Minimizing the pain of local anesthesia.

We studied the effect of depth of lidocaine injection into the skin, rate of injection, and temperature of the solution on pain experienced. The intervals of onset and duration of anesthesia were also evaluated. Intracutaneous instillation of lidocaine at body temperature (37 degrees C) is no less painful than injection at room temperature (21 degrees C), but superficial wheal-producing dermal injection is uniformly much more painful than that into the deep dermal-subcutaneous tissue region. Rapid injection almost always hurts more than slow. Full anesthesia to pinprick is produced immediately with superficial injection and is present 5 to 6 minutes after deep injection. We suggest that the best method for minimizing the discomfort of inducing local anesthesia is to use a syringe fitted with a No. 30 needle and to inject the smallest amount necessary slowly into the deep dermal-subcutaneous tissue as the needle is being slowly withdrawn.