High-flow nasal cannula (HFNC) oxygen therapy has been shown to improve oxygenation, reduce the need for intubation for patients with acute hypoxemic respiratory failure (AHRF) and avoid reintubation for post-extubation patients who had high-risk factors. HFNC refers to the delivery of gas at flows that exceed the patient peak inspiratory flow during tidal breathing, However, patient peak tidal inspiratory flow (PTIF) is found to vary greatly among different patients, from 20 to 50 L/min, making it difficult to properly set HFNC in a way to achieve the desired effects. In two recently published studies in intubated patients, PTIF varied from 25-65 L/min or 40-80 L/min, thus this study aims to investigate the correlation between pre-extubation PTIF in different modalities of SBT and post-extubation PTIF for adult patients, who are indicated to use HFNC immediately after extubation. In addition, the investigators aim to explore the patient response in terms of oxygenation and lung aeration to different flow ratios that matched and are above post-extubation PTIF.
In this study, patients who are ready for extubation and indicated for high-flow nasal cannula therapy after extubation will be enrolled, the investigators would measure the patient peak tidal inspiratory flow (PTIF) pre and post extubation to explore the correlation between the two PTIFs. Moreover, different HFNC flows would be applied, to explore the patient response in terms of oxygenation and lung aeration to different flow ratios that matched and are above post-extubation PTIF.