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Background  Neurally adjusted ventilatory assist (NAVA) delivers pressure in proportion to diaphragm electrical activity ( Eadi ). However, each patient responds differently to NAVA levels. This study aims to examine the matching between tidal volume ( Vt ) and patients’ inspiratory demand ( Eadi ), and to investigate patient-specific response to various NAVA levels in non-invasively ventilated patients.    Methods  12 patients were ventilated non-invasively with NAVA using three different NAVA levels. NAVA100 was set according to the manufacturer’s recommendation to have similar peak airway pressure as during pressure support. NAVA level was then adjusted ±50% (NAVA50, NAVA150). Airway pressure, flow and  Eadi  were recorded for 15 minutes at each NAVA level. The matching of  Vt  and integral of  Eadi  ( ʃEadi ) were assessed at the different NAVA levels. A metric, Range90, was defined as the 5-95% range of  Vt / ʃEadi  ratio to assess matching for each NAVA level. Smaller Range90 values indicated better matching of supply to demand.    Results  Patients ventilated at NAVA50 had the lowest Range90 with median 25.6  uVs/ml  [Interquartile range (IQR): 15.4-70.4], suggesting that, globally, NAVA50 provided better matching between  ʃEadi  and  Vt  than NAVA100 and NAVA150. However, on a per-patient basis, 4 patients had the lowest Range90 values in NAVA100, 1 patient at NAVA150 and 7 patients at NAVA50. Robust coefficient of variation for  ʃEadi  and  Vt  were not different between NAVA levels.    Conclusions  The patient-specific matching between  ʃEadi  and  Vt  was variable, indicating that to obtain the best possible matching, NAVA level setting should be patient specific. The Range90 concept presented to evaluate  Vt / ʃEadi  is a physiologic metric that could help in individual titration of NAVA level.

biomedical engineering online

Effects of Neurally Adjusted Ventilatory Assist (NAVA) levels in non-invasive ventilated patients: titrating NAVA levels with electric diaphragmatic activity and tidal volume matching