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. 2020 Jul;125(1):e69-e74.
doi: 10.1016/j.bja.2020.01.004. Epub 2020 Jan 31.

Effect of oxygen fraction on airway rescue: a computational modelling study

Marianna Laviola  1 , Christian Niklas  2 , Anup Das  3 , Declan G Bates  3 , Jonathan G Hardman  2
Affiliations

Effect of oxygen fraction on airway rescue: a computational modelling study

Marianna Laviola et al. Br J Anaesth. 2020 Jul.

Abstract

Background: During induction of general anaesthesia, patients frequently experience apnoea, which can lead to dangerous hypoxaemia. An obstructed upper airway can impede attempts to provide ventilation. Although unrelieved apnoea is rare, it continues to cause deaths. Clinical investigation of management strategies for such scenarios is effectively impossible because of ethical and practical considerations.

Methods: A population-representative cohort of 100 virtual (in silico) subjects was configured using a high-fidelity computational model of the pulmonary and cardiovascular systems. Each subject breathed 100% oxygen for 3 min and then became apnoeic, with an obstructed upper airway, during induction of general anaesthesia. Apnoea continued throughout the protocol. When arterial oxygen saturation (Sao2) reached 20%, 40%, or 60%, airway obstruction was relieved. We examined the effect of varying supraglottic oxygen fraction (Fo2) on the degree of passive re-oxygenation occurring without tidal ventilation.

Results: Relief of airway obstruction during apnoea produced a single, passive inhalation (caused by intrathoracic hypobaric pressure) in all cases. The degree of re-oxygenation after airway opening was markedly influenced by the supraglottic Fo2, with a supraglottic Fo2 of 100% providing significant and sustained re-oxygenation (post-rescue Pao2 42.3 [4.4] kPa, when the airway rescue occurred after desaturation to Sao2 60%).

Conclusions: Supraglottic oxygen supplementation before relieving upper airway obstruction improves the effectiveness of simulated airway rescue. Management strategies should be implemented to assure a substantially increased pharyngeal Fo2 during difficult airway management.

Keywords: airway management; airway obstruction apnoea; computer simulation; hypoxaemia; oxygen therapy.

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Conflict of interest statement

JGH is associate editor-in-chief of the British Journal of Anaesthesia. JGH accepts fees for the provision of advice to the police, crown prosecution service, coroners, and solicitors. The other authors have no conflicts to declare.

Figures

Fig. 1
Fig. 1
Time-course of Pao2 during pre-oxygenation, apnoea, and airway opening with supraglottic Fo2 100%, 60%, and 21% in 100 in silico subjects. Apnoea continued to Sao2 of 60%, 40%, or 20%. The grey vertical line indicates the transition from pre-oxygenation to apnoea (with an obstructed airway). Mean (sd) is denoted by the black line. Fo2, supraglottic oxygen fraction; Pao2, arterial partial pressure of oxygen; Sao2, arterial oxygen saturation; sd, standard deviation.
Fig. 2
Fig. 2
Time-course of Sao2 during pre-oxygenation, apnoea and airway opening with supraglottic Fo2 of 100%, 60%, and 21% in 100 in silico subjects. Apnoea continued to Sao2 of 60%, 40%, or 20%. The grey vertical line indicates the transition from pre-oxygenation to apnoea (with an obstructed airway). Mean (sd) is denoted by the black line. Fo2, supraglottic oxygen fraction; Pao2, arterial partial pressure of oxygen; Sao2, arterial oxygen saturation; sd, standard deviation.
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