Pre-oxygenation in pregnancy: the effect of fresh gas flow rates within a circle breathing system.
We have investigated the effect of oxygen flow rate on pre-oxygenation in pregnant patients at term using a circle system. Twenty patients presenting for elective Caesarean section maintained tidal volume breathing through a standard circle system for 3 min. Subjects were pre-oxygenated using oxygen flow rates of 5 l.min(-1), 10 l.min(-1) and 15 l.min(-1) presented in random order. The mean (SD) fractional end-tidal oxygen at the end of 3 min was 0.86 (0.07) for 5 l.min(-1), 0.92 (0.05) for 10 l.min(-1)and 0.90 (0.09) for 15 l.min(-1) (p < 0.001). Entrainment of air occurred in 22% of pre-oxygenation sessions. Oxygen flow rates of 10 l.min(-1) or above provide optimal pre-oxygenation using a circle system in term parturients. In our study, entrainment of air occurred in a surprisingly high percentage of cases.
Specialist Registrar, Nuffield Department of Anaesthetics, John Radcliffe Hospital, Oxford OX3 9DU, UK. iz.cr@talk21.com
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Russell
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Wrench
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Feast
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Mohammed
D000328:Adult; D000764:Anesthesia, Closed-Circuit; D000765:Anesthesia, Conduction; D000773:Anesthesia, Obstetrical / Q000379:methods; D002245:Carbon Dioxide / Q000502:physiology; D002585:Cesarean Section; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D010100:Oxygen / Q000008:administration & dosage / Q000502:physiology; D010102:Oxygen Inhalation Therapy / Q000379:methods*; D011247:Pregnancy; D013990:Tidal Volume
D002245:Carbon Dioxide; D010100:Oxygen