Objective: Neurally adjusted ventilatory assist uses the electrical activity of the diaphragm (EAdi)--a pneumatically-independent signal--to control the timing and pressure of the ventilation delivered, and should not be affected by leaks. The aim of this study was to evaluate whether NAVA can deliver assist in synchrony and proportionally to EAdi after extubation, with a leaky non-invasive interface.
Design and setting: Prospective, controlled experimental study in an animal laboratory.
Animals: Ten rabbits, anesthetized, mechanically ventilated.
Interventions: Following lung injury, the following was performed in sequential order: (1) NAVA delivered via oral endotracheal tube with PEEP; (2) same as (1) without PEEP; (3) non-invasive NAVA at unchanged NAVA level and no PEEP via a single nasal prong; (4) no assist; (5) non-invasive NAVA at progressively increasing NAVA levels.
Measurements and results: EAdi, esophageal pressure, blood gases and hemodynamics were measured during each condition. For the same NAVA level, the mean delivered pressure above PEEP increased from 3.9 +/ 1.4 cmH2O (intubated) to 7.5 +/- 3.8 cmH2O (non-invasive) (p<0.05) because of increased EAdi. No changes were observed in PaO2 and PaCO2. Increasing the NAVA level fourfold during non-invasive NAVA restored EAdi and esophageal pressure swings to pre-extubation levels. Triggering (106 +/- 20 ms) and cycling-off delays (40 +/- 21 ms) during intubation were minimal and not worsened by the leak (95 +/- 13 ms and 33 +/- 9 ms, respectively).
Conclusion: NAVA can be effective in delivering non-invasive ventilation even when the interface with the patient is excessively leaky, and can unload the respiratory muscles while maintaining synchrony with the subject's demand.