Assessment of Patient-ventilator Breath Contribution (PVBC) During Neurally Adjusted Ventilatory Assist (NAVA) in Patients With Acute Respiratory Failure

The primary purpose of mechanical ventilation is to sufficiently unload the respiratory muscles and maintain adequate ventilation in spontaneously breathing patients. When the mechanical ventilatory assist is synchronized to the patient's inspiratory effort, both the patient and the mechanical ventilator will contribute to the lung-distending pressure, necessary to overcome inspiratory load and generate the tidal volume (Vt). Unfortunately, conventional modes of mechanical ventilation cannot quantify the impact of the ventilatory assist performed by the ventilator and the patient. Inadequate levels of assist are associated with adverse effects such as development of fatigue or patient-ventilator dissynchrony and diaphragm impairment, and over assist also lead to diaphragm atrophy and weaning delay. The newly introduced neurally adjusted ventilatory assist (NAVA) has made it possible to measure the neural activity of the respiratory centers (expressed by the diaphragm electrical activity, EAdi). EAdi is a validated variable to quantify the neural respiratory drive, little is known about its usefulness to evaluate the contribution of the patient's inspiratory muscle effort relative to that of the mechanical ventilator, which would be of crucial importance to appropriately titrate the level of assist. During NAVA, the patient's efficiency to transform neural effort (EAdi) into Vt, expressed as neuroventilatory efficiency (NVE), may be a useful predictor for determining the contribution of the patient and the ventilator to generate a breath.