Interaction of PEEP and Neurally-Adjusted Ventilatory Assist in Infants With Acute Viral Bronchiolitis

BACKGROUND: Neurally Adjusted Ventilatory Assist (NAVA) is a ventilator mode providing improved patient-ventilator synchrony compared to flow- or pressure-triggering. We examined the effect of various NAVA, pressure support (PSV), and PEEP combinations in infants with acute viral bronchiolitis. METHODS: This was a mechanistic study, nested within a randomized controlled feasibility trial. A set of 16 ventilatory combinations (each of 10-15 min), including PEEP of 1, 5, and 10 cm H2O; PSV of 20 cm H2O; and NAVA support ranging from 0.5 to 2.0 cm H2O/μV, were administered on each of 2 consecutive days to 13 invasively ventilated infants: mean (range) age 4 months (0.1-10.0). Outcome measures were grouped according to respiratory drive, respiratory efficiency, expiratory air flow limitation, gas exchange, and tolerability. RESULTS: Higher PEEP levels were associated with better respiratory drive (P < .001 for electrical activity of the diaphragm and P0.1), respiratory efficiency (higher tidal volumes and lower breathing frequency, both P < .001) and improved oxygenation (P = .02). Minute ventilation remained constant (P = .67), as did transcutaneous CO2 (P = .60). Expiratory air flow limitation was minimal overall; however, it was reduced on NAVA compared with PSV (P < .001 for β angle). A NAVA support of 0.5 cm H2O/μV appeared inadequate for some outcome measures; conversely, the benefit of increasing support beyond 1.0 was modest, and not always apparent across all outcome measures. Altering PEEP did not produce clinically adverse effects on hemodynamics or patient tolerability (COMFORT-B score). CONCLUSIONS: Higher PEEP values of up to 10 cm H2O may improve respiratory mechanics in acute viral bronchiolitis, without adversely impacting on clinical state. We could not identify an optimal level of NAVA support; however, 0.5 cm H2O/μV may be inadequate.