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Neurally adjusted ventilatory assist (NAVA) is a new mode of assisted mechanical ventilation that uses the signal obtained from electromyography activity of the diaphragm (EAdi) to control the mechanical ventilator that delivers assist in proportion to the patient's respiratory drive. This study evaluated the monitoring Edi on conventional mode response, during the switch to pressure support assist and during the change to NAVA: a mode of predicting weaning from ventilation.
Sixteen adult patients ventilated with SERVO-I (Maquet) on pressure control or Bivent were randomized; we placed the specialized naso/orogastric tube (Edi catheter) and watched the Edi signal. PSV was set to obtain a Vt/kg of 6 to 8 ml/kg with an active inspiration. Were studied the peak airway pressure (Paw) and breathing pattern. Were registered the Edi minimum and Edi maximum for determining PEEP and peak pressure, respectively, Vt, respiratory rate, FiO2 and blood gases serially.
We observed synchrony between Edi signal and ventilator breaths in pressure control or Bivent, and when the patients have started spontaneous breaths (T signal) we move to pressure support. Low Edi minimum (0 to 1) was associated with overdistending the diaphragm and required decreasing the PEEP, contrary to high Edi minimum that was associated with higher tonic activity and dictated to raise the PEEP.
During NAVA, the pressure delivered was proportional to the Edi. The NAVA level was continuously readjusted in proportion to the predicted inspiratory effort from the Edi signal. At the highest assist level, we found lower Vt/kg (6.1 ± 3 ml/kg vs 8.1 ± 1.8, P < 0.001), and higher breathing frequency (19 ± 6.9 vs 11 ± 7, P < 0.001) and peak EAdi (11.8 ± 8.5 vs 8.1 ± 7.7, P < 0.002) in NAVA than in PSV.
The asynchrony during mechanical ventilation increases the cost of care, length of days on mechanical ventilation, and other morbidities associated with increased ICU stay. The Edi monitoring helps to understand other modes of ventilation and has been a great tool to decide the timing of a switch to NAVA and predict an early weaning. Systematically increasing the NAVA level reduces the respiratory drive, unloads respiratory muscles, and offers a method to determine an assist level that results in sustained unloading, low Vt, and stable respiratory function when implemented for 3 hours. NAVA gives us the opportunity to augment these patients' own drive to breathe enough to recover more quickly.