Neutrally Adjusted Ventilatory Assist (NAVA) is a new approach to mechanical ventilation based on neural respiratory output, says Eric Noronha, Manager-Operations, TBS India Private Limited to Elets News Network.
The act of breathing depends on rhythmic discharge from the respiratory centre of the brain. This discharge travels along the phrenic nerve, excites the diaphragm muscle cells, leading to muscle contraction and descent of the diaphragm dome. As a result, the pressure in the airway drops, causing an inflow of air into the lungs.
Conventional mechanical ventilators sense a patient’s effort by either a drop in airway pressure or a reversal in flow. The last and most slow reacting step in the chain of respiratory events is used to sense the patient effort, creating a system that is sensitive to hyperinflation, intrinsic PEEP (positive endexpiratory pressure) and secondary triggering problems.
With NAVA, the Electrical Activity of the Diaphragm (EAdi) is captured, fed to the ventilator and used to assist the patient’s breathing. As the ventilator and the diaphragm work with the same signal, mechanical coupling between the diaphragm and the ventilator is practically instantaneous.
Some of the Potential Benefits Improved synchrony: In NAVA the ventilator is cycled on as soon as neural inspiration starts. Moreover, the level of assistance provided during inspiration is determined by the patient’s own respiratory center demand. The same applies for the cycling off phase – the ventilator cycles off inspiration the instant it is alerted to the onset of neural expiration. By utilising the EAdi signal, maintenance of synchrony between the patient and the ventilator is improved.
Lung protection: With NAVA the patient’s own respiratory demands determine the level of assistance. It gives the opportunity to avoid over or under assistance of the patient.
Unique monitoring capability: The EAdi signal is a new unique parameter in mechanical ventilation. It can be used as a diagnostic tool to monitor the EAdi. The EAdi curve and its associated value can thus be used as a powerful monitoring tool in all ventilation modes, providing information on Respiratory Drive, Volume requirements and the effect of the ventilatory settings, and to gain indications for sedation and weaning.
NAVA for infants: The EAdi signal provides a tool that allows the clinicians to interpret the background of the chaotic breathing pattern so often seen in the infants. The direct access to the respiratory center output gives prompt information on the effect of any intervention relating to ventilation of the lung. PEEP adjustment and the degree of unloading can now are based on informed decisions.
Patient comfort: With NAVA, the respiratory muscles and the ventilator are driven by the same signal. The delivered assistance is matched to neural demands. This synchrony between patient and ventilator helps minimize patient discomfort and agitation, promoting spontaneous breathing.
Decision support for unloading and extubation: The EAdi signal can be used as an indicator to set the support level from the ventilator, and to optimize unloading. As the patient’s condition improves, EAdi amplitude decreases, resulting in reduction in ventilator-delivered pressure. This pressure drop is an indicator to consider weaning and extubation.