Predicting extubation in patients with traumatic cervical spinal cord injury using the diaphragm electrical activity during a single maximal maneuver.

BACKGROUND: The unsuccessful extubation in patients with traumatic cervical spinal cord injuries (CSCI) may result from impairment diaphragm function and monitoring of diaphragm electrical activity (EAdi) can be informative in guiding extubation. We aimed to evaluate whether the change of EAdi during a single maximal maneuver can predict extubation outcomes in CSCI patients. METHODS: This is a retrospective study of CSCI patients requiring mechanical ventilation in the ICU of a tertiary hospital. A single maximal maneuver was performed by asking each patient to inhale with maximum strength during the first spontaneous breathing trial (SBT). The baseline (during SBT before maximal maneuver), maximum (during the single maximal maneuver), and the increase of EAdi (ΔEAdi, equal to the difference between baseline and maximal) were measured. The primary outcome was extubation success, defined as no reintubation after the first extubation and no tracheostomy before any extubation during the ICU stay. RESULTS: Among 107 patients enrolled, 50 (46.7%) were extubated successfully at the first SBT. Baseline EAdi, maximum EAdi, and ΔEAdi were significantly higher, and the rapid shallow breathing index was lower in patients who were extubated successfully than in those who failed. By multivariable logistic analysis, ΔEAdi was independently associated with successful extubation (OR 2.03, 95% CI 1.52-3.17). ΔEAdi demonstrated high diagnostic accuracy in predicting extubation success with an AUROC 0.978 (95% CI 0.941-0.995), and the cut-off value was 7.0 µV. CONCLUSIONS: The increase of EAdi from baseline SBT during a single maximal maneuver is associated with successful extubation and can help guide extubation in CSCI patients.

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.

BACKGROUND: Mechanical 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). METHODS: In 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. RESULTS: All 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. CONCLUSION: During 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.

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.

Progress on monitoring technology and assessment indices of pediatric ventilator-induced diaphragm dysfunction / 中国小儿急救医学

Mechanical ventilation is becoming more and more common in clinical practice.It certainly helps patients to overcome the respiratory failure in children, but in the meantime, also lead to ventilator-induced diaphragm dysfunction(VIDD). VIDD is common in mechanical ventilation patients and are associated with prolonged duration of mechanical ventilation, difficult weaning, pulmonary infection and the mortality.With the development of clinical medical technology, more and more convenient devices are applied to monitor diaphragm function.This review expounded the latest monitoring technology and assessment indices of VIDD, including pressure-generating capacity, imaging examination and diaphragm electrical activity.

Neurally Adjusted Ventilatory Assist in Newborns.

Patient-ventilator asynchrony is very common in newborns. Achieving synchrony is quite challenging because of small tidal volumes, high respiratory rates, and the presence of leaks. Leaks also cause unreliable monitoring of respiratory metrics. In addition, ventilator adjustment must take into account that infants have strong vagal reflexes and demonstrate central apnea and periodic breathing, with a high variability in breathing pattern. Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation whereby the timing and amount of ventilatory assist is controlled by the patient's own neural respiratory drive. As NAVA uses the diaphragm electrical activity (Edi) as the controller signal, it is possible to deliver synchronized assist, both invasively and noninvasively (NIV-NAVA), to follow the variability in breathing pattern, and to monitor patient respiratory drive, independent of leaks. This article provides an updated review of the physiology and the scientific literature pertaining to the use of NAVA in children (neonatal and pediatric age groups). Both the invasive NAVA and NIV-NAVA publications since 2016 are summarized, as well as the use of Edi monitoring. Overall, the use of NAVA and Edi monitoring is feasible and safe. Compared with conventional ventilation, NAVA improves patient-ventilator interaction, provides lower peak inspiratory pressure, and lowers oxygen requirements. Evidence from several studies suggests improved comfort, less sedation requirements, less apnea, and some trends toward reduced length of stay and more successful extubation.

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 (cNAVAP+ ) was applied via intubation. Negative pressure cNAVA (cNAVAP- ) 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 cNAVAP+ , cNAVAP- , and a 50/50 combination of the two (cNAVAP± ). In part 2: During 5-min ventilation with cNAVAP+ or cNAVAP- we measured circuit, box, and esophageal (Pes) pressure, EAdi, blood pressure, and arterial blood gases. RESULTS: Part 1: During cNAVAP+ , pressure in the circuit increased with increasing cNAVA levels, reaching a plateau, and similarly for cNAVAP- , albeit reversed in sign. This was associated with downregulation of the EAdi. Pes swings became less negative with cNAVAP+ but, in contrast, Pes swings were more negative during increasing cNAVAP- levels. Increasing the cNAVA level during cNAVAP± 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 cNAVAP- were significantly more negative than during cNAVAP+ . CONCLUSION: Negative pressure ventilation synchronized and proportional to the diaphragm activity is feasible in small animals.

[Effect of different mechanical ventilation modes on patient-ventilator synchrony and diaphragm function in rabbit model of acute respiratory distress syndrome].

Objective: To observe the effect of different modes of mechanical ventilation on patient-ventilator synchrony and diaphragm function in rabbits with acute respiratory distress syndrome(ARDS). Methods: Eighteen New Zealand rabbit models of ARDS were induced by intratracheal infusion hydrochloric acid until the oxygenation index (PaO(2)/FiO(2)) was less than 200 mmHg, and then divided into three groups with random number: assisted-controlled mechanical ventilation (A/C) group, pressure support ventilation (PSV) group and neurally adjusted ventilatory assist (NAVA) group. All of them were ventilated for four hours with the targeted tidal volume (V(T)) (6 ml/kg) and the positive end-expiratory pressure (PEEP) titrated with the maximum oxygenation method. Gas exchange, pulmonary mechanics and patient-ventilator synchrony were determined during 4 h of ventilation and the concentrations of malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH) in diaphragm were measured after 4 h of ventilation. The q test was used for the multiple comparison of the sample mean. Results: There were no significant differences in PaO(2)/FiO(2) between three groups during ventilation 1-4 h (F=1.029, P>0.05). The V(T) in NAVA group was obviously lower than that in PSV group and the respiratory rate (RR) and the electrical activity of diaphragm(EAdi) were higher than those in A/C group(all P<0.05).The trigger delay and off cycle delay the in NAVA group were markedly lower than those in A/C and PSV group during ventilation 1-4 h(F=14.312, 9.342, both P<0.05). Asynchrony index in NAVA group (3.1%±1.0%) was obviously lower than those in A/C group (22.3%±5.2%) and PSV group(8.4%±2.3%) (F=7.192, P<0.05). In NAVA group, peak EAdi (EAdi(peak)) and peak airway pressure (Ppeak) were markedly correlated (r=0.97±0.16, P<0.05), while Ppeak delivery in A/C and PSV group was not correlated to EAdi(peak) (r=0.38±0.13,0.46±0.15, both P>0.05).Compared with A/C group, the concentration of MDA in the diaphragm in NAVA group was obviously lower(P<0.05). SOD and GSH level inthe diaphragm in NAVA group were both obviously higher than those in A/C group (both P<0.05). Conclusions: It is helpful to avoid eccentric contraction of diaphragm, lessen oxidative stress and alleviate ventilator-related diaphragm dysfunction by keeping spontaneous breathing as far as possible and subject-ventilator synchrony when ventilation in ARDS with NAVA.

Recognizing, quantifying and managing patient-ventilator asynchrony in invasive and noninvasive ventilation.

INTRODUCTION: Patient-ventilator asynchrony may occur with modes of partial ventilatory support. Because this problem is associated with worsened outcomes, identifying and managing asynchronies has been recognized as a relevant clinical problem during both invasive and noninvasive (NIV) mechanical ventilation. Areas covered: In this review article, we first describe the different forms of patient-ventilator asynchrony and how they are classified and quantified. Then, we show how these asynchronies can be recognized, considering the techniques used to properly detect asynchronies, by either ventilator waveform observation, or through systems based on more complexes mathematical algorithms, by means of adjunctive signals, such as the electrical activity of the diaphragm or esophageal pressure. Finally, we describe the actions that can be undertaken in order to limit the rate of asynchronies during both invasive ventilation and NIV mechanical ventilation, such as modifications of the ventilator mode and/or settings, variation of the sedation regimen (type and doses), and other technical pitfalls. Expert commentary: Detection of asynchronies is crucial in order to reduce their incidence, adopting adjustments of the ventilator settings, sedation regimen, and other technical pitfalls. It remains to be clarified whether the relationship between high incidence of asynchrony and worsened outcome is causative or just associative.

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

BACKGROUND: Endogenous pulmonary reflexes may protect the lungs during mechanical ventilation. We aimed to assess integration of continuous neurally adjusted ventilatory assist (cNAVA), delivering assist in proportion to diaphragm's electrical activity during inspiration and expiration, and Hering-Breuer inflation and deflation reflexes on lung recruitment, distension, and aeration before and after acute lung injury (ALI). METHODS: In 7 anesthetised rabbits with bilateral pneumothoraces, we identified adequate cNAVA level (cNAVAAL) at the plateau in peak ventilator pressure during titration procedures before (healthy lungs with endotracheal tube, [HLETT]) and after ALI (endotracheal tube [ALIETT] and during non-invasive ventilation [ALINIV]). Following titration, cNAVAAL was maintained for 5min. In 2 rabbits, procedures were repeated after vagotomy (ALIETT+VAG). In 3 rabbits delivery of assist was temporarily modulated to provide assist on inspiration only. Computed tomography was performed before intubation, before ALI, during cNAVA titration, and after maintenance at cNAVAAL. RESULTS: During ALIETT and ALINIV, normally aerated lung-regions doubled and poorly aerated lung-regions decreased to less than a third (p<0.05) compared to HLETT; no over-distension was observed. Tidal volumes were<5ml/kg throughout. Removing assist during expiration resulted in lung de-recruitment during ALIETT, but not during ALINIV. During ALIETT+VAG the expiratory portion of EAdi disappeared, resulting in cyclic lung collapse and recruitment. CONCLUSIONS: When using cNAVA in ALI, vagally mediated reflexes regulated lung recruitment preventing both lung over-distension and atelectasis. During non-invasive cNAVA the upper airway muscles play a role in preventing atelectasis. Future studies should be performed to compare these findings with conventional lung-protective approaches.

Non-invasive ventilation with neurally adjusted ventilatory assist in newborns.

Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation in which both the timing and degree of ventilatory assist are controlled by the patient. Since NAVA uses the diaphragm electrical activity (Edi) as the controller signal, it is possible to deliver synchronized non-invasive NAVA (NIV-NAVA) regardless of leaks and to monitor continuously patient respiratory pattern and drive. Advantages of NIV-NAVA over conventional modes include improved patient-ventilator interaction, reliable respiratory monitoring and self-regulation of respiratory support. In theory, these characteristics make NIV-NAVA an ideal mode to provide effective, appropriate non-invasive support to newborns with respiratory insufficiency. NIV-NAVA has been successfully used clinically in neonates as a mode of ventilation to prevent intubation, to allow early extubation, and as a novel way to deliver nasal continuous positive airway pressure. The use of NAVA in neonates is described with an emphasis on studies and clinical experience with NIV-NAVA.

The effect of caffeine citrate on neural breathing pattern in preterm infants.

BACKGROUND: Caffeine citrate is widely used to prevent and treat prematurity-associated apnea. AIMS: The aim of this study was to characterize the effect of caffeine citrate on the neural control of breathing, especially central apnea, in premature infants. STUDY DESIGN: Preterm infants were evaluated for 30min before and 30min after caffeine citrate loading (20mg/kg). A feeding tube including miniaturized sensors was used to measure the diaphragm electrical activity (Edi) waveform. Central apnea was defined as any period where the Edi waveform was flat for >5s. SUBJECTS: Seventeen preterm infants with a mean age of three days and mean birth weight of 900 grams were evaluated. OUTCOME MEASURES: In addition to central apnea, several parameters including neural inspiratory time, neural respiratory rate, peak Edi, delta inspiratory change in Edi (phasic Edi) and minimum Edi on exhalation were measured. RESULTS: The majority of the apnea were short (5 to 10s) and the number of apnea correlated with birth weight (p=0.039). Caffeine citrate reduced significantly the number of 5-to-10-second-long central apnea during the 30-minute periods (12±11 to 7±7; p=0.02). Caffeine citrate increased both peak and phasic Edi leading to a significant increase in the diaphragm energy expenditure. CONCLUSIONS: Edi signal can be reliably measured and processed to study changes in premature infants' neural breathing. The beneficial effect of caffeine citrate on the reduction of the number of apnea is mediated through stimulated neural breathing increasing the diaphragm energy expenditure.

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.