Respiratory pattern during neurally adjusted ventilatory assist in acute respiratory failure patients

To investigate the effect of a wide range of assistance levels during neurally adjusted ventilatory assist (NAVA) and pressure support ventilation (PSV) on respiratory pattern, breathing variability, and incidence of tidal volumes (V (T)) above 8 and 10 ml/kg in acute respiratory failure patients. Eight increasing NAVA levels (0.5, 1, 1.5, 2, 2.5, 3, 4, and 5 cmH(2)O/mu V) and four increasing pressure support (PSV) levels (4, 8, 12, and 16 cmH(2)O) were applied to obtain 10 min of stable recordings in 15 patients. One out of 15 patients did not sustain the NAVA levels of 3, 4, and 5 cmH(2)O/mu V and was excluded. The 5 cmH(2)O/mu V NAVA level was not tolerated by three patients and it was excluded. Increasing NAVA levels were associated with decreased diaphragm electrical activity (EAdi), and, at variance with PSV, with small changes in V (T), no changes in respiratory rate (RR), and increases in V (T) and EAdi variability. At high NAVA levels, an increase in V (T) variability was associated with increased incidence of V (T) above 8 and 10 ml/kg and an uncomfortable respiratory pattern in some patients. Increasing NAVA levels were associated with no effect on RR, small increase in V (T), and increase in V (T) and EAdi variability. Effective decrease in EAdi occurred at NAVA levels below 2-2.5 cmH(2)O/mu V, while preserving respiratory variability and low risks of V (T) above 8 or 10 ml/kg.