Ultrasound Assessment of Respiratory Workload With High-Flow Nasal Oxygen Versus Other Noninvasive Methods After...

To compare the respiratory workload using the diaphragm thickening fraction (DTf) determined by sonography during high-flow nasal oxygen (HFNO), standard oxygen therapy (SOT), and noninvasive bilevel positive airway pressure support (BIPAP) in patients with acute respiratory failure (ARF) after cardiothoracic surgery.

Prospective controlled clinical trial.

A French 23-bed cardiothoracic surgical intensive care unit.

Nonintubated patients with ARF after cardiothoracic surgery or while awaiting lung transplantation.

HFNO (50 L/min), SOT via a standard facemask, and BIPAP (pressure support, 4 cmH₂O; positive end-expiratory pressure [PEEP], 4 cmH₂O), with F_IO₂ kept constant were successively applied and compared. With BIPAP, pressure support or PEEP increments up to 8 cmH₂O were compared with baseline settings. Each measurement was made after stable breathing for 5 minutes.

Fifty patients aged 60.0 ± 12.2 years were enrolled, including 14 (28%) with obesity. Mean PaO₂/F_IO₂ was 153 ± 55 mmHg. DTf was lower with HFNO and BIPAP than with SOT (respectively 21.2% ± 15.1% v 30.9% ± 21.1% and 17.8% ± 19.1% v 30.9% ± 21.1%, p < 0.001) and was not different with HFNO versus BIPAP (p = 0.22). With BIPAP, increasing pressure support to 8 cmH₂O decreased DTf (21.0% ± 14.3% v 28.8% ± 19.8%, p = 0.009), whereas increasing PEEP to 8 cmH₂O did not (25.2% ± 17.2% v 28.8% ± 19.8%, p = 0.79). Tidal volume increased to 10.6 ± 3.4 mL/kg with 8 cmH₂O pressure support v 8.8 ± 2.7 mL/kg with 4 cmH₂O pressure support (p < 0.001).

HFNO provides a comparable respiratory workload decrease compared with BIPAP at lower levels of pressure support and PEEP compared with SOT. Increasing BIPAP pressure support may provide higher levels of assistance but carries a risk of overdistension.