Cutaneous Anesthesia

Anesthesia is required for excisional and electrosurgical procedures on the skin. If anesthesia is needed only momentarily (such as for a simple incision and drainage), Freon or ethyl chloride sprays can be used. For all longer procedures, injected anesthesia should be used. Almost all dermatologists currently use lidocaine (Xylocaine) because of its almost instantaneous effect and because it rarely causes allergic reactions. It can be used alone, but it is also prepackaged with epinephrine for use when better hemostasis or longer duration of action is desired. Lidocaine with epinephrine probably should not be used for anesthesia of the fingers or toes because of the possible development of digital ischemia.

Lidocaine in a 0.5% to 1.0% concentration is injected intradermally with a tuberculin syringe and a 26- to 30-gauge needle. Usually, 0.5 to 1.0 ml will be all that is necessary to obtain an anesthetized field 2 cm in diameter. When injecting the anesthesia, care should be taken that the tissue is not overly distended, as this tends to interfere with good suture closure. A burning discomfort is noticeable during injection. The pain of injection can be slightly reduced by using a slow injection rate or can be minimized appreciably by using buffered lidocaine. Buffered lidocaine is prepared by adding sodium bicarbonate to lidocaine such that a final concentration of 80 to 100 mq/liter is reached. This buffered solution should be made up weekly, since the effectiveness of epinephrine is gradually lost as the buffered preparation ages.

Allergic reactions to lidocaine are extraordinarily rare, but occasionally patients will indicate that for one reason or another they cannot tolerate lidocaine. In most instances, careful checking will reveal that their problem occurred with procaine (Novocaine) rather than with lidocaine. Cross reactions between these two products are not a problem. However, if there is doubt about the nature of a previous reaction, an alternate anesthetic must be chosen. Injectable diphenhydramine (Benadryl) or even normal saline can be used, but neither approaches the effectiveness of lidocaine. Toxic side effects can occur when very large amounts of lidocaine are used, but this is not often a consideration for minor surgery of the skin.

Children do not, of course, tolerate injections well. A topical lidocaine/ prilocaine cream (Eutectic Mixture of Local Anesthetics (EMLA)) is available and works fairly well if it is left in place long enough. This product has just been approved by the Food and Drug Administration for use in the United States.

This entry was posted on Monday, December 24th, 2007 at 5:13 am and is filed under Diagnostic and Therapeutic Techniques. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.