High-flow nasal Oxygen with or without alternating helmet Non-invasive ventilation for Oxygenation sUpport in acute Respiratory failure (HONOUR): a protocol for a pilot randomised controlled trial.

INTRODUCTION: Acute hypoxaemic respiratory failure is a common reason for intensive care unit (ICU) admission. Non-invasive respiratory support strategies such as high-flow nasal oxygen (HFNO) and helmet non-invasive ventilation may reduce the need for invasive mechanical ventilation and death. The High-flow nasal Oxygen with or without alternating helmet Non-invasive ventilation for Oxygenation sUpport in acute Respiratory failure pilot trial is designed to compare helmet non-invasive ventilation combined with HFNO vs HFNO alone in patients with acute hypoxaemic respiratory failure and to determine the feasibility of a larger randomised controlled trial. METHODS AND ANALYSIS: This is a pragmatic, open-label, multicentre randomised controlled pilot trial enrolling 200 critically ill adults with acute hypoxaemic respiratory failure across 12 Canadian ICUs. Participants are randomised 1 to 1 to receive either helmet non-invasive ventilation plus HFNO or HFNO alone for at least 48 hours. The primary aim is to assess feasibility metrics including recruitment rate, protocol adherence and fidelity to pre-specified intubation criteria. Secondary outcomes include rates of intubation, all-cause mortality, ventilator-free days, ICU length of stay and quality of life at 6 months. Primary and secondary outcomes will be analysed using Bayesian methods. ETHICS AND DISSEMINATION: Ethics approval has been obtained at all participating centres. Findings will inform the feasibility and design of a future full-scale trial and be disseminated through peer review publications and conference presentations. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Identifier: NCT05078034.