Background: Injection of local anaesthetics is an uncomfortable procedure. The purpose of this study was to determine the influence of lidocaine temperature on pain during subcutaneous injection.
Methods: A randomised, double blind trial with 36 healthy volunteers was performed. Each subject received three injections of 4.5 ml 1% lidocaine subcutaneously on the abdomen; refrigerated (8 °C), at room temperature (21 °C), and warmed to body temperature (37 °C). By giving every subject injections of all three temperatures they served as their own controls. The participants were asked to evaluate the pain felt during the injection by placing a pencil mark on a 100 mm Visual Analogue Scale without intermediate markings immediately after every injection. They were told that the scale ranged from no pain to worst imaginable pain (0 = best; 100 = worst). Retrospectively the participants did a verbal assessment of the most and least painful injection.
Results: The median VAS score for the heated lidocaine was 16 (range =11-28), lidocaine at room temperature 25 (13-40) and for the cold 24 (11-35). The VAS scores for the heated lidocaine was significantly lower than for lidocaine at room temperature (p = 0.004). Also, the verbal assessment of heated lidocaine being less painful than the injection at room temperature was statistically significant (p = 0.015).
Conclusions: Injection with lidocaine heated to around body temperature was less painful than injection with lidocaine at room temperature. There was no statistically significant difference in verbal assessment or VAS scores between the cold lidocaine and that at room temperature.
Keywords: Anaesthetics; heating lidocaine; injection pain; temperature.