Section VIII. LOCAL ANESTHETICS
Pain can be abolished by inducing unconsciousness with the general anesthetics
or by preventing painful impulses from reaching the cortex by blocking the sensory
nerve impulses from a localized area. This loss of feeling and sensation to a localized
portion of the body is known as local anesthesia. It is accomplished by using local
anesthetic drugs. Local anesthetics can be broken down into two main categories;
those that lower skin temperature and those that have a specific effect on sensory
a. Skin Refrigerants. The local anesthetics that create anesthesia through the
production of cold are liquids of low boiling point. Since ethyl chloride evaporates from
the skin rapidly, it quickly reduces skin temperature and thereby produces its anesthetic
action. Dichlorotetrafluoroethane also belongs to this group.
b. Specifics. The specific local anesthetics are those drugs that have a specific
effect on the sensory nerve or on nerve endings. This category can be further
subdivided into drugs of the water-soluble group that are intended for injection, such as
procaine hydrochloride, and those that are only slightly water-soluble which are
intended for topical use, such as benzocaine. Local anesthetics are detoxified by the
liver. In the later discussion of specific local anesthetics, notice that almost all the
names end in "caine." When you see a drug name with this suffix, you should
immediately recognize it as a probable local anesthetic.
2-38. METHODS OF ADMINISTRATION
The ways in which local anesthetic agents may be applied so that they will
produce their anesthetizing action are as follows:
a. Topical application to the skin or mucous membrane may be used.
b. The drug may be infiltrated (injected) into the tissue, thus anesthetizing
c. The drug may be injected into or around a nerve trunk, producing regional
anesthesia (the region of the body supplied by the nerve trunk is anesthetized).
d. The drug may be introduced into the spinal canal (spinal block anesthesia), or
at certain sites around the spinal canal (such as peridural or caudal anesthesia). Use of
this method results in a more extensive area of anesthesia than is possible with the
other methods above.