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.
Key findings of the study include:
- After adjustment for sex, cool and rapid injections were independently associated with greater pain (+0.4750 units vs warm, and 85 +0.5786 units vs slow, respectively).
- Female sex was independently associated with less pain (−0.5306 units vs male).
- Both slow/cool injections and rapid/warm injections were more than 25% less painful than rapid/cool injections.
- Rapid/cool injections were >2 times more painful than slow/warm injections.
"The findings showed that lidocaine injection pain can be reduced by injecting slowly and by warming the injectant. Neither intervention is a resource- or time-intensive," wrote the authors.
"Although individual patient considerations will determine when slow or warm lidocaine injections are appropriate, the surgeon now has additional tools to make surgery under local anesthesia more comfortable," they concluded.
The study titled, "The effect of rate and temperature on patient-reported pain during local anesthesia injection: A single-blinded, randomized, controlled trial," is published in the Journal of the American Academy of Dermatology.