Objective  

Neurally adjusted ventilatory assist (NAVA) is a new mode wherein the assistance is provided in proportion to diaphragm electrical activity (EAdi). We assessed the physiologic response to varying levels of NAVA and pressure support ventilation (PSV).

Setting  

ICU of a University Hospital.

Patients  

Fourteen intubated and mechanically ventilated patients.

Design and protocol  

Cross-over, prospective, randomized controlled trial. PSV was set to obtain a V t/kg of 6–8 ml/kg with an active inspiration. NAVA was matched with a dedicated software. The assistance was decreased and increased by 50% with both modes. The six assist levels were randomly applied.

Measurements  

Arterial blood gases (ABGs), tidal volume (V t/kg), peak EAdi, airway pressure (Paw), neural and flow-based timing. Asynchrony was calculated using the asynchrony index (AI).

Results  

There was no difference in ABGs regardless of mode and assist level. The differences in breathing pattern, ventilator assistance, and respiratory drive and timing between PSV and NAVA were overall small at the two lower assist levels. At the highest assist level, however, we found greater V t/kg (9.1 ± 2.2 vs. 7.1 ± 2 ml/kg, P < 0.001), and lower breathing frequency (12 ± 6 vs. 18 ± 8.2, P < 0.001) and peak EAdi (8.6 ± 10.5 vs. 12.3 ± 9.0, P < 0.002) in PSV than in NAVA; we found mismatch between neural and flow-based timing in PSV, but not in NAVA. AI exceeded 10% in five (36%) and no (0%) patients with PSV and NAVA, respectively (P < 0.05).

Conclusions  

Compared to PSV, NAVA averted the risk of over-assistance, avoided patient–ventilator asynchrony, and improved patient–ventilator interaction.