Physiologic response to varying levels of pressure support and neurally adjusted ventilatory assist in patients with acute respiratory failure
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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).
ICU of a University Hospital.
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.
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).
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).
Compared to PSV, NAVA averted the risk of over-assistance, avoided patient–ventilator asynchrony, and improved patient–ventilator interaction.
KeywordsMechanical ventilation Patient–ventilator interaction Diaphragm electrical activity Pressure support ventilation Neurally adjusted ventilatory assist
We thank Maquet Critical Care that provided us with all the equipment used for the study. We are indebted to Jeffrey Franc-Law who carefully revised the manuscript. Last but not least, we wish to acknowledge all physicians and nurses of our Intensive Care Unit for their helpful and continuous support.
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