The monitoring of electrical activity of the diaphragm (EAdi) is a new minimally invasive bedside technology that was developed for the neurally adjusted ventilatory assist (NAVA) mode of ventilation. In addition to its role in NAVA ventilation, this technology provides the clinician with previously unavailable and essential information on diaphragm activity. In this paper, we review the clinical interests of EAdi in the pediatric intensive care setting. Firstly, the monitoring of EAdi allows the clinician to tailor the ventilatory settings on an individual basis, avoiding frequent overassistance leading potentially to diaphragmatic atrophy. Increased inspiratory EAdi levels can also suggest insufficient support, while a strong tonic activity may reflect the patient efforts to increase its lung volume. EAdi monitoring also allows detection of patient-ventilator asynchrony. It can play a role in evaluation of extubation readiness. Finally, EAdi monitoring provides the clinician with better understanding of the ventilatory capacity of patients with acute neuromuscular disease. Further studies are warranted to evaluate the clinical impact of these potential benefits.
In the pediatric intensive care unit (PICU), up to half of patients require mechanical ventilation (MV) [
Over the last decade, a new minimally invasive technology has been developed to continuously record the electrical activity of diaphragm (EAdi) at bedside. The main purpose of this technology is to synchronize and adapt the ventilatory support following the EAdi signal during the neurally adjusted ventilatory assist (NAVA) mode [
This paper is based on both data from the medical literature and the authors’ experience in the field. The authors are pediatric intensive care specialists with extensive clinical and research experience in pediatric mechanical ventilation and particularly in EAdi monitoring. In the last two years, we conducted more than 150 EAdi recordings in our PICU for clinical or research purposes. The extensive review of the medical literature on monitoring of the diaphragm and other respiratory muscles function in critically ill children was conducted using the PubMed research tool. The research strategy is described in Table
Search strategy for identifying related articles in Medline.
No. 1 | Pediatric OR paediatric OR infant* OR child OR children [All] |
No. 2 | Mechanical ventilation [All] |
No. 3 | Assisted ventilation [All] |
No. 4 | No. 2 OR No. 3 |
No. 5 | Diaphragm electromyography [All] |
No. 6 | Diaphragmatic electromyography [All] |
No. 7 | Electrical activity diaphragm [All] |
No. 8 | Diaphragm* function [All] |
No. 9 | Respiratory muscle monitoring [All] |
No. 10 | No. 5 OR No. 6 OR No. 7 OR No. 8 OR No. 9 |
No. 11 | No. 1 AND No. 4 AND No. 10 |
No limits were set for the time period or the language of publication.
EAdi monitoring in our PICU is conducted using the technology provided by the servo I ventilator (MAQUET Critical Care, Solna, Sweden). The signal is obtained using specific nasogastric feeding tube (Figure
Specific nasogastric 8F catheter for EAdi monitoring (b), with an enlargement of the distal tip of the catheter equipped with microelectrodes (a). Screenshot of the specific interface for catheter positioning (c) with the three key components of the optimal position: (1) presence of P waves in the proximal lead with disappearance in distal lead; (2) decrease in the QRS amplitude from the upper to the lower leads; and (3) diaphragm electrical activity highlighted mostly in the central leads (in blue).
In our PICU, as recommended by the manufacturer, the EAdi catheter is initially positioned using the “NAVA catheter positioning” screen on the servo I, as illustrated in Figure
In the past decade, there has been growing concerns regarding the impact of prolonged intubation on diaphragmatic function. As little as 12 hours of full mechanical support can suffice to induce diaphragmatic atrophy [
EAdi variation in response to modification of respiratory assistance in conventional mechanical ventilation as well as in NAVA mode has been described by Colombo et al. [
Evolution of ventilatory pressure (a) and electrical activity of the diaphragm (b) surrounding extubation (arrow) in a 2-year-old girl with meningitis. Note the very low diaphragm activity prior to extubation on low level of assisted ventilation (pressure support of 7 cm H2O).
On the other hand, very high inspiratory EAdi can be observed in patients with severe respiratory conditions (severe bronchiolitis, severe bronchopulmonary dysplasia, extubation failure, acute respiratory distress syndrome, and so on). Adjusting the support (e.g., increase of the support level, or introduction of noninvasive ventilation in case of post-extubation distress) usually succeeds in normalizing levels of EAdi. Figure
Evolution of respiratory rate, minute ventilation, and EAdi in a 15-day-old girl in the postoperative period of aortic valvotomy. After extubation (arrow), the infant was immediately supported with high flow nasal cannula. Progressive respiratory failure led to the introduction of noninvasive ventilation with NAVA 3 hours after extubation. An increase in EAdi was evident shortly after extubation, prior to the onset of clinical respiratory distress. The improvement of the respiratory failure with noninvasive ventilation was rapidly followed by a decrease in EAdi, toward preextubation levels.
Noteworthy, certain patients (typically infants with severe bronchopulmonary dysplasia) continue to maintain elevated drive despite MV adjustment, demonstrating the severity of their lung disease.
This shows how the level of ventilatory support can interfere with the child’s respiratory drive. It is a challenge for physicians to detect both excessive or insufficient support based solely on clinical examination. This often leads to inappropriate assistance and increased risk of diaphragmatic atrophy. EAdi provides unique information to the clinician and allows better tailoring of the ventilatory support.
Tonic EAdi is the diaphragm activity that persists until the end of expiration above baseline. Tonic EAdi is usually absent in normal adult or children older than one year [
Example of very high level of tonic EAdi (*) observed in a 2-year-old boy with acute respiratory distress and hypoxemia. Tonic EAdi rapidly decreased following the increase in PEEP from 7 to 10 cm H2O (arrow) (see text for details).
Adequate diaphragmatic function is paramount to ventilator weaning [
In patients with acute neuromuscular disease, it is essential to be able to rapidly detect the worsening of the disease and its impact on ventilatory function. Clinical observation alone might be insufficient. A recent case report illustrates the clinical utility of EAdi monitoring in the particular setting of two infants with botulism [
Daily evaluation of ventilatory drive in a 5-year-old patient with cervical myelitis. Each day, mean inspiratory EAdi was recorded during 5 minutes with the ventilation prescribed by the attending physician (grey bars) and 5 minutes under continuous positive airway pressure (CPAP, white bars). Inspiratory EAdi was also measured during 2 voluntary maximal inspiratory efforts (triangle). A period of overassistance with absent ventilatory drive was detected at day 3 (*). The recovery of the ventilatory drive was observed rapidly after adjustment of the support. (PSV: pressure-support ventilation; SIMV: synchronized intermittent mechanical ventilation).
To maintain an appropriate respiratory drive, synchronization is key. Patient-ventilator asynchrony is defined as a mismatch between the inspiratory and expiratory phases of the patient and the ventilator. This includes the inspiratory and expiratory delays (time between patient demand and ventilator response), wasted efforts (efforts undetected by the ventilator), autotriggering (ventilator assist delivered in absence of patient demand), and double-triggering (two rapidly successive ventilator assists following a single effort). In adults, asynchrony is associated with prolonged ventilator support, longer stay in the intensive care unit, and total hospital length of stay [
The EAdi technology is relatively new. Many of the concepts mentioned in this paper are theoretical and have not been confirmed by large studies. In particular, the impact of this monitoring on clinical outcomes (MV duration, extubation failure, and so on) remains to be validated. Like any new technology, it is important to balance its risks, costs, and benefits. So far, no complications have been detected.
Another limitation to EAdi monitoring is the lack of reference values for both healthy and critically ill children. With experience, it becomes rather easy to interpret clearly abnormal values. More studies are needed to determine the optimal individual EAdi target.
It is important to emphasize that EAdi represents respiratory drive and not diaphragmatic contractility. Diaphragmatic strength can be estimated by the volume or pressure generated by a given EAdi value (neuromechanical efficiency). This has not been studied in children. Contractile performance can also be tested using other more complex methods, for example, airway occlusion pressure generated by the diaphragm during phrenic nerve stimulation [
Finally, this technology is simple to use but can also be misinterpreted. In particular, the appropriate position of the catheter should always be confirmed before interpretation of EAdi values.
In conclusion, EAdi monitoring is a very accessible bedside technology that provides relevant information regarding the patient’s respiratory drive during critical illness. It allows the clinician to better adjust ventilatory settings to each patient’s particular condition and protect against asynchrony and diaphragmatic atrophy. Further studies are needed to evaluate the impact of this new technology on clinical outcome.
All the authors have no conflict of interests to declare.
MAQUET Critical Care provided 100 NAVA catheters and lent a servo I to facilitate a study on asynchrony in the authors’ PICU.