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Local anesthesia is the condition that results when sensory transmission
from a local area of the body to the central nervous system (CNS)
is blocked. The local anesthetics constitute a group of chemically
similar agents that block the sodium channels of excitable membranes.
Because these drugs can be administered by topical application or
by injection in the target area, the anesthetic effect can be restricted
to a localized area (e.g., cornea, arm, foot). Even when these drugs
are given in the vicinity of the spinal cord, it is still considered
a form of local anesthesia because only a specific level of cord
impulse transmission is blocked. When given intravenously, however,
these drugs can have effects on other tissues.
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Local anesthetics are used for a variety of purposes, including
localized surgical procedures, labor and delivery, and joint manipulations.
They can also be used for short-term pain relief in conditions such
as tendonitis or in long-term situations such as pain associated
with cancer. Table 16–1 presents some of the methods of
delivery of local anesthetics and the common clinical uses of each
method.
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Most local anesthetics in current use are esters or amides. In
addition, they are amines with the ability to bind a proton (H...