Adding Bicarbonate to Lidocaine with Epinephrine for Local Anesthesia
Yes, it is safe and beneficial to add sodium bicarbonate to a local anesthetic mixture of lidocaine and epinephrine, and this practice reduces injection pain while maintaining anesthetic efficacy.
Safety Profile
Adding bicarbonate to lidocaine-epinephrine mixtures is safe and does not compromise the effectiveness of the anesthetic or vasoconstrictor properties 1. The American Academy of Dermatology guidelines support mixing local anesthetics with various additives for dermatologic procedures, and no safety concerns have been raised regarding bicarbonate addition 2.
Rationale for Bicarbonate Addition
pH Considerations
- Lidocaine 1% with epinephrine 1:100,000 has a mean pH of 4.24, making it approximately 1000 times more acidic than subcutaneous tissue (pH 7.38-7.62) 3
- Lidocaine 2% with epinephrine is even more acidic with a pH of 3.93 3
- This extreme acidity is the primary cause of injection pain 3
Pain Reduction Benefits
- Buffering with sodium bicarbonate significantly decreases the pain of injection 3, 4
- Studies show that 65% of patients experience less pain with buffered solutions compared to unbuffered solutions 4
- Bicarbonate concentrations of 40-100 meq/L of anesthetic solution cause significantly less pain than unbuffered solutions 5
Recommended Mixing Ratio
The proper volume ratio is approximately 1 mL of 8.4% sodium bicarbonate to 10 mL of 1% lidocaine with 1:100,000 epinephrine 3. This ratio achieves the target tissue pH of 7.38-7.62 3.
Alternative concentrations that have been studied:
- 0.06 meq/mL sodium bicarbonate (approximately 1:5 ratio of bicarbonate to lidocaine) has been shown to decrease onset time of anesthesia 6
- A 1:5 ratio (bicarbonate:lidocaine) has demonstrated significant pain reduction in digital anesthesia 7
Important Caveats
Epinephrine Stability
- Epinephrine concentration declines approximately 25% per week in buffered solutions containing 100 meq/L sodium bicarbonate 5
- Buffered solutions should be prepared fresh on the day of use and not stored long-term 5
Precipitate Formation
- Monitor for precipitate formation when mixing, though this is rare at recommended ratios 3
- Use clear solutions only; discard if cloudiness or precipitate develops 3
Clinical Application
The addition of bicarbonate is:
- Simple to perform 3
- Inexpensive 3
- Compatible with standard dermatologic procedures including biopsies, excisions, and wound closures 2
- Safe for use in digits and other anatomical locations where lidocaine with epinephrine is appropriate 1
Mix bicarbonate immediately before use, use the 1:10 ratio as your standard approach, and discard any unused buffered solution at the end of the day 3, 5.