Local anesthetic dilution for peripheral nerve block: Comparative evaluation of saline VS 5% dextrose

Abstract

Introduction: High perineural sodium concentration is known to antagonize the analgesic effect of local anesthetic (LA) due to competitive sodium channel blockade. Therefore LA diluted with normal saline (NS) may alter onset/regression of blockade (Kanai 2006). Five percent dextrose (D5W) is painless on injection and is not known to cause any long-term sequelae in animals or humans when injected around neurological tissue (Tsui 2005). The hypothesis of this study is that dilution of LA with D5W reduces the onset time of peripheral nerve block. The objective was to prospectively compare and evaluate the onset and duration of action of LA drug when diluted with D5W or NS in patients scheduled for upper limb surgery under regional block. Methods: In this double blind trial, following REB approval, 550 patients scheduled for upper limb surgery under axillary brachial plexus block were randomized into two groups. All blocks were done under ultrasound guidance with 0.5% ropivacaine. Group 1 received ropivacaine diluted with D5W and group 2 received ropivacaine diluted with NS. Motor and sensory block was tested every 5 minutes for the next 30 minutes. Postoperatively, a telephonic interview was conducted after 24 hours and 7 days to document side effects, patient satisfaction and time of block resolution. Any nerve deficits were followed up until completely resolved. Parametric data was analysed by studentaTMs t test and non-parametric data was analysed by ANOVA. The mean time for onset of complete sensory block was 9.6 (A+/-6.8) min in D5W group vs. 12.9 (A+/-6.2) min in NS group and this was highly significant (p<0.003). Time of onset of motor block was similar between the two groups (table). The time taken for block recession was not different between the groups. One patient developed tingling of the lips during the block procedure that could be attributed to possible LA toxicity. Six patients had sensory deficit and one had sensory as well as motor deficit. However, forty-seven patients had non-specific neurological symptoms with no actual deficits (no difference between groups). All patients made full recovery. Discussion: Influence of dilution agent on the outcome of peripheral regional block is currently unknown. In this randomized controlled double blind study, we determined that D5W is a safe and effective diluent for LA and reduces the time of onset of regional block, which may have implications in improving the efficiency of operating room time utilization. (Table presented).