Evidence-based emergency medicine/review articleSystematic Review and Meta-analysis of the Effect of Warming Local Anesthetics on Injection Pain
Introduction
Local anesthetics are frequently used to anesthetize the skin or oral cavity before painful medical procedures. Injection of local anesthetics, however, is itself painful. Local anesthetics cause a burning or stinging sensation while being infiltrated into tissue, and this pain has been reported to cause people to avoid dental procedures.1 Some strategies to reduce pain from infiltration include slowing the rate of injection,2, 3 avoiding the use of epinephrine, and raising the pH with buffering agents such as sodium bicarbonate.3
Warming local anesthetics was first described as a pain-reducing measure by Boggia4 in 1967, but the mechanism of action is still unknown. One theory suggests that colder solutions stimulate nociceptors to a greater degree than warmer solutions.5 Another possible explanation is that as temperature increases, more uncharged local anesthetic passes through cell membranes, resulting in a faster onset of effect.6, 7, 8, 9 A survey in the United Kingdom found that 34% of maxillofacial surgeons and 8% of general surgeons regularly warmed local anesthetics to reduce pain.10
Many studies have investigated warming local anesthetics to reduce pain from infiltration, but at present the overall effectiveness has not been determined. The purpose of this systematic review and meta-analysis was to determine the effectiveness of warmed local anesthetics as an analgesic strategy for reducing local anesthetic infiltration pain.
Section snippets
Study Design
The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for reporting meta-analyses of randomized controlled trials were followed.11 A protocol was developed but not published in advance; post hoc analyses are indicated in the “Results” sections.
We accepted randomized controlled trials or pseudorandomized trials with adults or children. The following were our inclusion criteria: (1) randomized or pseudorandomized design, (2) healthy subjects or patients requiring local
Results
The search strategy (Appendix E1, available online at http://www.annemergmed.com) identified 449 studies (Figure 1). Studies were screened by title or abstract, and 29 were retrieved for further assessment. From these, 6 were excluded because they injected local anesthetic into the periorbital area, and 1 used regional anesthesia23, 24, 25, 26, 27, 28, 29; 1 was excluded because it was a review.30 Two did not have comparisons that met the inclusion criteria,31, 32 and 1 did not provide a median
Limitations
Limitations to the meta-analysis may arise from the presence of heterogeneity among the study populations, interventions, outcome assessments, and potential bias within the individual studies. Variability in the types of subjects enrolled was investigated through grouping the studies by patients and volunteers. Heterogeneity of interventions was explored by grouping studies according to the pH of solution, type of tissue infiltrated, use of epinephrine, volume, drug, and needle size used during
Discussion
This systematic review and meta-analysis determined that warming local anesthetics before injection reduced pain compared with injecting at room temperature. The results were consistent when the following subgroup analyses were performed: buffered and unbuffered solutions, subcutaneous or intradermal infiltration, anchoring pain from needle insertion at the midpoint of the visual analog scale or not specifying an anchor, presence or absence of epinephrine, and using patients or healthy
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Cited by (83)
Effects of fixation of clavicle fracture using wide-awake local anesthesia no tourniquet (WALANT) technique on intra-operative bleeding volume, surgical duration, and post-operatively visual analog scale (VAS); A case series study
2023, InjuryCitation Excerpt :NaHCO3 is added to increase the pH reaching closer to the physiological pH to prolong the effects of the local anesthetic agent [17,18]. Adding warm normal saline is shown to increase the efficacy of local anesthesia by reducing injection pain [19,20]. The prepared solution was injected by a single surgeon in all cases using 22-gage needles under aseptic technique in the Anesthetic room about 20 min prior to surgical incision.
The effect of rate and temperature on patient-reported pain during local anesthesia injection: A single-blinded, randomized, controlled trial
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2024, Journal of Pharmacy and Bioallied SciencesMinimizing the Pain of Local Anesthetic Injection
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Supervising editor: Michael D. Brown, MD, MSc
Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article as per ICMJE conflict of interest guidelines (see www.icmje.org). The authors have stated that no such relationships exist.
Publication date: Available online February 12, 2011.