High flow nasal oxygen: Urgent need to standardize the terminology

Healthcare constituencies (including authors of guidelines, regulators, healthcare professionals, providers of clinical management and patients) benefit by standardised terminology on high flow nasal oxygen. This is imperative when new techniques and equipment in this area are introduced to the healthcare market.

High flow nasal oxygen has been utilized in the intensive care setting for more than 15 years and recently during anaesthesia. ¹ It provides a high inspiratory oxygen fraction and positive end-expiratory pressure effect, while improving lung compliance, inhibiting bronchoconstriction and reducing the work of breathing.^2–5 In order to reduce confusion, standardization of the terminology surrounding high flow nasal oxygen should begin with firstly defining what is meant by ‘high flow’ and secondly rationalizing the variety of abbreviations used in this area.

The fundamental concept of ‘high flow’ requires an accurate definition. This definition should be based on oxygen flow in relation to the patient's inspiratory flow rate rather than arbitrarily assigning flow rate as either ‘low’ or ‘high’. The inspiratory flow rate in adults during quiet breathing (in contrast to peak inspiratory flow rate) is approximately 0.5 l/s or 30 l/min. Conventional oxygen therapy (including nasal prongs and facemasks) delivers oxygen at up to 15 l/min. Consequently, air is entrained with these devices and the oxygen is diluted by a variable degree during the respiratory cycle, giving a fraction of inspired oxygen (FiO₂) < 1.0.^6,7 Patients with respiratory distress may breathe with inspiratory flow rates ≥100 l/min, resulting in greater air entrainment and further lowering of the FiO₂ administered. ⁸ It is logical to define devices as ‘high flow’ when they deliver oxygen at a rate ≥30 l/min and the patient’s FiO₂ is close to the device-delivered FiO₂. ⁹ In contrast, any device delivering flow rates < 30 l/min are ‘low flow’ (including the NO DESAT (nasal oxygen during efforts securing a tube) system ¹⁰ at 15 l/min).

The second issue is the current tendency to overuse acronyms and initialisms when describing high flow nasal oxygen apparatus and techniques. An acronym is formed from the first letters of a term to form a new word, such as NASA (the National Aeronautics and Space Administration). In contrast, initialism is a series of letters that is read individually, for example FBI (the Federal Bureau of Investigation). Both acronyms and initialisms should be used thoughtfully and sparingly when writing for a broad audience. Whilst acronyms and initialisms may be considered adequate descriptors within a single study or clinical scenario, a comparative review of the various techniques requires shared terminology across all medical specialties. A wide and complex array of acronyms and initialisms for high flow nasal oxygen devices and techniques has been used in the literature, and some are included in Table 1 (Available supplementary material online). This makes keyword searching of online systems cumbersome and frequently flawed, with a high likelihood of missing important work. ¹¹

In summary, a more rational approach to defining and describing high flow nasal oxygen techniques in the medical literature is imperative to ensure robust research and teaching in the future.

Supplemental Material

Supplemental material for High flow nasal oxygen: Urgent need to standardize the terminology

Supplemental Material for High flow nasal oxygen: Urgent need to standardize the terminology by Keith B Greenland and Benedict Devereaux in Anaesthesia and Intensive Care