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BJA Advance Access originally published online on May 2, 2009
British Journal of Anaesthesia 2009 102(6):806-811; doi:10.1093/bja/aep095
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© The Author [2009]. Published by Oxford University Press on behalf of The Board of Directors of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournal.org

Effect of i.v. phenylephrine or ephedrine on the ED50 of intrathecal bupivacaine with fentanyl for Caesarean section

M. C. Hennebry1, G. M. Stocks1,*, P. Belavadi1, J. Barnes1, S. Wray1, M. O. Columb2 and G. Lyons3

1 Department of Anaesthesia, Queen Charlotte's and Chelsea Hospital, Du Cane Road, London W12 0HS, UK
2 University Hospital of South Manchester, Wythenshawe, UK
3 St James' University Hospital, Leeds, UK

* Corresponding author. E-mail: gary.stocks{at}imperial.nhs.uk

Background: Prophylactic infusion of phenylephrine to prevent hypotension at Caesarean section has been shown to decrease the rostral spread of intrathecal plain levobupivacaine and intrathecal hyperbaric bupivacaine by a median of two dermatomes compared with ephedrine. The aim of this study was to determine the median effective dose (ED50) of intrathecal bupivacaine required to achieve a block to touch at the xiphisternum in patients undergoing Caesarean section when phenylephrine or ephedrine are used to prevent hypotension.

Methods: Seventy women were randomized in two groups to receive either phenylephrine at a rate of 16.6 µg min–1 (concentration 1µg ml–1) or ephedrine at a rate of 1.5 mg min–1 (concentration 90 µg ml–1). Patients received varying doses of hyperbaric bupivacaine with fentanyl 25 µg using a double-blinded, up-down sequential allocation design. Effective doses were defined as anaesthesia to touch with ethyl chloride spray to the xiphisternum within 20 min.

Results: The ED50 estimates of bupivacaine were similar in the two groups: 7.8 mg [95% confidence interval (CI) 6.7–8.9] with phenylephrine and 7.6 mg (95% CI 6.8–8.4) with ephedrine. Systolic blood pressure control was similar (P=0.18) with vasopressors but heart rate was higher with ephedrine (P=0.0014).

Conclusions: Under the conditions of this study, we have shown that when phenylephrine or ephedrine were used to prevent post-spinal hypotension, the dosing requirement of hyperbaric bupivacaine was similar for intrathecal anaesthesia.

Keywords: anaesthetic techniques, subarachnoid; surgery, Caesarean section; sympathetic nervous system, phenylephrine; sympathetic nervous system, ephedrine


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