High flow nasal oxygen (HFNO) has been available for many years. 1 Apnoeic oxygenation during head and neck surgery was described as Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) by Patel in 2015. 1 It has been available in our institution for delivery by Optiflow (Fisher and Paykel) since April 2015. 2 After our report of its use in patients with subglottic stenosis, we reviewed its use for all situations within theatres including when it might fail. Caldicott approval was granted for the voluntary prospective collection of data on all patients with HFNO from May 3, 2016 to July 17, 2018. Data were collated using Microsoft Excel (Microsoft Corp., Redmond, WA, USA) and analysed with GraphPad Prism v6.3 (t-test and ManneWhitney U-test). We recorded the age, weight, BMI, ASA physical status, gender, procedure, indication, anaesthetic technique, duration of apnoea (if apnoeic), preoperative, lowest and highest SpO 2 , and the highest end tidal CO 2 at case end. Failure was saturation <92% or peri-procedure change in airway management. Use in bronchoscopy is reported separately. Data on 117 episodes were analysed, and not all data fields were complete. In 81 (69%) patients, THRIVE was used for apnoeic oxygenation and the median duration of apnoea was 19 (range 1e60) min. Non-apnoeic HFNO was used in 12 (10%) for awake tracheal intubation and optimal pre-oxygenation in 24 (21%). Fifty (42.7%) were male, the mean age 52.8 (standard deviation [SD], 17.9) yr, median ASA physical status 2 [1e4], mean weight 84 (25.5) kg, and BMI 29.6 (8.6). Failure occurred in 14 (12%) cases, of which nine (64%) occurred when the THRIVE technique was utilised, 4 (29%) when Optiflow was used for pre-oxygenation, and one (7%) for awake intubation. A change in airway management was required in three cases. Patients that desaturated had a higher ASA status (median 2.5 vs 2; P¼0.0421) and BMI (mean 35.7 vs 26.4; P¼0.048). There was no significant difference between the two groups in duration of apnoea (P¼0.9923) or in age, current smoking status, preoperative and highest SpO 2. Figure 6 demonstrates the lowest saturation vs duration of apnoea with THRIVE.