Comparison of diaphragmatic function between pressure support and NAVA using ultrasonography

Pressure support (PS) is the most widely used mode for weaning from mechanical ventilation, yet 20-30% of ICU patients fail to wean successfully. Neurally adjusted ventilatory assist (NAVA), which triggers and supports breathing based on diaphragmatic electrical activity, improves patient-ventilator asynchrony and diaphragmatic efficiency. However, its effects on diaphragmatic function and weaning outcomes remain unclear.

To compare diaphragmatic function between PS and NAVA using ultrasonographic indices sensitive to predicting weaning failure. We hypothesized that NAVA would yield more favorable measurements even after brief implementation.

In this prospective study, 19 adult ICU patients with difficulty weaning were consecutively enrolled. Patients were initially ventilated with NAVA titrated to achieve ∼6 ml/kg tidal volume, followed by PS adjusted to match peak pressure and tidal volume. After stabilization in each mode, diaphragmatic ultrasound was performed by a blinded operator. Tissue Doppler parameters (peak contraction velocity, peak relaxation velocity, maximal relaxation rate) and thickening fraction were measured over 2-3 stable cycles per method. Ventilatory and diaphragmatic electrical activity parameters were also recorded. Paired-samples t-test or Wilcoxon signed-rank test was used to detect differences between modes.

Two-hundred and nineteen breathing cycles were analyzed (109 PS, 110 NAVA). No significant differences were observed between PS and NAVA in ventilatory parameters, diaphragmatic electrical activity, tissue Doppler indices, or thickening fraction (all p > 0.2).

In this first ultrasonographic comparison of diaphragmatic function between PS and NAVA, no clinically meaningful differences were detected despite matched ventilatory parameters. Larger studies with longer exposure are needed to clarify potential advantages of NAVA.

The study protocol was approved prior to the initiation of enrolment by the Ethics Committee of Papageorgiou General Hospital of Thessaloniki, reference number ΕΣ 352η/16-03-2022.