The Effects of Warming and Buffering on Pain of Infiltration of Lidocaine


Department of Emergency Medicine Albany Medical College 47 New Scotland Avenue Albany, NY 12208


Objectives: To investigate the effects of warming vs buffering, and warming with buffering, on the pain of lidocaine infiltration.

Methods: A randomized, double-blind clinical trial was conducted using volunteers aged 18 years or more and without an allergy to lidocaine. The study consisted of two parts, each comparing two solutions. The solutions for Part I were warm (38.9°C; 102°F) plain lidocaine and room-temperature buffered lidocaine. Warm buffered lidocaine and room-temperature buffered lidocaine were used for Part II. The subjects received two standardized 0.5-mL intradermal injections, one study solution in each forearm. Immediately after each injection, pain was assessed using a 100-mm visual analog pain scale. Pain scores were analyzed by the sign test, with significance defined as p < 0.05.

Results: Part I (n = 10): Nine subjects reported room-temperature buffered lidocaine to be less painful than warm plain lidocaine. Mean pain scores were 28 mm lower for room-temperature buffered lidocaine than they were for warm plain lidocaine (p < 0.01). Part II (n = 24): Eleven subjects found warm buffered lidocaine to be the least painful, 11 reported room-temperature buffered lidocaine to be the least painful, and two reported no difference. A mean pain score difference of 2.1 mm favoring warm buffered lidocaine was not statistically significant. Part II had a power of 80% to detect a 10-mm difference between the two solutions at a = 0.05.

Conclusion: To reduce the pain of lidocane infiltration, buffering is more effective than warming. Warming does not enhance buffering.