Use of high flow nasal oxygen in bariatric surgery: a randomised controlled trial

After manually oxygenating the patient to an end-tidal oxygen concentration (FEO2) of 0.9 via bag-mask-ventilation, oxygen will be administered via the Optiflow THRIVE device, at a flow rate of 50-70LPM as tolerated, humidified using the Fisher and Paykel 850 humidifier, to a humidity of 70% relative humidity. The oxygen concentration delivered from the device will be 100%, but the actual inspired oxygen concentration will vary with the degree of air entrainment. Pre-operatively an arterial line will be inserted for baseline and post-apnoea arterial blood gas analysis and blood pressure measurement. Arterial line insertion and invasive blood pressure monitoring is current practice in our institution in the management of an obese patient due to the lack of reliability of non-invasive blood pressure measurements in this population. Additionally, the use of an arterial line allows for repeated blood samples to be taken without exposing the patient to repeated skin puncture. Induction of anaesthesia will be conducted with alfentanil or fentanyl, propofol and rocuronium 1mg/kg of calculated lean body weight. Maintenance of anaesthesia during the period of data collection will be via intravenous propofol infusion. The patient will be ventilated with bag mask ventilation and the treating anaesthetist will perform gentle laryngoscopy with a CMAC video laryngoscope when the patient is pharmacologically paralysed. Laryngoscopy will take approximately 60 seconds. If the patient is judged to be an easy bag-mask ventilation and Cormack-Lehane laryngoscopy grade I or II, the laryngoscope will be removed and the patient will be bag-mask ventilated to an end-tidal oxygen of 90%. Once this target it reached, Optiflow THRIVE will be applied to the patient, an adequately sized an oropharyngeal airway inserted and airway manoeuvres (chin lift, head tilt, jaw thrust) performed to ensure airway patency. The patient will remain anaesthetised and apnoeic until an SpO2 of 95% or a time of six minutes is reached. At this point Optiflow THRIVE will be removed and the patient manually bag mask ventilated until SpO2 of 98% is achieved, and the patient will be intubated. During the period of apnoeic oxygenation, anaesthesia will be maintained with a propofol infusion. The intervention will only be performed once during the trial, for a maximum time period of 6 minutes. The procedure will be performed by a specialist anaesthetist with at least 5 years of anaesthetic experience, or by an anaesthetic trainee with a consultant anaesthetist present. The trial will occur at a tertiary hospital. The trial will be performed under direct supervision by the research practitioner in order to ensure that the intervention and control groups are being adhered to.