![]() The clinical application of this phenomenon is known in modern anaesthetic practice as apnoeic oxygenation (i.e. The size of this reservoir can be increased by reducing dependent atelectasis through head-up patient positioning and raising mean airway pressure but ultimately, the size of the oxygen reservoir is fixed at the end of pre-oxygenation and once apnoea begins, it does not get replenished.Īventilatory mass flow (AVMF) is a physiological phenomenon in which, provided that a patent air passageway exists between the lungs and the exterior, the difference between the alveolar rates of oxygen removal and carbon dioxide excretion generates a negative pressure gradient of up to 20 cmH 2O that drives oxygen into the lungs. Pre-oxygenation denitrogenises the lungs and creates an alveolar oxygen reservoir. The mainstay method of increasing the apnoeic window is through pre-oxygenation, which entails spontaneous facemask ventilation with 100% oxygen. This can deleteriously impact on human factors that are intrinsic to a highly pressured clinical scenario, and can readily cascade into a ‘cannot intubate, cannot ventilate’ scenario with significant attending morbidity and mortality. ![]() Multiple attempts at difficult laryngoscopy increase the risk of airway trauma, which in turn makes subsequent attempts at laryngoscopy and facemask ventilation more difficult. In some patients, the combination of unfavourable pharyngolaryngeal anatomy and reduced apnoea time due to cardiorespiratory decompensation makes this stop-start approach hazardous. Failure to do so normally results in recommencement of facemask ventilation, re-oxygenation and a further attempt at securing a definitive airway. As the patient transitions from wakefulness to anaesthesia and receives neuromuscular blockade, the anaesthetist is afforded a finite time (‘apnoeic window’) during which to secure a definitive airway. The principal objective of airway management during anaesthesia is maintenance of oxygenation. It has the potential to transform the practice of anaesthesia by changing the nature of securing a definitive airway in emergency and difficult intubations from a pressured stop–start process to a smooth and unhurried undertaking. We conclude that THRIVE combines the benefits of ‘classical’ apnoeic oxygenation with continuous positive airway pressure and gaseous exchange through flow-dependent deadspace flushing. The rate of increase in end-tidal carbon dioxide was 0.15 kPa.min −1. Mean (SD ) post-apnoea end-tidal (and in four patients, arterial) carbon dioxide level was 7.8 (2.4 ) kPa. No patient experienced arterial desaturation < 90%. The median (IQR ) apnoea time was 14 (9–19 ) min. There were 12 obese patients and nine patients were stridulous. ![]() ![]() The median (IQR ) Mallampati grade was 3 (2–3 ) and direct laryngoscopy grade was 3 (3–3 ). Mean (SD ) age at treatment was 49 (15 ) years. Transnasal Humidified Rapid-Insufflation Ventilatory Exchange (THRIVE) was used in 15 males and 10 females. During this time, upper airway patency was maintained with jaw-thrust. Apnoea time commenced at administration of neuromuscular blockade and ended with commencement of jet ventilation, positive-pressure ventilation or recommencement of spontaneous ventilation. This was achieved through continuous delivery of transnasal high-flow humidified oxygen, initially to provide pre-oxygenation, and continuing as post-oxygenation during intravenous induction of anaesthesia and neuromuscular blockade until a definitive airway was secured. Between 20, we extended the apnoea times of 25 patients with difficult airways who were undergoing general anaesthesia for hypopharyngeal or laryngotracheal surgery. Emergency and difficult tracheal intubations are hazardous undertakings where successive laryngoscopy–hypoxaemia–re-oxygenation cycles can escalate to airway loss and the ‘can't intubate, can't ventilate’ scenario. ![]()
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