ORIGINAL ARTICLE| Volume 20, ISSUE 3, P219-223, July 2011

Comparison of relative potency of intrathecal bupivacaine for motor block in pregnant versus non-pregnant women



      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.


      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.


      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).


      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.


      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to International Journal of Obstetric Anesthesia
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Bromage P.R.
        Spread of analgesic solutions in the epidural space and their site of action: a statistical study.
        Br J Anaesth. 1962; 34: 161-178
        • Fagraeus L.
        • Urban B.J.
        • Bromage P.R.
        Spread of epidural analgesia in early pregnancy.
        Anesthesiology. 1983; 58: 184-187
        • Hirabayashi Y.
        • Shimizu R.
        • Saitoh K.
        • Fukuda H.
        Spread of subarachnoid hyperbaric amethocaine in pregnant women.
        Br J Anaesth. 1995; 74: 384-386
        • Hirabayashi Y.
        • Shimizu R.
        • Saitoh K.
        • Fukuda H.
        Cerebrospinal fluid progesterone in pregnant women.
        Br J Anaesth. 1995; 75: 683-687
        • Hirabayashi Y.
        • Shimizu R.
        • Saitoh K.
        • Fukuda H.
        • Igarashi T.
        Acid–base state of cerebrospinal fluid during pregnancy and its effect on spread of spinal anesthesia.
        Br J Anaesth. 1996; 77: 352-355
        • Hocking G.
        • Wildsmith J.A.W.
        Intrathecal drug spread.
        Br J Anaesth. 2004; 93: 568-578
        • Capogna G.
        • Camorcia M.
        • Columb M.O.
        Effects of gender and pregnancy on the potency of intrathecal bupivacaine.
        Eur J Anaesthesiol. 2011; 28: 240-244
        • Columb M.O.
        • Lyons G.
        Determination of the minimum local analgesic concentrations of epidural bupivacaine and lidocaine in labor.
        Anesth Analg. 1995; 81: 833-837
        • Camorcia M.
        • Capogna G.
        • Lyons G.
        • Columb M.
        Epidural test dose with levobupivacaine and ropivacaine: determination of the ED50 for motor block after spinal administration.
        Br J Anaesth. 2004; 92: 850-853
        • Dixon W.J.
        • Massey F.J.
        Introduction to statistical analysis.
        4th ed. McGraw-Hill, New York1983 (p. 28–39)
        • Lacassie H.J.
        • Columb M.O.
        The relative motor blocking potencies of bupivacaine and levobupivacaine in labor.
        Anesth Analg. 2003; 97: 1509-1513
        • Polley L.S.
        • Columb M.O.
        • Wagner D.S.
        • Naughton N.N.
        Dose-dependent reduction of the minimum local analgesic concentration (MLAC) of bupivacaine by sufentanil for epidural analgesia in labor.
        Anesthesiology. 1998; 89: 626-632
        • Bromage P.R.
        A comparison of the hydrochloride and carbon dioxide salts of lidocaine and prilocaine in epidural analgesia.
        Acta Anaesthesiol Scand. 1965; 16: 55-69
        • Barclay D.L.
        • Renegar O.J.
        • Nelson E.W.
        The influence of inferior vena cava compression on the level of spinal anesthesia.
        Am J Obstet Gynecol. 1968; 101: 792-800
        • Bromage P.R.
        Continuous lumbar epidural analgesia for obstetrics.
        Can Med Assoc J. 1961; 85: 1136-1140
        • Hirabayashi Y.
        • Shimizu R.
        • Fukuda H.
        • Saitoh K.
        Anatomical configuration of the spinal column in the supine position. II. Comparison of pregnant and non-pregnant women.
        Br J Anaesth. 1995; 75: 6-8
        • Takiguchi T.
        • Yamaguchi S.
        • Tezuka M.
        • Furukawa N.
        • Kitajima T.
        Compression of the subarachnoid space by the engorged epidural venous plexus in pregnant women.
        Anesthesiology. 2006; 105: 848-851
        • Onuki E.
        • Higuchi H.
        • Takagi S.
        Gestation-related reduction in lumbar cerebrospinal fluid volume and dural sac surface area.
        Anesth Analg. 2010; 110: 148-153
        • Datta S.
        • Hurley R.J.
        • Naulty J.S.
        • Stern P.
        • Lambert D.H.
        Plasma and cerebrospinal fluid progesterone concentrations in pregnant and nonpregnant women.
        Anesth Analg. 1986; 65: 950-954
        • Hirabayashi Y.
        • Shimizu R.
        • Saitoh K.
        • Fukuda H.
        • Igarashi T.
        Acid–base state of cerebrospinal fluid during pregnancy and its effect on spread of spinal anaesthesia.
        Br J Anaesth. 1996; 77: 352-355
        • Leo S.
        • Sng B.L.
        • Lim Y.
        • Sia A.T.
        A randomized comparison of low doses of hyperbaric bupivacaine in combined spinal–epidural anesthesia for cesarean delivery.
        Anesth Analg. 2009; 109: 1600-1605
        • Lauretti G.R.
        • Oliveira A.P.
        • Julião M.C.
        • Reis M.P.
        • Pereira N.L.
        Transdermal nitroglycerine enhances spinal neostigmine postoperative analgesia following gynecological surgery.
        Anesthesiology. 2000; 93: 943-946
        • Camorcia M.
        • Capogna G.
        • Columb M.O.
        Estimation of the minimum motor blocking potency ratio for intrathecal bupivacaine and lidocaine.
        Int J Obstet Anesth. 2008; 17: 223-227
        • Higuch H.
        • Adach Y.
        • Kazama T.
        Effects of epidural saline injection on cerebrospinal fluid volume and velocity waveform: a magnetic resonance imaging study.
        Anesthesiology. 2005; 102: 285-292
        • Broadbent C.R.
        • Maxwell W.B.
        • Ferrie R.
        • Wilson D.J.
        • Gawne-Cain M.
        • Russell R.
        Ability of anaesthetists to identify a marked lumbar interspace.
        Anaesthesia. 2000; 55: 1122-1126
        • Camorcia M.
        • Capogna G.
        • Berritta C.
        • Columb M.O.
        The relative potencies for motor block after intrathecal ropivacaine, levobu-pivacaine and bupivacaine.
        Anesth Analg. 2007; 104: 904-907