Preprocedure Patient Preparation

There are few complications with field and nerve blocks. The benefits of the blocks versus the alternatives (e.g., general anesthesia, no anesthesia, and Bier block) may be explained. Depending on the agent used, the duration of anesthesia may be prolonged, and the patient should be informed of the expected length of action. In rare instances a nerve could be traumatized, but long-term consequences are rare. Any precautionary advice, such as avoidance of heat or cold after the procedure, should be given to the patient. The possibility of paresthesia during the injection should be explained.

Technique

Field Block

The technique of administering a field block is similar to the technique discussed for local anesthetics (see Chapter 4, Local Anesthesia). In this instance, however, the area to be incised is spared from the injection. Rather, the area around the site is injected (see Fig. 8-1). Repeat injections are made until the entire border of the field has been infiltrated. Allowing 5 to 10 minutes for the block to take effect improves the resulting anesthesia.

Nerve Block

1 Before beginning any peripheral nerve block, perform a neurologic examination of the area to be anesthetized and document the results in the medical record. If any neurologic defect is present, include a description of it in the document of informed consent for the procedure, and have the patient sign a statement agreeing that the defect was present before the administration of the anesthetic.

2 Identify the appropriate nerve(s) and anatomic sites to accomplish the block.

3 Carefully clean and prepare the skin over the injection site in a sterile fashion.

4 Draw up the anesthetic. Usually a 25- to 30-gauge needle can be used to inject the anesthetic. The amount of anesthetic used varies depending on the location of the nerve.

5 Insert the needle into the site, withdrawing the plunger slightly to test for intravascular placement of the needle and moving the needle if necessary to avoid intravascular injection. If the patient experiences paresthesia, withdraw the needle slightly because it is probably within the nerve. The goal is to inject perineurally, not into the nerve itself. If no paresthesia is noted at the expected site, confirm that there is no potential for intravascular injection and slowly inject the anesthetic. If the proper site has been identified, often as little as 1 or 2 mL will provide an excellent anesthetic field.

6 Allow 5 to 15 minutes for the block to take effect. Confirm anesthesia to pinprick before making an incision.

Common Nerve Blocks

Also see Chapter 9, Oral and Facial Anesthesia.

1 Digital block of finger or toe and nail anesthesia (Fig. 8-2): Use 4 to 6 mL of 1% to 2% lidocaine without epinephrine for each finger, and 6 to 8 mL of the same for toes. Insert the 25- to 30-gauge,

-inch needle fully into the skin at the base of the finger or toe into the web space and inject 1 mL (see Fig. 8-2B). Repeat this on the other side unless it is the first or fifth digit. Then insert the needle perpendicular to the bone at the base of the digit, touch the bone, and pull back a little (see Fig. 8-2B and D). Inject 1 mL into the lateral aspect, then 1 mL across the dorsal and another 1 mL under the ventral surfaces in the subcutaneous space. Repeat this on the contralateral side of the digit. Alternatively, the needle can be inserted dorsally, then ventrally (see Fig. 8-2E). The dorsal digital nerves in both instances lie close to bone. As the bone is touched with the needle tip, withdraw 1 or 2 mm and inject the solution.