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Updated: Jul 7, 2026

A Model to Simulate Clinically Relevant Hypoxia in Humans
Published on: December 22, 2016
Pre-oxygenation in pregnancy: an investigation using physiological modelling
S H McClelland1, D G Bogod, J G Hardman
1Queen's Medical Centre campus, Nottingham University Hospitals NHS Trust, Derby Road, Nottingham NG7 2UH, UK.
Hypoxaemia during anaesthetic induction in obstetrics is hazardous for mother and baby, but the onset of desaturation can be delayed by pre-oxygenation. This study investigated pre-oxygenation during pregnancy using computer simulation. The Nottingham Physiology Simulator was configured to replicate normal pregnant physiology. Three pregnant and three non-pregnant subjects were created, representing population variation according to published physiological values. They underwent pre-oxygenation by tidal and vital capacity breathing of 100% oxygen. Pre-oxygenation during tidal breathing proceeded more rapidly in pregnancy, the median [range] time to achieve 95% of the maximum change in P(E)O2 being 1 min 37 s [1:23-1:52] in pregnant subjects, compared to 2 min 51 s [2:28-3:15] in non-pregnant subjects. Vital capacity pre-oxygenation required seven breaths [5-10] in pregnant subjects, compared to six breaths [4-9] in non-pregnant subjects, to achieve the same P(E)O2 as after 95% complete tidal pre-oxygenation. We recommend 2 min of tidal breathing for pre-oxygenation in pregnancy.
Hypoxaemia during anaesthetic induction in obstetrics is hazardous for mother and baby, but the onset of desaturation can be delayed by pre-oxygenation. This study investigated pre-oxygenation during pregnancy using computer simulation. The Nottingham Physiology Simulator was configured to replicate normal pregnant physiology. Three pregnant and three non-pregnant subjects were created, representing population variation according to published physiological values. They underwent pre-oxygenation by tidal and vital capacity breathing of 100% oxygen. Pre-oxygenation during tidal breathing proceeded more rapidly in pregnancy, the median [range] time to achieve 95% of the maximum change in P(E)O2 being 1 min 37 s [1:23-1:52] in pregnant subjects, compared to 2 min 51 s [2:28-3:15] in non-pregnant subjects. Vital capacity pre-oxygenation required seven breaths [5-10] in pregnant subjects, compared to six breaths [4-9] in non-pregnant subjects, to achieve the same P(E)O2 as after 95% complete tidal pre-oxygenation. We recommend 2 min of tidal breathing for pre-oxygenation in pregnancy.
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