In modern podiatric practice, the use of local anaesthetic is routine. For the patient, it can potentially be a painful experience. To make the procedure more comfortable, over the years there have been many suggested technique modifications to reduce the patient’s discomfort. For example, buffering the pH of the solution, warming the local anaesthetic prior to injection, injecting slowly or adjusting the angle of the needle entry [1-3]. I have even reviewed a technique involving a glove and an old electric toothbrush to dull sensation prior to injection (Click Here).
A recent study from dermatologists in the US [4] has attempted to build on previous work that has shown how warming anaesthetic reduces pain as does injecting slowly but what would be the best combination? Researchers from New York, Chicago, and California designed a randomised control trial examining both the speed of injection and local anaesthetic temperature. Adult patients received two injections of lidocaine 1% to the upper arm with two types of injection either:
1. Rapid and cool (21 degrees centigrade).
2. Rapid and warm (40 degrees centigrade).
3. Slow and cool.
4. Or, a slow and warm injection.
All of these injections used a standardised protocol of 90-degree angle of approach, tissue depth and standard duration of injection. The participant's pain levels were recorded using a visual analogue scale immediately after injecting. A raft of statistics were then used to examine and identify factors independently associated with pain during injection.
In total, 70 patients received 280 injections. Perhaps unsurprisingly both cool anaesthetic temperature and rapid injection technique were associated with more painful injections. Female sex was associated with less pain but no difference in pain levels related to age or race were noted. Of the most painful combination - rapid and cool, the researchers found the rapidity of the injection to be more painful than the lower temperature of the anaesthetic.
As previously suspected, this work reinforces the idea that both adjustments to increase the local anaesthetic temperature and slow the local anaesthetic delivery during the can improve the patient's overall experience and reduce the pain associated with injections both individually, and in combination. Reassuringly, these adjustments should not add an additional burden onto busy clinicians.
References
1. Colaric KB, Overton DT, Moore K: Pain reduction in lidocaine administration through buffering and warming. The American Journal of Emergency Medicine 1998, 16(4):353-356.
2. Scarfone RJ, Jasani M, Gracely EJ: Pain of Local Anesthetics: Rate of Administration and Buffering. Ann Emerg Med 1998, 31(1):36-40.
3. Strazar AR, Leynes PG, Lalonde DH: Minimizing the pain of local anesthesia injection. Plast Reconstr Surg 2013, 132(3):675-684.
4. Maisel-Campbell A, Weil A, Lazaroff JM, Council ML, Eisen DB, Lawrence N, Minkis K, Chen BR, Kang BY, Ibrahim SA et al: The Effect of Rate and Temperature on Patient-Reported Pain During Local Anesthesia Injection: A Single-Blinded, Randomized, Controlled Trial. J Am Acad Dermatol 2021.