High-flow nasal cannula – a versatile device
Sanjay Agrawal, Baha Al-Shaikh and Joep Vroemen give a brief review of the high-flow nasal cannula and its use in a patient with a difficult airway
There are a wide range of devices to choose from when it comes to providing oxygen therapy. Most of these devices use low flows of oxygen and have variable efficiency. Recently the use of high-flow nasal cannula oxygen therapy is becoming popular and is being increasingly used in a wide range of clinical areas ranging from A&E, acute care wards, intensive care units and theatres. In this article, we present a case report of managing a difficult airway with the use of a high-flow nasal cannula (HFNC) and we briefly review the wide range of therapeutic utility of HFNCs.
HFNC – A case report
An ASA-1 young female patient presented to our district general hospital with a history of dental abscess. She had erythema extending to the chest and difficulty swallowing. There was no stridor. Her airway assessment was limited mouth opening, Mallampati grade 3, and prominent upper two teeth making her an anticipated difficult airway.
In view of several recent case reports of successful use of HFNC to keep the patient oxygenated for longer duration during airway intervention, it was decided to use it.
The patient was pre-oxygenated with HFNC (OptiflowTM) at 70 litres per minute, FiO2 1.0 for 10 minutes. The patient appeared to be comfortable breathing warm and humidified oxygen through HFNC. A difficult airway trolley including a fibreoptic bronchoscope was kept in immediate vicinity. The patient was induced with propofol (200mg), and fentanyl (100mcg). Tracheal intubation was facilitated with rocuronium (40mg). A videolaryngoscope (GlidescopeTM) was used to visualise the larynx. It took a total of 5 minutes to intubate the trachea. The patient maintained an SpO2 of 100 per cent throughout. After tracheal intubation it was noticed that the patient had a tracheal tube cuff leak, probably due to damage to the cuff from the prominent teeth. The tracheal tube was changed over a gum elastic bougie which took a further 150 seconds. The patient was kept asleep with boluses of propofol. The position of the tracheal tube was confirmed with capnography and bilateral chest auscultation. The surgery proceeded uneventfully and the patient was extubated post-operatively and after a period of observation in the recovery room was sent back to the ward. The total apnoea time during intubation was 7 minutes 30 sec. The oxygen saturation was 100 per cent throughout and end-tidal CO2 was within the normal range after intubation. This anecdotally suggests that during HFNC oxygen therapy some gas exchange takes place and is enough to keep the patient well oxygenated and avoid dangerous rise in CO2 levels for a varied period of time, hypothetically much longer than a conventional face mask oxygen or a non-rebreathing mask would provide. The patient was haemodynamically stable and had no dysrhythmias during the prolonged intubation.
There are several devices available to oxygenate the patient with variable efficiency and most of these devices use low flows.
Traditionally nasal oxygen therapy has been delivered at low flows through nasal cannulae.
In recent years, nasal cannulae designed to administer heated and humidified oxygen at high flows have been gaining popularity.
HFNC oxygen therapy comprises an air/oxygen blender, an active humidifier, a single heated circuit and a nasal cannula. It delivers adequately heated and humidified medical gas at up to 70 litres per minute of flow. It is considered to have a number of physiological effects, such as the reduction of anatomical dead space, a moderate positive airway pressure effect (PEEP) that may generate alveolar recruitment, more reliable delivery of high FiO2 levels and good humidification [1–4]. All of these factors lead to reduced work of breathing, improved oxygenation and ventilatory efficiency. HFNC provides an increased FiO2 because the higher flow rates are capable of matching or exceeding the patient’s peak inspiratory flow, preventing room air entrainment . Nasal and oropharyngeal dead space is washed out with oxygen-rich air and acts as a reservoir [6,7]. Warmed and humidified high-flow oxygen causes attenuation of the inspiratory resistance associated with the nasopharynx, improvement in conductance and pulmonary compliance, mild distending pressure (PEEP) and reduction in energy expenditure for gas conditioning.
These high-flow nasal cannula systems enhance patient comfort and tolerance compared with other oxygenation systems such as nasal masks and non-rebreathing systems. Many published reports suggest that HFNC decreases breathing frequency and work of breathing and reduces need of escalation of respiratory support in patients with diverse underlying diseases . In addition, it is minimally invasive compared with tracheal intubation and the skills needed to provide it can be easily learnt.
There are several case reports in the literature about the versatility of HFNC and its use in a wide range of clinical conditions in A&E, acute care wards, intensive care units, operating theatres, etc. The indications of HFNC are vast, encompassing most causes of acute hypoxaemic respiratory failure such as exacerbation of chronic obstructive pulmonary disease (COPD), acute heart failure, pneumonia, pre-oxygenation before intubation, awake fibreoptic intubation (AFOI), bronchoscopy, sleep apnoea post-extubation, oxygenation during invasive procedures, etc. [7–10].
Recently, it has been shown that the use of HFNC in patients undergoing awake fibreoptic intubation improves oxygenation and patient tolerance, and enhances the safety of the procedure, by reducing the episodes of desaturation and increasing the tolerance to apnoeic episodes . The soft nasal prongs allow simultaneous nasal passage of the fibrescope and tracheal tube, uniquely allowing for continuous oxygenation, with no instances of nasal trauma . The authors of this study also speculate that the high flow rate can potentially aid the atomisation and delivery of the local anaesthetic through the upper airway to the trachea and could also help prevent the collapse of the nasal passage for better visualisation and instrumentation .
Another recently published study, Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE), emphasises the role of transnasal high-flow humidified oxygen therapy in successfully increasing the apnoea time in patients with difficult airways undergoing airway intervention . The authors of this study conclude that THRIVE combines the benefits of ‘classical’ apnoeic oxygenation with continuous positive airway pressure and gaseous exchange through flow-dependent deadspace flushing . They noted that the rate of rise of end-tidal CO2 during this technique was 0.15kPa per minute. This technique has the potential to transform the practice of anaesthesia in patients undergoing management of difficult airway by improving the ventilatory efficiency during prolonged periods of apnoea .
Our case report and several others like it suggest that HFNC is a simple, easy-to-use and readily available device with potentially several physiological benefits to the patient – the most important of which is its ability to prolong the safe duration of apnoea and very low likelihood of causing any harm. This makes it a useful device to incorporate in the armamentarium of an anaesthetist, intensivist and acute care physicians.
To conclude, although there is no hard-core evidence to substantiate the claim, HFNC is a humble device with a myriad of physiological benefits to the patient and is a serious contender among the wide range of oxygenation devices.
Sanjay Agrawal is a speciality trainee, and Baha Al-Shaikh and Joep Vroemen are consultant anaesthetists at William Harvey Hospital in Ashford.
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