High-Flow Oxygen for Children’s Airway Surgery: A Randomised controlled trial

Infants and children with airway abnormality often require surgery of their upper airway to improve their breathing; a procedure called microlaryngoscopy. During this procedure the child is anaesthetised and the anaesthetist controls their breathing. In these situations, known as ‘shared airway’ cases, both the surgeon and anaesthetist require simultaneous access to the child’s airway. The anaesthetist needs to maximise oxygen delivery and provide adequate depth of anaesthesia while the surgeon requires direct access to the airway and an unobstructed view to perform the procedure. In these circumstances it is often impractical for the anaesthetist to place an artificial breathing (endotracheal) tube to deliver oxygen and inhaled anaesthetic gases, therefore oxygen delivery must be achieved by other means.

During this kind of surgery, it is not uncommon for blood oxygen levels to fall (hypoxia). Surgery may need to be interrupted by the anaesthetist to correct this, potentially compromising patient safety, prolonging the procedure, increasing exposure to anaesthesia and reducing surgical efficiency. At Queensland Children’s Hospital (QCH), we recently conducted a clinical audit of the anaesthetic care of children undergoing airway surgery and found that 32% of children experienced one or more hypoxemic events (low oxygen levels). A further 23% of surgeries required interruption to apply rescue oxygenation.

The method the anaesthetist chooses to oxygenate the child may help prevent this type of serious complication. Traditionally, anaesthesia technique has involved the delivery of low flow oxygen via a ‘Nasopharyngeal Low Flow Oxygen’ (NLFO) system, in which oxygen is delivered at flow rates of 2-6L/min, typically via an oxygen catheter tube placed in the nose. Our research team at QCH has been investigating the use of a new mode of oxygenation for children undergoing anaesthesia called ‘High-Flow Nasal Oxygen Insufflation’ (HFNOI). In HFNOI, warm and humidified oxygen is delivered to the airway via nasal cannulae at weight-specific flow rates. For example, HFNOI can be delivered at rates of 2L/kg therefore a 10kg infant the child would receive 20L/min. Matching flow to the patient’s breathing demand allows the anaesthetist to deliver oxygen to the child at the required concentration. Recent studies conducted in anaesthetised children at QCH, have demonstrated HFNOI is an effective alternative oxygen delivery technique that can be safely used in infants and children with abnormal airways. The choice of oxygenation method may have significant ramifications for the child and for surgical efficiency. However, to date there have been no high-quality studies evaluating HFNOI in comparison to other oxygenation techniques during paediatric airway surgery. Therefore, we would like to test the two techniques to determine whether HFNOI is superior to traditional anaesthesia oxygenation methods during paediatric airway surgery. We will achieve this aim using a randomised controlled trial to compare HFNOI with NLFO as the mode of oxygen delivery, during microlaryngoscopy in infants and children. The investigators hypothesise that HFNOI will present advantages over the alternative techniques when used as an airway management and oxygenation technique during anaesthesia of spontaneously breathing infants or children undergoing microlaryngoscopy surgery. It is important to determine which mode or modes of oxygenation give the lowest incidence of hypoxia and rescue oxygenation during these surgeries. If we can demonstrate that HFNOI reduces the risk of hypoxia and surgical interruption, this has the potential to improve both the safety and the operating efficiency of these surgeries for children.

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Information for parents and guardians of our patients

Why are we conducting this trial?

We are doing this study to find out if the nasal cannulae method of delivering oxygen will reduce the interruptions and low oxygen levels that can come about during children’s airway surgery. For this study, half (50%) of the children will receive oxygen by either facemask or a nasal tube, and the other half (50%) will receive the extra nasal cannulae oxygen delivery method during their airway surgery. The chance is 50% like tossing a coin. The study is finished when the procedure has taken place.

What is the aim of this trial?

The aim of this project is to compare two techniques for delivering oxygen during anaesthesia for children who need to have surgery on their airways.

What are we trying to find out?

During airway procedures, giving enough oxygen to the patient is a very important part of the anaesthetist’s job. Currently oxygen is delivered by either facemask, a nasal tube or a new method of nasal cannulae during airway surgery. We know that in our department, 34% of children who have an airway procedure have low oxygen levels at least once during their procedure. To fix this problem the procedure has to be interrupted so that more oxygen can be given to the patient. Interrupting the procedure makes the overall procedure take longer and means that the child is under anaesthesia for more time.

We are comparing these methods of oxygen delivery in the practice of paediatric anaesthesia to evaluate how effective the newer, less invasive nasal cannulae method of is. The results of this study may change the way that we do things and improve the safety of our children during these procedures in our hospital.

Which patients can take part?

Children less than 16 years old who are having an airway procedure at participating centres can be included in this study.

What does the trial involve for the children in the study?

Children at QCH who are less than 16 years of age and require airway surgery will be enrolled into the study by the clinical research nurse or study coordinator. The children will be randomised into one of the two treatment arms:

  1. Standard method
  2. Nasal Cannulae method

For this study, half (50%) of the children will receive oxygen by either facemask or a nasal tube, and the other half (50%) will receive the extra nasal cannulae oxygen method of oxygen delivery during their airway surgery. The chance is 50% like tossing a coin. The study is finished when the procedure has taken place.

Your child will be carefully monitored and cared for as they normally would be whether they are randomised into the standard method or the nasal cannulae method.


In the weeks before the surgery an email will be sent out about the study. It will have information about the study and explain how you have the opportunity to participate.

Consent will be obtained from the parent/guardian of each child undergoing airway surgery on the day of admission. An information pamphlet and information sheet will also be given to the family at the same time.

Information for participating study centres

Background on the trial

Suspension microlaryngoscopy surgery is commonly performed in infants and children for a variety of diagnostic and therapeutic procedures. These cases often pose particular challenges to both anaesthetist and surgeon. In particular, the simultaneous maintenance of airway patency, adequate oxygenation and ventilation, and sufficient depth of anaesthesia can be complex. In principle, the anaesthetist and surgeon share the same “real estate”, the anaesthetist concerned with maintaining oxygenation and providing adequate ventilation, the surgeon concerned with achieving the best surgical result without any interruption of the procedure. In many cases, spontaneous ventilation is needed to allow dynamic airway assessment. These conditions must all be achieved whilst allowing for an unobstructed operative field. In such situations, it is often impractical to place an endotracheal tube.

Current practice

Current practices in paediatric anaesthesia include either intravenous or inhalational induction with sevoflurane in oxygen/nitrous oxide followed by maintenance with either inhalational agent or transition to total intravenous anaesthesia (TIVA) once intravenous access is established. TIVA may incorporate propofol alone or in combination with short acting opioids and/or dexemedetomidine. This is followed by topicalisation of the airway with 4 mg/kg lignocaine. For microlaryngoscopy procedures, maintaining oxygenation is achieved by either insufflation via a nasopharyngeal oxygen catheter attached to T-piece or anaesthesia breathing circuit with flow rates of 2-6L/min or via high-flow nasal cannulae at weight related flow rates aiming for maintenance of spontaneous ventilation.

The differences between the techniques lies in the method of delivering fresh gas for oxygenation. The High-Flow Nasal Oxygen Insufflation (HFNOI) is insufflation of heated (37 degrees Celsius) and humidified oxygen at weight related flow rates matching peak inspiratory flow thereby allowing a known inspired fraction of inspired oxygen. This enabled higher flow rate is also known to provide a positive expiratory pressure of 4-6cmH2O which may help maintain the airway patency. We have conducted studies in anaesthetised paediatric patients which demonstrated HFNO is an effective alternative oxygen delivery technique in normal children for the preservation of adequate oxygen saturation during apnoea and in children with abnormal airways undergoing tubeless airway surgery.

Alternatively, a Low Flow Nasal Oxygen Insufflation (LFNOI) catheter, a more traditional technique for microlaryngoscopy, is used, which is limited by its inability to humidify or heat the inhaled gas and thus the flow rates delivered are lower with subsequently no added positive pressure respiratory support.

Knowledge Gap

Inadvertent hypoxemia during airway surgery has implications for both surgical efficiency and efficacy, also for patient safety. We conducted a clinical audit within our department of children undergoing upper and lower airway assessment (HREC/16/QRCH/351). The study showed that more than 32% of children undergoing upper airway surgery experienced at least one hypoxemic event and in general 23% of surgeries required surgical interruption and the application of a rescue oxygenation technique due to a hypoxemic event. Apnoea is another additional risk particularly for small infants with abnormal airways as balancing an adequate depth of anaesthesia with spontaneous ventilation to facilitate the procedure is often very difficult. The onset of desaturation in apnoeic infants and children is much faster than in adults and is known to be age-dependent. After our first report to use HFNOI as an oxygenation method during microlaryngoscopy, high-flow very quickly became a standard anaesthetic technique in our department. We have conducted an electronic survey of practice of anaesthetists in our department and report 90% of our colleagues incorporate HFNOI for microlaryngoscopy at their discretion.

To date, the rigorous evaluation of HFNOI’s role in the reduction of anaesthetic complications such as hypoxemia and interruption of procedure for rescue oxygenation has not been undertaken. Further, we don’t know which of our current practices, LFNO or HFNOI is superior in reducing hypoxemia anaesthetic events.

Specifics of study

Study aim

The aim of this study is to compare LFNO versus HFNOI in infants and children requiring microlaryngoscopy.


HFNOI is superior to LFNOI and HFNOI will reduce the incidence of hypoxia requiring rescue oxygenation by 20% compared to alternative anaesthesia methods not using high-flow nasal oxygen insufflation.

Study design

A randomised controlled trial (RCT) to demonstrate superiority of HFNOI compared to alternative anaesthesia practices without high-flow nasal oxygen insufflation. Participants will be randomised individually, to either anaesthesia using HFNOI or alternatively to anaesthesia without high-flow technique. Due to the nature of the procedure it is not possible to have blind operators or outcome assessors.

Sample size

QCH will be recruiting 496 patients who will be randomized in a 1:1 ratio stratified by age (<1 year, 1-5 year and 5-16 year of age), with randomly varied block sizes within each stratum.

Outcomes, significance and innovation

Primary outcome

The primary outcome is defined as successful anaesthesia without any rescue oxygenation attempt for a hypoxic event.

Secondary outcomes

  1. Total length of time patient experiences hypoxemia [seconds].
  2. Minor adverse events: occurrence of epistaxis, laryngospasm, bronchospasm, coughing at any time during procedure.
  3. Major adverse events: occurrence of hypotension requiring treatment, bradycardia requiring treatment, cardiac arrest with or without return of spontaneous circulation at any time during procedure.
  4. Requirement for unexpected paediatric intensive care admission.
  5. Requirement for unanticipated post-operative mechanical ventilation or any other form of non-invasive ventilation including HFNO.
  6. Length of PICU and/or hospital stay.

Inclusion criteria

  • 0 (>37 weeks) – 16 years of age (15 years + 364 days)
  • Elective microlaryngoscopy*

*Where a tubeless airway management technique is required for the procedure.

Exclusion criteria

Children are NOT eligible for study inclusion if they meet any of the following criteria:

  • Tracheostomy in situ
  • Requirement for laser surgery
  • Known choanal atresia
  • HFNOI contraindication**
  • Emergency airway cases

**Recent cranial and/or mid-face surgery/trauma; CSF leak.

Secondary outcome measures

The secondary objectives of this study include assessment of rates of adverse events categorised by:
Serious adverse event (SAE)
SAEs for this study are defined as:

  • hypoxemia leading to cardiac massage which the clinician believes is related to one of the study interventions
  • cardiac arrest: Loss of spontaneous cardiac output
  • mortality (all events will be reported)
  • any life threatening medical event or reaction which the clinician believes may be study related.

Adverse event (AE)
AE data is being collected as part of the study design, and informs the outcomes of the study. Data on each AE will be collected on the CRF. For this study AE are defined as:

  • hypotension: requiring treatment with fluid and/or vasoconstrictors
  • bradycardia: bradycardia not requiring treatment; bradycardia of <60/min or < 40 if older than 6 years (8, 9).


Hypoxia: Normally hypoxemia for anaesthesia is defined as an oxygen saturation of ≤90%. However, dependent of the patient’s physiology, age and starting saturation levels prior to the procedure, the anaesthetist can accept transiently lower oxygen levels if required to allow an uninterrupted surgical procedure. For this study we will not define a specific threshold for acceptable oxygen saturations as these are defined case by case. Similarly, the surgical procedure can contribute to hypoxemia and acceptance of this is again at the discretion of the anaesthetist and surgeon or proceduralist. The investigators’ view is that a hypoxemic event that requires rescue intervention irrespective of the cause is the true and important outcome measure for this study.

Rescue oxygenation: The surgical procedure is interrupted and the anaesthetist attempts to improve oxygenation of the child using either bag mask ventilation, insertion of an endotracheal tube or laryngeal mask followed by positive pressure ventilation.

Data collection methods

Streamlined data collection instruments and procedures will be used. All data will be collected by the research nurse onto the case report form (CRF) directly from the source data. Data will be entered into the electronic data platform REDCapTM (Research Electronic Data Capture, Vanderbuilt) Version 6.10.6.


REDCap is a secure, web-based application for building and managing online databases and surveys. The HAMSTER trial uses REDCap for electronic data collection. If you have any concerns or questions please contact the Central Study Co-Ordinator, Tara Williams.
RECap Weblink.

Participating sites

  • Queensland Children’s Hospital, Queensland
  • Royal Children’s Hospital Melbourne, Victoria
  • Perth Children’s Hospital
  • The Children’s Hospital at Westmead
  • Women and Children’s Hospital, Adelaide

Collaborators and sponsors

Our collaborators include:

The University of Queensland
PREDICT (Paediatric Emergency Departments International Collaborative group)
PSG (Paediatric Study Group)
ANZICS (Australia and New Zealand Intensive Care Society)

Education and resources

Key references

  1. Mausser G, Friedrich G, Schwarz G. Airway management and anesthesia in neonates, infants and children during endolaryngotracheal surgery. Ped Anesthes. 2007;17(10):942-7.
  2. Humphreys S, Lee-Archer P, Reyne G, Long D, Williams T, Schibler A. Transnasal humidified rapid-insufflation ventilatory exchange (THRIVE) in children: a randomized controlled trial. Br J Anaesth. 2017;118(2):232-8.
  3. Humphreys S, Rosen D, Housden T, Taylor J, Schibler A. Nasal high-flow oxygen delivery in children with abnormal airways. Paediatr Anaesth. 2017;27(6):616-20.
  4. Patel R, Lenczyk M, Hannallah RS, McGill WA. Age and the onset of desaturation in apnoeic children. Can J Anaesth. 1994;41(9):771-4.
  5. Motoyama EK, Glazener CH. Hypoxemia after general anesthesia in children. Anesth Analg. 1986;65(3):267-72.
  6. Pullerits J, Burrows FA, Roy WL. Arterial desaturation in healthy children during transfer to the recovery room. Can J Anaesth. 1987;34(5):470-3.
  7. Vijayakumar HR, Metriyakool K, Jewell MR. Effects of 100% oxygen and a mixture of oxygen and air on oxygen saturation in the immediate postoperative period in children. Anesth Analg. 1987;66(2):181-4.
  8. Advanced Life Support Group. Part 3: The seriously ill child. Advanced Paediatric Life Support: The Practical Approach. 5th ed. Victoria: Advanced Life Support Group; 2011.
  9. Boriosi JP, Sapru A, Hanson JH, Asselin J, Gildengorin G, Newman V, et al. Efficacy and safety of lung recruitment in pediatric patients with acute lung injury. Pediatr Crit Care Med. 2011;12(4):431-6.
  10. National Health and Medical Research Council, A.R.C., Australian Vice-Chancellors’ Committee. The National Statement on Ethical Conduct in Human Research 2007.
  11. World Medical Association. World Medical Association Declaration of Helskini; Ethical Principles for Medical Research Involving Human Subjects. 2008.
  12. Schulz KF, Altman DG, Moher D. CONSORT 2010 Statement: updated guidelines for reporting parallel group randomised trials. BMJ. 2010;340.
  13. Hoffmann TC, Glasziou PP, Boutron I, Milne R, Perera R, Moher D, et al. Better reporting of interventions: template for intervention description and replication (TIDieR) checklist and guide. BMJ. 2014;348.


Centre for Children’s Health Research
Queensland Children’s Hospital Precinct
Paediatric Critical Care Research Group: KIDS THRIVE
Level 7, 62 Graham Street
South Brisbane, Qld, 4101

Central team (QCH – Brisbane)

For study queries contact

Study Coordinator

Tara Williams
e: tara.williams@health.qld.gov.au
p: 07 3069 7480

Chief Investigator

Dr Susan Humpherys
e: susan.humphreys@uq.edu.au