SummaryA postal survey investigating the administration of supplemental oxygen to women undergoing Caesarean section under regional anaesthesia was sent to 262 lead consultant obstetric anaesthetists in the UK. Two hundred and fifteen (82%) completed questionnaires were returned. In 139 units (65%) supplemental oxygen was administered routinely to all Caesarean sections under regional techniques, while in 71 (33%), supplemental oxygen was given only if the procedure was an emergency or if there was evidence of fetal or maternal compromise. In 196 units (91%), the common gas outlet was used as the source of supplemental oxygen, with the standard anaesthetic breathing circuit disconnected in 194 (90%) and the vaporisers left on the back bar in 191 (89%). Critical incidents had occurred in 39 (18%) units using the common gas outlet as a source of supplemental oxygen and 63 (30%) had experience of critical incidents with this practice in a non-obstetric setting. We suggest that supplemental oxygen is more safely administered from a separate and dedicated source.Keywords Anaesthesia: obstetric. Anaesthetic techniques: regional. Oxygen: delivery systems. Equipment: breathing systems. Caesarean section. It is usual for mothers undergoing Caesarean section under regional anaesthesia to receive supplemental oxygen. From our own experience it is often the common gas outlet of the anaesthetic machine that is the source of such oxygen, with the standard anaesthetic breathing circuit disconnected from the anaesthetic machine and replaced by simple tubing and an oxygen mask. It also seems to be usual for the vaporisers to be left in position on the back bar. Following a critical incident in one of our units, we decided to explore practices of supplemental oxygen administration for Caesarean section under regional anaesthesia in obstetric units in the UK. We wanted to ascertain whether it is common practice to use the common gas outlet as a source of supplemental oxygen, with the standard breathing circuit disconnected and the vaporisers left in situ. We aimed to establish whether this was a factor leading to critical incidents in other obstetric units. We also wanted to establish whether problems had been encountered with such practices in a non-obstetric setting. Finally, as the value of supplemental oxygen for elective Caesarean sections has recently been questioned [1, 2], we took the opportunity to look into which groups of mothers routinely receive supplemental oxygen. MethodsAfter approval from the Obstetric Anaesthetists' Association (OAA), a questionnaire and covering letter were distributed in a single posting to the 262 lead consultants in obstetric anaesthesia in the UK listed on the OAA database. Respondents were asked about departmental, rather than personal, use of supplemental oxygen for Caesarean section under regional anaesthesia in that unit (which cases received it; whether the common gas outlet was used; whether the standard breathing system was disconnected; whether the vaporisers are removed from the ba...