Warming and injecting slowly reduces lidocaine injection pain, study finds

USA: The pain of local anesthetic injections can be reduced by injecting slowly and by warming the injectant, slow injection seems more important than temperature, according to a recent study published as a research letter in the Journal of the American Academy of Dermatology.

Previous studies have shown separately that warming and injecting slowly reduce pain during local anesthetic infiltration. Amanda Maisel-Campbell, Department of Dermatology, Columbia University Medical Center, New York, New York, and colleagues aimed to assess the cumulative impact of anesthetic temperature and injection speed in a participant blinded, split-body, randomized, controlled trial.

The study recruited 70 healthy adults aged 18 to 70 years to receive. They were recruited to receive two 1-mL injections of 1% lidocaine with 1:100,000 epinephrine into each upper arm 4 cm apart, with the order and location randomized — rapid (0.2 mL/s)/cool (21 °C), rapid/warm (40 °C), slow (0.033 mL/s)/cool, and slow/warm. The depth was to the dermal-subcutaneous junction, and needle insertion was for 30 seconds. The patients rated pain on a visual analog scale.