Preoxygenation for caesarean section under general anaesthesia ...

Preoxygenation for caesarean section under  general anaesthesia ‐ can we do better? M.J. Diacon, R. Porter and I.J. Wrench Royal Hallamshire Hospital, Glossop Road, Sheffield, S10 2JF, UK Question 3.   What anaesthetic circuit would you normally use?

Introduction Previous work in our unit suggested that preoxygenation in  pregnancy could be achieved more rapidly and effectively by using a  target end‐tidal oxygen (EtO2) level rather than a set time.1 We  decided to establish what the practice was for obstetric  anaesthetists elsewhere across the UK.

Methods Following a successful application to the Obstetric Anaesthetists’ Association Surveys Subcommittee, 238 questionnaires were posted to lead obstetric anaesthetists (figure 1).  A pre‐paid reply envelope  was provided. The clinical scenario was a sustained foetal bradycardia requiring  general anaesthesia for a category one caesarean section. This survey has the OAA ‘Seal of Approval’ Survey No: 97 approved 2009-10-14

Question 4.   How many vital capacity breaths would you ask the  patient to take? Average 4.3 (standard deviation 2.1).

A survey of obstetric anaesthetists regarding the techniques used to preoxygenate patients for caesarean section under general anaesthesia. You are giving a general anaesthetic to a fit and well 22 year old female with a BMI of 30, for an emergency category 1 caesarean section for a sustained fetal bradycardia.

Question 5.   Which of the following would you use to ensure  effective pre‐oxygenation (select more than one if appropriate)?

1. How long would you pre-oxygenate for? ____________________________________ 2. What oxygen flow rate would you normally use? ______________________________ 3. What anaesthetic circuit would you normally use? _____________________________ 4. How many vital capacity breaths would you ask the patient to take? _______________ 5. Which of the following would you use to ensure effective pre-oxygenation? Please select by ticking the boxes. Select more than one if appropriate:

Figure 1. Questionnaire sent to  lead obstetric anaesthetists

A B C D E F

Please tick if appropriate Movement of the reservoir bag Holding the mask on for 3 to 5 minutes Oxygen saturation of more than 99% Expired oxygen concentration of more than 80% Presence of end-tidal carbon dioxide trace Other – please specify below

Results A total of 153 forms (64%) were returned. Question 1.   How long would you preoxygenate for?

Discussion The majority of anaesthetists use a fixed time to preoxygenate patients with a high oxygen flow rate using a circle breathing circuit. A large proportion of anaesthetists (36%) do not use EtO2 to ensure  effective oxygenation prior to the induction of anaesthesia in this  population. Preoxygenation guided by reference to EtO2 would result in many  more patients being ready for for the induction of anaesthesia  within 3 minutes.1 This would also improve the quality of  preoxygenation by detecting the entrainment of air.

Question 2.   What oxygen flow rate would you normally use? Range 4 to 20 litres/minute (median 10 litres/minute).

We believe that a fixed preoxygenation time should be abandoned  and replaced by the induction of anaesthesia once a target EtO2 level had been attained.

Reference Russell EC, Wrench I, Feast M, Mohammed F. Pre‐oxygenation in pregnancy: the effect of fresh gas flow rates within a circle breathing system.  Anaesthesia 2008; 63: 833‐6.