Neural control of ventilation prevents both over-distension and de-recruitment of experimentally injured lungs

Synchronized and proportional sub-diaphragmatic unloading in an animal model of respiratory distress

BACKGROUND

A sealed abdominal interface was positioned below the diaphragm (the "NeoVest") to apply synchronized and proportional negative pressure ventilation (NPV) and was compared to positive pressure ventilation (PPV) using neurally adjusted ventilatory assist (NAVA). Both modes were controlled by the diaphragm electrical activity (Edi).

METHODS

Eleven rabbits (mean weight 2.9 kg) were instrumented, tracheotomized, and ventilated with either NPV or PPV (sequentially) with different loads (resistive, dead space, acute lung injury). Assist with either PPV or NPV was titrated to reduce Edi by 50%.

RESULTS

In order to achieve a 50% reduction in Edi, NPV required slightly more negative pressure (-8 to -12 cm H₂O) than observed in PPV (+6 to +10 cm H₂O). The efficiency of pressure transmission from the NeoVest into gastric pressure was 69.6% (range 61.3-77.4%). Swings in esophageal pressure were more negative during NPV than PPV, for all conditions, due to transmission of negative pressure. Transpulmonary pressure was lower during NPV. Transdiaphragmatic pressure swings were reduced similarly for PPV and NPV, suggesting equivalent unloading of the diaphragm. NPV did not affect hemodynamics.

CONCLUSIONS

It is feasible to apply NPV sub-diaphragmatically in synchrony and in proportion to Edi in an animal model of respiratory distress.

IMPACT

Negative pressure ventilation (NPV), for example, the "Iron Lung," may offer advantages over positive pressure ventilation. In the present work, we describe the "NeoVest," a system consisting of a sealed abdominal interface and a ventilator that applies NPV in synchrony and in proportion to the diaphragm electrical activity (Edi).

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.

Continuous neurally adjusted ventilation: a feasibility study in preterm infants

OBJECTIVES

To assess the feasibility and tolerance of NeuroPAP, a new non-invasive ventilation mode which continuously adjusts (during both inspiration and expiration) the pressure support proportionally to the diaphragm electrical activity (Edi), in preterm infants and to evaluate the impact on ventilation pressure and Edi.

DESIGN

Prospective cross-over single-centre feasibility study.

SETTING

One level 3 neonatal intensive care unit in Canada.

PATIENTS

Stable preterm infants ventilated with non-invasive positive pressure ventilation (NIPPV).

INTERVENTIONS

Subjects were successively ventilated in NIPPV with prestudy settings (30 min), in NeuroPAP with minimal pressure similar to NIPPV PEEP (positive end-expiratory pressure) (60 min), in NeuroPAP with minimal pressure reduced by 2 cmH₂0 (60 min), in continuous positive airway pressure (15 min) and again in NIPPV (30 min). Main outcome measures included tolerance, ventilation pressure, Edi and patient-ventilator synchrony.

RESULTS

Twenty infants born at 28.0±1.0 weeks were included. NeuroPAP was well tolerated and could be delivered during 100% of planned period. During NeuroPAP, the PEEP was continuously adjusted proportionally to tonic diaphragm Edi, although the average PEEP value was similar to the set minimal pressure. During NeuroPAP, 83 (78-86)% breaths were well synchronised vs 9 (6-12)% breaths during NIPPV (p<0.001).

CONCLUSIONS

NeuroPAP is feasible and well tolerated in stable preterm infants, and it allows transient adaptation in PEEP in response to tonic diaphragm electrical activity changes. Further studies are warranted to determine the impact of these findings on clinical outcomes.

TRIAL REGISTRATION NUMBER

NCT02480205.

Electrical impedance tomography reveals pathophysiology of neonatal pneumothorax during NAVA

Pneumothorax is a potentially life-threatening complication of neonatal respiratory distress syndrome (RDS). We describe a case of a tension pneumothorax that occurred during neurally adjusted ventilatory assist (NAVA) in a preterm infant suffering from RDS. The infant was included in a multicenter study examining the role of electrical impedance tomography (EIT) in intensive care and therefore continuously monitored with this imaging method. The attending physicians were blinded for EIT findings but offline analysis revealed the potential of EIT to clarify the underlying cause of this complication, which in this case was heterogeneous lung disease resulting in uneven ventilation distribution. Instantaneous increase in end-expiratory lung impedance on the affected side was observed at time of the air leak. Real-time bedside availability of EIT data could have modified the treatment decisions made.

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).

Effect of Neurally Adjusted Ventilatory Assist on Patient-Ventilator Interaction in Mechanically Ventilated Adults: A Systematic Review and Meta-Analysis

OBJECTIVES

Patient-ventilator asynchrony is common among critically ill patients undergoing mechanical ventilation and has been associated with adverse outcomes. Neurally adjusted ventilatory assist is a ventilatory mode that may lead to improved patient-ventilator synchrony. We conducted a systematic review to determine the impact of neurally adjusted ventilatory assist on patient-ventilator asynchrony, other physiologic variables, and clinical outcomes in adult patients undergoing invasive mechanical ventilation in comparison with conventional pneumatically triggered ventilatory modes.

DATA SOURCES

We searched Medline, EMBASE, Cochrane Database of Systematic Reviews, Cochrane Central, CINAHL, Scopus, Web of Science, conference abstracts, and ClinicalTrials.gov until July 2018.

STUDY SELECTION

Two authors independently screened titles and abstracts for randomized and nonrandomized controlled trials (including crossover design) comparing the occurrence of patient-ventilator asynchrony between neurally adjusted ventilatory assist and pressure support ventilation during mechanical ventilation in critically ill adults. The asynchrony index and severe asynchrony (i.e., asynchrony index > 10%) were the primary outcomes.

DATA EXTRACTION

Two authors independently extracted study characteristics and outcomes and assessed risk of bias of included studies.

DATA SYNTHESIS

Of 11,139 unique citations, 26 studies (522 patients) met the inclusion criteria. Sixteen trials were included in the meta-analysis using random effects models through the generic inverse variance method. In several different clinical scenarios, the use of neurally adjusted ventilatory assist was associated with significantly reduced asynchrony index (mean difference, -8.12; 95% CI, -11.61 to -4.63; very low quality of evidence) and severe asynchrony (odds ratio, 0.42; 95% CI, 0.23-0.76; moderate quality of evidence) as compared with pressure support ventilation. Furthermore, other measurements of asynchrony were consistently improved during neurally adjusted ventilatory assist.

CONCLUSIONS

Neurally adjusted ventilatory assist improves patient-ventilator synchrony; however, its effects on clinical outcomes remain uncertain. Randomized controlled trials are needed to determine whether the physiologic efficiency of neurally adjusted ventilatory assist affects patient-important outcomes in critically ill adults.

Physiological Effect of Prone Position in Children with Severe Bronchiolitis: A Randomized Cross-Over Study (BRONCHIO-DV)

OBJECTIVE

To assess the effect of the prone position on physiological measures, including inspiratory effort, metabolic cost of breathing, and neural drive to the diaphragm as compared with the supine position in infants with severe bronchiolitis requiring noninvasive ventilation.

STUDY DESIGN

Fourteen infants, median age 33 days (IQR [first and third quartiles], 25-58) were randomized to receive 7 cmH₂O continuous positive airway pressure for 1 hour in the prone position or in the supine position, which was followed by cross-over to the supine position and the prone position for 1 hour, respectively. Flow, esophageal, airway, gastric, and transdiaphragmatic pressures, as well as electrical activity of the diaphragm were simultaneously recorded. The modified Wood clinical asthma score was also assessed.

RESULTS

Median esophageal pressure-time product per minute was significantly lower in the prone position than in the supine position (227 cmH₂O*s/minute [IQR, 156-282] cmH₂O*s/minute vs 353 cmH₂O*s/minute [IQR, 249-386 cmH₂O*s/minute]; P = .048), as were the modified Wood clinical asthma score (P = .033) and electrical activity of the diaphragm (P = .006). The neuromechanical efficiency of the diaphragm, as assessed by transdiaphramagtic pressure to electrical activity of the diaphragm swing ratio, was significantly higher in the prone position than in the supine position (1.1 cmH₂O/µV [IQR, 0.9-1.3 cmH₂O/µV] vs 0.7 cmH₂O/µV [IQR, 0.6-1.2 cmH₂O/µV], respectively; P = .022).

CONCLUSIONS

This study suggests a benefit of the prone position for infants with severe bronchiolitis requiring noninvasive ventilation by significantly decreasing the inspiratory effort and the metabolic cost of breathing. Further studies are needed to evaluate the potential impact of these physiological findings in a larger population.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT02602678.

Neural Breathing Pattern and Patient-Ventilator Interaction During Neurally Adjusted Ventilatory Assist and Conventional Ventilation in Newborns

OBJECTIVE

To compare neurally adjusted ventilatory assist and conventional ventilation on patient-ventilator interaction and neural breathing patterns, with a focus on central apnea in preterm infants.

DESIGN

Prospective, observational cross-over study of intubated and ventilated newborns. Data were collected while infants were successively ventilated with three different ventilator conditions (30 min each period): 1) synchronized intermittent mandatory ventilation (SIMV) combined with pressure support at the clinically prescribed, SIMV with baseline settings (SIMVBL), 2) neurally adjusted ventilatory assist, 3) same as SIMVBL, but with an adjustment of the inspiratory time of the mandatory breaths (SIMV with adjusted settings [SIMVADJ]) using feedback from the electrical activity of the diaphragm).

SETTING

Regional perinatal center neonatal ICU.

PATIENTS

Neonates admitted in the neonatal ICU requiring invasive mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Twenty-three infants were studied, with median (range) gestational age at birth 27 weeks (24-41 wk), birth weight 780 g (490-3,610 g), and 7 days old (1-87 d old). Patient ventilator asynchrony, as quantified by the NeuroSync index, was lower during neurally adjusted ventilatory assist (18.3% ± 6.3%) compared with SIMVBL (46.5% ±11.7%; p < 0.05) and SIMVADJ (45.8% ± 9.4%; p < 0.05). There were no significant differences in neural breathing parameters, or vital signs, except for the end-expiratory electrical activity of the diaphragm, which was lower during neurally adjusted ventilatory assist. Central apnea, defined as a flat electrical activity of the diaphragm more than 5 seconds, was significantly reduced during neurally adjusted ventilatory assist compared with both SIMV periods. These results were comparable for term and preterm infants.

CONCLUSIONS

Patient-ventilator interaction appears to be improved with neurally adjusted ventilatory assist. Analysis of the neural breathing pattern revealed a reduction in central apnea during neurally adjusted ventilatory assist use.