The optimal method for conducting spontaneous breathing trials (SBTs) remains a subject of ongoing debate. High-flow oxygen via endotracheal tube (HFOT) has emerged as a novel alternative for SBTs. However, studies investigating the associated physiological changes are lacking. Compared to high-flow nasal cannula (HFNC), HFOT has demonstrated diminished physiological effects, likely due to the bypassing of the upper airway, which may limit its widespread adoption as an SBT strategy. Two HFOT interfaces with different expiratory port diameters will be evaluated. It is hypothesised that the narrower interface would generate higher airway pressure and mitigate weakening physiological effects compared to the HFNC. This study aims to compare the physiological effects of two HFOTs compared to T-piece during SBTs.

This is a single-centre, prospective, physiological randomised crossover study in adult patients receiving mechanical ventilation for more than 24 hours who are deemed ready for SBT. After enrolment, each patient will be disconnected from the ventilator and undergo five SBT phases in random order: T-piece at 6 L/min, HFOT via interface with an expiratory port diameter of 9.8 mm at 40 L/min and 60 L/min and HFOT via interface with an expiratory port diameter of 6.9 mm at 40 L/min and 60 L/min. To reduce carryover effects, each phase will be separated by a 10-min washout period during which baseline mechanical ventilation is resumed. Key physiological parameters will be assessed in each study phase, including airway pressure, changes in end-expiratory lung volume, vital signs, oxygenation levels and inspiratory effort. Postextubation inspiratory effort will also be measured. Finally, 20 patients with the complete five SBT phases and postextubation datasets will be analysed

The study protocol has been approved by the Institutional Ethics Committee and Review Board of Beijing Shijitan Hospital, Capital Medical University (IIT2024-157-002). The data generated in the present study will be available from the corresponding author on reasonable request. The results of the trial will be submitted to international peer-reviewed journals.

NCT06816706.