Comparison of apnoeic oxygenation efficiency using high flow nasal cannula at two different flow rates in patients posted for surgery under general anaesthesia

This study is a prospective, randomized, comparative, single centre study comparing the efficiency of apnoeic oxygenation using high flow nasal cannula at 40 L/min and 60L/min in adult patients posted for surgery under general anaesthesia. A total of 56 patients will be recruited with 28 patients in each group. We hypothesized that HFNC flow of 40 L/min during apnoea period should provide similar oxygenation as that obtained by HFNC flow of 60 L/min. In both groups, pre-oxygenation will be done using high flow nasal cannula at 40 L/min for 3 minutes. After induction, the flow rate will be kept at 40 L/min in group F and increased to 60 L/min in group S for 3 minutes after which a definitive airway will be secured. The primary outcome will be partial pressure of arterial oxygen (PaO2) at the end of 3 minutes of apnoeic oxygenation in both groups. The secondary outcomes will be mean difference in PaO2 and PaCO2 levels in both groups (baseline, after 3 minutes of pre-oxygenation, after 3 minutes of apnoeic oxygenation, End-tidal oxygen (FETO2) and End-tidal carbon dioxide (ETCO2) after securing a definitive airway and after 3 minutes, percentage of population with hypoxemia (SpO2 < 92%), patient comfort during pre-oxygenation immediately before induction on a 5 point Likert scale.