Drip Lidocaine On Skin Before Injection to Reduce Pain

Written by Nicole McCoin

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When performing common bedside procedures, drip 1-2 mL of the lidocaine that you are getting ready to inject onto the skin prior to injection. This study suggests that it decreases the patient’s report of pain associated with the procedure.

Why does this matter?
Bedside procedures are common, and they hurt. Any tricks of the trade to decrease pain associated with these procedures are welcome!

It’s already there. It’s easy to do. It’s cheap. Why not?
Lidocaine dripped directly on the skin from a syringe is water soluble. It has no direct anesthetic effect. However, the authors of this study postulated that when the lidocaine is dripped onto the skin, the mere touch and the cooler temperature of the lidocaine (relative to the skin) can interfere with the transmission of acute pain signals through A-delta fibers and C fibers. In this study, the authors used 1-2 cc of 1% lidocaine from the syringe that was going to be used to perform local anesthesia. It was dripped right onto the skin just prior to locally anesthetizing that area subcutaneously in standard fashion. This was the intervention group. The control group proceeded with subcutaneous lidocaine injection for local anesthesia as we have typically performed it in the past.

481 patients were randomized to either the intervention or control group. The authors found that there was a statistically significant improvement in the primary outcome of procedural pain with the intervention group (dripped lidocaine) when assessed with the visual analog scale score. The control group rated their pain on the visual analog scale (VAS) at 16.6 +/- 24.8 mm, while the intervention group rated their pain on the same scale at 12.2 +/- 18.2 mm. These findings imply that this simple lidocaine dripping intervention led to a 26% relative reduction in procedural pain.

So here are my thoughts. The VAS goes from 0 to 100 mm. So, if you look at the pain ratings above, they are already starting out pretty low. In fact, the minimum clinically important difference in VAS score is approximately 10 mm, which was not met in the study. Also, the subgroup analysis shows that PICC insertion was the only procedure in which pain scores showed a statistically significant drop when lidocaine was dripped onto the skin pre-procedure. There wasn’t a statistically significant drop in pain scores with other procedures such as paracentesis or lumbar punctures. However, upon reviewing the data, this looks like it may have been the case due to under-powering. However, why not do it? It has very little to no downside. The lidocaine is already there in the syringe. You don’t have to cool it or prepare it in any different way. It is only a cc or two. Plus, this study shows that it may help. So, let’s all get out our syringes of lidocaine and drip a few drops out before these bedside procedures. It’s worth a try!

Source
Comparison of Two Lidocaine Administration Techniques on Perceived Pain From Bedside Procedures: A Randomized Clinical Trial. Chest. 2018 Oct;154(4):773-780. doi: 10.1016/j.chest.2018.04.018. Epub 2018 Apr 24.

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Reviewed by Clay Smith

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