A level of neurally adjusted ventilatory assist corresponds to low levels of continuous positive airway pressure and pressure support ventilation in patients preparing to be extubated from mechanical ventilation

Introduction

Neurally adjusted ventilator assist (NAVA) is a new mode of mechanical ventilation which delivers ventilator assist in proportion to electrical activity of the diaphragm (EAdi), as assessed by trans-esophageal electromyography, and an adjustable supporting level called the NAVA level. NAVA can be used as a supporting and weaning mode of ventilation [1–3]. However, a level of NAVA corresponding to continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) in patients ready for extubation has not been established.

Methods

We carried out a prospective study in the medical ICU at Phramongkutklao Hospital involving patients who were considered by their physicians to be ready for extubation. Patients initially received PSV of 5 cmH₂O, PEEP of 5 cmH₂O, and FiO₂ of 40% for 15 minutes (PS). Subsequently, each patient received a trial of NAVA mode with PEEP of 5 cmH₂O, and FiO₂ of 40% for 15 minutes (NAVA), and, finally, a 30-minute spontaneously breathing trial without ventilatory support (SBT). During these trials, the minute volume (MV), respiratory rate, EAdi, and airway pressure were measured. We determined the corresponding NAVA level with the level of PSV of 5 cmH₂O and PEEP of 5 cmH₂O using the NAVA level matching MV (±10%) received from the PSV.

Results

The NAVA level corresponding to the PSV of 5 cmH₂O and PEEP of 5 cmH₂O was 0.52 cmH₂O/μV (0.2 to 1.2). The airway pressure during NAVA was 5.97 cmH₂O (3.2 to 8) above PEEP level. The peak EAdi was not significantly different between the PS, NAVA, and SBT (11.58, 12.06 vs 12.65 μV; P = 0.6). Also, there was no significant difference in MV during the PS, NAVA, and SBT.

Conclusions

NAVA mode can be used as a weaning mode by decreasing the NAVA level. The reduced level of NAVA to 0.5 cmH₂O/μV did not load respiratory muscle more than a low level of PSV and SBT. Thus, a NAVA level of 0.5 cmH₂O/μV might be the level that is safe to discontinue ventilator support in patients without problems for resuming spontaneous breathing.