As of late January 2021 there are widespread shortages of 1% lidocaine with epinephrine. This is due to manufacturing delays from Fresenius Kabi and Pfizer. Right now you can still (likely) get 1% lidocaine alone, along with 2% lidocaine with epinephrine. Bupivacaine is also an option. I wanted to briefly answer a few questions that had been bouncing around my head for a while in this post.

Why add epinephrine to local anesthetics

Lidocaine with epinephrine is a great option for local anesthesia that combines numbing with regional vasoconstriction. Vasoconstriction may lead to less bleeding, and it also means that the local anesthetic will stay, well, local, longer therefore increasing the duration of action.

Wait, aren’t anesthetics with epinephrine dangerous to digits?

I was taught back in med school and residency that you should never use lidocaine with epinephrine on fingers, toes, nose, ears, lips, or penises. the circulation is too distal they said – you could risk gangrene, which is bad. It turns out that a lot of this concern stems from reports of local anesthetic associated gangrene in the mid-1900s. Initially it was thought that the epinephrine in procaine + epinephrine preparations was responsible for the damage. In reality it was more likely that was the procaine itself – as it is naturally quite acidic with a pH of 3.6, but can become substantially more acidic (pH as low as 1) if it sits on the shelf unused for awhile. As an aside the acidity is the main reason for the initial “burning” of local anesthetics. Lidocaine has a pH of 4.4 and is shelf stable. Additionally, reviews from early this century (Denkler et al.) as well as the fact that no one has lost a digit with an accidental on-the-job epinephrine auto-injector poke.

Is there really that big of a difference between 1% and 2% lidocaine?

The short and sweet version is that there is no difference in pain reduction. However, in smaller patients the more highly concentrated 2% lidocaine (20mg/mL versus 10mg/mL) runs the risk of hitting that toxicity threshold with half the volume. That’s why in younger children 1% lidocaine is preferred.

Hol’ up playa! Some folks like bupivacaine too!

Okay, so I’ve always used lidocaine. it’s what I was taught to use, have become comfortable with, and locally, it is our most well-stocked anesthetic that has the highest level of familiarity across provider categories. The classic differentiation of the two is that lidocaine has faster onset, and bupivacaine a longer duration of action. There are many local anesthetics to choose from, but few concise comparative studies. Here is a summary table of some properties of lidocaine and bupivacaine preparations with and without epinephrine. I assembled it after reviewing a number of sources.

Anesthetic	Concentration	Onset in minutes	Duration in hours	Dosing
1% Lidocaine	10mg/mL	<2	1.5 to 2	4 mg/kg, not to exceed 280 mg or 28mL
2% Lidocaine	20mg/mL	<2	1.5 to 2	4 mg/kg, not to exceed 140 mg or 14mL
1% Lidocaine with Epinephrine	1% lidocaine, 1:100,000 or 1:200,000 epinephrine	<2	2 to 6	7 mg/kg, not to exceed 500 mg or 50mL
2% Lidocaine with Epinephrine	2% lidocaine, 1:100,000 or 1:200,000 epinephrine	<2	2 to 6	7 mg per kg, not to exceed 250 mg or 25mL
Bupivacaine	0.25%	5	2 to 4	2 mg/kg in neonates and 2.5 mg/kg in children not to exceed 175mg/dose. May repeat in 3 hours; max of 400 mg in 24 hours
Bupivacaine with Epinephrine	0.25%	5	2 to 4	2 mg/kg in neonates and 2.5 mg/kg in children not to exceed 175mg/dose. May repeat in 3 hours; max of 400 mg in 24 hours

Does duration matter?

It does – and perhaps not for the reasons you’re suspecting. Consider the following scenario. You are repairing a lip laceration that crosses the vermilion border in a 21 month old. You will be sedating the child and performing a mental nerve block. The repair goes well and everyone is pleased with the cosmetic result. The child recovers from sedation and they are immediately grabbing at their lower lip? Why? Because it feels numb and weird! In this situation a shorter duration of action (lidocaine) would be of benefit because the toddler would be pawing and licking at their numb lip, and potentially knocking out a suture or two, for a shorter period of time.

Don’t forget about buffering your anesthetic with bicarb

And finally, I’d be remiss if I didn’t drive home the point that buffering your lidocaine with sodium bicarb and make the injection less painful – because the solution is less acidic. The “recipe” is:

1 mL 8.4% sodium bicarbonate : 10 mL 1% lidocaine with 1:100,000 epinephrine

In your EMR you may be able to order “buffered lidocaine” or, separately, order 1 mL 8.4% sodium bicarbonate, plus your lidocaine of choice (10 mL). Fill a syringe first with the 1mL of bicarbonate, then add the 10 mL of lidocaine. Flip the syringe over several times to mix (no need to shake vigorously). Label according to your local practices. This can be “shelf stable” for up to 24 hours.