Comparison of apnoeic oxygen techniques in term pregnant subjects: a computational modelling study

Ellis, Reena; Laviola, Marianna; Stolady, Daniel; Valentine, Rebecca L.; Pillai, Arani; Hardman, Jonathan G.

Abstract

Background
Hypoxaemia during general anaesthesia can cause harm. Apnoeic oxygenation extends safe apnoea time, reducing risk during airway management. We hypothesised that low-flow nasal oxygenation (LFNO) would extend safe apnoea time similarly to high-flow nasal oxygenation (HFNO), whilst allowing face-mask preoxygenation and rescue.

Methods
A high-fidelity, computational, physiological model was used to examine the progression of hypoxaemia during apnoea in virtual models of pregnant women in and out of labour, with BMI of 24–50 kg m−2. Subjects were preoxygenated with oxygen 100% to reach end-tidal oxygen fraction (FE'O2) of 60%, 70%, 80%, or 90%. When apnoea started, HFNO or LFNO was commenced. To simulate varying degrees of effectiveness of LFNO, periglottic oxygen fraction (FgO2) of 21%, 60%, or 100% was configured. HFNO provided FgO2 100% and oscillating positive pharyngeal pressure.

Results
Application of LFNO (FgO2 100%) after optimal preoxygenation (FE'O2 90%) resulted in similar or longer safe apnoea times than HFNO FE'O2 80% in all subjects in labour. For BMI of 24, the time to reach SaO2 90% with LFNO was 25.4 min (FE'O2 90%/FgO2 100%) vs 25.4 min with HFNO (FE'O2 80%). For BMI of 50, the time was 9.9 min with LFNO (FE'O2 90%/FgO2 100%) vs 4.3 min with HFNO (FE'O2 80%). A similar finding was seen in subjects with BMI ≥40 kg m−2 not in labour.

Conclusions
There is likely to be clinical benefit to using LFNO, given that LFNO and HFNO extend safe apnoea time similarly, particularly when BMI ≥40 kg m−2. Additional benefits to LFNO include the facilitation of rescue face-mask ventilation and ability to monitor FE'O2 during preoxygenation.

Citation

Ellis, R., Laviola, M., Stolady, D., Valentine, R. L., Pillai, A., & Hardman, J. G. (2022). Comparison of apnoeic oxygen techniques in term pregnant subjects: a computational modelling study. British Journal of Anaesthesia, 129(4), 581-587. https://doi.org/10.1016/j.bja.2022.06.021

• Journal Article Type: Article
• Acceptance Date: Jun 9, 2022
• Online Publication Date: Aug 10, 2022
• Publication Date: Oct 1, 2022
• Deposit Date: Jun 14, 2022
• Publicly Available Date: Aug 11, 2023
• Print ISSN: 0007-0912
• Electronic ISSN: 1471-6771
• Peer Reviewed: Peer Reviewed
• Volume: 129
• Issue: 4
• Pages: 581-587
• DOI: https://doi.org/10.1016/j.bja.2022.06.021
• Public URL: https://nottingham-repository.worktribe.com/output/8496098
• Publisher URL: https://www.bjanaesthesia.org/article/S0007-0912(22)00322-1/fulltext