Physiologic comparison between NAVA, PAV+ and PSV in critically ill patients

Introduction

The aim of the present study was to compare, in a group of difficult to wean critically ill patients, the short-term effects of PSV, PAV+ and NAVA on breathing pattern, patient effort and patient- ventilator interaction.

Methods

Seventeen patients were studied during NAVA, PAV+ and PSV with and without artificial increase in ventilator demands (challenge) using either dead space (DS, n = 10) or chest elastic load (CL, n = 7) application. Airway and transdiaphragmatic (Pdi) pressures, electrical activity of the diaphragm (EAdi), volume and flow were measured breath by breath, while inspiratory integral of Pdi (PTPPdi) and EAdi (jEAdi) were calculated.

Results

At resting conditions all modes provided equal support as indicated by a similar PTPPdi per breath, per minute and per liter of ventilation. Apart from triggering delay, which with and without the challenge was significantly higher with PAV+ than that with NAVA and PSV, patient-ventilatory synchrony did not differ among modes. Independent of challenging conditions, inspiratory effort to trigger the ventilator was significantly higher with PAV+ than with NAVA and PSV. Compared with PSV, PAV+ and NAVA favored a more variable breathing pattern as indicated by the significantly higher coefficient of variation of tidal volume (VT). CL increased PTPPdi significantly less with PAV+ than with PSV and NAVA, while the increase of PTPPdi after DS did not differ among modes. The relationship between VT and PTPPdi was weaker with NAVA (median (IQR) r² = 25.6% (2.7 to 58.1%)) than with PAV+ (55.6% (34.4 to 61.6%)) and PSV (53.9% (23.2 to 77.4%)) on account of a poor jEAdi-PTPPdi relationship (R² = 16.2% (1.4 to 30.9%)) during NAVA.

Conclusion

Compared with PSV proportional modes favored breathing variability, while in the face of changing respiratory system mechanics PAV+ might be superior. However, significant drawbacks of both NAVA and PAV+ limit the effectiveness of these modes to proportionally assist the inspiratory effort.