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

Sammanfattning: 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 to 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. High-flow nasal oxygen did not decrease the incidence of desaturation during induction of anaesthesia compared to 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. 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 to 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 to a traditional facemask. 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 to 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. 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 to 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.