COMPARISON OF ROPIVACAINE 0.2% AND LIDOCAINE 0.5% FOR INTRAVENOUS REGIONAL ANESTHESIA

Abstract

S255 INTRODUCTION: Intravenous regional anesthesia (IVRA) is a relatively simple anesthetic technique employed mostly for upper limb surgical procedures. Lidocaine, the only FDA-approved local anesthetic agent for IVRA, can produce serious systemic and central nervous system (CNS) side effects upon release of the tourniquet. Ropivacaine, a new local anesthetic, was shown to produce only minor CNS side effects following direct intravenous injection [1], and therefore could be associated with less side effects when used for IVRA. We have elected to evaluate the safety and potential efficacy of ropivacaine for IVRA. METHODS: Following IRB approval, ten healthy, unpremedicated volunteers participated in this double-blind, cross-over investigation. Randomized, and at least 4 days apart, 40 ml of 0.5% lidocaine or 0.2% ropivacaine were injected into the non-dominant forearm for IVRA. Pain was evaluated with a verbal numeric scale (VNS) (ranging from 0 = no pain to 10 = worst pain imaginable) in response to a 50 Hz tetanic stimulus in 10 mA increments up to a maximum of 60 mA, since this has been shown to be an equivalent stimulus to surgical incision [2]. Loss of sensation was evaluated by pinprick. Following exsanguination of the extremity, the proximal cuff of a double-cuff tourniquet was inflated on the upper arm to a pressure of 250 mm Hg and the local anesthetic agent was injected over one minute. When tourniquet pain from the proximal tourniquet was rated 10 on a VNS, the distal tourniquet was inflated, followed by release of the proximal tourniquet. The distal tourniquet remained inflated until a VNS score of 10 was reached again. Baseline measurements were performed before tourniquet inflation, every 5 min during tourniquet inflation, and at 3, 10, and 30 min after deflation of the distal tourniquet. After release of the distal tourniquet the volunteers were questioned about CNS side effects and asked to rate them on a VNS between 0.10. Data are expressed as mean +/- standard deviation and range and were analyzed using paired t- and Wilcoxon rank tests for parametric and non-parametric data, respectively. RESULTS: There were no significant differences between lidocaine and ropivacaine with regard to loss of pinprick sensation, onset time of surgical anesthesia, and tolerance time of the distal tourniquet (Table 1). In contrast, the regimens differed during recovery. Recovery of sensation to pinprick was incomplete at 30 min post-tourniquet release with ropivacaine, but not with lidocaine (p=0.0002). CNS side effects after tourniquet release were rated significantly more intense after lidocaine than after ropivacaine (Table 2).Table 1: Times (min)Table 2: VNS Scores (0-10)DISCUSSION: Ropivacaine 0.2% and lidocaine 0.5% appear to have similar clinical features during tourniquet inflation when used for IVRA. After tourniquet release, ropivacaine may prove to be superior, in that it provided a block of longer duration and was associated with less side effects. The longer lasting block and decreased incidence and intensity of CNS side effects upon release of the tourniquet may be attributable to the higher lipid solubility [2] and continued tissue binding of ropivacaine when compared to lidocaine. The advantages warrant further investigation.