Neurally Adjusted Ventilatory Assist: A Ventilation Tool or a Ventilation Toy?

Abstract

Mechanical ventilation has, since its introduction into clinical practice, undergone a major evolution from controlled ventilation to various modes of assisted ventilation. Neurally adjusted ventilatory assist (NAVA) is the newest development. The implementation of NAVA requires the introduction of a catheter to measure the electrical activity of the diaphragm (EA di ). NAVA relies, opposite to conventional assisted ventilation modes, on the EA di to trigger the ventilator breath and to adjust the ventilatory assist to the neural drive. The amplitude of the ventilator assist is determined by the instantaneous EA di and the NAVA level set by the clinician. The NAVA level amplifies the EA di signal and determines instantaneous ventilator assist on a breath-to-breath basis. Experimental and clinical data suggest superior patient-ventilator synchrony with NAVA. Patient-ventilator asynchrony is present in 25% of mechanically ventilated patients in the intensive care unit and may contribute to patient discomfort, sleep fragmentation, higher use of sedation, development of delirium, ventilator-induced lung injury, prolonged mechanical ventilation, and ultimately mortality. With NAVA, the reliance on the EA di signal, together with an intact ventilatory drive and intact breathing reflexes, allows integration of the ventilator in the neuro-ventilatory coupling on a higher level than conventional ventilation modes. The simple monitoring of the EA di signal alone may provide the clinician with important information to guide ventilator management, especially during the weaning process. Although, until now, little evidence proves the superiority of NAVA on clinically relevant end points, it seems evident that patient populations (eg, COPD and small children) with major patient-ventilator asynchrony may benefit from this new ventilatory tool.

Neurally Adjusted Ventilatory Assist: Insufficient Evidence of Broad Clinical Outcomes

“…9 NAVA triggering was applied when the EAdi reached 0.5 V, and the EAdi signal was measured every 16 ms, both of which are consistent with the application of NAVA in other literature. 6,8 Delisle et al have identified a statistically significant increase in tidal volume variability when supported breaths were flow assisted by NAVA, a finding that is consistent with the conclusions of other recent publications. 6,10 The authors suggest that the greater tidal volume variability measured during NAVA may be associated with the elimination of all central apneas during non-rapid-eye-movement sleep in their study.…”

“…[3][4][5][6] Considering a current healthcare context that is increasingly concerned with safety, clinically important patient outcomes, and cost containment, I believe that the use of NAVA has not yet been adequately justified in the literature. What is the clinical importance of this study; the "So what?"…”

“…[3][4][5] Neurally adjusted ventilatory assist (NAVA) represents one such improvement that uses signals from the diaphragm to facilitate synchrony of patient-ventilator interactions. [4][5][6] NAVA measures electrical activity of the diaphragm (EAdi) during inhalation, using an esophageal catheter. 4 The EAdi signals are filtered and amplified, and can be used to accomplish triggering and cycling of assisted or supported breaths, as well as modulation of airway pressure.…”

“…4 The EAdi signals are filtered and amplified, and can be used to accomplish triggering and cycling of assisted or supported breaths, as well as modulation of airway pressure. [4][5][6][7][8] A growing body of research concludes that NAVA is associated with less timing (trigger and cycle) and flow asynchrony than conventionally applied mechanical ventilation. 6,8 Delisle et al, in this issue of RESPIRATORY CARE, report results of their study examining any association between the occurrence of central apneas during weaning and the application of NAVA or pressure support ventilation.…”

“…[4][5][6][7][8] A growing body of research concludes that NAVA is associated with less timing (trigger and cycle) and flow asynchrony than conventionally applied mechanical ventilation. 6,8 Delisle et al, in this issue of RESPIRATORY CARE, report results of their study examining any association between the occurrence of central apneas during weaning and the application of NAVA or pressure support ventilation. 9 NAVA triggering was applied when the EAdi reached 0.5 V, and the EAdi signal was measured every 16 ms, both of which are consistent with the application of NAVA in other literature.…”