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

• Published in: British journal of anaesthesia : BJA Vol. 102; no. 6; pp. 806 - 811
• Main Authors: Hennebry, M.C., Stocks, G.M., Belavadi, P., Barnes, J., Wray, S., Columb, M.O., Lyons, G.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-06-2009; Oxford University Press; Oxford Publishing Limited (England)
• Subjects: Adult; anaesthetic techniques; anaesthetic techniques, subarachnoid; Anesthesia; Anesthesia, Obstetrical - methods; Anesthesia, Spinal - methods; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Biological and medical sciences; Bupivacaine - administration & dosage; Caesarean section; Cesarean Section; Double-Blind Method; Drug Administration Schedule; Drug Interactions; ephedrine; Ephedrine - administration & dosage; Ephedrine - pharmacology; Female; Fentanyl - administration & dosage; Hemodynamics - drug effects; Humans; Hydrogen-Ion Concentration - drug effects; Hypotension - chemically induced; Hypotension - prevention & control; Medical sciences; phenylephrine; Phenylephrine - administration & dosage; Phenylephrine - pharmacology; Pregnancy; Prospective Studies; subarachnoid; surgery; surgery, Caesarean section; sympathetic nervous system; sympathetic nervous system, ephedrine; sympathetic nervous system, phenylephrine; Vasoconstrictor Agents - administration & dosage; Vasoconstrictor Agents - pharmacology; anaesthetic techniques, subarachnoid; sympathetic nervous system, ephedrine; surgery, Caesarean section; sympathetic nervous system, phenylephrine; Agonist; μ Opioid receptor; Ephedrine; α1-Adrenergic receptor; Fentanyl; Opiates; Narcotic analgesic; β-Adrenergic receptor; Alkaloid; Bupivacaine; Surgery; Phenylephrine; Anesthesia; Vasoconstrictor agent; Anilide; Caesarean section; Antihypotensive agent; Bronchodilator; Sympathomimetic; Sympathetic nervous system; Local anesthetic; α-Adrenergic receptor; Subarachnoid; Carboxamide; Organic amide; α-Adrenergic receptor agonist; Phenylpiperidine derivatives; anaesthetic techniques
• ISSN: 0007-0912; 1471-6771
• DOI: 10.1093/bja/aep095

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.
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.
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).
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.