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. 2012 Summer;20(2):71-3.
doi: 10.1177/229255031202000207.

How acidic is the lidocaine we are injecting, and how much bicarbonate should we add?

Simon G Frank  1 , Donald H Lalonde
Affiliations

How acidic is the lidocaine we are injecting, and how much bicarbonate should we add?

Simon G Frank et al. Can J Plast Surg. 2012 Summer.

Abstract
in English, French

Background: The infiltration of local anesthetics can be painful, which is likely due, in part, to their acidity. In spite of a Cochrane study that recommended neutralizing lidocaine with bicarbonate to decrease the pain of injection, not many surgeons have adopted the practice, and there are many 'recipes' for how much bicarbonate one should add.

Objective: To determine the acidity of lidocaine and the correct ratio of bicarbonate that should be added to neutralize lidocaine to achieve body pH.

Methods: Fifty samples each of commonly used anesthetics (lidocaine 1% and 2%, with and without epinephrine 1:100,000) were obtained and tested for pH. Data were also analyzed according to whether the vials had been previously opened. Ten additional samples of lidocaine 1% with 1:100,000 epinephrine were titrated against sodium bicarbonate 8.4% and tested for pH and the presence of precipitate.

Results: A solution of 1% lidocaine with 1:100,000 epinephrine had a mean (± SD) pH of 4.24±0.42, and 2% lidocaine with 1:100,000 epinephrine had a mean pH of 3.93±0.43. Plain 1% lidocaine had a pH of 6.09±0.16, and plain 2% lidocaine had a pH of 6.00±0.27. Epinephrine-containing solutions were more acidic when they had been previously opened. One per cent lidocaine with epinephrine required 8.4% sodium bicarbonate at a ratio of 1.1 mL:10 mL to 1.8 mL:10 mL to achieve the target tissue pH of 7.38 to 7.62.

Conclusion: Lidocaine with epinephrine was approximately 1000 times more acidic than subcutaneous tissue. The addition of bicarbonate to the local anesthetic solution is simple to perform and is inexpensive. The proper volume ratio of 8.4% sodium bicarbonate to 1% lidocaine with 1:100,000 epinephrine is approximately 1 mL:10 mL. Surgeons should be more aware of the simplicity and value of buffering with bicarbonate to decrease the pain of injection.

Historique: L’infiltration d’anesthésiques locaux peut être douloureuse, ce qui est probablement causé, en partie, par leur acidité. Même si une étude antérieure a recommandé de neutraliser la lidocaïne avec du bicarbonate pour atténuer la douleur de l’injection, peu de chirurgiens ont adopté cette pratique, et il existe de nombreuses « recettes » de la quantité de bicarbonate à ajouter.

Objectif: Déterminer l’acidité de la lidocaïne et le bon ratio de bicarbonate à y ajouter pour la neutraliser et parvenir au pH corporel.

Méthodologie: Les chercheurs ont obtenu 50 échantillons de chacun des anesthésiques couramment utilisés (lidocaïne 1% et 2%, avec et sans dilution d’adrénaline 1:100 000) et en ont vérifié le pH. Ils ont également analysé les données pour vérifier si les fioles avaient été ouvertes au préalable. Ils ont titré dix échantillons supplémentaires de lidocaïne1% contenant de l’adrénaline 1:100 000 à l’aide de bicarbonate de sodium 8,4 %, puis ont vérifié le pH et la présence de précipité.

Résultats: Une dilution 1:100 000 de lidocaïne 1 % contenant de l’adrénaline avait un pH moyen (±ÉT) de 4,24±0,42, et la lidocaïne 2 % contenant de l’adrénaline, un pH de 3,93±0,43. La lidocaïne 1 % seule avait un pH de 6,09±0,16, et la lidocaïne 2 % seule, un pH de 6,00±0,27. Les solutions contenant de l’adrénaline étaient plus acides lorsqu’elles avaient été ouvertes au préalable. De la lidocaïne 1 % contenant de l’adrénaline devait contenir 8,4 % de bicarbonate de sodium à une dilution de 1,1:10 à 1,8:10 pour parvenir au pH tissulaire ciblé de 7,38 à 7,62.

Conclusion: La lidocaïne contenant de l’adrénaline était environ 1 000 fois plus acide que les tissus sous-cutanés. Il est simple et peu coûteux d’ajouter du bicarbonate à une solution anesthésique locale. La bonne proportion entre le volume de bicarbonate de sodium 8,4 % et la lidocaïne 1 % accompagnée d’adrénaline 1:100 000 est d’environ 1:10. Les chirurgiens devraient connaître la simplicité et la valeur d’utiliser une solution tampon de bicarbonate pour atténuer la douleur de l’injection.

Keywords: Anesthetics; Epinephrine; Lidocaine; Local; Pain of injection; pH.

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Figures

Figure 1)
Figure 1)
pH of lidocaine 1% and 2%, with and without 1:100,000 epinephrine. Error bars represent 95% CIs
Figure 2)
Figure 2)
pH of factory sealed versus previously opened multiuse vials of lidocaine. Error bars represent 95% CIs
Figure 3)
Figure 3)
Titration curve of 8.4% sodium bicarbonate against 1% lidocaine with 1:100,000 epinephrine. Dotted lines represent tissue pH (7.38 to 7.62) (3). Error bars represent 95% CIs
Figure 4)
Figure 4)
Bicarbonate 8.4% is readily available and costs less than CAD$5 per bottle. It has no preservative, and is therefore usually discarded at the end of the day
Figure 5)
Figure 5)
Syringes with 1 mL 8.4% bicarbonate (top) and with 1 mL sodium bicarbonate and 10 additional mL 1% lidocaine with 1:100,000 epinephrine for a total of 11 mL of solution (bottom)
See this image and copyright information in PMC

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