Thurs. Feb. 10, 2011 — Warming a local anesthetic to body temperature before injection can help ease the pain experienced when a the drug enters the blood stream.
Results from 18 studies that included 831 patients found that patients injected with “warmed” anesthetics said they felt less pain than patients injected with room temperature or chilled anesthetics, according to Dr. Anna Taddio, of the University of Toronto, and colleagues.
The findings were reported online in the Annals of Emergency Medicine.
8 Alternative Treatments for Pain Management
Although a number of trials have investigated the effects of heating local anesthetics, efficacy has not thus far been established.
Accordingly, Taddio's team conducted a systematic review of studies exploring this.
Participants in all but one study were adolescents or adults. Eight studies included only healthy volunteers, while the remainder used patients.
Among methods of warming were the use of thermostatically controlled water baths, incubators, and warming trays.
Most studies used lidocaine, while a few used other anesthetics such as bupivacaine.
The only circumstance when there was no benefit for warming local anesthetics was when the injection was given orally for dental procedures in children.
The authors noted that earlier studies have found that a clinically meaningful reduction in pain can be considered a decrease of 9 to 13 mm on a 100-mm visual analog scale.
The overall reductions of 7 to 13 mm seen in this study therefore were consistent with a clinically significant decrease in pain, they noted.
"There are important clinical implications to these findings," the researchers stated.
"Because local anesthetic injections are planned procedures (and thus pain is predictable), all efforts should be made to prevent or at least minimize iatrogenic pain," they wrote.
They also pointed out that warming of anesthetics could be done regardless of the clinical setting, and with equipment likely to be already available for other uses.
Use of warming for local anesthetics as a means of lessening pain was first proposed more than 40 years ago — yet the mechanism of action has never been identified.
Possible explanations include less stimulation of nociceptors and more rapid passage of the anesthetic through cell membranes with increased temperature, they explained.
Limitations of the study included the fact that there was considerable heterogeneity in the study populations, types of anesthetics used, and outcome measurements.
There also was limited blinding and insufficient explanation of statistical analyses in some trials.
The authors stated that they have no conflicts of interest.