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Thursday, March 22, 2012

Local anesthesia with lidocaine, buffered lidocaine, warmed buffered lidocaine, slow injection of lidocaine: publishing the results of perforating my own arm

I have done procedures using local anesthesia with subcutaneous lidocaine for over 20 years, and by the look on peoples' faces, I know that lidocaine stings. About 10 years ago I heard that adding a small amount of bicarbonate to the lidocaine took the sting away, but I never really had a chance to try it since my clinic never had any bicarbonate around. Just recently I went over the literature about reducing pain with injections and read that slowing the injection and warming the lidocaine is also effective in reducing the sting.

The pharmacy of my home hospital is very understanding and cooperative and they treated me to a vial of lidocaine 2%, a vial of 8.4% bicarb and all the insulin syringes I wanted. The insulin syringes have 28 g needles which are only slightly thicker than an eyelash so hardly hurt at all. I buffered the lidocaine with 1 part bicarb to 9 parts lidocaine. (It turns out that despite concerns that lidocaine would not be stable in a buffered solution, it actually is, if kept refrigerated: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2827006/) I injected about 0.1 ml subcutaneously into my left forearm for each variable.

My conclusions:
1. Lidocaine stings when injected quickly.
2. It pretty much doesn't sting at all if it is injected slowly, but it is very difficult to inject it slowly because a tiny syringe wants to give way quickly when pressure is applied to the plunger. I suspect I could get good at this if I practiced and used two hands.
3. After a little bit of lidocaine goes in, the rest of the injection, if not given too quickly, is painless.
4. Buffered lidocaine is less painful than straight lidocaine if injected quickly, and painless if warmed and injected slowly.
5. Warmed lidocaine (just warmed in the hands for a little while) injected slowly is quite painless. Warming it matters.

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