Background: Compared to pneumatically controlled pressure support (PSP), neurally adjusted ventilatory assist (NAVA) was proved to improve patient-ventilator interactions, while not affecting comfort, diaphragm electrical activity (EAdi), and arterial blood gases (ABGs). This study compares neurally controlled pressure support (PSN) with PSP and NAVA, delivered through two different helmets, in hypoxemic patients receiving noninvasive ventilation for prevention of extubation failure. Methods: Fifteen patients underwent three (PSP, NAVA, and PSN) 30-min trials in random order with both helmets. Positive end-expiratory pressure was always set at 10 cm H2O. In PSP, the inspiratory support was set at 10 cm H2O above positive end-expiratory pressure. NAVA was adjusted to match peak EAdi (EAdi(peak)) during PSP. In PSN, the NAVA level was set at maximum matching the pressure delivered during PSP by limiting the upper pressure. The authors assessed patient comfort, EAdi(peak), rates of pressurization (i.e., airway pressure-time product[PTP] of the first 300 and 500 ms after the initiation of patient effort, indexed to the ideal pressure-time products), and measured ABGs. Results: PSN significantly increased comfort to (median[25 to 75% interquartile range]) 8[7 to 8] and 9[8 to 9] with standard and new helmets, respectively, as opposed to both PSP (5[5 to 6] and 7[6 to 7]) and NAVA (6[5 to 7] and 7[6 to 8]; P < 0.01 for all comparisons). Regardless of the interface, PSN also decreased EAdi(peak) (P < 0.01), while increasing PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP (P < 0.01) and PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP (P < 0.001). ABGs were not different among trials. Conclusions: When delivering noninvasive ventilation by helmet, compared to PSP and NAVA, PSN improves comfort and patient-ventilator interactions, while not ABGs.