Intradermal injection of local anesthetic often results in pain on injection due in part to the acidic pH of commercially prepared solutions, which are optimized to prolong shelf life. Although there are other possible explanations (eg, noxious properties of local anesthetics, pressure effect of infiltration), the etiology is most likely multifactorial. Although addition of bicarbonate to local anesthetics may decrease pain on intradermal injection, the extent of this analgesic effect is uncertain. We performed a meta-analysis of available trials investigating pain during intradermal injection of buffered local anesthetic preparations.
We searched the National Library of Medicine's PubMed database for all relevant articles published on the topic through November 2006. Inclusion criteria included double-blind, randomized controlled trials and use of a visual analog scale to measure pain on infiltration of local anesthetic buffered with sodium bicarbonate compared with that of unbuffered local anesthetic. Meta-analysis was performed using the Review Manager 4.2.7 (The Cochrane Collaboration, 2004). A random-effects model was used.
Our search resulted in 86 abstracts, of which 12 articles met all inclusion criteria. Overall, there were 609 observations for buffered local anesthetic and 615 for unbuffered local anesthetic. Use of buffered local anesthetic resulted in a statistically lower weighted mean difference in visual analog scale of −1.17 (95% confidence interval, −1.68 to −0.67) compared with unbuffered local anesthetic.
Our systematic review suggests that the use of buffered local anesthetics seems to be associated with a statistical decrease in pain of infiltration when compared with unbuffered local anesthetic.
From the Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University and School of Medicine, Baltimore, MD.
Accepted for publication June 20, 2008.
Address correspondence to: Christopher L. Wu, MD, The Johns Hopkins Hospital, Carnegie 280; 600 N Wolfe St, Baltimore, MD 21287 (e-mail: firstname.lastname@example.org).