High-flow oxygen for children’s airway surgery: a randomized, controlled, prospective protocol (HAMSTER) trial

Myron Yaster MD, Melissa Brooks Peterson MD, and Jamie Peyton MD

I’ve got to admit that whenever I see an article by Britta von Ungern-Sternberg AND/OR Andrew Davidson,¹ it goes right to the top of the articles to be reviewed in the PAAD.  And if I had any doubts, the acronym for the study, HAMSTER, well, settled it and made the review a priority! Also, a little fun fact about Britta VU-S one of the authors today’s article: each of the major trials she has run have an animal acronym, and that animal acronym comes along with a stuffed animal that lives in her office and research institute. Ask her to see the pictures of her “stuffie zoo” the next time you see her! Myron Yaster MD  (fun fact provided by Melissa)   

Original article

Humphreys S, von Ungern-Sternberg BS, Taverner F, Davidson A, Skowno J, Hallett B, Sommerfield D, Hauser N, Williams T, Spall S, Pham T, Atkins T, Jones M, King E, Burgoyne L, Stephens P, Vijayasekaran S, Slee N, Burns H, Franklin D, Hough J, Schibler A. High-flow nasal oxygen for children's airway surgery to reduce hypoxaemic events: a randomised controlled trial. Lancet Respir Med. 2024 Jul;12(7):535-543. doi: 10.1016/S2213-2600(24)00115-2. Epub 2024 May 21. PMID: 38788748.

Many diagnostic and therapeutic upper airway examinations and surgeries require a shared, non-controlled, non-intubated (“tubeless”) airway.^2,3  Some of the surgical condition requirements, like an open airway, spontaneous ventilation and oxygenation +/- intermittent pressure support, and anesthesia deep enough to tolerate airway surgical stimulation makes hypoventilation and hypoxemia almost inevitable.⁴  How to best deliver oxygen in these open airway cases and avoid hypoxemia and interruption of the surgical procedure to reoxygenate an hypoxic patient has never been rigorously studied in children.  In today’s PAAD, Humphreys et al. “conducted the HAMSTER randomized clinical trial protocol⁵ to assess whether high-flow oxygen improves the likelihood of successful anesthesia without any interruption of the surgical procedure compared to simple nasal oxygen supplementation in children undergoing tubeless upper airway surgery”.¹

Children undergoing a tubeless upper airway procedure, aged between 37 weeks' gestation and up to 16 years, were randomized to either high flow nasal oxygen, 2 L/kg/minute at an FiO2 of 1 or standard care oxygen flows of up to 6 L/min by nasopharyngeal or oropharyngeal catheter attached to the anesthesia machine.  “The primary distinction between standard care and the high-flow oxygen delivery technique lies in the approach to maintaining general anesthesia. For nearly half of the procedures in the standard group, maintenance involved either inhaled anesthetic agents or a combination of inhaled and intravenous agents. In the case of high-flow oxygen, total intravenous anesthesia was employed in all patients, as the accurate delivery of inhaled anesthetic agents is not feasible under high-flow conditions.”¹

What did they find?  “The oxygen saturation in these children, measured with transcutaneous oxygen probes, was similar in both study groups during the procedure. High-flow oxygen during tubeless upper airway surgery did not reduce the proportion of hypoxemic events compared with standard care.  Further, the likelihood of successful anesthesia without interruption of tubeless upper airway surgery in children younger than 16 years was not superior with high-flow oxygen compared with standard care oxygen therapy.”¹

JP comments:

I have a conflict of interest I should declare before stating anything else. I was one of the reviewers of this paper and pushed to get it published for several reasons, which I shall elaborate on below. I was also asked to write an editorial discussing it, but unfortunately, at the time, I was unable to commit to the required deadlines. So, I am grateful to Myron and the PAAD team for giving me the opportunity to briefly share my thoughts.

As we all know, positive trials are more likely to be published than negative or neutral trials. When we  first heard about the HAMSTER trial, we were expecting to see results that would demonstrate the superiority of high-flow oxygen delivery systems, particularly given the positive outcomes in adult studies. However, the trial's findings revealed no significant differences between the studied groups, which was a surprise. Despite our initial expectations of the study outcomes, we fully support publication of this study with “nill” as the difference. In my view, even without a difference between the two groups, this trial adds valuable information to the literature on both supplemental oxygen provision and shared airway surgery in children.

Currently in both the PAAD coverage and broader pediatric anesthesia literature, supplemental oxygen use during airway management is a hot topic. As discussed in several recent PAADs, there are now formal recommendations from multiple societies advocating the use of supplemental oxygen during both emergency and routine tracheal intubation. Still, nobody is sure of the best way to do this. High-flow systems have been used in ICU for many years but have only recently been studied in pediatric anesthesia, and the expectation has been that this equipment would improve oxygenation in both apneic and spontaneously breathing patients compared to traditional low-flow systems. This does not seem to be the case, and this well-conducted randomized controlled trial shows us that during airway surgery and manipulation, providing oxygen is key, regardless of the equipment used to provide that oxygen. This is the most important take away from this study

Secondary takeaways from this study relate to the equipment used for high-flow oxygen provision is an extra expense and takes up sparse ergonomic space in the OR; additionally, high flow  nasal cannula are relatively bulky and need to be rapidly removed if rescue mask ventilation is needed. In contrast, our normal nasal cannula can be attached to the auxiliary oxygen port or breathing circuit of our anesthesia machine (therefore require no extra equipment) and are small enough that it is possible to effectively mask ventilate with them in place (while appreciating the risks of barotrauma that may occur in a closed system without adequate pressure relief), so have some advantages over the high flow systems. The information from this trial can be immediately translated into our practice during tracheal intubation using readily available, cheap equipment in hospitals worldwide.  Finally, an additional benefit to simple nasal cannula is that they can be left in place at the conclusion of the anesthetic and used to provide supplemental O2 during transport to and in the PACU.

This trial is also useful for those of us who regularly anesthetize children for shared airway surgery. It gives us the best modern estimation of the rate of complications and interruptions during surgery, and can help guide our discussions with families about tailored and specific risks of open airway procedures. It also helps us to involve our surgical colleagues in discussions about different oxygenation techniques with evidence to back up our choices where disagreements may arise.

For emphasis, we reiterate the take away message of this study:  It really doesn’t matter if you use high flow or standard supplemental oxygen during these procedures as long as you give some form of supplemental oxygen.  We are reaching the point in the PAAD and arguably in the recent pediatric anesthesia literature that the provision of supplemental oxygen during any airway manipulation may become standard of care. As discussed in several previous PAADs, the need for supplemental oxygen should be routine in all intubations of patients with difficult airways including all newborn intubations and potentially added to the routine intubation sequence for all general anesthetics.

Have you made this change in your practice?  Send your thoughts and comments to Myron who will post in a Friday reader response.

References

1.            Humphreys S, von Ungern-Sternberg BS, Taverner F, et al. High-flow nasal oxygen for children's airway surgery to reduce hypoxaemic events: a randomised controlled trial. Lancet Respir Med 2024;12(7):535-543. (In eng). DOI: 10.1016/s2213-2600(24)00115-2.

2.            Wang JT, Peyton J, Hernandez MR. Anesthesia for pediatric rigid bronchoscopy and related airway surgery: Tips and tricks. Paediatric anaesthesia 2022;32(2):302-311. (In eng). DOI: 10.1111/pan.14360.

3.            Bradley J, Lee GS, Peyton J. Anesthesia for shared airway surgery in children. Paediatric anaesthesia 2020;30(3):288-295. (In eng). DOI: 10.1111/pan.13815.

4.            Hsu G, von Ungern-Sternberg BS, Engelhardt T. Pediatric airway management. Current opinion in anaesthesiology 2021;34(3):276-283. (In eng). DOI: 10.1097/aco.0000000000000993.

5.            Humphreys S, von Ungern-Sternberg BS, Skowno J, et al. High-flow oxygen for children's airway surgery: randomised controlled trial protocol (HAMSTER). BMJ Open 2019;9(10):e031873. (In eng). DOI: 10.1136/bmjopen-2019-031873.