Ropivacaine 0.75% Versus Levobupivacaine 0.5% for Conversion of Labour Epidural

Ropivacaine 0.75% Versus Levobupivacaine 0.5% for Conversion of Labour Epidural to Surgical Anaesthesia for Emergency Caesarean Section.

The aim of this trial is to compare the local anaesthetic ropivacaine to local anaesthetic levobupivacaine in converting the standard patient controlled labour epidural to provide anaesthesia for an emergency Caesarean section. This is a technique commonly known as an epidural top-up. The investigators set out to disprove the hypothesis that there is no difference between the 2 local anaesthetics in the time of onset and number of times epidural top-up needs supplementing during surgery.

In a randomised controlled trial involving 45 patients the speed of onset of the effects of 20mls of 0.75% ropivacaine was found to be similar to that of 20mls of 0.5% bupivacaine1. However it was also found to be more efficacious at preventing 'breakthrough' pain and therefore had a lower intra-operative supplementation rate. Unfortunately the study was probably not powered adequately to confirm this finding. Bupivacaine has now largely been replaced in the this field by the less cardio-toxic stereoisomer levobupivacaine. A trial comparing 0.75% ropivacaine to 0.5% levobupivacaine and a lignocaine/adrenaline/fentanyl mixture was conducted in Singapore in 20082. It did not show a clinical difference between any of the agents. Whether the population studied is comparable to that in the UK is doubtful and it was not adequately powered to detect a difference in intra-operative supplementation rate. Local experience has shown ropivacaine 0.75% to provide a block with a rapid onset that has little requirement for supplementation intra-operatively. The need to supplement a local anaesthetic block during surgery means that the mother is experiencing a degree of pain that is unacceptable and we view this as a major consideration in choice of local anaesthetic for an epidural top-up. Whilst speed of onset is important, in that it influences the decision to delivery time of the baby, the evaluation of intraoperative supplementation will be a major focus of this trial.

Inclusion Criteria:

Any subject requiring a grade 2 or 3 EmCS on the Hospital Birth Centre, St Thomas' who has:

1. Labour analgesia provided by the standard patient controlled epidural (solution containing 0.1% levobupivacaine and 2mcg/ml fentanyl). That is providing analgesia via the patient controlled epidural analgesia infusion pump without the need for multiple extra boluses of epidural local anaesthetic and or opiates from the anaesthetist on the labour ward..
2. Singleton pregnancy.
3. Established labour, determined by the midwife responsible for the patient (usually by vaginal examination of the cervix).
4. Gestation >36 weeks
5. No complex past medical history according to the judgement of the investigator
6. > 18 years of age
7. EmCS starts between the hours 0800 and 1800.
8. The ability to understand the patient information sheet and willing to provide informed consent.
9. Had a minimal total dose of 50mcg of fentanyl since insertion of epidural

Exclusion Criteria:

1. Pre-eclampsia / Eclampsia
2. Antepartum haemorrhage
3. Any congenital, structural or ischaemic heart disease.
4. Category 1 EmCS.
5. Participation in another therapeutic study in the last 12 weeks. -