A randomized double-blinded comparison of phenylephrine and ephedrine infusion combinations to maintain blood pressure during spinal anesthesia for cesarean delivery: the effects on fetal acid-base status and hemodynamic control.
BACKGROUND
Phenylephrine and ephedrine are both used to maintain arterial blood pressure during spinal anesthesia for cesarean delivery. Usually, either drug is given alone but several previous studies have described combining the drugs. However, the effect of varying the proportion of vasopressors in such combinations has not been reported.


METHODS
One-hundred-twenty-five parturients having spinal anesthesia for elective cesarean delivery were randomized to receive an IV infusion of phenylephrine and ephedrine combined in one of five different concentration ratios. Assuming phenylephrine 100 microg to be approximately equipotent to ephedrine 8 mg, the groups contained the proportional potency equivalent of 100%, 75%, 50%, 25% or 0% of phenylephrine and 0%, 25%, 50%, 75% or 100%, respectively, of ephedrine. The infusions were adjusted to maintain systolic blood pressure (SBP) near baseline until uterine incision. Hemodynamic changes and umbilical cord blood gases were compared.


RESULTS
As the proportion of phenylephrine decreased and proportion of ephedrine increased among the groups, the following significant trends were detected: the incidences of hypotension and nausea/vomiting increased, the median magnitude of deviations of SBP above or below baseline and the bias for SBP to be above baseline increased, maternal heart rate was faster, fetal pH and base excess decreased, umbilical arterial oxygen content decreased and umbilical venous Po2 increased.


CONCLUSIONS
When varying combinations of phenylephrine and ephedrine were given by infusion to maintain arterial blood pressure during spinal anesthesia for cesarean delivery, as the proportion of phenylephrine decreased and the proportion of ephedrine increased, hemodynamic control was reduced and fetal acid-base status was less favorable. Combinations of phenylephrine and ephedrine appear to have no advantage compared with phenylephrine alone when administered by infusion for the prevention of hypotension associated with spinal anesthesia for cesarean delivery.
Ngan Kee
Warwick D
WD
Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China. warwick@cuhk.edu.h
Lee
Anna
A
Khaw
Kim S
KS
Ng
Floria F
FF
Karmakar
Manoj K
MK
Gin
Tony
T
D000136:Acid-Base Equilibrium / Q000187:drug effects; D000328:Adult; D000773:Anesthesia, Obstetrical; D000775:Anesthesia, Spinal; D001794:Blood Pressure / Q000187:drug effects*; D002245:Carbon Dioxide / Q000097:blood; D002585:Cesarean Section; D004311:Double-Blind Method; D004338:Drug Combinations; D004809:Ephedrine / Q000008:administration & dosage* / Q000009:adverse effects / Q000494:pharmacology; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D005333:Fetus / Q000187:drug effects* / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007022:Hypotension / Q000139:chemically induced; D007262:Infusions, Intravenous; D010100:Oxygen / Q000097:blood; D010656:Phenylephrine / Q000008:administration & dosage* / Q000009:adverse effects / Q000494:pharmacology; D020250:Postoperative Nausea and Vomiting / Q000209:etiology; D011247:Pregnancy; D014662:Vasoconstrictor Agents / Q000008:administration & dosage* / Q000494:pharmacology
D004338:Drug Combinations; D006454:Hemoglobins; D014662:Vasoconstrictor Agents; D002245:Carbon Dioxide; D010656:Phenylephrine; D004809:Ephedrine; D010100:Oxygen