What is the optimal NAVA (Neurally Adjusted Ventilation Assist) level for a critically ill patient with a neurological condition requiring mechanical ventilation?

NAVA Level in Neurally Adjusted Ventilation

The optimal NAVA level should be titrated systematically by increasing from low to high while monitoring airway pressure and tidal volume, identifying the "adequate NAVA level" (NAVAal) at the point where the steep increase in these parameters transitions to a less steep increase—typically resulting in a NAVA level of approximately 0.5-2.0 cmH₂O/μV. 1

Understanding the NAVA Level

The NAVA level is the gain factor that amplifies the diaphragmatic electrical activity (EAdi) signal to determine the instantaneous ventilatory assist delivered on each breath 2. Essentially, it represents the amount of pressure support (in cmH₂O) delivered per unit of EAdi (in μV) 1, 2.

• The NAVA level is set by the clinician and determines how much pressure the ventilator delivers in proportion to the patient's neural respiratory drive 2
• Unlike fixed pressure support, NAVA provides breath-by-breath variability in assist proportional to the instantaneous EAdi signal 1

Systematic Titration Protocol

The most evidence-based approach involves a structured titration procedure rather than arbitrary selection: 1

• Start with a low NAVA level (NAVAlow, typically 0.5 cmH₂O/μV or lower) and systematically increase in increments 1
• Monitor airway pressure (Paw) and tidal volume (Vt) continuously during the titration 1
• Identify the breakpoint where the relationship between NAVA level and Paw/Vt changes from a steep increase to a less steep increase—this is the "adequate NAVA level" (NAVAal) 1
• This breakpoint typically occurs when respiratory muscle unloading is optimized without over-assistance 1

Physiologic Effects at Different NAVA Levels

Research demonstrates clear dose-response relationships: 1

• At NAVAal: Esophageal pressure-time product (PTPes) reduced by 47% and EAdi reduced by 18% compared to low levels, indicating substantial but not excessive respiratory muscle unloading 1
• At high NAVA levels (NAVAhigh): PTPes reduced by 74% and EAdi reduced by 36%, suggesting over-assistance with excessive unloading 1
• Typical resulting parameters at NAVAal: Tidal volume of 5.9 mL/kg predicted body weight, respiratory rate of 29 breaths/min, and mean inspiratory pressure of 16 cmH₂O 1

Practical Implementation

When implementing the identified NAVAal for sustained ventilation: 1

• The respiratory pattern and muscle unloading remain stable over at least 3 hours 1
• Gas exchange (PaO₂/FiO₂ ratio, PaCO₂) and cardiac performance remain stable 1
• Tidal volumes are typically lower and respiratory rates higher compared to conventional pressure support ventilation 1

For spontaneous breathing trials, NAVA can be titrated to generate equivalent peak airway pressure to PSV of 5 cmH₂O (typically requiring lower NAVA levels) 3

Critical Prerequisites for NAVA Use

NAVA requires intact neuromuscular pathways to function effectively: 4, 5

• The respiratory centers, phrenic nerves, and diaphragm must be functional 4
• Severe bilateral diaphragmatic dysfunction represents an absolute contraindication to NAVA, as the EAdi signal will be inadequate (amplitude 1-2 μV) to trigger and control ventilation 4
• In such cases, pressure support ventilation with pneumatic triggering should be used instead, as accessory respiratory muscles can still trigger the ventilator effectively 4
• The EAdi signal itself serves as a diagnostic tool—very low amplitude signals (<2 μV) indicate diaphragmatic dysfunction and predict NAVA failure 4

Monitoring During NAVA

Continuous EAdi monitoring provides critical information for ventilator management: 2

• EAdi amplitude reflects neural respiratory drive and can guide weaning decisions 5, 2
• A decreasing tidal volume/EAdi ratio during recovery suggests improving respiratory muscle function 5
• In Guillain-Barré syndrome, NAVA levels can be progressively decreased from 1.2 cmH₂O/μV to zero as neuromuscular function recovers 5

Advantages Over Conventional Modes

NAVA demonstrates superior patient-ventilator synchrony compared to pressure support ventilation: 6, 7, 3

• The asynchrony index is significantly reduced with NAVA (median 11.5%) compared to PSV (median 24.3%) during spontaneous breathing trials 3
• NAVA may improve sleep quality in critically ill patients, though data remain limited 6, 7
• Patient-ventilator asynchrony affects 25% of mechanically ventilated patients and contributes to prolonged ventilation and worse outcomes 2

Common Pitfalls to Avoid

• Setting NAVA levels arbitrarily without systematic titration leads to either inadequate support or over-assistance 1
• Attempting NAVA in patients with severe diaphragmatic dysfunction will fail and cause patient distress 4
• Ignoring the EAdi signal amplitude—values <2 μV indicate the patient is not a candidate for NAVA 4
• Failing to recognize that NAVA requires specialized equipment (EAdi catheter) and is not universally available 2