• S H McClelland, D G Bogod, and J G Hardman.
• Queen's Medical Centre campus, Nottingham University Hospitals NHS Trust, Derby Road, Nottingham NG7 2UH, UK.
• Anaesthesia. 2008 Mar 1; 63 (3): 259-63.

AbstractHypoxaemia 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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