Adjusting Non-Invasive NAVA Settings in Stable Premature Infants
In stable premature infants with a correctly positioned diaphragmatic catheter and reliable EAdi signal, adjust the NAVA level using a systematic titration protocol: start at 0.5 cmH₂O/µV and increase by 0.5 cmH₂O/µV increments every 3 minutes while monitoring for a breakpoint—the level at which peak EAdi stops decreasing despite further increases in NAVA level—which typically occurs around 2.3 cmH₂O/µV in preterm infants with RDS. 1
Understanding the NAVA Level Titration Principle
The NAVA level determines how much pressure the ventilator delivers per unit of diaphragmatic electrical activity (cmH₂O/µV). 2, 3 This proportional relationship means that as the infant's neural respiratory drive (measured by EAdi) increases, the ventilator automatically delivers more support, and vice versa. 4, 5
The Biphasic Response and Breakpoint Concept
Preterm infants display a characteristic biphasic response during NAVA level titration: initially, as you increase the NAVA level, the peak EAdi decreases (indicating effective respiratory unloading), but beyond a certain point—the breakpoint—further increases in NAVA level do not reduce EAdi further. 1
The breakpoint represents the optimal NAVA level where the infant achieves adequate respiratory support without over-assistance. 1 Operating above this breakpoint provides no additional benefit and may risk lung overdistension due to immature neural feedback mechanisms in premature infants. 1
In the study of preterm infants with RDS, the breakpoint occurred at an average of 2.33 cmH₂O/µV (range influenced by individual variability), which is notably higher than levels commonly used empirically in clinical practice. 1
Step-by-Step Titration Protocol
Initial Setup Verification
Confirm proper catheter positioning by ensuring the EAdi signal shows clear inspiratory peaks with minimal cardiac artifact and that the catheter position indicator on the ventilator screen shows optimal placement at the diaphragmatic level. 6 The esophageal electrode array must be positioned with electrodes at the level of the crural diaphragm to capture reliable signals. 6
Verify that the infant is clinically stable with no acute deterioration, adequate oxygenation, and no signs of severe respiratory distress requiring immediate escalation of support. 1, 5
Systematic NAVA Level Adjustment
Begin titration at a NAVA level of 0.5 cmH₂O/µV and allow 3 minutes of stabilization at each level before making changes. 1 This stabilization period allows the infant's respiratory pattern to equilibrate and provides reliable measurements.
Increase the NAVA level in increments of 0.5 cmH₂O/µV every 3 minutes, progressing through levels of 1.0,1.5,2.0,2.5,3.0,3.5, and up to 4.0 cmH₂O/µV if needed. 1
At each NAVA level, record the peak EAdi (µV), peak inspiratory pressure (cmH₂O), respiratory rate, and observe for signs of patient comfort or distress. 1, 5
Identifying the Optimal NAVA Level
Plot peak EAdi values against NAVA levels to identify the breakpoint—the NAVA level where peak EAdi plateaus and stops decreasing despite further increases in support. 1 This graphical approach makes the breakpoint visually apparent.
Select a NAVA level at or just below the identified breakpoint as the optimal setting. 1 This ensures adequate support while avoiding excessive assistance that provides no additional respiratory unloading.
Monitor for a decrease in respiratory rate as NAVA levels increase, which is a normal physiological response indicating effective respiratory support. 1
Monitoring Parameters During NIV-NAVA
Real-Time EAdi Monitoring
Continuously monitor the EAdi waveform to assess neural respiratory drive, breathing pattern variability, and the presence of central apnea or periodic breathing, which are common in premature infants. 3, 5 The EAdi signal provides real-time feedback independent of leaks, making it superior to flow-based monitoring in non-invasive ventilation. 2, 3
Observe EAdi peak values: persistently high peak EAdi (>15-20 µV) despite adequate NAVA levels may indicate insufficient support, airway obstruction, or increased work of breathing requiring intervention. 5
Watch for absent or very low EAdi signals (<2 µV), which may indicate central apnea, catheter displacement, or inadequate neural drive. 5 In premature infants, frequent apnea is common and may necessitate backup ventilation settings. 5
Pressure and Ventilation Metrics
Monitor peak inspiratory pressure (PIP) delivered during NIV-NAVA, ensuring it remains within safe limits (typically <20-25 cmH₂O for premature infants) to avoid barotrauma. 1, 3 NAVA typically delivers lower peak pressures compared to conventional ventilation while maintaining adequate ventilation. 3
Assess tidal volume trends if available, though leak compensation in NIV-NAVA makes absolute tidal volume measurements less reliable. 4, 2 The proportional relationship between EAdi and delivered pressure is more important than absolute volume measurements. 4
Track respiratory rate: a decrease in respiratory rate with increasing NAVA levels indicates effective respiratory unloading, while persistently high rates may suggest inadequate support. 1
Patient-Ventilator Synchrony Assessment
Evaluate trigger delays (time from EAdi onset to ventilator pressure onset), which should be minimal (~70-75 ms) during NIV-NAVA, indicating excellent synchrony. 4 This is a key advantage over conventional ventilation, where trigger delays are longer and more variable. 4
Check cycling-off synchrony (time from EAdi termination to end of ventilator pressure), which should also be minimal (~30 ms) during NAVA. 4 Conventional ventilation often cycles off prematurely, before the infant's neural inspiration ends. 4
Observe the correlation between EAdi and delivered pressure waveforms: a high correlation coefficient (>0.7-0.8) indicates good proportional assist and synchrony. 4
Adjusting for Clinical Response
Signs of Adequate Support
Clinical indicators of adequate NIV-NAVA support include reduced work of breathing (less retractions, nasal flaring, grunting), improved oxygen saturation, stable heart rate, and infant appearing comfortable without agitation. 3, 5
Transcutaneous CO₂ monitoring, when available and properly calibrated, should show stable or decreasing PtcCO₂ values (ideally <50-55 mmHg) indicating adequate ventilation. 6 Validate PtcCO₂ readings with arterial or capillary blood gas measurements when possible. 6
Signs of Insufficient Support
Persistent high peak EAdi values (>15-20 µV), increasing respiratory rate, worsening retractions, oxygen desaturation, or rising PtcCO₂ indicate inadequate support requiring higher NAVA levels. 1, 5
If the infant reaches the maximum tested NAVA level (4.0 cmH₂O/µV) without achieving a breakpoint or adequate clinical response, consider alternative causes such as airway obstruction, catheter malposition, or disease progression requiring escalation to invasive ventilation. 1, 5
Signs of Excessive Support
Excessively low peak EAdi values (<3-5 µV) with very low respiratory rates may indicate over-assistance, potentially leading to respiratory muscle atrophy or suppression of respiratory drive. 5
Paradoxically, very high NAVA levels beyond the breakpoint do not further reduce EAdi but may increase the risk of lung overdistension due to immature neural feedback mechanisms in premature infants. 1 This is a critical difference from adults, where neural feedback typically prevents over-inflation.
Critical Pitfalls and How to Avoid Them
Immature Neural Feedback in Premature Infants
Premature infants have immature vagal reflexes and neural feedback mechanisms, meaning they may not adequately self-regulate to prevent lung overdistension even with NAVA's proportional control. 1, 3 This contrasts with older children and adults, where neural feedback is more reliable.
Avoid assuming that NAVA automatically prevents lung injury in premature infants; continuous monitoring of delivered pressures and clinical status is mandatory. 1
Frequent Apnea and Central Respiratory Instability
Premature infants commonly exhibit central apnea, periodic breathing, and high breathing pattern variability, which can result in insufficient EAdi triggering and treatment failure. 5 Unlike older patients, premature infants may not consistently generate adequate neural drive.
Ensure backup ventilation settings are appropriately configured in the spontaneous-timed (ST) mode to provide mandatory breaths during apneic episodes. 3, 5 Set a backup rate slightly below the infant's spontaneous rate (e.g., 30-40 breaths/min for a premature infant breathing 40-50/min).
Catheter Displacement and Signal Quality
Regularly verify catheter position and EAdi signal quality, as catheter migration or poor electrode contact can result in unreliable signals and inappropriate ventilator response. 6, 5 Look for sudden changes in EAdi amplitude or waveform morphology as indicators of displacement.
Cardiac artifact contamination of the EAdi signal can occur if electrodes are not optimally positioned; the ventilator's continuous electrode optimization algorithm should minimize this, but manual verification is prudent. 6
Leak Management
Large leaks are common during non-invasive ventilation but do not impair NIV-NAVA's ability to synchronize or deliver proportional assist, as the system uses the EAdi signal rather than flow or pressure to trigger and cycle. 4, 2 This is a major advantage over conventional NIV modes.
However, excessive leaks can reduce effective pressure transmission to the lungs; ensure proper mask fit and consider using different interface types (nasal mask, nasal prongs, or face mask) if leaks are problematic. 6
Empirical Settings Without Titration
Avoid using arbitrarily low NAVA levels (e.g., 0.5-1.0 cmH₂O/µV) without titration, as evidence shows the optimal breakpoint in preterm infants with RDS averages 2.3 cmH₂O/µV—significantly higher than commonly used empirical settings. 1 Under-support increases work of breathing and may lead to extubation failure.
Conversely, avoid using excessively high NAVA levels (>3.5-4.0 cmH₂O/µV) without documented benefit, as this increases the risk of barotrauma and lung overdistension without additional respiratory unloading. 1
Ongoing Monitoring and Adjustment
Reassess NAVA settings at least every 4-6 hours initially and whenever there is a change in clinical status, as the infant's respiratory mechanics and neural drive can change rapidly with disease evolution or improvement. 5
Use EAdi monitoring as a continuous vital sign to guide sedation administration (high EAdi may indicate inadequate sedation or pain), assess readiness for extubation (stable, low EAdi suggests low respiratory drive), and evaluate respiratory status during procedures. 5
Document the NAVA level, peak EAdi, peak inspiratory pressure, respiratory rate, oxygen saturation, and clinical assessment at regular intervals to track trends and guide adjustments. 1, 5