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

Abstract

T he infiltration of local anesthetics can be painful, and some of this pain may be attributed to the acidity of the anesthetic solution (1). In spite of the fact that a Cochrane study recommended buffering lidocaine with bicarbonate to decrease the pain of injection (2), the use of bicarbonate with lidocaine has only been adopted by a minority of practicing surgeons.One of the possible reasons that surgeons do not use buffered lidocaine is that most hospital pharmacies only premix bicarbonate and lidocaine without epinephrine, which is not as useful as buffered solutions containing epinephrine. In addition, there is a lack of knowledge about how exactly one is required to mix bicarbonate with the local anesthetic and what ratio of the mixture is ideal.The present study aimed to measure the pH of commonly used lidocaine-containing anesthetic agents available at our institutions and to validate the proper concentration of bicarbonate that should be added to lidocaine with epinephrine to neutralize its pH. The present article also aims to generate awareness among surgeons about how simple and inexpensive it is to mix bicarbonate with lidocaine to eliminate the acidity-related pain of local anesthetic injection. MethodsCommercially available solutions of 1% and 2% lidocaine, with and without epinephrine 1:100,000 were obtained (AstraZeneca Inc, Canada; Alveda Pharma, Canada). These were collected from various settings throughout a tertiary care institution (Dalhousie University, Halifax, Nova Scotia; Saint John, New Brunswick) to capture the possible effects of prolonged storage, previously opened bottles or improper storage conditions, to simulate true clinical use conditions. A total of 200 samples were collected (50 samples of each solution) from a variety of lots and ranging in expiration dates. Note was made of whether each multiuse vial was factory sealed or had been opened previously. The pH of each sample was measured using a temperaturecompensating pH meter (Model 98128, Hanna Instruments, Canada) with a resolution of 0.01 and a mean (± SD) accuracy ±0.05.To determine the proper concentration of bicarbonate for neutralization, additional samples of 1% lidocaine with 1:100,000 epinephrine were obtained, along with samples of 8.4% sodium bicarbonate (Hospira, Canada). Ten samples of each were collected. Aliquots of sodium bicarbonate (0.5 mL) were added to 20 mL of lidocaine and 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 tes...

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“…Epinephrine has a maximum dose of 50 mg/kg body weight and is added to LTA to achieve vasoconstriction, therefore, reducing blood flow. 7,11 Our study objectified a significant reduction in pain during injection of LTA diluted with sodium bicarbonate 1.4%. This is in line with a Cochrane review, which showed a reduction in pain during injection with alkalinization of LTA compared with LTA without alkalinization.…”

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