Neurally Adjusted Ventilatory Assist Level Research Articles

Neurally Adjusted Ventilatory Assist Versus Pressure Support Ventilation: A Comprehensive Review.

Mechanical ventilation serves as crucial life support for critically ill patients. Although it is life-saving prolonged ventilation carries risks and complications like barotrauma, Ventilator-associated pneumonia, sepsis, and many others. Optimizing patient-ventilator interactions and facilitating early weaning is necessary for improved intensive care unit (ICU) outcomes. Traditionally Pressure support ventilation (PSV) mode is widely used for weaning patients who are intubated and mechanically ventilated. Neurally adjusted ventilatory assist (NAVA) mode of the ventilator is an emerging ventilator mode that delivers pressure depending on the patient's respiratory drive, which in turn prevents over-inflation and improves the patient's ventilator interactions. Our article revises and compares the effectiveness of NAVA compared to PSV ventilation under different contexts. Overall we conclude that NAVA level of ventilation can be safely administered in a patient with acute respiratory failure, provided diaphragmatic paralysis is not considered. NAVA improves asynchrony index, wean-off time, and sleep quality and is associated with increased ventilator-free days. These results are based on small-scale studies with low power, and further studies are warranted in large-scale cohorts with more diverse populations to confirm these results.

Evaluation of NAVA-PAP in premature neonates with apnea of prematurity: minimal backup ventilation and clinically significant events.

Neonates with apnea of prematurity (AOP) clinically deteriorate because continuous positive airway pressure (CPAP) provides inadequate support during apnea. Neurally adjusted ventilatory assist (NAVA) provides proportional ventilator support from the electrical activity of the diaphragm. When the NAVA level is 0 cmH2O/mcV (NAVA-PAP), patients receive CPAP when breathing and backup ventilation when apneic. This study evaluates NAVA-PAP and time spent in backup ventilation. This was a prospective, two-center, observational study of preterm neonates on NAVA-PAP for AOP. Ventilator data were downloaded after 24 h. The number of clinically significant events (CSEs) was collected. A paired t-test was used to perform statistical analysis. The study was conducted on 28 patients with a gestational age of 25 ± 1.8 weeks and a study age of 28 ± 23 days. The number of CSEs was 4 ± 4.39/24 h. The patients were on NAVA-PAP for approximately 90%/min, switched to backup mode 2.5 ± 1.1 times/min, and spent 10.6 ± 7.2% in backup. Preterm neonates on NAVA-PAP had few CSEs with minimal time in backup ventilation.

Estimation of transpulmonary driving pressure during synchronized mechanical ventilation using a single lower assist maneuver (LAM) in rabbits: a comparison to measurements made with an esophageal balloon

BackgroundMechanical ventilation is applied to unload the respiratory muscles, but knowledge about transpulmonary driving pressure (ΔPL) is important to minimize lung injury. We propose a method to estimate ΔPL during neurally synchronized assisted ventilation, with a simple intervention of lowering the assist for one breath (“lower assist maneuver”, LAM).MethodsIn 24 rabbits breathing spontaneously with imposed loads, titrations of increasing assist were performed, with two neurally synchronized modes: neurally adjusted ventilatory assist (NAVA) and neurally triggered pressure support (NPS). Two single LAM breaths (not sequentially, but independently) were performed at each level of assist by acutely setting the assist to zero cm H2O (NPS) or NAVA level 0 cm H2O/uV (NAVA) for one breath. NPS and NAVA titrations were followed by titrations in controlled-modes (volume control, VC and pressure control, PC), under neuro-muscular blockade. Breaths from the NAVA/NPS titrations were matched (for flow and volume) to VC or PC. Throughout all runs, we measured diaphragm electrical activity (Edi) and esophageal pressure (PES). We measured ΔPL during the spontaneous modes (PL_PES) and controlled mechanical ventilation (CMV) modes (PL_CMV) with the esophageal balloon. From the LAMs, we derived an estimation of ΔPL (“PL_LAM”) using a correction factor (ratio of volume during the LAM and volume during assist) and compared it to measured ΔPL during passive (VC or PC) and spontaneous breathing (NAVA or NPS). A requirement for the LAM was similar Edi to the assisted breath.ResultsAll animals successfully underwent titrations and LAMs for NPS/NAVA. One thousand seven-hundred ninety-two (1792) breaths were matched to passive ventilation titrations (matched Vt, r = 0.99). PL_LAM demonstrated strong correlation with PL_CMV (r = 0.83), and PL_PES (r = 0.77). Bland–Altman analysis revealed little difference between the predicted PL_LAM and measured PL_CMV (Bias = 0.49 cm H2O and 1.96SD = 3.09 cm H2O). For PL_PES, the bias was 2.2 cm H2O and 1.96SD was 3.4 cm H2O. Analysis of Edi and PES at peak Edi showed progressively increasing uncoupling with increasing assist.ConclusionDuring synchronized mechanical ventilation, a LAM breath allows for estimations of transpulmonary driving pressure, without measuring PES, and follows a mathematical transfer function to describe respiratory muscle unloading during synchronized assist.

Pulmonary volume-feedback and ventilatory pattern after bilateral lung transplantation using neurally adjusted ventilatory assist ventilation

BackgroundBilateral lung transplantation results in pulmonary vagal denervation, which potentially alters respiratory drive, volume-feedback, and ventilatory pattern. We hypothesised that Neurally Adjusted Ventilatory Assist (NAVA) ventilation, which is driven by diaphragm electrical activity (EAdi), would reveal whether vagally mediated pulmonary-volume feedback is preserved in the early phases after bilateral lung transplantation. MethodsWe prospectively studied bilateral lung transplant recipients within 48 h of surgery. Subjects were ventilated with NAVA and randomised to receive 3 ventilatory modes (baseline NAVA, 50%, and 150% of baseline NAVA values) and 2 PEEP levels (6 and 12 cm H2O). We recorded airway pressure, flow, and EAdi. ResultsWe studied 30 subjects (37% female; age: 37 (27–56) yr), of whom 19 (63%) had stable EAdi. The baseline NAVA level was 0.6 (0.2–1.0) cm H2O μV−1. Tripling NAVA level increased the ventilatory peak pressure over PEEP by 6.3 (1.8), 7.6 (2.4), and 8.7 (3.2) cm H2O, at 50%, 100%, and 150% of baseline NAVA level, respectively (P<0.001). EAdi peak decreased by 10.1 (9.0), 9.5 (9.4) and 8.8 μV (8.7) (P<0.001), accompanied by small increases in tidal volume, 8.3 (3.0), 8.7 (3.6), and 8.9 (3.3) ml kg−1 donor's predicted body weight at 50%, 100%, and 150% of baseline NAVA levels, respectively (P<0.001). Doubling PEEP did not affect tidal volume. ConclusionsNAVA ventilation was feasible in the majority of patients during the early postoperative period after bilateral lung transplantation. Despite surgical vagotomy distal to the bronchial anastomoses, bilateral lung transplant recipients maintained an unmodified respiratory pattern in response to variations in ventilatory assistance and PEEP. Clinical trial registrationNCT03367221.

Evaluating peak inspiratory pressures and tidal volume in premature neonates on NAVA ventilation.

Neurally adjusted ventilatory assist (NAVA) ventilation allows patients to determine their peak inspiratory pressure and tidal volume on a breath-by-breath basis. Apprehension exists about premature neonates’ ability to self-regulate breath size. This study describes peak pressure and tidal volume distribution of neonates on NAVA and non-invasive NAVA. This is a retrospective study of stored ventilator data with exploratory analysis. Summary statistics were calculated. Distributional assessment of peak pressure and tidal volume were evaluated, overall and per NAVA level. Over 1 million breaths were evaluated from 56 subjects. Mean peak pressure was 16.4 ± 6.4 in the NAVA group, and 15.8 ± 6.4 in the NIV-NAVA group (t test, p < 0.001). Mean tidal volume was 3.5 ± 2.7 ml/kg.Conclusion:In neonates on NAVA, most pressures and volumes were within or lower than recommended ranges with pressure-limited or volume-guarantee ventilation.What is known:• Limiting peak inspiratory pressures or tidal volumes are the main strategies to minimize ventilator-induced lung injury in neonates. Neurally adjusted ventilatory assist allows neonates to regulate their own peak inspiratory pressures and tidal volumes on a breath-to-breath basis using neural feedback.What is new:• When neonates chose the size of their breaths based on neural feedback, the majority of peak inspiratory pressures and tidal volumes were within or lower than the recommended peak inspiratory pressure or tidal volume ranges with pressure-limited or volume guarantee ventilation.

New setting of neurally adjusted ventilatory assist for noninvasive ventilation by facial mask: a physiologic study

BackgroundNoninvasive ventilation (NIV) is generally delivered using pneumatically-triggered and cycled-off pressure support (PSP) through a mask. Neurally adjusted ventilatory assist (NAVA) is the only ventilatory mode that uses a non-pneumatic signal, i.e., diaphragm electrical activity (EAdi), to trigger and drive ventilator assistance. A specific setting to generate neurally controlled pressure support (PSN) was recently proposed for delivering NIV by helmet. We compared PSN with PSP and NAVA during NIV using a facial mask, with respect to patient comfort, gas exchange, and patient-ventilator interaction and synchrony.MethodsThree 30-minute trials of NIV were randomly delivered to 14 patients immediately after extubation to prevent post-extubation respiratory failure: (1) PSP, with an inspiratory support ≥8 cmH2O; (2) NAVA, adjusting the NAVA level to achieve a comparable peak EAdi (EAdipeak) as during PSP; and (3) PSN, setting the NAVA level at 15 cmH2O/μV with an upper airway pressure (Paw) limit to obtain the same overall Paw applied during PSP. We assessed patient comfort, peak inspiratory flow (PIF), time to reach PIF (PIFtime), EAdipeak, arterial blood gases, pressure-time product of the first 300 ms (PTP300-index) and 500 ms (PTP500-index) after initiation of patient effort, inspiratory trigger delay (DelayTR-insp), and rate of asynchrony, determined as asynchrony index (AI%). The categorical variables were compared using the McNemar test, and continuous variables by the Friedman test followed by the Wilcoxon test with Bonferroni correction for multiple comparisons (p < 0.017).ResultsPSN significantly improved patient comfort, compared to both PSP (p = 0.001) and NAVA (p = 0.002), without differences between the two latter (p = 0.08). PIF (p = 0.109), EAdipeak (p = 0.931) and gas exchange were similar between modes. Compared to PSP and NAVA, PSN reduced PIFtime (p < 0.001), and increased PTP300-index (p = 0.004) and PTP500-index (p = 0.001). NAVA and PSN significantly reduced DelayTR-insp, as opposed to PSP (p < 0.001). During both NAVA and PSN, AI% was <10% in all patients, while AI% was ≥10% in 7 patients (50%) with PSP (p = 0.023 compared with both NAVA and PSN).ConclusionsCompared to both PSP and NAVA, PSN improved comfort and patient-ventilator interaction during NIV by facial mask. PSN also improved synchrony, as opposed to PSP only.Trial registrationClinicalTrials.gov, NCT03041402. Registered (retrospectively) on 2 February 2017.

Noninvasive Neurally Adjusted Ventilatory Assist in Premature Infants Postextubation.

Background Neurally adjusted ventilatory assist (NAVA) has distinct advantages when used invasively compared with conventional ventilation techniques. Evidence supporting the use of noninvasive NAVA is less robust, especially in the very low birth weight (VLBW) population. Objective To determine whether synchronized noninvasive ventilation via neurally adjusted ventilatory assist (NIV NAVA) supports ventilation postextubation in premature infants. Methods A retrospective analysis of a cohort of twenty-four former VLBW (<1.5 kg) infants from July 2011 to October 2012. Decreased or unchanged capillary pCO2 after increasing NAVA support was used as a marker for adequately supported noninvasive ventilation. The Wilcoxon signed-rank test was used to compare pre- and post-NAVA intervention (α = 0.05). Results Ventilation improved after an increase in NIV NAVA level in 83% of the premature infants studied (20/24) with a decrease in median pCO2 by 5 mm Hg (p = 0.0001). Conclusion NIV NAVA can provide synchronized postextubation ventilatory support as measured by decreased pCO2 in premature infants.

New Setting of Neurally Adjusted Ventilatory Assist during Noninvasive Ventilation through a Helmet

Compared to pneumatically controlled pressure support (PSP), neurally adjusted ventilatory assist (NAVA) was proved to improve patient-ventilator interactions, while not affecting comfort, diaphragm electrical activity (EAdi), and arterial blood gases (ABGs). This study compares neurally controlled pressure support (PSN) with PSP and NAVA, delivered through two different helmets, in hypoxemic patients receiving noninvasive ventilation for prevention of extubation failure. Fifteen patients underwent three (PSP, NAVA, and PSN) 30-min trials in random order with both helmets. Positive end-expiratory pressure was always set at 10 cm H2O. In PSP, the inspiratory support was set at 10 cm H2O above positive end-expiratory pressure. NAVA was adjusted to match peak EAdi (EAdipeak) during PSP. In PSN, the NAVA level was set at maximum matching the pressure delivered during PSP by limiting the upper pressure. The authors assessed patient comfort, EAdipeak, rates of pressurization (i.e., airway pressure-time product [PTP] of the first 300 and 500 ms after the initiation of patient effort, indexed to the ideal pressure-time products), and measured ABGs. PSN significantly increased comfort to (median [25 to 75% interquartile range]) 8 [7 to 8] and 9 [8 to 9] with standard and new helmets, respectively, as opposed to both PSP (5 [5 to 6] and 7 [6 to 7]) and NAVA (6 [5 to 7] and 7 [6 to 8]; P < 0.01 for all comparisons). Regardless of the interface, PSN also decreased EAdipeak (P < 0.01), while increasing PTP of the first 300 ms from the onset of patient effort, indexed to the ideal PTP (P < 0.01) and PTP of the first 500 ms from the onset of patient effort, indexed to the ideal PTP (P < 0.001). ABGs were not different among trials. When delivering noninvasive ventilation by helmet, compared to PSP and NAVA, PSN improves comfort and patient-ventilator interactions, while not ABGs. (Anesthesiology 2016; 125:1181-9).

Comparing changing neurally adjusted ventilatory assist (NAVA) levels in intubated and recently extubated neonates.

Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation that delivers ventilatory support in synchrony to the patient's respiratory needs using NAVA level, a proportionality constant that converts the electrical activity of the diaphragm (Edi) into a peak pressure (PIP). Recent published studies suggest that neonates can control the delivered ventilatory support through neural feedback. Systematically increasing the NAVA level initially increases the PIP while maintaining a constant Edi until an inflection point or breakpoint (BrP) is reached, at which time the PIP plateaus and the Edi signal decreases. This study was performed to establish if there is a correlation of pre- and post-extubation BrP in premature neonates. NAVA level was increased by 0.5 cm H2O mcV-1 every 3 min from 0.1 to 3.0 cm H2O mcV-1. PIP and Edi Peak and Minimum were recorded. PIP and phasic Edi (Edi peak-Edi min) were averaged for each NAVA level, plotted on a graph, and the BrP was determined by visual inspection of the inflection point for PIP. The data from the studies were then combined by averaging each variable at the BrP and for each change in NAVA level above and below the BrP. Fifteen infants were studied for paired titration studies. PIP increased until the BrP was reached and then plateaued during both the intubated and extubated titration studies. Edi decreased after the BrP was reached during the titration studies. The BrP increased when patients were extubated from NAVA to noninvasive (NIV) NAVA. As the NAVA level rose above the BrP, PIP plateaued at a higher level and Edi decreased less during the NIV NAVA titration study. Neonates demonstrated an increase in BrP, higher PIP and Edi when extubated from NAVA to NIV NAVA. This is most likely owing to the inefficiencies of NIV ventilation and suggests that neonates require a higher NAVA level when transitioning from NAVA to NIV NAVA.

Feasibility of neurally adjusted positive end-expiratory pressure in rabbits with early experimental lung injury.

BackgroundDuring conventional Neurally Adjusted Ventilatory Assist (NAVA), the electrical activity of the diaphragm (EAdi) is used for triggering and cycling-off inspiratory assist, with a fixed PEEP (so called “Triggered Neurally Adjusted Ventilatory Assist” or “tNAVA”). However, significant post-inspiratory activity of the diaphragm can occur, believed to play a role in maintaining end-expiratory lung volume. Adjusting pressure continuously, in proportion to both inspiratory and expiratory EAdi (Continuous NAVA, or cNAVA), would not only offer inspiratory assist for tidal breathing, but also may aid in delivering a “neurally adjusted PEEP”, and more specific breath-by-breath unloading.MethodsNine adult New Zealand white rabbits were ventilated during independent conditions of: resistive loading (RES1 or RES2), CO2 load (CO2) and acute lung injury (ALI), either via tracheotomy (INV) or non-invasively (NIV). There were a total of six conditions, applied in a non-randomized fashion: INV-RES1, INV-CO2, NIV-CO2, NIV-RES2, NIV-ALI, INV-ALI. For each condition, tNAVA was applied first (3 min), followed by 3 min of cNAVA. This comparison was repeated 3 times (repeated cross-over design). The NAVA level was always the same for both modes, but was newly titrated for each condition. PEEP was manually set to zero during tNAVA. During cNAVA, the assist during expiration was proportional to the EAdi. During all runs and conditions, ventilator-delivered pressure (Pvent), esophageal pressure (Pes), and diaphragm electrical activity (EAdi) were measured continuously. The tracings were analyzed breath-by-breath to obtain peak inspiratory and mean expiratory values.ResultsFor the same peak Pvent, the distribution of inspiratory and expiratory pressure differed between tNAVA and cNAVA. For each condition, the mean expiratory Pvent was always higher (for all conditions 4.0 ± 1.1 vs. 1.1 ± 0.5 cmH2O, P < 0.01) in cNAVA than in tNAVA. Relative to tNAVA, mean inspiratory EAdi was reduced on average (for all conditions) by 19 % (range 14 %–25 %), p < 0.05. Mean expiratory EAdi was also lower during cNAVA (during INV-RES1, INV-CO2, INV-ALI, NIV-CO2 and NIV-ALI respectively, P < 0.05). The inspiratory Pes was reduced during cNAVA all 6 conditions (p < 0.05). Unlike tNAVA, during cNAVA the expiratory pressure was comparable with that predicted mathematically (mean difference of 0.2 ± 0.8 cmH2O).ConclusionContinuous NAVA was able to apply neurally adjusted PEEP, which led to a reduction in inspiratory effort compared to triggered NAVA.

Heart–lung interactions during neurally adjusted ventilatory assist

IntroductionAssist in unison to the patient’s inspiratory neural effort and feedback-controlled limitation of lung distension with neurally adjusted ventilatory assist (NAVA) may reduce the negative effects of mechanical ventilation on right ventricular function.MethodsHeart–lung interaction was evaluated in 10 intubated patients with impaired cardiac function using esophageal balloons, pulmonary artery catheters and echocardiography. Adequate NAVA level identified by a titration procedure to breathing pattern (NAVAal), 50% NAVAal, and 200% NAVAal and adequate pressure support (PSVal, defined clinically), 50% PSVal, and 150% PSVal were implemented at constant positive end-expiratory pressure for 20 minutes each.ResultsNAVAal was 3.1 ± 1.1cmH2O/μV and PSVal was 17 ± 2 cmH20. For all NAVA levels negative esophageal pressure deflections were observed during inspiration whereas this pattern was reversed during PSVal and PSVhigh. As compared to expiration, inspiratory right ventricular outflow tract velocity time integral (surrogating stroke volume) was 103 ± 4%, 109 ± 5%, and 100 ± 4% for NAVAlow, NAVAal, and NAVAhigh and 101 ± 3%, 89 ± 6%, and 83 ± 9% for PSVlow, PSVal, and PSVhigh, respectively (p < 0.001 level-mode interaction, ANOVA). Right ventricular systolic isovolumetric pressure increased from 11.0 ± 4.6 mmHg at PSVlow to 14.0 ± 4.6 mmHg at PSVhigh but remained unchanged (11.5 ± 4.7 mmHg (NAVAlow) and 10.8 ± 4.2 mmHg (NAVAhigh), level-mode interaction p = 0.005). Both indicate progressive right ventricular outflow impedance with increasing pressure support ventilation (PSV), but no change with increasing NAVA level.ConclusionsRight ventricular performance is less impaired during NAVA compared to PSV as used in this study. Proposed mechanisms are preservation of cyclic intrathoracic pressure changes characteristic of spontaneous breathing and limitation of right-ventricular outflow impedance during inspiration, regardless of the NAVA level.Trial registrationClinicaltrials.gov Identifier: NCT00647361, registered 19 March 2008Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-014-0499-8) contains supplementary material, which is available to authorized users.

Neuro-ventilatory efficiency during weaning from mechanical ventilation using neurally adjusted ventilatory assist

Neuro-ventilatory efficiency (NVE), defined as the tidal volume to electrical diaphragm-activity ratio (VT/EAdi) at the beginning and end of the weaning process after acute hypoxaemic respiratory failure, may provide valuable information about patient recovery. This observational study included 12 patients breathing with neurally adjusted ventilatory assist (NAVA). When a spontaneous breathing trial (SBT) with pressure support of 7 cm H2O and PEEP was unsuccessful, NAVA was used and the level was adjusted to obtain an EAdi of ∼60% of maximal EAdi during SBT. VT and EAdi were recorded continuously. We compared changes in NVE between NAVA and SBT at the first failed and first successful SBT. When patients were switched from NAVA to SBT, NVE was significantly reduced during both unsuccessful and successful SBT (-56 and -38%, respectively); however, this reduction was significantly lower when SBT was successful (P=0.01). Between the first and last day of weaning, we observed that NVE decreased with NAVA [40.6 (27.7-89.5) vs 28.8 (18.6-46.7); P=0.002] with a significant decrease in NAVA level, whereas it remained unchanged during SBT [15.4 (10.7-39.1) vs 19.5 (11.6-29.6); P=0.50] with significant increases in both EAdi and VT and no difference in respiratory rhythm. These results suggest that in patients after respiratory failure and prolonged mechanical ventilation, changes in VT and NVE, between SBTs are indicative of patient recovery. Larger clinical trials are needed to clarify whether changes in NVE reliably predict weaning in patients ventilated with NAVA.

Physiologic response to various levels of pressure support and NAVA in prolonged weaning

Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation wherein the delivered assistance is proportional to diaphragm electrical activity (EAdi) throughout inspiration. We assessed the physiologic response to varying levels of NAVA and pressure support ventilation (PSV) in 13 tracheostomised patients with prolonged weaning. Each patient randomly underwent 8 trials, at four levels of assistance either in PSV and NAVA. i - high (no dyspnoea and/or distress); iv - low (associated with dyspnoea and/or distress; ii and iii - at ∼75% and ∼25% of the difference between high and low support respectively. We measured tidal volume (VT), peak EAdi, (EAdipeak) and airway pressure, ineffective efforts and breathing pattern variability. With both NAVA and PSV, decreasing assistance resulted in parallel significant increase in EAdipeak associated with a concomitant reduction in VT and minute ventilation in PSV, but not in NAVA. VT variability significantly increased when reducing ventilatory assistance in PSV only, while remained unchanged varying the NAVA level. The ineffective triggering index was not significantly different between the two modes. In patients with prolonged weaning, with the specific settings adopted, compared to PSV, NAVA reduced the risk of over-assistance and overall improved patient-ventilator interaction, while not significantly affecting patient-ventilator synchrony.

Effects of Neurally Adjusted Ventilatory Assist (NAVA) levels in non-invasive ventilated patients: titrating NAVA levels with electric diaphragmatic activity and tidal volume matching

BackgroundNeurally adjusted ventilatory assist (NAVA) delivers pressure in proportion to diaphragm electrical activity (Eadi). However, each patient responds differently to NAVA levels. This study aims to examine the matching between tidal volume (Vt) and patients’ inspiratory demand (Eadi), and to investigate patient-specific response to various NAVA levels in non-invasively ventilated patients.Methods12 patients were ventilated non-invasively with NAVA using three different NAVA levels. NAVA100 was set according to the manufacturer’s recommendation to have similar peak airway pressure as during pressure support. NAVA level was then adjusted ±50% (NAVA50, NAVA150). Airway pressure, flow and Eadi were recorded for 15 minutes at each NAVA level. The matching of Vt and integral of Eadi (ʃEadi) were assessed at the different NAVA levels. A metric, Range90, was defined as the 5-95% range of Vt/ʃEadi ratio to assess matching for each NAVA level. Smaller Range90 values indicated better matching of supply to demand.ResultsPatients ventilated at NAVA50 had the lowest Range90 with median 25.6 uVs/ml [Interquartile range (IQR): 15.4-70.4], suggesting that, globally, NAVA50 provided better matching between ʃEadi and Vt than NAVA100 and NAVA150. However, on a per-patient basis, 4 patients had the lowest Range90 values in NAVA100, 1 patient at NAVA150 and 7 patients at NAVA50. Robust coefficient of variation for ʃEadi and Vt were not different between NAVA levels.ConclusionsThe patient-specific matching between ʃEadi and Vt was variable, indicating that to obtain the best possible matching, NAVA level setting should be patient specific. The Range90 concept presented to evaluate Vt/ʃEadi is a physiologic metric that could help in individual titration of NAVA level.

Assessment of patient–ventilator breath contribution during neurally adjusted ventilatory assist

During neurally adjusted ventilatory assist (NAVA), it is difficult to quantify the relative contribution of the patient versus the ventilator to the inspiratory tidal volume (Vt(insp)). To solve this problem, we developed an index, the "patient-ventilator breath contribution" (PVBC), using the inspiratory deflection of the diaphragmatic electrical activity (∆EAdi) and Vt(insp) during assisted and non-assisted breaths. This study evaluated the PVBC index in an experimental setup. Nine intubated and sedated rabbits were studied during repeated ramp increases of the NAVA level. One breath was non-assisted at each NAVA level. The PVBC index was evaluated during resistive loading and after acute lung injury. PVBC was calculated by relating Vt(insp)/∆EAdi of a non-assisted breath to that of the preceding assisted breath. The PVBC was compared to the relative contribution of esophageal pressure (∆Pes) to transpulmonary pressure deflections (∆P (L,dyn)). The relationship between PVBC and ∆Pes/∆P (L,dyn) was slightly curvilinear with an intercept different from zero (y=-1x (2)+1.64x+0.21) and a determination coefficient (R (2)) of 0.95. Squaring the PVBC values resulted in a near perfect linear relationship (y=1.02x+0.05) between PVBC(2) and ∆Pes/∆P (L,dyn) with an R (2) of 0.97. This study shows that Vt(insp) and EAdi can be used to predict the contribution of the inspiratory muscles versus that of the ventilator during NAVA. If clinically applicable, this could serve to quantify and standardize the adjustment of the level of assist, and hence reduce the risks of excessive ventilatory assist. Further studies are required to evaluate if this method is clinically applicable.

Asynchrony, neural drive, ventilatory variability and COMFORT: NAVA versus pressure support in pediatric patients. A non-randomized cross-over trial

PurposeTo determine if neurally adjusted ventilatory assist (NAVA) improves asynchrony, ventilatory drive, breath-to-breath variability and COMFORT score when compared to pressure support (PS).MethodsThis is a non-randomized short-term cross-over trial in which 12 pediatric patients with asynchrony (auto-triggering, double triggering or non-triggered breaths) were enrolled. Four sequential 10-min periods of data were recorded after 20 min of ventilatory stabilization (wash-out) at each of the following settings: baseline PS with the ventilator settings determined by the attending physician (1-PSb); PS after optimization (2-PSopt); NAVA level set so that maximum inspiratory pressure (P max) equaled P max in PS (3-NAVA); same settings as in 2-PSopt (4-PSopt).ResultsThe median asynchrony index was significantly lower during NAVA (2.0 %) than during 2-PSopt (8.5 %, p = 0.017) and 4-PSopt (7.5 %, p = 0.008). In NAVA mode, the NAVA trigger accounted on average for 66 % of triggered breaths. The median trigger delay with respect to neural inspiratory time was significantly lower during NAVA (8.6 %) than during 2-PSopt (25.2 %, p = 0.003) and 4-PSopt (28.2 %, p = 0.0005). The median electrical activity of the diaphragm (EAdi) change during trigger delay normalized to maximum inspiratory EAdi difference was significantly lower during NAVA (5.3 %) than during 2-PSopt (21.7 %, p = 0.0005) and 4-PSopt (24.6 %, p = 0.001). The coefficient of variation of tidal volume was significantly higher during NAVA (44.2 %) than during 2-PSopt (19.8 %, p = 0.0002) and 4-PSopt (23.0 %, p = 0.0005). The median COMFORT score during NAVA (15.0) was lower than that during 2-PSopt (18.0, p = 0.0125) and 4-PSopt (17.5, p = 0.039). No significant changes for any variable were observed between 1-PSb and 2-PSopt.ConclusionsNeurally adjusted ventilatory assist as compared to optimized PS results in improved synchrony, reduced ventilatory drive, increased breath-to-breath mechanical variability and improved patient comfort.Electronic supplementary materialThe online version of this article (doi:10.1007/s00134-012-2535-y) contains supplementary material, which is available to authorized users.

Respiratory pattern during neurally adjusted ventilatory assist in acute respiratory failure patients

To investigate the effect of a wide range of assistance levels during neurally adjusted ventilatory assist (NAVA) and pressure support ventilation (PSV) on respiratory pattern, breathing variability, and incidence of tidal volumes (V (T)) above 8 and 10ml/kg in acute respiratory failure patients. Eight increasing NAVA levels (0.5, 1, 1.5, 2, 2.5, 3, 4, and 5cmH(2)O/μV) and four increasing pressure support (PSV) levels (4, 8, 12, and 16cmH(2)O) were applied to obtain 10min of stable recordings in 15 patients. One out of 15 patients did not sustain the NAVA levels of 3, 4, and 5cmH(2)O/μV and was excluded. The 5cmH(2)O/μV NAVA level was not tolerated by three patients and it was excluded. Increasing NAVA levels were associated with decreased diaphragm electrical activity (EAdi), and, at variance with PSV, with small changes in V (T), no changes in respiratory rate (RR), and increases in V (T) and EAdi variability. At high NAVA levels, an increase in V (T) variability was associated with increased incidence of V (T) above 8 and 10ml/kg and an uncomfortable respiratory pattern in some patients. Increasing NAVA levels were associated with no effect on RR, small increase in V (T), and increase in V (T) and EAdi variability. Effective decrease in EAdi occurred at NAVA levels below 2-2.5cmH(2)O/μV, while preserving respiratory variability and low risks of V (T) above 8 or 10ml/kg.

Neurally adjusted ventilatory assist in patients with critical illness-associated polyneuromyopathy

Diaphragmatic electrical activity (EA(di)), reflecting respiratory drive, and its feedback control might be impaired in critical illness-associated polyneuromyopathy (CIPM). We aimed to evaluate whether titration and prolonged application of neurally adjusted ventilatory assist (NAVA), which delivers pressure (P (aw)) in proportion to EA(di), is feasible in CIPM patients. Peripheral and phrenic nerve electrophysiology studies were performed in 15 patients with clinically suspected CIPM and in 14 healthy volunteers. In patients, an adequate NAVA level (NAVAal) was titrated daily and was implemented for a maximum of 72h. Changes in tidal volume (V (t)) generation per unit of EA(di) (V (t)/EA(di)) were assessed daily during standardized tests of neuro-ventilatory efficiency (NVET). In patients (median [range], 66 [44-80]years), peripheral electrophysiology studies confirmed CIPM. Phrenic nerve latency (PNL) was prolonged and diaphragm compound muscle action potential (CMAP) was reduced compared with healthy volunteers (p<0.05 for both). NAVAal could be titrated in all but two patients. During implementation of NAVAal for 61 (37-64)h, the EA(di) amplitude was 9.0 (4.4-15.2)μV, and the V (t) was 6.5 (3.7-14.3)ml/kg predicted body weight. V (t), respiratory rate, EA(di), PaCO(2), and hemodynamic parameters remained unchanged, while PaO(2)/FiO(2) increased from 238 (121-337) to 282 (150-440)mmHg (p=0.007) during NAVAal. V (t)/EA(di) changed by -10 (-46; +31)% during the first NVET and by -0.1 (-26; +77)% during the last NVET (p=0.048). In most patients with CIPM, EA(di) and its feedback control are sufficiently preserved to titrate and implement NAVA for up to 3days. Whether monitoring neuro-ventilatory efficiency helps inform the weaning process warrants further evaluation.

Neurally adjusted ventilatory assist vs. pressure support ventilation in critically ill patients: an observational study

During neurally adjusted ventilatory assist (NAVA), the inspiratory support is controlled by the patients' respiratory drive influenced by an operator-controlled gain factor (NAVA level). The purpose of our observational study was to transfer patients from conventional pressure support ventilation (PSV) to NAVA safely. We compared two approaches to set the NAVA level and evaluated the effect of NAVA. We studied mechanically ventilated patients capable of spontaneous breathing. For the change of the ventilator mode, we used a NAVA level calculated to generate a peak inspiratory pressure equal to PSV. We compared this NAVA level with a NAVA level determined by a NAVA level titration. Ventilatory and haemodynamic data were recorded during an observational period of 6 h. All 20 patients included in the study could be transferred from PSV to NAVA and completed the observation interval. Setting the NAVA level according to prior PSV settings proved to be a feasible approach, but in 75% of our patients, we modified the NAVA level according to the titration results. Gas exchange and ventilatory mechanics during the observation interval remained stable. The ventilator mode NAVA seems to be well tolerated in a heterogeneous group of critically ill patients. Pre-setting of the NAVA level during PSV can result in an overestimation of the required ventilator support. An additional titration of the NAVA level ads valuable information although difficult to interpret in some cases.

Identification of Adequate Neurally Adjusted Ventilatory Assist (NAVA) During Systematic Increases in the NAVA Level

Neurally adjusted ventilatory assist (NAVA) delivers airway pressure (Paw) in proportion to the electrical activity of the diaphragm (EAdi) using an adjustable proportionality constant (NAVA level, cm⋅H 2O/n}{}muV). During systematic increases in the NAVA level, feedback-controlled down-regulation of the EAdi results in a characteristic two-phased response in Paw and tidal volume (Vt). The transition from the 1st to the 2nd response phase allows identification of adequate unloading of the respiratory muscles with NAVA (NAVAAL). We aimed to develop and validate a mathematical algorithm to identify NAVAAL. Paw, Vt, and EAdi were recorded while systematically increasing the NAVA level in 19 adult patients. In a multistep approach, inspiratory Paw peaks were first identified by dividing the EAdi into inspiratory portions using Gaussian mixture modeling. Two polynomials were then fitted onto the curves of both Paw peaks and Vt. The beginning of the Paw and Vt plateaus, and thus NAVA AL, was identified at the minimum of squared polynomial derivative and polynomial fitting errors. A graphical user interface was developed in the Matlab computing environment. Median NAVAAL visually estimated by 18 independent physicians was 2.7 (range 0.4 to 5.8) cm⋅H 2O/n}{}muV and identified by our model was 2.6 (range 0.6 to 5.0) cm⋅H 2O/n}{}muV. NAVAAL identified by our model was below the range of visually estimated NAVAAL in two instances and was above in one instance. We conclude that our model identifies NAVAAL in most instances with acceptable accuracy for application in clinical routine and research.