Laryngeal oxygen concentration and apnoea time during microlaryngeal surgery using transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) with different oxygen concentrations: A randomised controlled clinical trial

The study includes the following steps: 1. The patient is identified when seen in the otolaryngology outpatient clinic as potentially suitable to participate in the study. Participation is discussed with the patient and informed consent to participate is obtained. 2. The patient is randomised to one of two groups,either Group A: ‘Apnoea Group’ (no delivery of high-flow oxygen, environmental room air oxygen only) or Group B: ‘30% Oxygen Group’ (Delivery of high-flow oxygen at 30% concentration), using an online randomisation tool. The patient is assigned a study ID which is on all further study documentation. 3. Patient enters the operating room. An investigator (DDN, DN, or a clinical fellow) enters demographic data into the Data Collection Form using patient’s study ID. All data collection throughout the procedure is recorded by an associate investigator or member of the clinical team. 4. The anaesthetic team will administer the intervention. The patient (both groups) is provided with pre-oxygenation using an Optiflow High Flow Nasal Oxygen at 100%, starting at 40L/Min prior to induction of anaesthesia and increasing to 70 litres/minute (once the patient is asleep). Duration of pre-oxygenation is at least three minutes. Baseline oxygen saturation and vital parameters are recorded using readings shown in a monitor screen during pre-oxygenation. 5. Anaesthesia is implemented by the anaesthetist. Oxygen delivery is maintained at 100%, 70 litres/minute. The time anaesthesia starts is recorded in the Data Collection Form. 6. Microlaryngeal surgical procedure starts. The start time of the procedure is recorded in the Data Collection Form. 7. Oxygen concentration in the larynx is measured using a cannula connected to a gas sampling tube which is in turn connected to a sampling unit built into the anaesthetic machine. The oxygen concentration (%) is shown on the monitor screen and is recorded in the Data Collection Form. 8. Delivered high-flow nasal oxygen is either switched off completely (Group A) or reduced to 30% oxygen (Group B). For patient from Group A, delivery of high-flow oxygen will cease and the patient will be apnoeic. For patients from Group B, high-flow would be reduced to 30% oxygen concentration. A sampling cannula is used to measure the real-time laryngeal oxygen concentration after these adjustments. The time from adjusting oxygen concentration until the laryngeal oxygen concentration drops is measured using a stopwatch. Vital parameters and oxygen saturation data are recorded from the readings shown in the monitor screen. 9. Microlaryngeal procedure proceeds as planned. Patient’s vital parameters (e.g. breathing rate, heart rate, blood pressure) and oxygen saturation (SpO2) is monitored intra-operatively as per normal practice. 10. When patient’s oxygen saturation reaches 89%, the delivery of 100% oxygen/70 litre min-1 is resumed and rescue supraglottic jet ventilation is employed as required. The time from the decrease in delivered oxygen concentration until rescue is recorded in the data collection form. The 89% oxygen saturation is used as a guideline for initiation of rescue ventilation, however, the ultimate decision as to when this occurs will be determined by the anaesthetist who may advise earlier implementation of rescue ventilation, in which case patient oxygen saturation at that point will be recorded. Should rescue jet ventilation fail to recover oxygen saturations, the next line of intervention will be endotracheal intubation as per our standard practice, and timing of this will be guided by the anaesthetist. The intervention will be in place until rescue jet ventilation is required or until the end of the case if rescue ventilation is not required. The same parameters (e.g. vital parameters, oxygen saturation and desaturation rate) will be collected from the two groups. The same nasal cannula will be in place for both groups. The length of the intervention is one of the outcome measures that we are trying to measure for comparing between the two groups. 11. When surgery is complete and patient resumes spontaneous breathing, end-tidal carbon dioxide is recorded. An anaesthetic chart is printed out from the anaesthetic machine. The study procedure is complete. 12. This study will be overseen by a DSMB comprised of three experts, an ENT surgeon, anaesthetist and biostatistician. They will meet initially, following recruitment of the first three patients, every six months and then again at the conclusion of the trial. The DSMB will be guided by a charter which outlines their responsibilities. 13. Follow up of the participants in this study will not be different to their routine clinical follow up which is guided by their clinical pathology. All patients will be reviewed post-operatively prior to discharge from the hospital. Review of anaesthetic chart and anaesthetist's notes will be used to assess adherence to the intervention.