Layering Anesthesia May Benefit Deep Wounds

Topical anesthesia can eliminate the need for an anesthetic injection. “Layering,” a technique for administering topical anesthetics, has been studied mainly in children and in small wounds, but a Harvard study suggests that the practice might have a broader application.

Researchers compared a sequential layered application of anesthetic ingredients with 2% lidocaine infiltration in 100 patients with lacerations that needed to be sutured.

Three ingredients are usually used: lidocaine, epinephrine, and tetracaine. The researchers used only topical lidocaine and epinephrine (TLE) to limit toxicity. They soaked a piece of cotton just large enough to cover the laceration, plus 2 mm of surrounding skin, with TLE, placed it on the wound for 10 to 15 minutes, and then removed it. They then placed a second piece of TLE-soaked cot ton deeper inside the wound for 10 to 15 minutes and removed it.

For deeper wounds, they packed a third layer farther into the wound. When the wound edges showed a 3-mm-wide or greater area of vasoconstrictive pallor, the wound was considered anesthetized and ready for suturing.

In the controls, the time necessary for adequate anesthesia ranged from 1 to 12 minutes (mean, 5 minutes). The amount of lidocaine needed to achieve adequate anesthesia varied from 10 to 340 mg.
In the layered-anesthesia group, the time needed for anesthesia varied from 20 to 40 minutes, (mean, 29 minutes). One to four layer applications were needed. Half of the patients required three layers. Deeper lacerations were more time-consuming.

Although it took longer for the anesthesia to work, the TLE patients reported less pain and 66% of them reported no pain, compared with 0% of controls. On follow-up, 95% of the TLE patients rated their experience as “excellent,” com pared with 5% of the control patients.

Is layering worth the time? The renated painful injections, the risk of needle injury, and distortion of infiltrated wound tissue. They also felt that patient satisfaction justified the extra time. They waited 10 to 15 minutes for anesthesia to take effect for each layer. They also thought that the time could be reduced without compromising the effectiveness of anesthesia.

(Source: Am J Emerg Med 2007)