Cochrane Review: Adjusting the pH of lidocaine for reducing pain on injection

Abstract

BackgroundLidocaine administration produces pain due to its acidic pH.ObjectivesThe objective of this review was to determine if adjusting the pH of lidocaine had any effect on pain resulting from non‐intravascular injections in adults and children. We tested the hypothesis that adjusting the pH of lidocaine solution to a level closer to the physiologic pH reduces this pain.Search methodsWe searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, to June 2010); Ovid MEDLINE (1966 to June 2010); EMBASE (1988 to June 2010); LILACS (1982 to June 2010); CINAHL (1982 to June 2010); ISI Web of Science (1999 to June 2010); and abstracts of the meetings of the American Society of Anesthesiologists (ASA). We checked the full articles of selected titles. We did not apply any language restrictions.Selection criteriaWe included double‐blinded, randomized controlled trials that compared pH‐adjusted lidocaine with unadjusted lidocaine. We evaluated pain at the injection site, satisfaction and adverse events. We excluded studies in healthy volunteers.Data collection and analysisWe separately analysed parallel‐group and crossover trials; trials that evaluated lidocaine with or without epinephrine; and trials with pH‐adjusted lidocaine solutions < 7.35 and ≥ 7.35. To explain heterogeneity, we separately analysed studies with a low and higher risk of bias due to the level of allocation concealment; studies that employed a low and a higher volume of injection; and studies that used lidocaine for different types of procedures.Main resultsWe included 23 studies of which 10 had a parallel design and 13 were crossover studies. Eight of the 23 studies had moderate to high risk of bias due to the level of allocation concealment.Pain associated with the infiltration of buffered lidocaine was less than the pain associated with infiltration of unbuffered lidocaine in both parallel and crossover trials. In the crossover studies, the difference was ‐1.98 units (95% confidence interval (CI) ‐2.62 to ‐1.34) and in the parallel‐group studies it was ‐0.98 units (95% CI ‐1.49 to ‐0.47) on a 0 to 10 scale. The magnitude of the pain decrease associated with buffered lidocaine was larger when the solution contained epinephrine. The risk of bias, volume of injection, and type of procedure failed to explain the heterogeneity of the results.Patients preferred buffered lidocaine (odds ratio 3.01, 95% CI 2.19 to 4.15). No adverse events or toxicity were reported.Authors' conclusionsIncreasing the pH of lidocaine decreased pain on injection and augmented patient comfort and satisfaction.Plain Language SummaryAdjusting the pH of lidocaine solution for reducing pain on injectionLidocaine is frequently used to anaesthetize the skin prior to invasive procedures. Its administration produces pain that is thought to be due to the acidic pH of commercial preparations (pH levels between 3.5 and 7.0 compared with the physiologic pH which is between 7.35 and 7.45). The objective of this review was to determine the effect of increasing the pH of a commercial lidocaine preparation on pain associated with its injection in adults and children. We included 23 studies with 1067 participants in the meta‐analysis. Increasing the pH of lidocaine reduced pain and improved patients' comfort and satisfaction. No adverse events were reported. Therefore, increasing the pH of commercial lidocaine solutions with bicarbonate immediately prior to their use should be considered.

Commercial Separation Systems Designed for Preparation of Platelet-Rich Plasma Yield Differences in Cellular Composition

“…Unique to this study, the pH of each PRP sample was also analyzed, revealing that several of the systems produced acidic PRP samples (pH = 6.95-7.32), falling outside of the normal physiologic range of 7.35 to 7.45. Several studies have previously correlated increased subjective pain with the injection of acidic substances, falling below a pH of 7.35 [5,10,28]. Consequently, the injection of these acidic PRP preparations may be a potential source of pain for patients.…”

“…Human/Animal Rights: All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008 (5).…”

Buffering mepivacaine with sodium bicarbonate speeds and potentiates analgesia of median and ulnar nerve blocks performed on horses

“…Local anaesthetics, especially lidocaine, are often buffered with NaHCO 3 for injection in people to lessen the pain of injection, which is thought to be caused by their acidic pH 19 . The pain of subcutaneous infiltration of mepHCl in people was shown to significantly decrease when mepHCl was buffered with NaHCO 3 20 .…”

Local Anesthesia Prior to Ultrasound‐Guided Hip Joint Injections: A Double‐Blind Randomized Controlled Trial of Bacteriostatic Saline versus Buffered Lidocaine

“…The most commonly used local anesthetic is lidocaine, which achieves maximal anesthetic effect within approximately 30 seconds 5 . It is well established that lidocaine infiltration into tissues may be painful 6‐8 . Several strategies have been attempted to minimize the pain of lidocaine infiltration.…”

“…Several strategies have been attempted to minimize the pain of lidocaine infiltration. Much of the pain associated with lidocaine infiltration is hypothesized to be because of its acidic pH with most commercially available formulations ranging from pH 3.5 to 7.0 6,9 . As a result, several authors have recommended buffering lidocaine with sodium bicarbonate to increase the pH to values closer to physiologic pH, thereby reducing pain upon infiltration 9,10 .…”