Neurally Adjusted Ventilatory Assist (NAVA)
Primary Recommendation
NAVA is recommended as an alternative to pressure support ventilation in intubated patients with acute respiratory failure who can breathe spontaneously, as it reduces duration of mechanical ventilation by approximately 4 days and significantly improves patient-ventilator synchrony. 1
When NAVA Should Be Used
Patient Selection Criteria
Intubated patients with acute respiratory failure who have been ventilated for ≤5 days, are expected to require mechanical ventilation for ≥72 hours, and can breathe spontaneously are ideal candidates for NAVA 1
NAVA requires intact respiratory centers, functioning phrenic nerves, and preserved diaphragmatic function to work effectively 2
The mode uses diaphragmatic electrical activity (EAdi) to trigger the ventilator and provide proportional respiratory assistance 3
Clinical Benefits Over Conventional Ventilation
NAVA increases ventilator-free days at 28 days (median 22 vs 18 days) compared to conventional lung-protective mechanical ventilation, representing a clinically meaningful 4-day reduction in ventilator duration 1
NAVA reduces patient-ventilator asynchrony index from 24.3% to 11.5% during spontaneous breathing trials 4
The mode eliminates ineffective efforts and late cycling entirely, which are common problems with pressure support ventilation 5
NAVA reduces trigger delay from approximately 178-199 ms with pressure support to 69 ms 5
NAVA reduces inspiratory time in excess from 204-220 ms with pressure support to 126 ms 5
Physiologic Advantages
Prevention of Over-Assistance
At high assist levels, NAVA prevents over-assistance that commonly occurs with pressure support ventilation 3
With pressure support at highest settings, tidal volumes reach 9.1 mL/kg compared to 7.1 mL/kg with NAVA, indicating excessive ventilator support 3
NAVA maintains appropriate respiratory drive (peak EAdi 12.3 μV) while pressure support suppresses it (8.6 μV) at high assist levels 3
Improved Patient-Ventilator Interaction
NAVA reduces the asynchrony index to below 10% in all patients, whereas 36% of patients on pressure support have asynchrony index >10% 3
The mode achieves better matching between neural and flow-based timing compared to pressure support 3
NAVA reduces total asynchrony events from 3.04-3.15 events/min with pressure support to 1.21 events/min 5
Practical Implementation
Initial Setup
NAVA requires placement of a specialized nasogastric tube with electrodes to measure diaphragmatic electrical activity 2, 3
The NAVA level (gain) should be titrated to generate equivalent peak airway pressure to what would be used with pressure support 4
A typical starting NAVA gain is 5 cmH₂O/μV with an inspiratory trigger of 0.3 μV 2
Monitoring Requirements
Monitor the EAdi signal amplitude continuously—adequate diaphragmatic function produces EAdi amplitudes >2 μV during spontaneous breathing 2
If EAdi amplitude is very low (1-2 μV), this indicates severe diaphragmatic dysfunction and NAVA will fail 2
In such cases, switch to pressure support ventilation which can utilize accessory respiratory muscles via pneumatic triggering 2
Standard monitoring of tidal volume, respiratory rate, arterial blood gases, and patient comfort should continue 3, 4
Use During Weaning
Spontaneous Breathing Trials
NAVA can be used during spontaneous breathing trials with the same objective criteria used for pressure support trials 4
Set NAVA to generate equivalent peak airway pressure as would be used with 5 cmH₂O pressure support 4
The ICU team can evaluate readiness for extubation using standard clinical criteria regardless of whether NAVA or pressure support is used 4
NAVA produces similar respiratory patterns (tidal volume 6.1 vs 5.5 mL/kg, respiratory rate 27 vs 26 breaths/min) compared to pressure support during spontaneous breathing trials 4
Important Limitations and Contraindications
Absolute Requirements for NAVA Function
NAVA will fail in patients with bilateral diaphragmatic dysfunction, even if accessory respiratory muscles are preserved 2
The mode depends entirely on diaphragmatic electrical activity for triggering and proportional assist 2
Patients with impaired phrenic nerve function, diaphragmatic paralysis, or severe diaphragmatic weakness cannot be effectively supported with NAVA 2
In these cases, pressure support ventilation is superior because it uses pneumatic triggering that responds to any inspiratory effort, including from accessory muscles 2
Clinical Outcomes
While NAVA reduces duration of mechanical ventilation, it does not reduce hospital mortality (25.5% vs 30.7%, p=0.31) 1
The mode should be viewed primarily as a tool to improve ventilator synchrony and reduce ventilator days, not as a mortality-reducing intervention 1
Comparison to Standard Modes
When NAVA Offers Clear Advantage
NAVA is superior to pressure support when patient-ventilator asynchrony is problematic or when there is concern about over-assistance at higher support levels 3, 5
The mode is particularly beneficial in patients with obstructive pulmonary disease where asynchrony is common 5
NAVA maintains better synchrony across varying levels of respiratory support 3
When Pressure Support Remains Appropriate
Pressure support ventilation remains effective and appropriate for most patients with acute respiratory failure 6
If diaphragmatic function is questionable or EAdi signal quality is poor, pressure support should be used instead of NAVA 2
Bi-level pressure support ventilators are simpler to use, cheaper, and more widely available than NAVA-capable ventilators 6
Diagnostic Role of EAdi Monitoring
EAdi monitoring can help diagnose the cause of weaning failure by identifying diaphragmatic dysfunction 2