Effect of i.v. phenylephrine or ephedrine on the ED50 of intrathecal bupivacaine with fentanyl for caesarean section.
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 microg min(-1) (concentration 1microg ml(-1)) or ephedrine at a rate of 1.5 mg min(-1) (concentration 90 microg ml(-1)). Patients received varying doses of hyperbaric bupivacaine with fentanyl 25 microg 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.
Department of Anaesthesia, Queen Charlotte's and Chelsea Hospital, Du Cane Road, London W12 0HS, UK.
M C
MC
Hennebry
G M
GM
Stocks
P
P
Belavadi
J
J
Barnes
S
S
Wray
M O
MO
Columb
G
G
Lyons
D000328:Adult; D000773:Anesthesia, Obstetrical / Q000379:methods*; D000775:Anesthesia, Spinal / Q000379:methods*; D002045:Bupivacaine / Q000008:administration & dosage; D002585:Cesarean Section; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D004347:Drug Interactions; D004809:Ephedrine / Q000008:administration & dosage / Q000494:pharmacology; D005260:Female; D005283:Fentanyl / Q000008:administration & dosage*; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007022:Hypotension / Q000139:chemically induced / Q000517:prevention & control; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology; D011247:Pregnancy; D011446:Prospective Studies; D014662:Vasoconstrictor Agents / Q000008:administration & dosage* / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D004809:Ephedrine; D005283:Fentanyl; D002045:Bupivacaine