Local anesthetic solutions are very acidic and cause tissue irritation when injected. Addition of epinephrine to an anesthetic lowers the pH even more. McKay et al rationalize that positive hydrogen ions cause pain and that buffered solutions decrease pain due to a reduction in this cation resulting in reduced acidity. It is also thought that buffered anesthetics may diffuse more rapidly and inhibit pain perception more quickly. It is also recommended that multi-dose bottles of buffered solution be discarded within 24 hours of mixing to decrease the risk of possible contamination.
Sodium bicarbonate can produce a cloudy solution when added to lidocaine.
The cloudiness does not seem to decrease the effectiveness of the lidocaine. Pain reduction in local anesthetic administration through pH buffering. Micromedix Inc. Vol. Sodium bicarbonate attenuates pain on skin infiltration with lidocaine, with or without epinephrine.