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Central nervous system side effects are less important after iv regional anesthesia with ropivacaine 0.2% compared to lidocaine 0.5% in volunteers

[Les effets secondaires neurologiques sont moins importants après une anesthésie régionale iv réalisée avec de la ropivacaïne à 0,2 % comparée à la lidocaïne à 0,5 %]

From the Department of Anesthesiology Yale University School of Medicine New Haven Connecticut USA.

Address correspondence to: Dr. Peter G. Atanassoff, Yale University School of Medicine, Department of Anesthesiology, P.O. Box 208051, 333 Cedar Street, New Haven, Connecticut 06520, USA. Phone: 203-785-2802; Fax: 203-785-6664; E-mail: peter.atanassoff{at}yale.edu

Purpose: Following release of a double tourniquet for intravenous regional anesthesia (IVRA), ropivacaine was shown to have a longer duration of action and less central nervous system (CNS) side effects than lidocaine. This study examines the correlation of CNS side effects to plasma levels of lidocaine 0.5% and ropivacaine 0.2% when injected intravenously for IVRA.

Methods: In a double-blind, cross-over study, ten volunteers received IVRA with 40 mL ropivacaine 0.2% or lidocaine 0.5% at least four days apart. Both cuffs of a double-cuff tourniquet remained inflated until they could no longer be tolerated. The incidence, duration and intensity of CNS side effects were recorded at three, ten, and 30 min after tourniquet release and correlated with simultaneous venous blood samples.

Results: There was a lower incidence of CNS side effects with ropivacaine (6/10 volunteers) when compared to lidocaine (10/10 volunteers). There was also less duration of these side effects (mean ± SD, 5.1 ± 5.2 min vs 11.7 ± 6.7 min). Measured total plasma levels were highest at ten minutes with ropivacaine 0.2% (1.2 ± 0.3 µg•mL^-1) and at three minutes with lidocaine 0.5% (1.7 ± 0.6 µg•mL^-1). Peak CNS symptoms correlated with measured venous plasma levels for lidocaine, but occurred earlier with ropivacaine.

Conclusions: We observed a lower incidence of CNS side effects with ropivacaine as compared to lidocaine. Although ropivacaine's greater lipid solubility should, theoretically, lead to more CNS side effects, this was, likely, offset by slower release from tissues and lesser percentage of unbound (free) drug.