The effect of pH buffering on reducing the pain associated with subcutaneous infiltration of bupivicaine.

The authors propose that pH buffering of bupivicaine with sodium bicarbonate reduces the pain associated with its local subcutaneous infiltration. In a double-blind, prospective study, 62 healthy adult volunteers received a 0.5 mL subcutaneous infiltration of 0.5% buffered bupivicaine into the dorsum of a randomly chosen hand. The pH was adjusted to 7.0 by adding 0.05 mL of sodium bicarbonate (1 mEq/L [corrected]) to 10 mL vials of commercially available bupivicaine (1:200 dilution). The control hand was injected with the same amount of unbuffered agent. Pain was scored after each infiltration using a nonsegmented visual analogue scale. Student's t-test for paired measurements was used to analyze intergroup pain score differences. Forty-three subjects (69%) reported less pain with buffered bupivicaine and only 17 (27%) noted a modest increase: two subjects (3%) reported no difference. The mean pain score for the buffered agent was 22 mm compared with 30 mm for the control. The mean difference (control-experimental) was 8 mm (t = 4.64, df = 61, P less than .001). The authors conclude that the addition of sodium bicarbonate to bupivicaine reduces the pain associated with its local infiltration.