Authors Richard Buckley and Tony Hodgetts, of the Department of Anaesthetics, Queen Elizabeth The Queen Mother Hospital, East Kent University NHS Foundation Trust, discuss their case series demonstrating the use of HFNO with sedation as an effective anaesthetic technique
High-flow nasal oxygen (HFNO) has been described in the literature as a safe technique of oxygenation for obese patients undergoing short procedures such as electroconvulsive therapy (ECT). Following the desaturation of an obese patient who had been administered a GA for hysteroscopy and subsequently required overnight admission, this case series discusses whether HFNO with sedation is an effective and safe technique for such patients in maintaining oxygenation and avoiding the need for overnight admission post-op. Three patients have been included in this case series. All underwent a hysteroscopy and were given the same anaesthetic technique of HFNO 40L/min pre-oxygenation, the same opiate analgesic and anti-emetics, followed by target-controlled infusion (TCI) propofol sedation with the HFNO flow rate increased to 60-70L/min post-induction. Continuous monitoring of the patients was performed throughout. Of the three patients, all were successfully maintained on HFNO during the procedure and were able to be discharged home on the same day. The results from this case series demonstrate the use of HFNO with sedation as an effective anaesthetic technique for high BMI patients undergoing hysteroscopies and avoids the need for airway instrumentation in a cohort that is higher risk for difficult airways.
The use of high-flow nasal oxygen (HFNO) is a technique that is regularly used in anaesthesia for pre-oxygenation and apnoeic oxygenation of patients, whilst also delivering an element of positive pressure that allows gaseous exchange to continue through ‘dead-space flushing’ . Benefits of HFNO in anaesthesia have been cited in the literature, with several studies concluding that it was an effective technique in prolonging the safe apnoea time during emergency intubation, allowing for a smoother process for intubation [1,2]. Other studies have considered HFNO as a technique in more anaesthetically high-risk patients. In relation to the obese population, current literature highlights the advantages of HFNO in both pre-oxygenation and also reducing the incidence of accidental gastric insufflation [3,4] … One study investigating the use of HFNO for obese patients undergoing Electroconvulsive therapy (ECT) found that no patients desaturated during the procedure, compared to 2 who desaturated whilst receiving a standard facemask ventilation technique .
This case series describes the use of HFNO in a gynaecology theatre setting, specifically for obese patients undergoing hysteroscopies. The inspiration for this case series was where a patient with raised BMI was due to undergo a repeat hysteroscopy. The patient had undergone a recent hysteroscopy under general anaesthetic (GA) with a supraglottic airway device and desaturated both intra-op and post-op requiring overnight admission instead of same day discharge. The repeat hysteroscopy was undertaken with Propofol TCI sedation and HFNO, with no desaturation and same day discharge. Therefore, it was decided to review whether the use of HFNO accompanying sedation was an improved technique for obese patients undergoing hysteroscopies.
Three patients were included in this case series with a mean age of 54.3 years, mean weight of 127.3kg, and a mean Body Mass Index (BMI) of 47.5 [Table 1]. All received the same standard anaesthetic technique; they were prepared in theatre on the operating table to minimise moving and time, pre-oxygenated with HFNO (THRIVE, transnasal humidified rapid-insufflation ventilatory exchange. Fisher & Paykel Healthcare, Auckland, New Zealand) at a flow rate of 40L/min whilst awake and then received fentanyl 25-50mcg, ondansetron 4mg and dexamethasone 6.6mg (post induction) with propofol target-controlled infusion (TCI). Oxygen flow rate was increased to 60-70 l/min after induction.
The patients’ oxygen saturations were continuously monitored as part of the Association of Anaesthetists for Great Britain and Ireland (AAGBI) recommendations for monitoring a sedated patient, and the lowest saturations were compared to the starting saturations, which are summarised in Table 2, along with the outcome of the technique.
As Table 2 summarises, all three patients were successfully maintained on HFNO with propofol TCI sedation for the procedure. Patient 2 had a brief desaturation to 89% but recovered quickly and maintained oxygen saturations at 95%. All were able to be discharged on the same day.
Discussion and conclusion
In conclusion, this case series demonstrates that the use of HFNO alongside propofol TCI sedation for hysteroscopy is an elegant anaesthetic technique, avoiding the need for airway instrumentation in high-risk patients. However, care needs to be taken when selecting patients for the use of this technique as some patients are at higher risk of desaturation, for example, patients on home-oxygen. Following this initial series, further research is required to assess whether this technique is superior to a general anaesthetic with insertion of supraglottic airway/endotracheal tube for hysteroscopy in high-risk patients.
We would like to thank Dr S. Laxman for his guidance and proof-reading in the writing of this case series.
RB, TH-no competing interests declared.
 Patel, A. and Nouraei, S.A.R. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE): a physiological method of increasing apnoea time in patients with difficult airways. Anaesthesia; Mar 2015; vol. 70 (no. 3); p. 323-329
 Pratt, Matt; Miller, Ann B. Apneic Oxygenation: A Method to Prolong the Period of Safe Apnea. AANA journal; Oct 2016; vol. 84 (no. 5); p. 322-328
 Weiqing, J. et al. Ultrasound assessment of gastric insufflation in obese patients receiving transnasal humidified rapid-insufflation ventilatory exchange during general anesthesia induction. Nan fang yi ke da xue xue bao = Journal of Southern Medical University; Nov 2020; vol. 40 (no. 11); p. 1543-1549
 Jaewoong, J. et al. A novel application of Transnasal Humidified Rapid Insufflation Ventilatory Exchange via the oral route in morbidly obese patient during monitored anesthesia care – A case report. Anesthesia and pain medicine; Oct 2020; vol. 15 (no. 4); p. 505-509
 Saxena, A. et. al. THRIVE and Desaturation in Obese Patients Undergoing Electroconvulsive Therapy. Abstract. The Anaesthesiology Annual Meeting. Oct 2017.