Improved synchrony and respiratory unloading by neurally adjusted ventilatory assist (NAVA) in lung-injured rabbits

Induction of subject-ventilator asynchrony by variation of respiratory parameters in a lung injury model in pigs

BACKGROUND

Subject-ventilator asynchrony (SVA) was shown to be associated with negative clinical outcomes. To elucidate pathophysiology pathways and effects of SVA on lung tissue histology a reproducible animal model of artificially induced asynchrony was developed and evaluated.

METHODS

Alterations in ventilator parameters were used to induce the three main types of asynchrony: ineffective efforts (IE), auto-triggering (AT), and double-triggering (DT). Airway flow and pressure, as well as oesophageal pressure waveforms, were recorded, asynchrony cycles were manually classified and the asynchrony index (AIX) was calculated. Bench tests were conducted on an active lung simulator with ventilator settings altered cycle by cycle. The developed algorithm was evaluated in three pilot experiments and a study in pigs ventilated for twelve hours with AIX = 25%.

RESULTS

IE and AT were induced reliably and fail-safe by end-expiratory hold and adjustment of respiratory rate, respectively. DT was provoked using airway pressure ramp prolongation, however not controlled specifically in the pilots. In the subsequent study, an AIX = 28.8% [24.0%-34.4%] was induced and maintained over twelve hours.

CONCLUSIONS

The method allows to reproducibly induce and maintain three clinically relevant types of SVA observed in ventilated patients and may thus serve as a useful tool for future investigations on cellular and inflammatory effects of asynchrony.

Trends in the Incidence of Bronchopulmonary Dysplasia after the Introduction of Neurally Adjusted Ventilatory Assist (NAVA)

OBJECTIVE

This study investigates the difference in the rates of bronchopulmonary dysplasia in very low birth weight infants before and after the introduction of neurally adjusted ventilatory assist (NAVA).

STUDY DESIGN

A retrospective cohort study comparing rates of Bronchopulmonary dysplasia (BPD) before and after implementation of NAVA. Eligibility criteria included all very low birth weight VLBW neonates needing ventilation. For analysis, each cohort was divided into three subgroups based on gestational age. Changes in the rate of BPD, length of stay, tracheostomy rates, invasive ventilator days, and home oxygen therapy were compared.

RESULTS

There were no differences in the incidence of BPD in neonates at 23-25 6/7 weeks' and 29-32 weeks' gestation between the two cohorts. A higher incidence of BPD was seen in the 26-28 5/7 weeks' gestation NAVA subgroup compared to controls (86% vs. 68%, p = 0.05). No significant difference was found for ventilator days, but infants in the 26-28 6/7 subgroup in the NAVA cohort had a longer length of stay (98 ± 34 days vs. 82 ± 24 days, p = 0.02), a higher percentage discharged on home oxygen therapy (45% vs. 18%, respectively, p = 0.006), and higher tracheostomy rates (3/36 vs. 0/60, p = 0.02), compared to the control group.

CONCLUSIONS

The NAVA mode was not associated with a reduction in BPD when compared to other modes of ventilation. Unexpected increases were seen in BPD rates, home oxygen therapy rates, tracheostomy rates, and the length of stay in the NAVA subgroup born at 26-28 6/7 weeks' gestation.

Monitoring the patient-ventilator asynchrony during non-invasive ventilation

Patient-ventilator asynchrony is a major issue during non-invasive ventilation and may lead to discomfort and treatment failure. Therefore, the identification and prompt management of asynchronies are of paramount importance during non-invasive ventilation (NIV), in both pediatric and adult populations. In this review, we first define the different forms of asynchronies, their classification, and the method of quantification. We, therefore, describe the technique to properly detect patient-ventilator asynchronies during NIV in pediatric and adult patients with acute respiratory failure, separately. Then, we describe the actions that can be implemented in an attempt to reduce the occurrence of asynchronies, including the use of non-conventional modes of ventilation. In the end, we analyzed what the literature reports on the impact of asynchronies on the clinical outcomes of infants, children, and adults.

Neurally Adjusted Ventilatory Assist in Acute Respiratory Failure-A Narrative Review

Maintaining spontaneous breathing has both potentially beneficial and deleterious consequences in patients with acute respiratory failure, depending on the balance that can be obtained between the protecting and damaging effects on the lungs and the diaphragm. Neurally adjusted ventilatory assist (NAVA) is an assist mode, which supplies the respiratory system with a pressure proportional to the integral of the electrical activity of the diaphragm. This proportional mode of ventilation has the theoretical potential to deliver lung- and respiratory-muscle-protective ventilation by preserving the physiologic defense mechanisms against both lung overdistention and ventilator overassistance, as well as reducing the incidence of diaphragm disuse atrophy while maintaining patient–ventilator synchrony. This narrative review presents an overview of NAVA technology, its basic principles, the different methods to set the assist level and the findings of experimental and clinical studies which focused on lung and diaphragm protection, machine–patient interaction and preservation of breathing pattern variability. A summary of the findings of the available clinical trials which investigate the use of NAVA in acute respiratory failure will also be presented and discussed.

A narrative review of advanced ventilator modes in the pediatric intensive care unit

Respiratory failure is a common reason for pediatric intensive care unit admission. The vast majority of children requiring mechanical ventilation can be supported with conventional mechanical ventilation (CMV) but certain cases with refractory hypoxemia or hypercapnia may require more advanced modes of ventilation. This paper discusses what we have learned about the use of advanced ventilator modes [e.g., high-frequency oscillatory ventilation (HFOV), high-frequency percussive ventilation (HFPV), high-frequency jet ventilation (HFJV) airway pressure release ventilation (APRV), and neurally adjusted ventilatory assist (NAVA)] from clinical, animal, and bench studies. The evidence supporting advanced ventilator modes is weak and consists of largely of single center case series, although a few RCTs have been performed. Animal and bench models illustrate the complexities of different modes and the challenges of applying these clinically. Some modes are proprietary to certain ventilators, are expensive, or may only be available at well-resourced centers. Future efforts should include large, multicenter observational, interventional, or adaptive design trials of different rescue modes (e.g., PROSpect trial), evaluate their use during ECMO, and should incorporate assessments through volumetric capnography, electric impedance tomography, and transpulmonary pressure measurements, along with precise reporting of ventilator parameters and physiologic variables.

Feasibility of neurally synchronized and proportional negative pressure ventilation in a small animal model

RATIONALE

Synchronized positive pressure ventilation is possible using diaphragm electrical activity (EAdi) to control the ventilator. It is unknown whether EAdi can be used to control negative pressure ventilation.

AIM

To evaluate the feasibility of using EAdi to control negative pressure ventilation.

METHODS

Fourteen anesthetized rats were studied (380-590 g) during control, resistive breathing, acute lung injury or CO₂ rebreathing. Positive pressure continuous neurally adjusted ventilatory assist (cNAVA^P+ ) was applied via intubation. Negative pressure cNAVA (cNAVA^P- ) was applied with the animal placed in a sealed box. In part 1, automatic stepwise increments in cNAVA level by 0.2 cmH₂ O/µV every 30 s was applied for cNAVA^P+ , cNAVA^P- , and a 50/50 combination of the two (cNAVA^P± ). In part 2: During 5-min ventilation with cNAVA^P+ or cNAVA^P- we measured circuit, box, and esophageal (Pes) pressure, EAdi, blood pressure, and arterial blood gases.

RESULTS

Part 1: During cNAVA^P+ , pressure in the circuit increased with increasing cNAVA levels, reaching a plateau, and similarly for cNAVA^P- , albeit reversed in sign. This was associated with downregulation of the EAdi. Pes swings became less negative with cNAVA^P+ but, in contrast, Pes swings were more negative during increasing cNAVA^P- levels. Increasing the cNAVA level during cNAVA^P± resulted in an intermediate response. Part 2: no significant differences were observed for box/circuit pressures, EAdi, blood pressure, or arterial blood gases. Pes swings during cNAVA^P- were significantly more negative than during cNAVA^P+ .

CONCLUSION

Negative pressure ventilation synchronized and proportional to the diaphragm activity is feasible in small animals.

Neural control of pressure support ventilation improved patient-ventilator synchrony in patients with different respiratory system mechanical properties: a prospective, crossover trial

Background

Conventional pressure support ventilation (PS_P) is triggered and cycled off by pneumatic signals such as flow. Patient-ventilator asynchrony is common during pressure support ventilation, thereby contributing to an increased inspiratory effort. Using diaphragm electrical activity, neurally controlled pressure support (PS_N) could hypothetically eliminate the asynchrony and reduce inspiratory effort. The purpose of this study was to compare the differences between PS_N and PS_P in terms of patient-ventilator synchrony, inspiratory effort, and breathing pattern.

Methods

Eight post-operative patients without respiratory system comorbidity, eight patients with acute respiratory distress syndrome (ARDS) and obvious restrictive acute respiratory failure (ARF), and eight patients with chronic obstructive pulmonary disease (COPD) and mixed restrictive and obstructive ARF were enrolled. Patient-ventilator interactions were analyzed with macro asynchronies (ineffective, double, and auto triggering), micro asynchronies (inspiratory trigger delay, premature, and late cycling), and the total asynchrony index (AI). Inspiratory efforts for triggering and total inspiration were analyzed.

Results

Total AI of PS_N was consistently lower than that of PS_P in COPD (3% vs. 93%, P = 0.012 for 100% support level; 8% vs. 104%, P = 0.012 for 150% support level), ARDS (8% vs. 29%, P = 0.012 for 100% support level; 16% vs. 41%, P = 0.017 for 150% support level), and post-operative patients (21% vs. 35%, P = 0.012 for 100% support level; 15% vs. 50%, P = 0.017 for 150% support level). Improved support levels from 100% to 150% statistically increased total AI during PS_P but not during PS_N in patients with COPD or ARDS. Patients’ inspiratory efforts for triggering and total inspiration were significantly lower during PS_N than during PS_P in patients with COPD or ARDS under both support levels (P < 0.05). There was no difference in breathing patterns between PS_N and PS_P.

Conclusions

PS_N improves patient-ventilator synchrony and generates a respiratory pattern similar to PS_P independently of any level of support in patients with different respiratory system mechanical properties. PS_N, which reduces the trigger and total patient's inspiratory effort in patients with COPD or ARDS, might be an alternative mode for PS_P.

Trial Registration

ClinicalTrials.gov, NCT01979627; https://clinicaltrials.gov/ct2/show/record/NCT01979627.

Neurally adjusted ventilatory assist after surgical treatment of intracerebral hemorrhage: a randomized crossover study

OBJECTIVE

We assessed the neuromechanical efficiency (NME), neuroventilatory efficiency (NVE), and diaphragmatic function effects between pressure support ventilation (PSV) and neutrally adjusted ventilatory assist (NAVA).

METHODS

Fifteen patients who had undergone surgical treatment of intracerebral hemorrhage were enrolled in this randomized crossover study. The patients were assigned to PSV for the first 24 hours and then to NAVA for the following 24 hours or vice versa. The monitored ventilatory parameters under the two ventilation models were compared. NME, NVE, and diaphragmatic function were compared between the two ventilation models.

RESULTS

One patient's illness worsened during the study. The study was stopped for this patient, and intact data were obtained from the other 14 patients and analyzed. The monitored tidal volume was significantly higher with PSV than NAVA (487 [443-615] vs. 440 [400-480] mL, respectively). NME, NVE, diaphragmatic function, and the partial pressures of arterial carbon dioxide and oxygen were not significantly different between the two ventilation models.

CONCLUSION

The tidal volume was lower with NAVA than PSV; however, the patients' selected respiratory pattern during NAVA did not change the NME, NVE, or diaphragmatic function.Clinical trial registration no. ChiCTR1900022861.

Noninvasive Neurally Adjusted Ventilator Assist Ventilation in the Postoperative Period Produces Better Patient-Ventilator Synchrony but Not Comfort

Background

Noninvasive neurally adjusted ventilatory assist (NAVA) has been shown to improve patient-ventilator interaction in many settings. There is still scarce data with regard to postoperative patients indicated for noninvasive ventilation (NIV) which this study elates. The purpose of this trial was to evaluate postoperative patients for synchrony and comfort in noninvasive pressure support ventilation (NIV-PSV) vs. NIV-NAVA.

Methods

Twenty-two subjects received either NIV-NAVA or NIV-PSV in an object-blind, prospective, randomized, crossover fashion (observational trial). We evaluated blood gases and ventilator tracings throughout as well as comfort of ventilation at the end of each ventilation phase.

Results

There was an effective reduction in ventilator delays (p < 0.001) and negative pressure duration in NIV-NAVA as compared to NIV-PSV (p < 0.001). Although we used optimized settings in NIV-PSV, explaining the overall low incidence of asynchrony, NIV-NAVA led to reductions in the NeuroSync-index (p < 0.001) and all types of asynchrony except for double triggering that was significantly more frequent in NIV-NAVA vs. NIV-PSV (p = 0.02); ineffective efforts were reduced to zero by use of NIV-NAVA. In our population of previously lung-healthy subjects, we did not find differences in blood gases and patient comfort between the two modes.

Conclusion

In the postoperative setting, NIV-NAVA is well suitable for use and effective in reducing asynchronies as well as a surrogate for work of breathing. Although increased synchrony was not transferred into an increased comfort, there was an advantage with regard to patient-ventilator interaction. The trial was registered at the German clinical Trials Register (DRKS no.: DRKS00005408).

Comparison of extubation success using noninvasive positive pressure ventilation (NIPPV) versus noninvasive neurally adjusted ventilatory assist (NI-NAVA)

OBJECTIVE

Compare rates of initial extubation success in preterm infants extubated to NIPPV or NI-NAVA.

STUDY DESIGN

In this pilot study, we randomized 30 mechanically ventilated preterm infants at the time of initial elective extubation to NI-NAVA or NIPPV in a 1:1 assignment. Primary study outcome was initial extubation success.

RESULTS

Rates of continuous extubation for 120 h were 92% in the NI-NAVA group and 69% in the NIPPV group (12/13 vs. 9/13, respectively, p = 0.14). Infants extubated to NI-NAVA remained extubated longer (median 18 vs. 4 days, p = 0.02) and experienced lower peak inspiratory pressures (PIP) than infants managed with NIPPV throughout the first 3 days after extubation. Survival analysis through 14 days post extubation showed a sustained difference in the primary study outcome until 12 days post extubation.

CONCLUSIONS

Our study is the first to suggest that a strategy of extubating preterm infants to NI-NAVA may be more successful.

Neurally adjusted ventilatory assist mitigates ventilator-induced diaphragm injury in rabbits

Background

Ventilator-induced diaphragmatic dysfunction is a serious complication associated with higher ICU mortality, prolonged mechanical ventilation, and unsuccessful withdrawal from mechanical ventilation. Although neurally adjusted ventilatory assist (NAVA) could be associated with lower patient-ventilator asynchrony compared with conventional ventilation, its effects on diaphragmatic dysfunction have not yet been well elucidated.

Methods

Twenty Japanese white rabbits were randomly divided into four groups, (1) no ventilation, (2) controlled mechanical ventilation (CMV) with continuous neuromuscular blockade, (3) NAVA, and (4) pressure support ventilation (PSV). Ventilated rabbits had lung injury induced, and mechanical ventilation was continued for 12 h. Respiratory waveforms were continuously recorded, and the asynchronous events measured. Subsequently, the animals were euthanized, and diaphragm and lung tissue were removed, and stained with Hematoxylin-Eosin to evaluate the extent of lung injury. The myofiber cross-sectional area of the diaphragm was evaluated under the adenosine triphosphatase staining, sarcomere disruptions by electron microscopy, apoptotic cell numbers by the TUNEL method, and quantitative analysis of Caspase-3 mRNA expression by real-time polymerase chain reaction.

Results

Physiological index, respiratory parameters, and histologic lung injury were not significantly different among the CMV, NAVA, and PSV. NAVA had lower asynchronous events than PSV (median [interquartile range], NAVA, 1.1 [0–2.2], PSV, 6.8 [3.8–10.0], p = 0.023). No differences were seen in the cross-sectional areas of myofibers between NAVA and PSV, but those of Type 1, 2A, and 2B fibers were lower in CMV compared with NAVA. The area fraction of sarcomere disruptions was lower in NAVA than PSV (NAVA vs PSV; 1.6 [1.5–2.8] vs 3.6 [2.7–4.3], p < 0.001). The proportion of apoptotic cells was lower in NAVA group than in PSV (NAVA vs PSV; 3.5 [2.5–6.4] vs 12.1 [8.9–18.1], p < 0.001). There was a tendency in the decreased expression levels of Caspase-3 mRNA in NAVA groups. Asynchrony Index was a mediator in the relationship between NAVA and sarcomere disruptions.

Conclusions

Preservation of spontaneous breathing using either PSV or NAVA can preserve the cross sectional area of the diaphragm to prevent atrophy. However, NAVA may be superior to PSV in preventing sarcomere injury and apoptosis of myofibrotic cells of the diaphragm, and this effect may be mediated by patient-ventilator asynchrony.

Nasal continuous positive airway pressure (NCPAP) or noninvasive neurally adjusted ventilatory assist (NIV-NAVA) for preterm infants with respiratory distress after birth: A randomized controlled trial

OBJECTIVES

To compare rates of treatment failure between the use of nasal continuous positive airway pressure (NCPAP) and noninvasive neurally adjusted ventilatory assist (NIV-NAVA) in infants with respiratory distress after birth.

METHODS

A randomized, unblinded, double-center trial was conducted in infants with birth weights (BWs) less than or equal to 1500 g and respiratory distress receiving noninvasive respiratory support for less than or equal to 48 hours of life; some infants were initially treated with minimally invasive surfactant therapy as the standard of care.

PRIMARY OUTCOME

need for endotracheal intubation with use of mechanical ventilation (MV) at less than or equal to 72 hours of life using prespecified failure criteria.

SECONDARY OUTCOMES

use of surfactant, duration of noninvasive support, duration of MV, bronchopulmonary dysplasia (BPD) and death.

RESULTS

A total of 123 infants were included (NCPAP group = 64 and NIV-NAVA group = 59). Population characteristics were similar between groups. No difference in the primary outcome was observed: NCPAP = 10 (15.6%) and NIV-NAVA = 12 (20.3%), P = .65. Groups were also similar in the use of surfactant (19 vs 17), duration of noninvasive support (147 ± 181 hours vs 127 ± 137 hours), BPD incidence and death. However, duration of MV was significantly longer in NCPAP group (95.6 ± 45.8 hours vs 28.25 ± 34.1 hour), P = .01.

CONCLUSION

In infants with respiratory distress after birth, no differences in treatment failures were observed between NIV-NAVA and NCPAP. These results require further evaluation in a larger study.

Monitoring of Electrical Activity of the Diaphragm Shows Failure of T-Piece Trial Earlier than Protocol-Based Parameters in Prolonged Weaning in Non-communicative Neurological Patients

BACKGROUND

The weaning target in tracheotomised patients is not extubation, but spontaneous breathing without the support of a ventilator. Overloading the respiratory pump during such spontaneous breathing trials is unfavorable, prolongs weaning time, and increases morbidity and mortality. The goal of this study was to evaluate the electrical activity of the diaphragm during a t-piece trial in non-communicative neurological patients and the comparison to clinical parameters of exhaustion.

METHODS

During multiple t-piece trials, the electrical activity of the diaphragm was obtained before, during and after the end of the trial. T-piece trials were grouped based on the reason for stopping the trial (exhaustion or allotted time period).

RESULTS

Twenty-nine tracheotomised patients in prolonged weaning (29 ± 22 days ventilated at the start of the study) were included in a prospective observational study. T-piece trials (n = 152; 5 ± 2 per patient) were grouped based on the reason for stopping the trial (n = 91 because of exhaustion; n = 61 because of the allotted time period). We found that the electrical activity of the diaphragm exhibits an earlier increase than protocol-based clinical parameters in patients who failed the trial due to exhaustion. The electrical activity of the diaphragm shows no relevant difference during the t-piece trial in patients in whom the trial was stopped due to the allotted time period per protocol.

CONCLUSIONS

Monitoring the electrical activity of the diaphragm in non-communicative neurological patients in prolonged weaning allows earlier detection of exhaustion than protocol-based parameters.

Effects of neurally adjusted ventilatory assist on air distribution and dead space in patients with acute exacerbation of chronic obstructive pulmonary disease

Background

Neurally adjusted ventilatory assist (NAVA) could improve patient-ventilator interaction; its effects on ventilation distribution and dead space are still unknown. The aim of this study was to evaluate the effects of varying levels of assist during NAVA and pressure support ventilation (PSV) on ventilation distribution and dead space in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

Methods

Fifteen mechanically ventilated patients with AECOPD were included in the study. The initial PSV levels were set to 10 cmH₂O for 10 min. Thereafter, the ventilator mode was changed to NAVA for another 10 min with the same electrical activity of the diaphragm as during PSV. Furthermore, the ventilation mode was switched between PSV and NAVA every 10 min in the following order: PSV 5 cmH₂O; NAVA 50%; PSV 15 cmH₂O; and NAVA 150% (relative to the initial NAVA support level). Ventilation distribution in the lung was evaluated in percentages in regions of interest (ROI) of four anteroposterior segments of equal height (ROI1 to ROI4 represents ventral, mid-ventral, mid-dorsal, and dorsal, respectively). Blood gases, ventilation distribution (electrical impedance tomography), diaphragm activity (B-mode ultrasonography), and dead space fraction (PeCO₂ and PaCO₂) were measured.

Results

The trigger and cycle delays were lower during NAVA than during PSV. The work of trigger was significantly lower during NAVA compared to PSV. The diaphragm activities based on ultrasonography were higher during NAVA compared to the same support level during PSV. The ventilation distribution in ROI4 increased significantly (P < 0.05) during NAVA compared to PSV (except for a support level of 50%). Similar results were found in ROI3 + 4. NAVA reduced dead space fraction compared to the corresponding support level of PSV.

Conclusions

NAVA was superior to PSV in AECOPD for increasing ventilation distribution in ROI4 and reducing dead space.

Trial registration

Clinicaltrials.gov, NCT02289573. Registered on 12 November 2014.

Bio-Inspired Controller on an FPGA Applied to Closed-Loop Diaphragmatic Stimulation

Cervical spinal cord injury can disrupt connections between the brain respiratory network and the respiratory muscles which can lead to partial or complete loss of ventilatory control and require ventilatory assistance. Unlike current open-loop technology, a closed-loop diaphragmatic pacing system could overcome the drawbacks of manual titration as well as respond to changing ventilation requirements. We present an original bio-inspired assistive technology for real-time ventilation assistance, implemented in a digital configurable Field Programmable Gate Array (FPGA). The bio-inspired controller, which is a spiking neural network (SNN) inspired by the medullary respiratory network, is as robust as a classic controller while having a flexible, low-power and low-cost hardware design. The system was simulated in MATLAB with FPGA-specific constraints and tested with a computational model of rat breathing; the model reproduced experimentally collected respiratory data in eupneic animals. The open-loop version of the bio-inspired controller was implemented on the FPGA. Electrical test bench characterizations confirmed the system functionality. Open and closed-loop paradigm simulations were simulated to test the FPGA system real-time behavior using the rat computational model. The closed-loop system monitors breathing and changes in respiratory demands to drive diaphragmatic stimulation. The simulated results inform future acute animal experiments and constitute the first step toward the development of a neuromorphic, adaptive, compact, low-power, implantable device. The bio-inspired hardware design optimizes the FPGA resource and time costs while harnessing the computational power of spike-based neuromorphic hardware. Its real-time feature makes it suitable for in vivo applications.

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

BACKGROUND

During 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.

METHODS

Nine adult New Zealand white rabbits were ventilated during independent conditions of: resistive loading (RES(1) or RES(2)), 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-RES(1), INV-CO2, NIV-CO2, NIV-RES(2), 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.

RESULTS

For 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-RES(1), 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).

CONCLUSION

Continuous NAVA was able to apply neurally adjusted PEEP, which led to a reduction in inspiratory effort compared to triggered NAVA.

Neurally adjusted ventilatory assist

Purpose of review

Compared with the conventional forms of partial support, neurally adjusted ventilatory assist was repeatedly shown to improve patient–ventilator synchrony and reduce the risk of overassistance, while guaranteeing adequate inspiratory effort and gas exchange. A few animal studies also suggested the potential of neurally adjusted ventilatory assist in averting the risk of ventilator-induced lung injury. Recent work adds new information on the physiological effects of neurally adjusted ventilatory assist.

Recent findings

Compared with pressure support, neurally adjusted ventilatory assist has been shown to improve patient–ventilator interaction and synchrony in patients with the most challenging respiratory system mechanics, such as very low compliance consequent to severe acute respiratory distress syndrome and high resistance and air trapping due to chronic airflow obstruction; enhance redistribution of the ventilation in the dependent lung regions; avert the risk of patient–ventilator asynchrony due to sedation; avoid central apneas; limit the risk of high (injurious) tidal volumes in patients with acute respiratory distress syndrome of varied severity; and improve patient–ventilator interaction and synchrony during noninvasive ventilation, irrespective of the interface utilized.

Summary

Several studies nowadays prove the physiological benefits of neurally adjusted ventilatory assist, as opposed to the conventional modes of partial support. Whether these advantages translate into improvement of clinical outcomes remains to be determined.

Neurally adjusted ventilator assist in very low birth weight infants: Current status

Continuous improvements in perinatal care have resulted in increased survival of premature infants. Their immature lungs are prone to injury with mechanical ventilation and this may develop into chronic lung disease (CLD) or bronchopulmonary dysplasia. Strategies to minimize the risk of lung injury have been developed and include improved antenatal management (education, regionalization, steroids, and antibiotics), exogenous surfactant administration and reduction of barotrauma by using exclusive or early noninvasive ventilatory support. The most frequently used mode of assisted ventilation is pressure support ventilation that may lead to patient-ventilator asynchrony that is associated with poor outcome. Ventilator-induced diaphragmatic dysfunction or disuse atrophy of diaphragm fibers may also occur. This has led to the development of new ventilation modes including neurally adjusted ventilatory assist (NAVA). This ventilation mode is controlled by electrodes embedded within a nasogastric catheter which detect the electrical diaphragmatic activity (Edi) and transmit it to trigger the ventilator in synchrony with the patient’s own respiratory efforts. This permits the patient to control peak inspiratory pressure, mean airway pressure and tidal volume. Back up pressure control (PC) is provided when there is no Edi signal and no pneumatic trigger. Compared with standard conventional ventilation, NAVA improves blood gas regulation with lower peak inspiratory pressure and oxygen requirements in preterm infants. NAVA is safe mode of ventilation. The majority of studies have shown no significant adverse events in neonates ventilated with NAVA nor a difference in the rate of intraventricular hemorrhage, pneumothorax, or necrotizing enterocolitis when compared to conventional ventilation. Future large size randomized controlled trials should be established to compare NAVA with volume targeted and pressure controlled ventilation in newborns with mature respiratory drive. Most previous studies and trials were not sufficiently large and did not include long-term patient oriented outcomes. Multicenter, randomized, outcome trials are needed to determine whether NAVA is effective in avoiding intubation, facilitating extubation, decreasing time of ventilation, reducing the incidence of CLD, decreasing length of stay, and improving long-term outcomes such as the duration of ventilation, length of hospital stay, rate of pneumothorax, CLD and other major complications of prematurity. In order to prevent barotrauma, next generations of NAVA equipment for neonatal use should enable automatic setting of ventilator parameters in the backup PC mode based on the values generated by NAVA. They should also include an upper limit to the inspiratory time as in conventional ventilation. The manufacturers of Edi catheters should produce smaller sizes available for extreme low birth weight infants. Newly developed ventilators should also include leak compensation and high frequency ventilation. A peripheral flow sensor is also essential to the proper delivery of all modes of conventional ventilation as well as NAVA.

Application of neurally adjusted ventilatory assist in neonates

Neurally adjusted ventilatory assist (NAVA) uses the electrical activity of the diaphragm (Edi) as a neural trigger to synchronize mechanical ventilatory breaths with the patient's neural respiratory drive. Using this signal enables the ventilator to proportionally support the patient's instantaneous drive on a breath-by-breath basis. Synchrony can be achieved even in the presence of significant air leaks, which make this an attractive choice for invasive and non-invasive ventilation of the neonate. This paper describes the Edi signal, neuroventilatory coupling, and patient-ventilator synchrony including the functional concept of NAVA. Safety features, NAVA terminology, and clinical application of NAVA to unload respiratory musculature are presented. The use of the Edi signal as a respiratory vital sign for conventional ventilation is discussed. The results of animal and adult studies are briefly summarized and detailed descriptions of all NAVA-related research in pediatric and neonatal patients are provided. Further studies are needed to determine whether NAVA will have significant impact on the overall outcomes of neonates.

Patient-ventilator asynchrony during noninvasive pressure support ventilation and neurally adjusted ventilatory assist in infants and children

OBJECTIVES

To document the prevalence of asynchrony events during noninvasive ventilation in pressure support in infants and in children and to compare the results with neurally adjusted ventilatory assist.

DESIGN

Prospective randomized cross-over study in children undergoing noninvasive ventilation.

SETTING

The study was performed in a PICU.

PATIENTS

From 4 weeks to 5 years.

INTERVENTIONS

Two consecutive ventilation periods (pressure support and neurally adjusted ventilatory assist) were applied in random order. During pressure support (PS), three levels of expiratory trigger (ETS) setting were compared: initial ETS (PSinit), and ETS value decreased and increased by 15%. Of the three sessions, the period allowing for the lowest number of asynchrony events was defined as PSbest. Neurally adjusted ventilator assist level was adjusted to match the maximum airway pressure during PSinit. Positive end-expiratory pressure was the same during pressure support and neurally adjusted ventilator assist. Asynchrony events, trigger delay, and cycling-off delay were quantified for each period.

RESULTS

Six infants and children were studied. Trigger delay was lower with neurally adjusted ventilator assist versus PSinit and PSbest (61 ms [56-79] vs 149 ms [134-180] and 146 ms [101-162]; p = 0.001 and 0.02, respectively). Inspiratory time in excess showed a trend to be shorter during pressure support versus neurally adjusted ventilator assist. Main asynchrony events during PSinit were autotriggering (4.8/min [1.7-12]), ineffective efforts (9.9/min [1.7-18]), and premature cycling (6.3/min [3.2-18.7]). Premature cycling (3.4/min [1.1-7.7]) was less frequent during PSbest versus PSinit (p = 0.059). The asynchrony index was significantly lower during PSbest versus PSinit (40% [28-65] vs 65.5% [42-76], p < 0.001). With neurally adjusted ventilator assist, all types of asynchronies except double triggering were reduced. The asynchrony index was lower with neurally adjusted ventilator assist (2.3% [0.7-5] vs PSinit and PSbest, p < 0.05 for both comparisons).

CONCLUSION

Asynchrony events are frequent during noninvasive ventilation with pressure support in infants and in children despite adjusting the cycling-off criterion. Compared with pressure support, neurally adjusted ventilator assist allows improving patient-ventilator synchrony by reducing trigger delay and the number of asynchrony events. Further studies should determine the clinical impact of these findings.

Advances in Ventilation — Neurally Adjusted Ventilatory Assist (NAVA)

This review aims to introduce neurally-adjusted ventilatory assist (NAVA) to readers who do not have experience in using this form of ventilation. We will describe the basic principles and theoretical advantages of NAVA together with our experiences of introducing and using this mode in an intensive care unit.

Electrical activity of the diaphragm (EAdi) as a monitoring parameter in difficult weaning from respirator: a pilot study

INTRODUCTION

A reliable prediction of successful weaning from respiratory support may be crucial for the overall outcome of the critically ill patient. The electrical activity of the diaphragm (EAdi) allows one to monitor the patients' respiratory drive and their ability to meet the increased respiratory demand. In this pilot study, we compared the EAdi with conventional parameters of weaning failure, such as the ratio of respiratory rate to tidal volume.

METHODS

We studied 18 mechanically ventilated patients considered difficult to wean. For a spontaneous breathing trial (SBT), the patients were disconnected from the ventilator and given oxygen through a T-piece. The SBT was evaluated by using standard criteria.

RESULTS

Twelve patients completed the SBT successfully, and six failed. The EAdi was significantly different in the two groups. We found an early increase in EAdi in the failing patients that was more pronounced than in any of the patients who successfully passed the SBT. Changes in EAdi predicted an SBT failure earlier than did conventional parameters.

CONCLUSIONS

EAdi monitoring adds valuable information during weaning from the ventilator and may help to identify patients who are not ready for discontinuation of respiratory support.

Ventilation distribution measured with EIT at varying levels of pressure support and Neurally Adjusted Ventilatory Assist in patients with ALI

PURPOSE

The purpose of this study was to compare the effect of varying levels of assist during pressure support (PSV) and Neurally Adjusted Ventilatory Assist (NAVA) on the aeration of the dependent and non-dependent lung regions by means of Electrical Impedance Tomography (EIT).

METHODS

We studied ten mechanically ventilated patients with Acute Lung Injury (ALI). Positive-End Expiratory Pressure (PEEP) and PSV levels were both 10 cm H₂O during the initial PSV step. Thereafter, we changed the inspiratory pressure to 15 and 5 cm H₂O during PSV. The electrical activity of the diaphragm (EAdi) during pressure support ten was used to define the initial NAVA gain (100 %). Thereafter, we changed NAVA gain to 150 and 50 %, respectively. After each step the assist level was switched back to PSV 10 cm H₂O or NAVA 100 % to get a new baseline. The EIT registration was performed continuously.

RESULTS

Tidal impedance variation significantly decreased during descending PSV levels within patients, whereas not during NAVA. The dorsal-to-ventral impedance distribution, expressed according to the center of gravity index, was lower during PSV compared to NAVA. Ventilation contribution of the dependent lung region was equally in balance with the non-dependent lung region during PSV 5 cm H₂O, NAVA 50 and 100 %.

CONCLUSION

Neurally Adjusted Ventilatory Assist ventilation had a beneficial effect on the ventilation of the dependent lung region and showed less over-assistance compared to PSV in patients with ALI.

Nontraditional modes of mechanical ventilation: progress or distraction?

As technology continues to develop, a wide range of novel and nontraditional modes of mechanical ventilation have become available for the management of critically ill patients. Proportional assist ventilation, neurally adjusted ventilatory assist and adaptive support ventilation are three novel modes of ventilation, which attempt to optimize patient-ventilator synchrony. Improved interactions between patient and ventilator may be important in improving clinical outcomes. Another important priority for mechanically ventilated patients is lung protection, and nontraditional modes of ventilation that may be implemented to minimize ventilator-associated lung injury include airway pressure release ventilation and high-frequency ventilation. Novel and nontraditional modes of ventilation may represent important tools in the critical care environment; however, continued investigation is needed to determine the overall impact of these various approaches on outcomes for mechanically ventilated patients.

Randomized crossover study of neurally adjusted ventilatory assist in preterm infants

OBJECTIVE

To determine whether neurally adjusted ventilatory assist (NAVA), a new method of mechanical ventilation that delivers pressure assistance that is proportional to the electrical activity of the diaphragm (EAdi), could lower the inspiratory pressure and respiratory muscle load in preterm infants supported with ventilators.

STUDY DESIGN

Twenty-six mechanically ventilated preterm infants were randomized to crossover ventilation with NAVA and synchronized intermittent mandatory ventilation (SIMV) with pressure support (PS) for 4 hours each in a randomized order. A 1-hour interval for washout was provided between the 2 modes of ventilation. The ventilator settings were adjusted to maintain similar levels of end-tidal partial pressure of CO(2). The ventilator parameters, vital signs, and gas exchange effects under the 2 ventilatory modes were compared.

RESULTS

Nineteen infants completed the 9-hour crossover comparison protocol. Peak inspiratory pressure (PIP), work of breathing, and peak EAdi with NAVA were lower than those in SIMV with PS. Calculated tidal volume to peak EAdi ratio and PIP to peak EAdi ratio were higher with NAVA. There were no significant differences in mean airway pressure, inspiratory oxygen fraction, and blood gas values. The measurements of vital signs did not differ significantly between the 2 modes.

CONCLUSION

NAVA lowered PIP and reduced respiratory muscle load in preterm infants at equivalent inspiratory oxygen fraction and partial pressure of CO(2) of capillary blood in comparison with SIMV with PS.

Synchronized mechanical ventilation using electrical activity of the diaphragm in neonates

The electrical activity of the diaphragm (Edi) is measured by a specialized nasogastric/orogastric tube positioned in the esophagus at the level of the crural diaphragm. Neurally adjusted ventilatory assist (NAVA) uses the Edi signal as a neural trigger and intrabreath controller to synchronize mechanical ventilatory breaths with the patient's respiratory drive and to proportionally support the patient's respiratory efforts on a breath-by-breath basis. NAVA improves patient-ventilator interaction and synchrony even in the presence of large air leaks, and might therefore be an optimal option for noninvasive ventilation in neonates.

Partial ventilatory support modalities in acute lung injury and acute respiratory distress syndrome-a systematic review

PURPOSE

The efficacy of partial ventilatory support modes that allow spontaneous breathing in patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is unclear. The objective of this scoping review was to assess the effects of partial ventilatory support on mortality, duration of mechanical ventilation, and both hospital and intensive care unit (ICU) lengths of stay (LOS) for patients with ALI and ARDS; the secondary objective was to describe physiologic effects on hemodynamics, respiratory system and other organ function.

METHODS

MEDLINE (1966-2009), Cochrane, and EmBase (1980-2009) databases were searched using common ventilator modes as keywords and reference lists from retrieved manuscripts hand searched for additional studies. Two researchers independently reviewed and graded the studies using a modified Oxford Centre for Evidence-Based Medicine grading system. Studies in adult ALI/ARDS patients were included for primary objectives and pre-clinical studies for supporting evidence.

RESULTS

Two randomized controlled trials (RCTs) were identified, in addition to six prospective cohort studies, one retrospective cohort study, one case control study, 41 clinical physiologic studies and 28 pre-clinical studies. No study was powered to assess mortality, one RCT showed shorter ICU length of stay, and the other demonstrated more ventilator free days. Beneficial effects of preserved spontaneous breathing were mainly physiological effects demonstrated as improvement of gas exchange, hemodynamics and non-pulmonary organ perfusion and function.

CONCLUSIONS

The use of partial ventilatory support modalities is often feasible in patients with ALI/ARDS, and may be associated with short-term physiological benefits without appreciable impact on clinically important outcomes.

Neurally adjusted ventilatory assist (NAVA) improves patient-ventilator interaction during non-invasive ventilation delivered by face mask

PURPOSE

To determine if, compared to pressure support (PS), neurally adjusted ventilatory assist (NAVA) reduces patient-ventilator asynchrony in intensive care patients undergoing noninvasive ventilation with an oronasal face mask.

METHODS

In this prospective interventional study we compared patient-ventilator synchrony between PS (with ventilator settings determined by the clinician) and NAVA (with the level set so as to obtain the same maximal airway pressure as in PS). Two 20-min recordings of airway pressure, flow and electrical activity of the diaphragm during PS and NAVA were acquired in a randomized order. Trigger delay (T(d)), the patient's neural inspiratory time (T(in)), ventilator pressurization duration (T(iv)), inspiratory time in excess (T(iex)), number of asynchrony events per minute and asynchrony index (AI) were determined.

RESULTS

The study included 13 patients, six with COPD, and two with mixed pulmonary disease. T(d) was reduced with NAVA: median 35 ms (IQR 31-53 ms) versus 181 ms (122-208 ms); p = 0.0002. NAVA reduced both premature and delayed cyclings in the majority of patients, but not the median T(iex) value. The total number of asynchrony events tended to be reduced with NAVA: 1.0 events/min (0.5-3.1 events/min) versus 4.4 events/min (0.9-12.1 events/min); p = 0.08. AI was lower with NAVA: 4.9 % (2.5-10.5 %) versus 15.8 % (5.5-49.6 %); p = 0.03. During NAVA, there were no ineffective efforts, or late or premature cyclings. PaO(2) and PaCO(2) were not different between ventilatory modes.

CONCLUSION

Compared to PS, NAVA improved patient ventilator synchrony during noninvasive ventilation by reducing T(d) and AI. Moreover, with NAVA, ineffective efforts, and late and premature cyclings were absent.

Neurally adjusted ventilatory assist improves patient–ventilator interaction in infants as compared with conventional ventilation

BACKGROUND

Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation controlled by the electrical activity of the diaphragm (Edi). The aim was to evaluate patient-ventilator interaction in infants during NAVA as compared with conventional ventilation.

METHODS

Infants were successively ventilated with NAVA, pressure control ventilation (PCV), and pressure support ventilation (PSV). Edi and ventilator pressure (Pvent) waveforms were compared and their variability was assessed by coefficients of variation.

RESULTS

Ten patients (mean age 4.3 ± 2.4 mo and weight 5.9 ± 2.2 kg) were studied. In PCV and PSV, 4 ± 4.6% and 6.5 ± 7.7% of the neural efforts failed to trigger the ventilator. This did not occur during NAVA. Trigger delays were shorter with NAVA as compared with PCV and PSV (93 ± 20 ms vs. 193 ± 87 ms and 135 ± 29 ms). During PCV and PSV, the ventilator cycled off before the end of neural inspiration in 12 ± 13% and 21 ± 19% of the breaths (0 ± 0% during NAVA). During PCV and PSV, 24 ± 11% and 25 ± 9% of the neural breath cycle was asynchronous with the ventilator as compared with 11 ± 3% with NAVA. A large variability was observed for Edi in all modes, which was transmitted into Pvent during NAVA (coefficient of variation: 24 ± 8%) and not in PCV (coefficient of variation 2 ± 1%) or PSV (2 ± 2%).

CONCLUSION

NAVA improves patient-ventilator interaction and delivers adequate ventilation with variable pressure in infants.

Clinical review: Update on neurally adjusted ventilatory assist--report of a round-table conference

Conventional mechanical ventilators rely on pneumatic pressure and flow sensors and controllers to detect breaths. New modes of mechanical ventilation have been developed to better match the assistance delivered by the ventilator to the patient's needs. Among these modes, neurally adjusted ventilatory assist (NAVA) delivers a pressure that is directly proportional to the integral of the electrical activity of the diaphragm recorded continuously through an esophageal probe. In clinical settings, NAVA has been chiefly compared with pressure-support ventilation, one of the most popular modes used during the weaning phase, which delivers a constant pressure from breath to breath. Comparisons with proportional-assist ventilation, which has numerous similarities, are lacking. Because of the constant level of assistance, pressure-support ventilation reduces the natural variability of the breathing pattern and can be associated with asynchrony and/or overinflation. The ability of NAVA to circumvent these limitations has been addressed in clinical studies and is discussed in this report. Although the underlying concept is fascinating, several important questions regarding the clinical applications of NAVA remain unanswered. Among these questions, determining the optimal NAVA settings according to the patient's ventilatory needs and/or acceptable level of work of breathing is a key issue. In this report, based on an investigator-initiated round table, we review the most recent literature on this topic and discuss the theoretical advantages and disadvantages of NAVA compared with other modes, as well as the risks and limitations of NAVA.

Absence of inspiratory laryngeal constrictor muscle activity during nasal neurally adjusted ventilatory assist in newborn lambs

In nonsedated newborn lambs, nasal pressure support ventilation (nPSV) can lead to an active glottal closure in early inspiration, which can limit lung ventilation and divert air into the digestive system, with potentially deleterious consequences. During volume control ventilation (nVC), glottal closure is delayed to the end of inspiration, suggesting that it is reflexly linked to the maximum value of inspiratory pressure. Accordingly, the aim of the present study was to test whether inspiratory glottal closure develops at the end of inspiration during nasal neurally adjusted ventilatory assist (nNAVA), an increasingly used ventilatory mode where maximal pressure is also reached at the end of inspiration. Polysomnographic recordings were performed in eight nonsedated, chronically instrumented lambs, which were ventilated with progressively increasing levels of nPSV and nNAVA in random order. States of alertness, diaphragm, and glottal muscle electrical activity, tracheal pressure, Spo(2), tracheal Pet(CO(2)), and respiratory inductive plethysmography were continuously recorded. Although phasic inspiratory glottal constrictor electrical activity appeared during nPSV in 5 of 8 lambs, it was never observed at any nNAVA level in any lamb, even at maximal achievable nNAVA levels. In addition, a decrease in Pco(2) was neither necessary nor sufficient for the development of inspiratory glottal constrictor activity. In conclusion, nNAVA does not induce active inspiratory glottal closure, in contrast to nPSV and nVC. We hypothesize that this absence of inspiratory activity is related to the more physiological airway pressurization during nNAVA, which tightly follows diaphragm electrical activity throughout inspiration.

Effort-adapted modes of assisted breathing

PURPOSE OF REVIEW

New developments in mechanical ventilation have focused on increasing the patient's control of the ventilator by implementing information on lung mechanics and respiratory drive. Effort-adapted modes of assisted breathing are presented and their potential advantages are discussed.

RECENT FINDINGS

Adaptive support ventilation, proportional assist ventilation with load adjustable gain factors and neurally adjusted ventilatory assist are ventilatory modes that follow the concept of adapting the assist to a defined target, instantaneous changes in respiratory drive or lung mechanics. Improved patient ventilator interaction, sufficient unloading of the respiratory muscles and increased comfort have been recently associated with these ventilator modalities. There are, however, scarce data with regard to outcome improvement, such as length of mechanical ventilation, ICU stay or mortality (commonly accepted targets to demonstrate clinical superiority).

SUMMARY

Within recent years, a major step forward in the evolution of assisted (effort-adapted) modes of mechanical ventilation was accomplished. There is growing evidence that supports the physiological concept of closed-loop effort-adapted assisted modes of mechanical ventilation. However, at present, the translation into a clear outcome benefit remains to be proven. In order to fill the knowledge gap that impedes the broader application, larger randomized controlled trials are urgently needed. However, with clearly proven drawbacks of conventional assisted modes such as pressure support ventilation, it is probably about time to leave these modes introduced decades ago behind.

Comparison of pressure-, flow-, and NAVA-triggering in pediatric and neonatal ventilatory care

OBJECTIVE

To compare conventional trigger modes (pressure and flow trigger) to neurally adjusted ventilatory assist (NAVA), a novel sensing technique, and to observe the patient-ventilator interactions during these modes.

METHODS

In this prospective, crossover comparison study in tertiary care pediatric and neonatal intensive care unit, 18 patients (age from 30 weeks of postconceptional age to 16 years) needing mechanical ventilation were randomized. Three patients were excluded from the analysis because of problems in data collection. Patients were ventilated with three different trigger modes (pressure, flow, NAVA), for 10 min each. Patients were randomly allocated to six groups according to the order of trigger modes used.

RESULTS

The primary end point was the time in asynchrony between the patient and the ventilator. Secondary end points were peak and mean airway pressures (MAP), breathing frequency, tidal volume (TV), and vital parameters during each trigger mode. The proportion of time in asynchrony was significantly shorter in the NAVA group (8.8%) than in the pressure (33.4%) and flow (30.8%) groups (P < 0.001 for both). In the NAVA group, the peak inspiratory pressure was 2 to 1.9 cmH(2) O lower than in the pressure and flow groups, respectively (P < 0.05 for both) and the breathing frequency was 10 breaths/min higher than in the pressure group (P = 0.001). There was a tendency toward a lower MAP (P = 0.047) but the mean TV was about the same (6.4-6.8 ml/kg) in all three groups (P = 0.55). There were no differences in oxygen saturation or vital parameters between the groups.

CONCLUSION

NAVA offers a novel way of sensing patients' spontaneous breathing and significantly improves short-term patient-ventilator synchrony in a pediatric population.

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

PURPOSE

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 10 ml/kg in acute respiratory failure patients.

METHODS

Eight increasing NAVA levels (0.5, 1, 1.5, 2, 2.5, 3, 4, and 5 cmH(2)O/μV) and four increasing pressure support (PSV) levels (4, 8, 12, and 16 cmH(2)O) were applied to obtain 10 min of stable recordings in 15 patients.

RESULTS

One out of 15 patients did not sustain the NAVA levels of 3, 4, and 5 cmH(2)O/μV and was excluded. The 5 cmH(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 10 ml/kg and an uncomfortable respiratory pattern in some patients.

CONCLUSIONS

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 2-2.5 cmH(2)O/μV, while preserving respiratory variability and low risks of V (T) above 8 or 10 ml/kg.

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

PURPOSE

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.

METHODS

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 72 h. 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).

RESULTS

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).

CONCLUSION

In most patients with CIPM, EA(di) and its feedback control are sufficiently preserved to titrate and implement NAVA for up to 3 days. 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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Influence of body position, PEEP and intra-abdominal pressure on the catheter positioning for neurally adjusted ventilatory assist

Purpose

Neurally adjusted ventilatory assist (NAVA) relies on the patient’s electrical activity of the diaphragm (EAdi) for actuating the ventilator. Thus a reliable positioning of the oesophageal EAdi catheter is mandatory. We aimed to evaluate the effects of body position (BP), positive end-expiratory pressure (PEEP) and intra-abdominal pressure (IAP) on catheter positioning.

Methods

Twenty-one patients were enrolled in this study. In six different situations [supine or 45° head of bed elevation (HBE) at PEEP 5 and 15 cmH₂O; left lateral anti-decubitus at PEEP 5 cmH₂O; supine at PEEP 5 cmH₂O with abdominal surgical belt (ASB)] the catheter position was evaluated for the stability of the EAdi signal and information provided by a catheter positioning tool (highlighted electrical activity in central leads, absence of p waves in the distal lead).

Results

With an optimal catheter position EAdi signals were stable for all tested situations. During “45° PEEP 15” and “supine PEEP 15” absence of p waves in the distal lead revealed a difference compared with “supine PEEP 5” (p = 0.03), suggesting a caudal shift of the diaphragm relative to the oesophagus. The analysis of the highlighted electrical activity in the central leads supports this finding, revealing an influence of PEEP, BP and IAP on EAdi catheter position (p < 0.01).

Conclusion

PEEP, BP and IAP may affect the EAdi catheter position, although not compromising a stable signal. Additional information as provided by the catheter positioning tool is needed to ensure an optimal EAdi catheter position.

Mechanical Ventilation in the Pediatric Cardiac Intensive Care Unit

Ventilating a child or newborn in the postoperative course after repair of congenital heart disease requires a solid basic understanding of respiratory system mechanics (pressure–volume relationship of the respiratory system and the concept of its time constants) and cardiopulmonary physiology. Furthermore, careful attention has to be paid to avoid damaging the lungs by potentially injurious mechanical ventilation. Optimizing ventilator settings during controlled and assisted ventilation, allowing as early as possible for spontaneous ventilation by still assisting mechanically the patient’s respiratory efforts are important features for lung protection, for minimizing potential hemodynamic side effects of positive pressure ventilation, and for early weaning from mechanical ventilation. In the search for being less invasive, the use of noninvasive ventilation in the cardiac intensive care setting is rapidly increasing despite still lacking evidence of its theoretical superiority and requires good knowledge of specific techniques and equipment available for this approach in this setting. This review will address many of these aspects and highlight the essentials to be known when ventilating a child in the Cardiac Intensive Care Unit (CICU).

Neurally triggered breaths reduce trigger delay and improve ventilator response times in ventilated infants with bronchiolitis

PURPOSE

Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation designed to improve patient-ventilator interaction by interpreting a neural signal from the diaphragm to trigger a supported breath. We hypothesized that neurally triggered breaths would reduce trigger delay, ventilator response times, and work of breathing in pediatric patients with bronchiolitis.

METHODS

Subjects with a clinical diagnosis of bronchiolitis were studied in volume support (pneumatic trigger) and NAVA (pneumatic and neural trigger) in a crossover design. Airway flow and pressure waveforms were obtained with a pneumotachograph and computerized digital recorder and were recorded for 120 s for each experiment.

RESULTS

Neurally triggered breaths had less trigger delay (ms) (40 ± 27 vs. 98 ± 34; p < 0.001) and reduced ventilator response times (ms) (15 ± 7 vs. 36 ± 25; p < 0.001) compared with pneumatically triggered breaths. Neurally triggered breaths had reduced pressure-time product (PTP) area A (cmH(2)O * s), the area of the pressure curve from initiation of breath to start of ventilator pressurization (0.013 ± 0.010; p < 0.001), and reduced PTP area B (cmH(2)O * s), the area of the pressure curve from start of ventilator pressurization to return of baseline pressure (0.008 ± 0.006 vs. 0.023 ± 0.009; p = 0.003). Reduced PTP may indicate decreased work of breathing.

CONCLUSION

Neurally triggered breaths reduce trigger delay, improve ventilator response times, and may decrease work of breathing in children with bronchiolitis. Further analysis is required to determine if neurally triggered breaths will improve patient-ventilator synchrony.

Identification of adequate neurally adjusted ventilatory assist (NAVA) during systematic increases in the NAVA level

Neurally adjusted ventilatory assist (NAVA) delivers airway pressure (P_aw) in proportion to the electrical activity of the diaphragm (EAdi) using an adjustable proportionality constant (NAVA level, cm⋅H ₂O/\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\mu$\end{document}V). During systematic increases in the NAVA level, feedback-controlled down-regulation of the EAdi results in a characteristic two-phased response in P_aw 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 (NAVA_AL). We aimed to develop and validate a mathematical algorithm to identify NAVA_AL. P_aw, Vt, and EAdi were recorded while systematically increasing the NAVA level in 19 adult patients. In a multistep approach, inspiratory P_aw 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 P_aw peaks and Vt. The beginning of the P_aw 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 NAVA_AL visually estimated by 18 independent physicians was 2.7 (range 0.4 to 5.8) cm⋅H ₂O/\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\mu$\end{document}V and identified by our model was 2.6 (range 0.6 to 5.0) cm⋅H ₂O/\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\mu$\end{document}V. NAVA_AL identified by our model was below the range of visually estimated NAVA_AL in two instances and was above in one instance. We conclude that our model identifies NAVA_AL in most instances with acceptable accuracy for application in clinical routine and research.

Pediatric respiratory diseases: 2011 update for the Rogers' Textbook of Pediatric Intensive Care

OBJECTIVES

To review articles relevant to the field of pediatric respiratory disease that were published after the 2008 Rogers' Textbook of Pediatric Intensive Care.

DATA SOURCES

The authors searched the PubMed database (http://www.ncbi.nlm.nih.gov/sites/entrez) from the National Library of Medicine for citations from the pediatric and adult literature relevant to pediatric status asthmaticus, bronchiolitis, pneumonia, acute lung injury, acute respiratory distress syndrome, and neonatal respiratory failure. The authors also searched the reference lists of key primary publications and recent review articles, and queried the National Institutes of Health's ClinicalTrials.gov Web site (www.clinicaltrials.gov) to obtain information about ongoing clinical trials for acute lung injury. The authors had knowledge of new publications in the field of respiratory monitoring, which were considered for inclusion in the review.

STUDY SELECTION AND DATA EXTRACTION

The authors reviewed the promising articles and the decision to include any article in the review was based on its potential to inform pediatric intensive care practice or future research.

DATA SYNTHESIS

Articles in six categories were selected for inclusion: status asthmaticus, bronchiolitis, pneumonia, acute lung injury/acute respiratory distress syndrome, respiratory monitoring, and neonatal respiratory failure.

CONCLUSIONS

There have been important new developments relevant to the pathogenesis and management of pediatric respiratory diseases. In particular, new insights into the causal pathways of respiratory syncytial virus-induced airways disease can potentially lead to novel therapies. Computed tomography imaging of the injured lung during mechanical ventilation has opened new avenues for future research directed at testing new treatments in acute lung injury subpopulations defined according to lung mechanics. Promising new monitoring techniques may play a supporting role in the conduct of these studies. Finally, evidence from the neonatal literature recently has shown how the course and future consequences of respiratory failure in this population may be modified through more widespread use of noninvasive support.

Neurally adjusted ventilatory assist: a new approach to mechanically ventilated infants

Neurally adjusted ventilator assist (NAVA) is a new mode of partial ventilatory support, in which neural inspiratory activity is monitored through the continuous esophageal recording of the electrical activity of the diaphragm. Assistance is triggered and cycled off in according to this signal and is delivered in proportion to its intensity. NAVA can improve patient-ventilator synchrony while maintaining spontaneous breathing. Small preliminary studies have shown that NAVA can be successfully used also in term and preterm infants, being safe and well tolerated. However, much additional work is still needed before NAVA can be recommended in the everyday practice of the neonatologist.