Critically ill patients may need support for breathing by means of intubation, which is placement of a breathing tube into the windpipe. Rapid sequence intubation (RSI) is a method commonly used and is performed by administering medications to induce coma and muscle paralysis, followed by intubation to allow the ventilator to provide oxygen into the lungs. This procedure may be filled with potential complications.

During RSI, the patient stops spontaneous breathing after medically induced muscle paralysis occurs. Adequate oxygenation before and during paralysis is crucial to increase the reserves and prolong the time that oxygen levels in the blood remain above 90%, called the safe apnoea period. If the oxygen reserves are insufficient, the blood oxygen level will drop and can lead to permanent brain damage or even death.

This study aims to explore if delivering high-flow humidified oxygen at 60L/min via the nostrils would be superior to current methods of mask ventilation at 15L/min and nasal cannula at 15L/min, before and during paralysis respectively. If successful, this new method would allow for a longer safe apnoeic period and increase the chances for doctors to perform intubation successfully without the blood oxygen dropping below 90%.

Maintaining adequate oxygenation during rapid sequence intubation (RSI) is imperative to prevent peri-intubation adverse events that can lead to increased duration of hospital and intensive care unit stay, or prolonged vegetative state requiring long-term institutionalisation.

Preliminary data from our emergency department (ED) airway registry revealed that 15% of patients experienced desaturation during intubation despite employing current best practices during RSI. In this multicentre randomised controlled trial in the ED, we aim to test the hypothesis that use of humidified high flow oxygenation via nasal cannula (HFNC) at 60L/min maintains higher oxygen saturation compared with current usual care using non-rebreather mask for preoxygenation and provides superior apnoeic oxygenation compared to the typical practice of 15L/min via standard nasal cannula.

The main goal of the study would be to improve on the lowest oxygen saturation during intubation, and thereby increase the safe apnoeic time during RSI. We plan to enrol adult patients who require rapid sequence intubation due to medical, surgical or traumatic conditions in the EDs of National University Hospital and Ng Teng Fong General Hospital.

Eligible patients will undergo block randomisation at equal ratio into 2 possible treatment combinations of pre-oxygenation and apnoeic oxygenation. The primary endpoint will be the lowest oxygen saturation achieved from time of administration of paralytic agent until quantitative end-tidal carbon dioxide is detected for the first intubation attempt.

Higher failure rates for intubation in unfasted patients in the ED compared to fasted patients in elective settings increase the risk of aspiration if re-oxygenation is required with bag-valve-mask ventilation. Prolongation of safe apnoea time through maintenance of oxygen saturation above 90% using HFNC oxygenation during RSI could potentially change current clinical practice, improve standard of care and translate to better outcomes for patients.

Inclusion Criteria:

• Adult patients aged 21 years and above, who require RSI due to medical, surgical and traumatic conditions, in the Emergency Departments of NUH and Ng Teng Fong General Hospital (NTFGH)

Exclusion Criteria:

• Patients with "do-not-resuscitate" orders
• Crash, awake or delayed sequence intubations
• Patients requiring non-invasive positive pressure ventilation
• Cardiac arrest
• Clinical suspicion or confirmed diagnosis of base of skull fractures or severe facial trauma that precludes nasal cannula placement
• Vulnerable patient populations (e.g. pregnant women, prisoners)