High flow oxygen for children's airway surgery

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 the child’s 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 Lady Cilento Children’s Hospital (LCCH), 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 LCCH 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 10 kg infant the child would receive 20L/min. Matching flow to the patient’s breathing demand this allows the anaesthetist to deliver oxygen to the child at the required concentration. Recent studies conducted in anaesthetised children at LCCH, 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 confer 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 confer 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 both improve both the safety and the operating efficiency of these surgeries for children.