Comparison of Conventional Non-Invasive Ventilation and Neurally-Adjusted Ventilatory Assistance (NAVA) Non-Invasive Ventilation for the Treatment of Bronchiolitis

Bronchiolitis is a common diagnosis in pediatric hospitals and critical care units. Viral infection in younger patients often results in increased work of breathing, hypoxemia, impaired ventilation, and increased secretion burden. In some cases, treatment of severe respiratory failure includes intubation and mechanical ventilation. Current practice for patients with bronchiolitis who require hospital admission is to initially provide non-invasive ventilation to improve the patient's respiratory mechanics. This non-invasive respiratory support can range from simple nasal cannula, to high-flow nasal cannula, to non-invasive positive pressure ventilation.

The high-flow nasal cannula (HFNC) provides warm, humidified, oxygen-enriched air. Therapy commonly is prescribed with a prescribed fraction of inhaled oxygen (FiO2) delivered at 1-2 L/kg/min. This helps to improve oxygenation as the high rate of flow can "wash-out" carbon dioxide in the upper airways and thus reduce the volume of dead space ventilation.

Non-invasive ventilation (NIV) essentially provides a similar method of support as invasive ventilation without the use of endotracheal tube. Prescribed airway support is instead delivered non-invasively through a specialized nasal cannula or for larger children an occlusive facemask of appropriate size. The ventilator provides positive-end expiratory pressure (PEEP) with a prescribed delivery rate of a set inspiratory pressure (positive inspiratory pressure, or pressure control). This ventilator support enables the delivery of a set FiO2, helps maintain open airways to reduce atelectasis and allow for improved oxygenation with better V/Q matching, and improves work of breathing. The ventilator analyzes the flow generated by the patient's inspiratory effort and attempts to provide the prescribed positive inspiratory pressure at the time of the patient's own effort.

One of the major drawbacks of non-invasive ventilation for young pediatric patients with bronchiolitis is the difficulty in achieving synchrony between patient effort and ventilator-delivered positive inspiratory pressure. This is secondary to the large air leak given the non-invasive apparatus and the low inspiratory flows generated by this patient population. Thus, the ventilator and patient are often dyssynchronous which may actually increase work of breathing and agitation while impeding on the ventilatory support provided.

Neurally-Adjusted Ventilatory Assistance (NAVA) attempts to mitigate the harms of ventilator/patient dyssynchrony. This modality utilizes a specialized catheter placed into the esophagus, often via a nasogastric route, which has the capability of monitoring the electrical activity of the patient's diaphragm. This catheter can also be utilized to deliver feeds similarly to a basic nasogastric tube. The NAVA catheter monitors both the activation of the patient's diaphragm (indicating patient respiratory effort) and the strength of this activation in, referred to as the electrical activity of the diaphragm (Edi) and measured in millivolts (µV). Both human and animal studies have positively correlated the peak Edi values with work-of-breathing and demonstrated higher Edi values when respiratory pathology is present . Based on the Edi tracing, the ventilator can then deliver positive inspiratory pressure that is synchronous with both the patient's respiratory effort and proportional to the strength of this effort through a multiplier referred to as the NAVA level on the ventilator. This modality has been shown to improve patient agitation levels, reduce the need for sedating medications, and enhance synchrony in non-invasive ventilation modes.