Clinical practice has often demonstrated the dangers of hypoxaemic events, so how best to handle the risks? Andi Richardson looks at how the danger can be mitigated and patient safety improved during anaesthesia.
High-flow nasal cannula (HFNC) is a humidified gas or oxygen delivery system that allows inspired oxygen (FIO2) to be delivered at very high flow rates. The use of a high flow, heated, humidified and controlled concentration of oxygen via the nasal route has several clinical benefits, including more precise oxygen delivery and improved patient comfort. Useful in both preoxygenation and apnoeic oxygenation, HFNC has been shown to prolong the safe apnoea window, reduce instances of hypoxaemia and allows clinicians more time to manage patients with difficult or compromised airways.1
Safe apnoea time refers to the time from cessation of breathing or ventilation, until the peripheral arterial oxygen saturation (SpO2) falls to 90%, after which it declines rapidly.2 Traditional pre-oxygenation techniques offer just 8 minutes of apnoea without desaturation.3 The high-flow rate and humidified system may extend the safe apnoeic up to 30 minutes (possibly more depending on the individual patient).4 Arterial oxyhaemoglobin desaturation caused by prolonged desaturation can trigger dysrhythmias, haemodynamic decompensation, hypoxic brain injury, and can ultimately be fatal.5 By extending this window of time, critical desaturation can be delayed, and clinicians have more time to implement the strategy that will ultimately prevent or reverse desaturation to prevent hypoxic injury.
In groups likely to show reduced oxygen reserves, such as obese, neonatal, paediatric, pregnant, septic, and critically ill patients, HFNC can be particularly effective. In these groups, there is an increased risk of faster desaturation and difficult airway management, both of which may be mitigated by employing HFNC pre-emptively
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