Dr. Anna Taddio and colleagues at the University of Toronto, Ontario, identified 18 studies on the topic that could be included in their analysis. Sixteen studies used lidocaine, 1 used bupivacaine and 1 procaine.
Warming was done using various methods, such as thermostatically controlled waterbaths, baby food warmers or syringe warmers. The primary outcome was self-reported pain as assessed by a visual analog or numeric rating scale.
“A mean difference of -11 mm on a 100-mm scale was found in favor of warming local anesthetics,” the team reports. When considering buffered or unbuffered local anesthetics, the effect of warming was similar with a -7 mm difference in perceived pain for buffered anesthetics and -13 mm for unbuffered solutions.
Pain reduction with warming was -14 mm with subcutaneous injection, and -5 mm with intradermal injection, according to the report.
The one study involving children looked at pain from dental anesthetic injections. This did not show a significant benefit from warming (-2 mm).
“According to our findings, local anesthetics should be warmed before subcutaneous or intradermal infiltration to reduce pain from infiltration,” Dr. Taddio and colleagues conclude
Reference:
Systematic Review and Meta-analysis of the Effect of Warming Local Anesthetics on Injection Pain
Ann Emerg Med 2011.
