Abstract
Background
Pregnancy is associated with facilitated spread of spinal and epidural anesthesia.
There are limited data available for relative potency of motor block of neuraxial
local anesthetics in non-pregnant versus pregnant women. The purpose of this study
was to investigate the median effective dose (ED50) of intrathecal isobaric bupivacaine for motor block in non-pregnant and pregnant
women and to estimate the respective potency ratio.
Methods
American Society of Anesthesiologists physical status I and II pregnant (n = 35) and non-pregnant (n = 35) patients undergoing elective cesarean delivery or elective gynecological surgery
under combined spinal–epidural anesthesia were enrolled. According to the up-down
sequential allocation technique, the dose of intrathecal isobaric bupivacaine for
each patient was determined by the response of the previous patient in both groups.
The initial dose of bupivacaine was 4 mg and the testing interval was set at 0.5 mg. Efficacy was determined by the occurrence of motor block in either lower limb
as assessed by the modified Bromage scale within 5 min of spinal injection.
Results
The ED50 of intrathecal bupivacaine for motor block was 4.51 (95% confidence interval (CI)
4.27–4.76) mg for non-pregnant women and 3.96 (95% CI 3.83–4.08) mg for pregnant women.
The relative potency ratio for motor block for pregnant versus non-pregnant women
was 1.14 (95% CI 1.05–1.24), (P = 0.0037).
Conclusions
Intrathecal bupivacaine was 1.14 times more potent for motor block in pregnant versus
non-pregnant women. Our current data confirm the difference in local anesthetic requirement
between non-pregnant and pregnant patients.
Keywords
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Article info
Publication history
Published online: May 27, 2011
Accepted:
January 8,
2011
Identification
Copyright
© 2011 Elsevier Ltd. Published by Elsevier Inc. All rights reserved.
