The Impact of High-Flow Nasal Cannula Therapy on Diaphragmatic Function Assessed by Ultrasound: A Pilot Clinical Study

Objectives: High-flow nasal cannula is increasingly used in patients with acute hypoxemic respiratory failure. However, its impact on diaphragmatic function remains poorly understood. Design: Observational crossover pilot study. Setting: Single-center ICU. Patients: Twenty-eight adult ICU patients with a Pa o 2 /F io 2 ratio less than or equal to 300 mm Hg were enrolled. Interventions: Patients underwent sequential 60-minute phases of noninvasive respiratory support using a Venturi mask, high-flow nasal cannula (40 L/min), and helmet continuous positive airway pressure (CPAP). Measurements and Main Results: Diaphragmatic function was assessed using ultrasound, while inspiratory effort was evaluated through esophageal pressure swings. Arterial blood gases were also collected. High-flow nasal cannula significantly improved the diaphragmatic thickening fraction compared with the Venturi mask (27% ± 9.9% vs. 20% ± 6%; p = 0.0013). Conversely, diaphragmatic excursion was lower with high-flow nasal cannula than with both the Venturi mask and CPAP (1.1 ± 0.63 cm vs. 1.5 ± 0.95 cm and 1.4 ± 0.59 cm, respectively; p = 0.0002). High-flow nasal cannula also reduced inspiratory effort compared with the Venturi mask. In patients with diaphragmatic dysfunction index greater than 100, both high-flow nasal cannula and CPAP enhanced diaphragmatic thickening and decreased esophageal pressure swings relative to the Venturi mask. Conclusions: This study shows that high-flow nasal cannula improves diaphragmatic function compared with Venturi mask oxygen therapy. Larger studies are needed to confirm these findings.