Peripheral Nerve Blocks and Field Blocks

CHAPTER 8 Peripheral Nerve Blocks and Field Blocks



Many ambulatory procedures lend themselves well to local anesthesia with a field block or a peripheral nerve block. A field block is a method of providing anesthesia to a relatively small area by injecting a “wall” of anesthetic solution across the path of the nerves supplying the operative field (Fig. 8-1). Instead of the injection being made directly into the area of the procedure, it is made into the soft tissue some distance away, where the nerves are situated. Advantages include longer duration of anesthesia and no distortion of the operative field.



A nerve block is the infiltration of a local anesthetic near the nerve branch supplying sensation to a particular area. Blocking a nerve provides longer duration of anesthesia than that obtained with local cutaneous infiltration. Knowledge of the anatomy of peripheral nerves and a scrupulous sterile technique are important for successful peripheral nerve blocks. Use of this technique may reduce the amount of anesthetic needed, reduce distortion of tissues, and allow palpation of pathology to be excised.


Ultrasonography-guided nerve blocks may increase block quality parameters and decrease the potential complications (see Chapter 185, Musculoskeletal Ultrasonography).


In some sites (e.g., the breast) a nerve block cannot be obtained, and thus the field block is the only reasonable alternative. However, where possible, the nerve block may be the procedure of choice.


Also see Chapter 9, Oral and Facial Anesthesia.







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










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, image-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.

May 14, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Peripheral Nerve Blocks and Field Blocks
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