Diaphragm electrical activity monitoring as a breakpoint in the management of a tetraplegic child

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.

Continuous assessment of neuro-ventilatory drive during 12 h of pressure support ventilation in critically ill patients

Introduction

Pressure support ventilation (PSV) should allow spontaneous breathing with a “normal” neuro-ventilatory drive. Low neuro-ventilatory drive puts the patient at risk of diaphragmatic atrophy while high neuro-ventilatory drive may causes dyspnea and patient self-inflicted lung injury. We continuously assessed for 12 h the electrical activity of the diaphragm (EAdi), a close surrogate of neuro-ventilatory drive, during PSV. Our aim was to document the EAdi trend and the occurrence of periods of “Low” and/or “High” neuro-ventilatory drive during clinical application of PSV.

Method

In 16 critically ill patients ventilated in the PSV mode for clinical reasons, inspiratory peak EAdi peak (EAdi_PEAK), pressure time product of the trans-diaphragmatic pressure per breath and per minute (PTP_DI/b and PTP_DI/min, respectively), breathing pattern and major asynchronies were continuously monitored for 12 h (from 8 a.m. to 8 p.m.). We identified breaths with “Normal” (EAdi_PEAK 5–15 μV), “Low” (EAdi_PEAK < 5 μV) and “High” (EAdi_PEAK > 15 μV) neuro-ventilatory drive.

Results

Within all the analyzed breaths (177.117), the neuro-ventilatory drive, as expressed by the EAdi_PEAK, was “Low” in 50.116 breath (28%), “Normal” in 88.419 breaths (50%) and “High” in 38.582 breaths (22%). The average times spent in “Low”, “Normal” and “High” class were 1.37, 3.67 and 0.55 h, respectively (p < 0.0001), with wide variations among patients. Eleven patients remained in the “Low” neuro-ventilatory drive class for more than 1 h, median 6.1 [3.9–8.5] h and 6 in the “High” neuro-ventilatory drive class, median 3.4 [2.2–7.8] h. The asynchrony index was significantly higher in the “Low” neuro-ventilatory class, mainly because of a higher number of missed efforts.

Conclusions

We observed wide variations in EAdi amplitude and unevenly distributed “Low” and “High” neuro ventilatory drive periods during 12 h of PSV in critically ill patients. Further studies are needed to assess the possible clinical implications of our physiological findings.

Monitoring of Respiratory Muscle Function in Critically Ill Children

OBJECTIVES

This review discusses the different techniques used at the bedside to assess respiratory muscle function in critically ill children and their clinical applications.

DATA SOURCES

A scoping review of the medical literature on respiratory muscle function assessment in critically ill children was conducted using the PubMed search engine.

STUDY SELECTION

We included all scientific, peer-reviewed studies about respiratory muscle function assessment in critically ill children, as well as some key adult studies.

DATA EXTRACTION

Data extracted included findings or comments about techniques used to assess respiratory muscle function.

DATA SYNTHESIS

Various promising physiologic techniques are available to assess respiratory muscle function at the bedside of critically ill children throughout the disease process. During the acute phase, this assessment allows a better understanding of the pathophysiological mechanisms of the disease and an optimization of the ventilatory support to increase its effectiveness and limit its potential complications. During the weaning process, these physiologic techniques may help predict extubation success and therefore optimize ventilator weaning.

CONCLUSIONS

Physiologic techniques are useful to precisely assess respiratory muscle function and to individualize and optimize the management of mechanical ventilation in children. Among all the available techniques, the measurements of esophageal pressure and electrical activity of the diaphragm appear particularly helpful in the era of individualized ventilatory management.

Severe diaphragmatic dysfunction with preserved activity of accessory respiratory muscles in a critically ill child: a case report of failure of neurally adjusted ventilatory assist (NAVA) and successful support with pressure support ventilation (PSV)

BACKGROUND

Neurally adjusted ventilatory assist (NAVA) is an alternative to pressure support ventilation (PSV) potentially improving patient-ventilator interaction. During NAVA, diaphragmatic electrical activity (EAdi) is used to trigger the ventilator and perform a proportional respiratory assistance. We present a case in which the presence of severe bilateral diaphragmatic dysfunction led to a failure of NAVA. On the contrary, the preserved activity of the accessory inspiratory muscles allowed a successful respiratory assistance using PSV.

CASE PRESENTATION

A 10-year-old girl developed quadriplegia after neurological surgery. Initially, no spontaneous breathing activity was present and volume controlled ventilation was necessary. Two months later spontaneous inspiratory efforts were observed and a maximal negative inspiratory force of - 20 cmH₂O was recorded. In addition, a NAVA nasogastric tube was placed. The recorded EAdi signal, despite showing a phasic activity, had a very low amplitude (1-2 μV). Two brief (15 min) breathing trials to compare PSV (pressure support = 8 cmH₂O) with NAVA (Gain = 5 cmH₂O/μV, inspiratory trigger = 0.3 μV) were performed. On PSV, the patient was well adapted with stable tidal volumes, respiratory rates, minute ventilation, end-tidal and venous carbon dioxide levels. When switched to NAVA, her breathing pattern became irregular and she showed clear sign of increased work of breathing and distress: tidal volume dropped and respiratory rate rose, leading to an increase in total minute ventilation. Nevertheless, end-tidal and venous carbon dioxide rapidly increased (from 49 to 55 mmHg and from 52 to 57 mmHg, respectively). An electromyographic study documented an impairment of the diaphragm with preserved activity of the accessory inspiratory muscles.

CONCLUSIONS

We document the failure of mechanical assistance performed with NAVA due to bilateral diaphragmatic dysfunction in a critically ill child. The preserved activity of some accessory respiratory muscles allowed to support the patient effectively with pressure support ventilation, i.e. by applying a pneumatic trigger. The present case underlines (i) the importance of the integrity of the respiratory centers, phrenic nerves and diaphragm in order to perform NAVA and (ii) the possible diagnostic role of EAdi monitoring in complex cases of weaning failure.