Neurally adjusted ventilatory assist vs. pressure support to deliver protective mechanical ventilation in patients with acute respiratory distress syndrome: a randomized crossover trial

Abstract

Background: Protective mechanical ventilation is recommended for patients with acute respiratory distress syndrome (ARDS), but it usually requires controlled ventilation and sedation. Using neurally adjusted ventilatory assist (NAVA) or pressure support ventilation (PSV) could have additional benefits, including the use of lower sedative doses, improved patient-ventilator interaction and shortened duration of mechanical ventilation. We designed a pilot study to assess the feasibility of keeping tidal volume (V_T) at protective levels with NAVA and PSV in patients with ARDS.

Methods: We conducted a prospective randomized crossover trial in five ICUs from a university hospital in Brazil and included patients with ARDS transitioning from controlled ventilation to partial ventilatory support. NAVA and PSV were applied in random order, for 15 min each, followed by 3 h in NAVA. Flow, peak airway pressure (Paw) and electrical activity of the diaphragm (EAdi) were captured from the ventilator, and a software (Matlab, Mathworks, USA), automatically detected inspiratory efforts and calculated respiratory rate (RR) and V_T. Asynchrony events detection was based on waveform analysis.

Results: We randomized 20 patients, but the protocol was interrupted for five (25%) patients for whom we were unable to maintain V_T below 6.5 mL/kg in PSV due to strong inspiratory efforts and for one patient for whom we could not detect EAdi signal. For the 14 patients who completed the protocol, V_T was 5.8 ± 1.1 mL/kg for NAVA and 5.6 ± 1.0 mL/kg for PSV (p = 0.455) and there were no differences in RR (24 ± 7 for NAVA and 23 ± 7 for PSV, p = 0.661). Paw was greater in NAVA (21 ± 3 cmH₂O) than in PSV (19 ± 3 cmH₂O, p = 0.001). Most patients were under continuous sedation during the study. NAVA reduced triggering delay compared to PSV (p = 0.020) and the median asynchrony Index was 0.7% (0-2.7) in PSV and 0% (0-2.2) in NAVA (p = 0.6835).

Conclusions: It was feasible to keep V_T in protective levels with NAVA and PSV for 75% of the patients. NAVA resulted in similar V_T, RR and Paw compared to PSV. Our findings suggest that partial ventilatory assistance with NAVA and PSV is feasible as a protective ventilation strategy in selected ARDS patients under continuous sedation. Trial registration ClinicalTrials.gov (NCT01519258). Registered 26 January 2012, https://clinicaltrials.gov/ct2/show/NCT01519258.

Keywords: Interactive ventilatory support; Neurally adjusted ventilatory assist; Positive-pressure respiration; Respiration, artificial; Respiratory distress syndrome, adult.

Fig. 1

Flow diagram of study patients and procedures. NAVA neurally adjusted ventilatory assist, PSV pressure support ventilation, EAdi electrical activity of the diaphragm

Fig. 2

Asynchrony analysis in NAVA and PSV. Lines represent each patient asynchrony index for each type of asynchrony. NAVA neurally adjusted ventilatory assist, PSV pressure support ventilation. p values obtained with the Wilcoxon signed-rank test. The asynchrony index (AI) includes the following major asynchrony types: auto-triggering, ineffective efforts, double triggering and short cycle

Fig. 3

Double triggering in NAVA. Pressure, flow and EAdi vs. time in a representative recording of a patient exhibiting double triggering in NAVA (visible in the last two respiratory cycles). The double triggering was related to EAdi signal showing a biphasic curve. Note that second cycle resulted in an increase in airway pressure, but had zero flow and did not result in breath stacking

Fig. 4

Tidal volume over the 3 h of ventilation with NAVA. Filled diamonds represent the mean tidal volume for predicted body weight of 13 patients who completed the 3 h of NAVA and bars represent standard deviation. V_T mL/kg: tidal volume for predicted body weight