Neurally adjusted ventilatory assist: letting the respiratory center take over control of ventilation

Excerpt

In 1999, Sinderby and colleagues [1] described a system based on the use of electrical diaphragmatic activity (Edi) for control of assisted ventilation, which was termed neurally adjusted ventilatory assist (NAVA). In NAVA, a catheter with an array of eight electrode pairs (or nine single electrodes) on its distal end is placed in the esophagus such that the center of the electrode pairs is ideally positioned at the diaphragm level in order to optimally collect the Edi signal (Fig. 1). The signal collected by every second electrodes pair is processed by cross-correlation to determine the position of the diaphragm with respect to the array of electrodes (center signal). Subtraction of signals above and below the diaphragm, which are in opposite phases, yields a new “double-subtracted” electrical signal. Finally, the root-mean-square of both the center and the double-subtracted signals are then combined to the Edi signal, which is converted to inspiratory pressure support using a gain factor (NAVA gain in cmH₂O/μV). Since the respiratory center activity changes according to gas exchange and lung stretching, assistance during NAVA is fairly constant within a wide range of NAVA gain values. Obviously, too high and too low NAVA gains may disturb the feedback to the respiratory center.

…