Alkalinization of Local Anesthetics 

Disclaimer: This article is intended solely for informational and educational purposes only. It does not constitute medical advice.

Alkalinization of local anesthetics is the process of raising the pH of an anesthetic solution, usually by adding sodium bicarbonate before injection. Local anesthetics such as lidocaine are weak bases and are commonly prepared in acidic solutions to improve their stability, especially when epinephrine is included. In an acidic solution, a larger proportion of the anesthetic exists in an ionized form that does not easily cross the nerve membrane. Raising the pH increases the amount of anesthetic in its nonionized form, allowing it to move more readily through the nerve membrane and reach its site of action. This is the main scientific reason for buffering local anesthetic solutions (1). 

One of the most useful effects of alkalinization is a reduction in the discomfort caused by the injection of local anesthetics. Commercial local anesthetic solutions can cause a burning or stinging sensation as they enter the tissues, partly because of their acidity. Evidence from systematic reviews suggests that buffering lidocaine with sodium bicarbonate can reduce injection pain (2). This may be especially helpful when anesthetic is being infiltrated into sensitive areas or when patient comfort is an important concern. 

Alkalinization may also affect how quickly local anesthetics begin to work. Because the nonionized forms of anesthetic drugs cross nerve membranes more easily, increasing their pH may allow anesthesia to develop more rapidly. However, the clinical effect on onset time is not as consistent as the effect on injection pain. Reviews of the available evidence have found that some studies report faster onset or improved anesthetic effectiveness, whereas others show little difference between buffered and nonbuffered solutions (3). Factors such as the type of local anesthetic, injection site, tissue condition, and anesthetic technique may influence the response. 

Buffering may be particularly relevant in inflamed or infected tissues. These tissues often have a lower pH than normal tissue, which can reduce the amount of local anesthetic able to enter the nerve. This helps explain why local anesthesia may be less effective in areas of inflammation. Raising the pH of the anesthetic solution may improve the amount of drug available to cross the nerve membrane, although alkalinization does not completely overcome the difficulties associated with anesthetizing inflamed tissue. Other factors, including increased nerve sensitivity and tissue swelling, can also contribute to reduced anesthetic effectiveness (3). 

In practice, lidocaine with epinephrine is often alkalinized by adding a small amount of 8.4% sodium bicarbonate shortly before administration. A commonly described mixture is approximately nine or ten parts local anesthetic to one part bicarbonate. Caution is necessary to prevent the addition of too much bicarbonate, which can cause the anesthetic to precipitate. Buffering can also affect the stability of the solution, so fresh preparation is important. Alkalinization does not change the maximum safe dose of local anesthetics and does not eliminate the risk of systemic toxicity. 

Overall, alkalinization is a simple method of modifying the solutions of local anesthetics and is consistently associated with reduced pain during injection (2). It may also improve onset or anesthetic effectiveness in certain situations, although these effects are less predictable. When prepared appropriately, bicarbonate-buffered local anesthetic can improve patient comfort without changing the basic principles of safe local anesthetic use. 

References  

1. Cepeda MS, Tzortzopoulou A, Thackrey M, Hudcova J, Arora Gandhi P, Schumann R. Adjusting the pH of lidocaine for reducing pain on injection. Cochrane Database Syst Rev. 2010;(12):CD006581. Published 2010 Dec 8. doi:10.1002/14651858.CD006581.pub2 

2. Hanna MN, Elhassan A, Veloso PM, et al. Efficacy of bicarbonate in decreasing pain on intradermal injection of local anesthetics: a meta-analysis. Reg Anesth Pain Med. 2009;34(2):122-125. doi:10.1097/AAP.0b013e31819a12a6 

3. Guo J, Yin K, Roges R, Enciso R. Efficacy of sodium bicarbonate buffered versus non-buffered lidocaine with epinephrine in inferior alveolar nerve block: A meta-analysis. J Dent Anesth Pain Med. 2018;18(3):129-142. doi:10.17245/jdapm.2018.18.3.129