Effect of body locale and addition of epinephrine on the duration of action of a local anesthetic agent.

STUDY OBJECTIVE

Little information exists relating body locale to the duration of action of local anesthetics. We tested the duration of action of a local anesthetic with and without epinephrine at different body locales.

PARTICIPANTS

Twenty healthy volunteers aged 27 to 48 years (mean, 32.0 years).

INTERVENTIONS

In the first of two experiments (L), 20 subjects had 1 mL buffered 1% lidocaine injected intradermally on the forehead, hand, forearm, and calf. In the second experiment (LE), ten subjects were injected at the same sites with lidocaine containing epinephrine.

METHODS

Subjects ranked anesthesia by reaction to pinprick from 0 (complete) to 20 (none) on a scale with testing done every 15 (L) or 30 (LE) minutes and continued until no anesthetic effect was present. Duration of effective and of any anesthesia were times until score of more than 5 and of more than 19, respectively. Mean duration of anesthesia was compared by analysis of variance (between body areas) and paired two-tailed t-test (L vs LE). Significance was taken as P less than or equal to .05.

RESULTS

Anesthesia was significantly briefer for the face than for all other body locales by both indexes of duration and for both plain lidocaine and lidocaine with epinephrine (P less than .001 to P less than .05). Anesthesia with epinephrine lasted significantly longer than with lidocaine alone at all body locales and for duration of both effective or any anesthesia (P = .0001 to P = .001). Based on 95% confidence interval limits, the duration of anesthesia at other body locales is predicted to be 1.3- to 3.2-fold that on the face. Confidence interval analysis indicated that addition of epinephrine to lidocaine increases the duration of anesthetic action by 1.3- to 13.0-fold that of lidocaine alone.

CONCLUSION

The duration of action of local anesthesia is considerably shorter for the face than for other body areas. Epinephrine significantly increases the duration of action of lidocaine at all body locales.