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Many procedures can be performed with the use of local anesthetic
alone, instilled at or near the site of surgery. Often this can be done by
the surgeon without the use or assistance of an anesthesiologist. Local
infiltration is also technically easy to perform and requires minimal
postoperative care. Together, these factors contribute to its popularity and
nearly ubiquitous application as a means of anesthesia for small minimally
invasive procedures and operations. This technique is relatively safe as
well, but does require an understanding of basic local anesthetic
pharmacology, especially with respect to dosing and toxicity, as well as
skill for successful application.
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History of Local Anesthesia
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There are several references throughout history of efforts to produce
local anesthesia by various means.1 Ancient Egyptians
believed that the fat of the crocodile could induce anesthesia if placed on
the skin of a patient. The same people also believed that the stone of
Memphis could produce local anesthesia if rubbed on the skin with vinegar.
Chinese physicians were known to use a mixture of jimson weed, marijuana,
deadly nightshade, and mandrake placed into calamus leaves and burned over
the operative or painful site to produce anesthesia. In the sixteenth
century, Marco Aurelio Severino, an Italian anatomist and surgeon, advocated
the use of cold to decrease pain, and this principle was frequently put to
use by Napoleon's military surgeons. Other methods of inducing anesthesia
locally included electrical current and superficial application of volatile
liquids. The first clinical use of a local anesthetic was in 1884, when
Austrian ophthalmologist Carl Koller used raw cocaine topically to
anesthetize a patient's eye. After this, the use of local anesthetics spread
quickly, especially with the synthesis of less toxic compounds such as
procaine and lidocaine.2
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General Principles of Local Infiltration Anesthesia
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The aim of local infiltration is to anesthetize nerve endings in a
finite area of tissue by the injection of local anesthetics nearby. This
stands in contrast to peripheral nerve blocks, in which nerve axons are the
target and the injection may take place in an area removed from the surgical
site (eg, brachial plexus block for hand surgery). The depth of the area to
be operated on typically determines the required extent of infiltration. For
superficial skin procedures such as suturing of lacerations and skin
biopsies, subcutaneous or intradermal infiltration is sufficient. More
extensive operations may demand infiltration into muscle, fascia, and other
deep tissues.
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Two general approaches exist for anesthetizing skin and subcutaneous
tissue. The first involves injecting local anesthetic directly into the line
of incision and nearby tissues, effectively flooding the individual local
nerve endings to produce anesthesia. This can be very effective, but may
require large volumes of local anesthetic to achieve complete coverage.
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In contrast, field or ring blocks encircle the site of incision with walls
of local anesthetic solution through which nerve fibers ...