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Local and regional anesthesia, defined as the selective numbing of a
specific nerve distribution or region of the body to facilitate surgery,
appear to be undergoing a renaissance, as judged by attendance at specialty
meetings and numbers of published manuscripts. In contrast to general
anesthesia, in which the molecular mechanism remains the subject of
speculation, the site at which local anesthetic drugs bind to produce nerve
blocks has been cloned and mutated. This chapter will focus on mechanisms of
anesthesia and toxicity, especially as knowledge of these mechanisms will
assist the clinician in conducting safer and more effective regional
anesthetics.
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The Incas regarded coca as a gift from the son of the sun god and
limited its use to the "upper crust" of society.1 The
Incas recognized and used the medicinal properties of cocaine long before
the compound was brought back to Europe for its properties to be
"discovered." The Incas sometimes treated persistent headaches with
trepanation (Figure 6–1), and coca was sometimes a part of this
procedure. Local anesthesia was accomplished by having the operator chew
coca leaves and apply the mascerated pulp to the skin and wound edges while
using a tumi knife (Figure 6–2) to bore through the bone.
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By the sixteenth century, the conquistadors had disrupted Incan society
and began paying laborers with cocaine paste. The laborers generally rolled
the cocaine leaves into balls (called cocadas), bound together by guano or
cornstarch.1,2 These cocadas released the free-base
cocaine as a consequence of the alkalinity of the guano and of the practice
of chewing the cocadas with ash or lime (such alkaline compounds increase
pH, favoring the free-base cocaine form over the positively charged
hydrochloride salt). This practice probably marks the birth of
“free-basing” cocaine and is the historic antecedent of the “rock” or
“crack” cocaine so often abused in Western societies.
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Cocaine was brought back to Vienna by an explorer/physician named
Scherzer.1 In Vienna, the chemist Albert Niemann isolated
and crystallized the pure cocaine hydrochloride in 1860. The Merck Company
distributed batches of this agent to physicians for investigational
purposes. Sigmund Freud was the most prominent of these cocaine
experimenters. Freud reviewed his experimental work in a monograph devoted
to cocaine titled Über Coca. Freud and Carl Koller (an ophthalmology trainee) took
cocaine orally and ...