Field block anesthesia describes the infiltration of local anesthetic in a circumferential pattern around a surgical site. Like nerve blocks, field blocks are used to anesthetize large areas of skin. Field blocks differ from nerve blocks in that more than one nerve experiences interruption of the nerve transmission. The technique permits large areas to be anesthetized, and it is useful for large dermatologic procedures. The field block does not disrupt the architecture of the surgical site and often is administered for facial or cosmetic repairs.
Infected tissues such as areas of cellulitis or abscesses can prove difficult to anesthetize because the acidic environment of an abscess can hydrolyze the anesthetic and render it ineffective. Field block provides adequate anesthesia around an abscess by working in the normal surrounding tissue. Localized structures are often amenable to field block technique. Facial (e.g., cheek, eyelid, nose, pinnae) and genital structures (e.g., penis, perineum) are particularly well suited for this technique. The administration of anesthetic into distensible skin surrounding taut skin (e.g., tissues surrounding the nose or ear) permits more comfortable injections for the patient.
Epinephrine can be added to lidocaine for some field blocks if the vasoconstrictive or anesthetic-prolonging action of epinephrine is desired. Epinephrine permits safe use of larger amounts of lidocaine because it prevents clearance of the anesthetic from the tissue. Epinephrine should be avoided in areas where vascular compromise could prove problematic, especially in individuals with vasculitis or vasoconstrictive disorders such as Raynaud's phenomenon. Many authorities discourage the addition of epinephrine for field blocks on digits, around the ear, on the nasal tip, or surrounding the penis.
INDICATIONS AND COMMON LOCATIONS FOR FIELD BLOCKS
The field block can be performed in a square pattern around a wound. Only two needlesticks are required. The needle passes along one side, anesthetic is administered as the needle is withdrawn, and the needle then redirected 90 degrees without coming out from the initial puncture site. This same technique is used on the opposite site of the wound.
(1) The field block can be performed in a square pattern surrounding a wound.
The nerve distribution for the pinna is demonstrated (Figure 2A). A field block is performed around the entire pinna (Figure 2B). To avoid motor paralysis of the facial nerve anterior to the pinna, the needle should pass in a superficial plane (i.e., subdermally in front of the ear). Separate injections may be needed for the concha and external auditory canal (Figure 2C).
(2) Field block for the ear.
Triangulated injections provide adequate circumferential anesthesia. Additional lidocaine without epinephrine must be administered to the tip of the nose to anesthetize the external nasal nerve, which arises from the deep tissues.
(3) Field block for thenose
Administration of anesthetic in a linear pattern through both eyebrows produces anesthesia of the supraorbital and supratrochlear nerves on each side. A long (1½-inch) needle should be used to provide near-complete anesthesia of the entire forehead to the scalp.
(4) Forehead anesthesia.
The penis is lifted upward (into the position of erection). Two skin wheals can be administered near the internal inguinal rings (Figure 5A). The long needle is placed subdermally to encircle the base of the penis with lidocaine without epinephrine (Figure 5B). A single injection method is described in Chapter 45.
(5) Penile block.
Anesthesia codes (00100–01999) are usually limited to anesthesiologists providing patient services for surgical procedures. Local anesthesia is not reported in addition to the surgical procedure. Some insurance providers permit billing of regional or general anesthesia by the physician or surgeon performing the procedure. If reporting additional anesthesia services, the -47 modifier is attached to the surgical code. It is unlikely that additional reimbursement will be provided for field blocks; the service is considered part of the reporting of the surgical procedure.
INSTRUMENT AND MATERIALS ORDERING
Syringes (5 or 10 mL), anesthetic solutions, and needles (18 or 20 gauge, 1 inch long for drawing up anesthetic; 25 or 27 gauge, 1¼ inch long for delivering anesthetic) can be ordered from surgical supply houses or pharmacies. A suggested anesthesia tray that can be used for this procedure is listed in Appendix G.
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