Role of Sodium Bicarbonate in Local Anesthetics for Pain Reduction
The addition of sodium bicarbonate to local anesthetic, particularly lidocaine with epinephrine, is strongly recommended to decrease the pain of delivery by subcutaneous or intradermal infiltration, with approximately 2 out of 3 patients experiencing a 20-40% reduction in injection pain compared to plain lidocaine with epinephrine. 1
Mechanism and Benefits
- Buffering local anesthetics with sodium bicarbonate raises the pH of the solution, which decreases the burning sensation during injection and reduces patient discomfort 1
- Multiple well-designed randomized controlled trials have consistently demonstrated that buffered lidocaine solutions cause significantly less pain than unbuffered solutions 1, 2
- The pain reduction effect is substantial enough that buffering is particularly beneficial for procedures involving sensitive areas such as the face, large areas requiring infiltration, and for pediatric patients 2
Preparation Guidelines
- For lidocaine with epinephrine, the recommended preparation involves mixing 8.4% sodium bicarbonate with 1% lidocaine with epinephrine in a 1:9 or 1:10 ratio by volume 1
- The concentrations of sodium bicarbonate used in studies varied from 10 to 100 mEq/L, with both 1:9 and 1:10 ratios found to be effective in clinical practice 1
- For procedures requiring immediate use, buffered solutions should be prepared just prior to injection for optimal effectiveness 3
Specific Applications and Considerations
- Buffering is particularly effective for lidocaine but is not recommended for bupivacaine, as precipitation of the anesthetic may lead to decreased efficacy 1
- For paracervical blocks, combining 2 mL of sodium bicarbonate with 18 mL of 1% lidocaine for a 20 mL block can effectively decrease the burning sensation during injection 1
- In dental procedures, buffered anesthetics have been shown to reduce pain during palatal injections, which are typically quite painful 4
Important Caveats and Limitations
- Buffered solutions containing epinephrine have limited stability - the concentration of epinephrine decreases by approximately 25% per week after the addition of 100 mEq/L of sodium bicarbonate 1
- For long-term storage, adrenaline-containing buffered solutions require refrigeration in closed containers 2
- Some studies suggest that diluting lidocaine with normal saline in a 1:10 ratio may be superior to buffering for pain reduction, though this is not the consensus view in current guidelines 5
Optimizing Technique
- Using a smaller gauge needle (30-gauge vs. 25-gauge) in combination with buffered lidocaine can further reduce injection pain 6
- The combination of buffering with other pain-reduction techniques such as slow infiltration rate, vibrating the skin, use of warm solution (40°C), or cold air skin cooling can provide additional comfort during local anesthetic administration 1, 7
- For maximum effectiveness, allow sufficient time for the buffered anesthetic to take effect before beginning the procedure 7
Buffering local anesthetics with sodium bicarbonate represents a simple, effective technique that significantly improves patient comfort during procedures requiring local anesthesia, with strong evidence supporting its routine use in clinical practice.