Safe use of high flow nasal oxygen in apnoeic patients for laryngotracheal surgery

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Introduction Interest in apnoeic oxygenation techniques has increased significantly since Patel and Nouraei1 described their technique for increasing safe apnoea time in patients undergoing endoscopic laryngotracheal surgical procedures, which they termed ‘Transnasal Humidified Rapid-Insufflation Ventilatory Exchange’ (THRIVE). In this article, we distinguish between patients receiving High-Flow Nasal Oxygen therapy who are spontaneously ventilating (HFNO-sv) and those receiving High-Flow Nasal Oxygen who have been rendered intentionally apnoeic (HFNO-ap). We accept that in certain situations, there is some crossover between these two oxygenation techniques. High-flow nasal oxygen HFNO-sv was used in the critical care setting long before it was described in anaesthetic practice, demonstrating improved patient oxygenation in several studies,2–5 reviews6 and a meta-analysis.7 Several studies have demonstrated the efficacy of HFNO-ap in extending the safe apnoea time in adults.8–10 We believe that the rapid uptake of HFNO-ap during anaesthesia for laryngotracheal surgery was largely driven by the opportunity to employ a low pressure oxygenation system that might offer improved safety over the existing high pressure jet ventilation techniques. High pressure jet ventilation is well recognised as a potential source of barotrauma, especially when used in the presence of an obstructed airway.11 Nevertheless, Bourgain et al.12 demonstrated relative safety and efficacy of transtracheal high-frequency, high-pressure jet ventilation (with an automated device) for endoscopic airway surgery, reporting an incidence of pneumothorax of approximately 1%. However, the high failure rate of transtracheal rescue jet ventilation reported in the UK Royal College of Anaesthetists 4th National Audit Project was nonetheless concerning.13 The apparent ability of HFNO-ap to provide some carbon dioxide clearance in adults undoubtedly encouraged the adoption of this technique, even though the first study exploring the potential mechanisms was not published until 2019.14 It is questionable whether this ventilatory component exists in children,15–17 and even studies in adults have cast doubt on the degree of CO2 clearance that occurs.8,10 A recent study demonstrated comparable rates of CO2 accumulation regardless of the oxygen flow rate during apnoea18 leading to calls to remove the idea of ‘ventilatory exchange’ from the extended apnoea provided.19 It is clear that full understanding of the physiological processes remains elusive,14 but clinicians will continue to use this therapy whilst these questions are being answered, making safe use the priority. The advantages of HFNO-sv in providing a degree of continuous positive airway pressure, decreased work of breathing and improved tidal volume have been well documented,20–22 and its benefits have now been demonstrated across a wide range of clinical applications. These include oxygenation during rapid sequence induction (although clearly there is a cross over between HFNO-sv and -ap in this group) and awake tracheal intubation, reduction of postoperative chest infections in patients with high BMI, and decreased length of stay in postoperative cardiac and thoracic surgical patients.23–27 Benefits of appropriately titrated HFNO in neonates undergoing tracheal intubation have also been demonstrated.28 We believe that HFNO-ap in laryngotracheal surgery offers a number of specific advantages over existing alternative oxygenation techniques, albeit patient and pathophysiology dependent: it provides a superior operative field to a microlaryngoscopy tube, jet ventilation catheter or Tritube (Ventinova Medical, Eindhoven, Netherlands); it avoids the risks of a high-pressure system and motion artefact associated with supraglottic high pressure jet ventilation; it necessitates fewer procedural interruptions than an intermittent facemask ventilation technique; and, reduced equipment requirements and the need for operator understanding compared with jet ventilation or Tritube. HFNO-sv during laryngotracheal surgery (sometimes referred to as SponTaneous Respiration using IntraVEnous anaesthesia, ‘STRIVE Hi’) has been described in adults29 and children,30 though reported case numbers are limited, and it is not the preferred technique at our institutions and is therefore not considered here. Nevertheless, HFNO-ap is not a perfect solution and can fail, with persisting controversies and limitations surrounding its use. Recent concerns regarding its potential for aerosol generation31 have been dispelled;32 it is not specifically listed as an aerosol-generating procedure in the latest (2023) European Centre for Disease Control Technical Report.33 Its use during LASER surgery remains contentious,34–36 especially following a case report describing ignition of diathermy shaft material within the oral cavity during HFNO-ap and monopolar diathermy.37 HFNO for LASER surgery should not be employed routinely without further clarification, and even then, should only be considered within specialist centres. There is ongoing debate regarding the impact of obesity on HFNO-ap efficacy, with clinical case series in patients undergoing endoscopic surgical procedures suggesting that BMI limited the duration of effective apnoeic oxygenation time.9,38,39 However, a randomised controlled trial in adults with a BMI more than 40 kg m−2 with no airway disease, positioned 45 degrees head up and undergoing no airway instrumentation demonstrated successful apnoeic oxygenation for up to 18 min.40 Further studies are still required to fully explore the effect of BMI on effective apnoea time, and whether a calculable time-dependent increase or reduction in safe apnoea time based upon a patient's weight or BMI can be determined for individuals. The potential for gastric insufflation, distension, regurgitation and pulmonary aspiration has been suggested; however, studies with ultrasound assessment of the cross-sectional area of the gastric antrum appear to show no change following both HFNO-sv and HFNO-ap.41,42 This is unsurprising given the low pressure that is generated with HFNO. Pressure values appear to be linearly dependent with gas flow rate when the mouth is shut (<1 cmH2O per 10 l of flow) in both apnoeic and spontaneously ventilating patients.20,43 These pressures are below the classic threshold value of 20 cmH2O reported to cause gastric insufflation (confirmed by auscultation)44 and the more recent value of 15 cmH2O (confirmed by ultrasound).45 This scenario of many known unknowns is further complicated by equipment developments, as different manufacturers develop their oxygen delivery systems in different ways with several manufacturers marketing HFNO devices (e.g. Armstrong Medical's POINT System, the Vapotherm Precision Flow and the Fisher and Paykel Optiflow). Safe administration of HFNO-ap requires users to understand not just the physiology of apnoeic oxygenation but also the physics and function of their chosen device. For example, the Optiflow Switch device permits flow diversion when the matching nasal cannulae are compressed. This innovation is likely to be mirrored by other manufacturers of HFNO delivery systems in the near future. It allows facemask ventilation to be undertaken whilst the HFNO cannulae remain in situ, minimising the risk of barotrauma, but at the same time, the modification exposes the patient to hypoxia caused by oxygen flow cessation from inadvertent compression of the cannulae by the surgeon's surgical laryngoscope.39 Despite apnoeic oxygenation having been known about for over 100 years,43 the renewed interest in its use and its rapid expansion into novel areas of clinical application, mean that ensuring its safe delivery is of paramount importance for patients, clinicians and institutions. We have devised a series of questions that clinicians may wish to consider when using any HFNO system to safely extend safe apnoea time. Patient fa

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.