Anesthesia Student Survival Guide.pdf - Index of

Anesthetic techniques: GenerAl, sedAtion, MAc ● 167
induced and maintained with either intravenous medications or the inhalation
of volatile anesthetics. Table 12.5 depicts the major components of a typical
general anesthetic. Table 12.6 lists the common drug classes employed to achieve
these components.
Physiology of General Anesthetics
Sedative-hypnotic medications such as propofol, etomidate, barbituates, and
benzodiazepines all appear to have similar mechanisms of actions. These medications
can be used for light sedation if given slowly and in small doses or can be
used to induce general anesthesia if given in large bolus doses. Sedative-hypnotic
agents act by binding to and activating GABA A receptor chloride channels in
neuron transmembrane proteins. Activation of these receptors causes an influx of
ions, results in cell hyperpolarization, and prevents depolarization. If a neuronal
cell cannot depolarize, it is said to be inhibited and cannot send information. This
is the neurobiological basis for the effect of these drugs. Sedative-hypnotics can
cause sedation, loss of consciousness and amnesia, but in general are not effective
at providing analgesia or inhibiting movement.
In contrast to sedative-hypnotic medications, volatile anesthetics can
produce both loss of consciousness and inhibit movement. We still do not
have a complete understanding of the mechanism of action of volatile anesthetics
(also see Chap. 5, Pharmacology of Inhalational Anesthestics). There is
no unified theory to explain how and why all volatile anesthetics work, but it
is felt that they must act on the central nervous system as well as at the level of
the spinal cord in order to produce amnesia, sedation, and inhibition of movement
to noxious stimuli. Unlike neuromuscular blocking agents which bind to
receptors at the neuromuscular endplates to prevent movement, volatile anesthetics
are thought to work at the level of the spinal cord to inhibit purposeful
and reflexive movement.
Table 12.5 Important components of a general anesthetic.
hypnosis rendering the patient unconscious
Analgesia removal of the sensation of pain
Amnesia Prevention of memory formation
Paralysis Prevention of movement
reflex blunting Prevention of exaggerated autonomic response