New ventilatory modes: PAV+ and NAVA

Abstract

Proportional assist ventilation with load-adjustable gain factors (PAV+) and neurally adjusted ventilatory assist (NAVA) are new ventilatory modes where assistance is delivered in proportion to the instantaneous respiratory effort and to a proportionality factor set by the clinician. However, the physiological signal used by the ventilator to detect the patient’s effort is different between these two modes. PAV+ delivers assistance in proportion to instantaneous flow as well as volume and respiratory load. In NAVA, the airway pressure is provided in proportion to diaphragm electrical activity, recorded using an esophageal catheter with an electrode array. The proportionality of the assistance allows an improvement in patient-ventilator interactions with both modes, due to several mechanisms: the ventilator adapts the amount of pressure delivered according to the instantaneous patient’s demand, the patient rapidly adjusts his own effort to receive a target tidal volume, the natural respiratory variability is respected, and the cycling off is closed to the neural inspiratory time. In these conditions, dynamic hyperinflation cannot occur and there are few patient-ventilator asynchronies. Furthermore, according to their properties of functioning, each mode allows additional interactions and neuro-ventilator coupling monitoring. However, although these modes are promising, how to adjust the proportionality factor is still a matter of research. These ventilatory modes must also demonstrate their benefit in clinical randomized trials before being considered for a widespread clinical use.