Buffered Versus Plain Lidocaine
Moderate evidence supports the use of buffered lidocaine rather than plain lidocaine for local anesthesia because it could result in less injection pain.

Rationale
There were two high quality studies evaluating the use of buffered lidocaine for local anesthesia. Vossinakis et al (2004) studied 21 patients undergoing sequential, bilateral carpal tunnel release under local anesthesia. In each case one hand was anesthetized with lidocaine buffered with sodium bicarbonate and the other hand with plain lidocaine. Following infiltration the patients reported pain on a 100 mm visual analog scale. Those receiving the buffered solution reported less pain and the difference between the groups was statistically significant.
 
Watts et al (2004) randomized 64 patients to have a carpal tunnel release under local anesthesia using either plain lidocaine or lidocaine buffered with sodium bicarbonate. One minute after infiltration, and before application of a tourniquet, pain was measured on a 100 mm visual analog scale. Although patients who received buffered lidocaine reported less pain, the difference from those receiving the plain lidocaine was not statistically significant.