PAIN OF LOCAL-ANESTHETICS - RATE OF ADMINISTRATION AND BUFFERING

Study objective: To determine the impact of administration rate and bu ffering on the pain associated with subcutaneous infiltration of lidoc aine. Methods: Forty-two adult volunteers employed at a tertiary care center participated in this prospective, single-blinded study. Each su bject received four lidocaine injections prepared and administered as follows: slow, buffered (SE); slow, unbuffered (SU:); rapid, buffered (RE); rapid, unbuffered (RU). Buffering was accomplished by mixing 1% lidocaine with 8.4% sodium bicarbonate in a 9:1 ratio. Slow administra tion was 30 seconds and rapid was 5 seconds. Needle size (27-gauge), i njection depth (.25 inch), lidocaine volume (1.0 mt), and temperature (room) were the same for each of the four injections. In all four cond itions, the needle remained in the forearm for 30 seconds, to ensure b linding. The main out come measure was the mean pain score for each co ndition, as recorded on a 10-cm visual analog scale. Results: The lowe st pain scores (mean+/-SE) were recorded for the SU and SE conditions at 1.49+/-.29 and 1.48+/-.26, respectively, and they were significantl y lower than the scores for RE (2.34+/-.28; P<.01) or RU (3.11+/-.33; P<.001). Each of the slow conditions was reported to be the ''least pa inful'' of the four significantly more often than either rapid conditi on. Conclusion: This is the largest blinded study to assess administra tion rate and the pain of a local anesthetic. We found that administra tion rate had a greater impact on the perceived pain of lidocaine infi ltration than did buffering.