Buffering lidocaine

Lidocaine hurts when you inject it into a patient. It hurts not just because we have to poke through the skin with a needle (this post won’t go into topical anesthetics, J-Tip etc,.) but mostly because lidocaine is acidic. In fact, according to Frank et al. “lidocaine with epinephrine [is] approximately 1000 times more acidic than subcutaneous tissue.” Per the same study here are some estimates of the mean pH of common injectable anesthetics.

  • 1% lidocaine with 1:100,000 epinephrine pH = 4.24±0.42
  • 2% lidocaine with 1:100,000 epinephrine pH = 3.93±0.43
  • 1% lidocaine pH = 6.09±0.16,
  • 2% lidocaine pH = 6.00±0.27

There are some advantages to lido w/ epinephrine, but clearly the solutions are more acidic. And either way, epi or not, the anesthetic is far below physiologic pH (7.35-45). We can increase the pH of our lidocaine solutions, and decrease the pain by adding 8.4% sodium bicarbonate solution to the mix as shown in a randomized trial from Matsumoto et al. A previous study from Denmark, as well as Frank et al’s established that the following ratio of 8.4% bicarbonate to lidocaine to be:

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

Their work shows that in general a 1:10 ratio would get lido w/ epi (again, the more acidic solution at ph approximately 4) to a more “physiologic” pH of 7.3-7.6. You won’t excessively buffer lidocaine without epi using this ratio either. In order to accomplish this do the following.

  • Order “buffered lidocaine” if your institution has this in the EMR (like mine) 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 solution will be stable for many hours – possibly up to 24 – but you shouldn’t plan on storing it in the pharmacy this way, or pre-mixing in the ED. And yes, you can do 0.5 mL bicarb and 5 mL lidocaine as well.

References

Frank et al. How acidic is the lidocaine we are injecting, and how much bicarbonate should we add? Can J Plast Surg. 2012 Summer; 20(2): 71–73. PMCID: PMC3383550

Momsen OH et al. Neutralization of lidocaine-adrenaline. A simple method for less painful application of local anesthesia. Ugeskr Laeger. 2000 Aug 14;162(33):4391-4.

Matsumoto et al. Reducing the discomfort of lidocaine administration through pH buffering. J Vasc Interv Radiol. 1994 Jan-Feb;5(1):171-5.

By |2017-11-20T09:35:04+00:00November 20th, 2017|Pharmacology, Procedures|

About the Author:

Brad Sobolewski, MD, MEd is an Associate Professor of Pediatric Emergency Medicine and an Assistant Director for the Pediatric Residency Training Program at Cincinnati Children's Hospital Medical Center. He is on Twitter @PEMTweets and authors the Pediatric Emergency Medicine site PEMBlog. All views are strictly my own and not official medical advice.

2 Comments

  1. Robert (Bo) Kennedy, MD, St. Louis Children's Hospital December 14, 2017 at 1:01 PM

    Fully agree on benefits of buffering lidocaine. Buffered lidocaine with or without epinephrine has been shown to be stable up to 28 days when refrigerated. [Elena Pascuet, Buffered Lidocaine Hydrochloride Solution With and Without Epinephrine: Stability in Polypropylene Syringes. Can J Hosp Pharm. 2009 Sep;62(5):375-80.] It was also found clinically effective after stored for 1 week at room temperature. [Joel Bartfield, Buffered Lidocaine as a Local Anesthetic: An Investigation of Shelf Life. Ann Emerg Med 1992;21:16-19]. Our pharmacy buffers lidocaine and dispenses in 0.5 ml syringes for I.V. insertion and in 5 ml syringes for lacerations, L.P.s, etc.

    • Brad Sobolewski December 14, 2017 at 1:03 PM

      Thanks for the comment and references! Those protocols would seem to be easy to adopt and enable Emergency Departments to have ready-made admixed buffered lido on hand.

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