Previous novel studies have demonstrated that PAV improves the synchrony between patient and ventilator, during several clinical conditions [8-12]. Based on the principles of the equation of motion, software (PAV+; Covidien, Boulder, Colorado, USA) has been developed that automatically adjusts the flow assist and the volume assist so that they always represent constant unloading fractions of the measured values of resistance and elastance loadings of the respiratory system [13-15]. Recent studies demonstrated that PAV+ is a safe and efficient ventilator mode in critically ill intubated patients [16,17]. During PAV the ventilator provides support only during the remaining duration of inspiratory effort, which can cause limitation when dynamic hyperinflation is present and when the inspiratory trigger is delayed due to intrinsic end-expiratory pressure.
The other support mode is NAVA, which will be discussed in this article. There are several similarities between PAV and NAVA, but this first round-table meeting focused on NAVA. A vast literature also exists concerning PAV, but this topic would require a whole chapter and will not be discussed in this current paper; hopefully PAV will be the topic of a different round table.The present article is based on an investigator-initiated round-table meeting. The article aims to review the available knowledge on the physiological rationale and feasibility of the recently introduced NAVA MV modality. Throughout the article, we place emphasis on the most recent findings concerning adjustment of the NAVA settings; on the one hand considering specific issues associated with assisted modes of MV, and on the other considering the expectations placed upon NAVA.
NAVA is an assist mode of MV that delivers a pressure proportional to the integral of the electrical activity of the diaphragm (EAdi) [18], and therefore proportional to the neural output of the patient’s central respiratory command. The level of pressure delivered is thus determined by the patient’s respiratory-center neural output. With NAVA, the ventilator is triggered and cycled-off based on the EAdi value, which directly reflects the activity of the neural respiratory command.
The inspiratory airway pressure applied by the ventilator is determined by the following equation:Paw=NAVAlevel��EAdi,where Paw is the instantaneous airway pressure (cmH2O), EAdi is the instantaneous integral of the diaphragmatic electrical activity signal (��V), and the NAVA level (cmH2O/��V or per arbitrary unit) is a proportionality constant set by the clinician.In Drug_discovery February 2011, several European and Canadian investigators with clinical results about NAVA available in publication or in abstract format organized a round-table discussion at the Geneva University Hospital to describe and discuss recent advances regarding NAVA.