Effect of pH modification by bicarbonate on pain after subcutaneous lidocaine injection

OBJECTIVE: TO quantify the pain experienced on subcutaneous injection of lidocaine, lidocaine with sodium bicarbonate (NaHCO3) and saline. DESIGN: A double-blind randomized prospective study. SETTING: A clinical research unit in a university-affiliated hospital: PARTICIPANTS: Forty-two healthy adult volunteers who did not have a history of adverse reaction to lidocaine or peripheral neuropathy and were not pregnant. The study was performed in two phases. In Phase 1, 1 mL each of thee solutions (2 mL of 8.4% NaHCO3 in 20 mL 1% lidocaine, 2 mL saline in 20 mL lidocaine and saline alone) were injected by an investigator, blinded as to the identity of the solutions, in random order to five volunteers to measure onset and duration of anesthesia and the perceived pain on injection. In Phase 2, 37 volunteers mere injected with the three solutions in random order, by an investigator blinded as to the identity of the solutions. MAIN OUTCOME MEASURE: Pain on injection measured with the visual analogue scale. RESULTS: There were no clinically significant differences between onset and duration of action of lidocaine with and without NaHCO3, as determined by Kruskal-Wallis one-way analysis of variance and the Wilcoxon signed-ranks test. Injection of lidocaine with NaHCO3 was significantly less painful than injection of plain lidocaine (p = 0.041). Injection of saline was the most painful. CONCLUSION: The addition of NaHCO3 to lidocaine produces significant reduction in pain experienced on injection without significantly affecting the onset or duration of action.