High-flow nasal oxygen (HFNO) has been used for many years to help people with breathing difficulties in the intensive care and after surgery. More recently, it has become a helpful tool during induction of anaesthesia to prevent oxygen levels from dropping when managing the airway. HFNO is particularly effective at delivering oxygen even when a patient is not breathing (apnoea), making it useful during surgeries on the voice box (larynx) because it eliminates the need for a breathing tube, giving surgeons a clear view. HFNO is now also being used to prepare patients for anaesthesia (preoxygenation). Research shows that it works just as well as traditional tight-fitting oxygen masks while offering added benefits like better comfort for patients, easier handling for anaesthetists, and a smooth transition to oxygen delivery during apnoea. One reason HFNO is effective is that it creates a mild pressure in the lungs, called positive end-expiratory pressure (PEEP), which improves oxygen storage in the lungs. This pressure depends on the flow rate of oxygen and is higher when the patient keeps their mouth closed. For every increase of 10 liters per minute in flow rate, HFNO generates 1 cmH2O of PEEP. This pressure helps increase the lung's capacity to hold oxygen, making the process of preoxygenation more efficient. Most studies on HFNO for preoxygenation have used flow rates of up to 60 liters per minute. However, we don't yet know if higher flow rates could further improve preoxygenation or extend the time patients can safely go without breathing.
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Safe apnoea time
Timeframe: From start of apnoea after anaesthesia induction until peripheral oxygen saturation drops to 93%. This time fram will probably be between 5 and 15 minutes.