Clinical and physiological consequences of preoxygenation using high‐flow nasal oxygen in emergency anaesthesia

Emergency anaesthesia is usually performed using a rapid sequence induction technique. The incidence of desaturation during rapid sequence induction is high, and preoxygenation prolongs the safe apnoea time. Apnoeic oxygenation using high-flow nasal oxygen can maintain adequate oxygenation in non-obese and pulmonary healthy patients for half an hour. High-flow nasal oxygen has also been shown to achieve a preoxygenation efficacy comparable with a traditional, tight-fitting facemask. Therefore, high-flow nasal oxygen has been proposed as a preoxygenation technique during rapid sequence induction, with a potential benefit being a seamless transition to apnoeic oxygenation. This thesis has investigated high-flow nasal oxygen during rapid sequence induction in various high-risk patient populations, aiming to explore its effectiveness in avoiding oxygen desaturation and the potential limitations of the technique. Study I explored high-flow nasal oxygen as preoxygenation among patients undergoing emergency surgical procedures.1 High-flow nasal oxygen did not decrease the incidence of desaturation during induction of anaesthesia compared with a traditional facemask. The frequency of regurgitation did not differ between the groups, and no differences in the incidence of desaturation were seen comparing office hours and on-call hours. The facemask group had higher end-tidal oxygen levels immediately following intubation. Study II investigated parturients, a population known to tolerate apnoea poorly. We, therefore, examined the use of high-flow nasal oxygen during induction of anaesthesia in pregnant women.2 All women in our cohort maintained well-oxygenated, and no patient showed signs of regurgitation. More parturients preoxygenated with high-flow nasal oxygen had end-tidal oxygen levels above 70% immediately following intubation compared with those preoxygenated with a facemask. This may indicate a greater oxygen reserve and superior conditions to maintain oxygen saturation during prolonged apnoea. Larger, randomised trials are needed to confirm our results. Pre-hospital data have shown a high incidence of desaturation in trauma patients undergoing emergency anaesthesia. In Study III, investigating trauma patients in need of in-hospital emergency anaesthesia, we could not detect any differences in the number of patients desaturating <93% if preoxygenation was performed with high-flow nasal oxygen compared with a traditional facemask.3 Using high-flow nasal oxygen did not increase the incidence of adverse events, although these results are limited by the size of the population. Anaesthetists assessed preoxygenation with high-flow nasal oxygen as easier compared with a traditional facemask which could be valuable given the stressful clinical situation. In this thesis, we also propose a new technique for preoxygenation. In Study IV, we have shown that using a standard nasal cannula, at high flow rates, generates a preoxygenation efficacy comparable to a traditional facemask and high-flow nasal oxygen, although at the expense of impaired comfort.4 Since the standard nasal cannula is inexpensive, user-friendly, and available globally, it could constitute an option when alternative methods are lacking. In summary, preoxygenation using high-flow nasal oxygen has shown to be a feasible method to use during rapid sequence induction in various high-risk populations, equally effective as a traditional facemask in avoiding oxygen desaturation. Potential benefits are anaesthetists assessed ease, high-patient comfort, and a smooth transition to apnoeic oxygenation. This thesis demonstrated no increased risks of using high-flow nasal oxygen compared with a traditional facemask, although these results are limited by the size of our populations and need to be further explored. Finally, this thesis proposes a new method for preoxygenation, using a standard nasal cannula. Even though it impairs comfort, it could serve as an option when alternative methods are lacking. AS: Design of the studies, patient recruitment and acquisition of data, analysing data, drafting the articles, revising the articles, final approval of the articles. MJF: Design of the studies, patient recruitment and acquisition of data, analysing data, drafting the articles, revising the articles, final approval of the articles. MH: Design of the studies, patient recruitment and acquisition of data, analysing data, drafting the articles, revising the articles, final approval of the articles. IMF: Design of the studies, patient recruitment and acquisition of data, analysing data, drafting the articles, revising the articles, final approval of the articles. The work of this study was supported by grants from Stockholm Research Council, Swedish Research Council, Gösta Fraenckel Foundation and Capio Foundation. The author has no conflicts of interest. Data available on request due to privacy/ethical restrictions.