Understanding Anesthesiology - The Global Regional Anesthesia ...

SECTION 3
General Anesthesia
In This Section
1. Induction
2. Maintenance
3. Drugs Used in the
Maintenance of Anesthesia
4. Emergence
General Anesthesia is a pharmacologically induced
reversible state of unconsciousness which
is maintained despite the presence of noxious
stimuli. With the continual development of new
drugs, there is an ever-increasing variety of techniques
used to provide general anesthesia. All
techniques strive to achieve the following goals,
known as the “Four A’s of Anesthesia”:
• Lack of Awareness: unconsciousness.
• Amnesia: lack of memory of the event.
• Analgesia: the abolition of the subconscious reactions
to pain, including somatic reflexes
(movement or withdrawal) and autonomic reflexes
(hypertension, tachycardia, sweating
and tearing).
• Akinesia: lack of overt movement. In some
cases, the provision of muscle relaxation may
be required.
In the past, general anesthesia was achieved using
a single agent such as ether or chloroform. Because
the above-described goals were achieved
by a progressive depression of the central nervous
system rather than by any direct or specific
effect, relatively high concentrations of the gases
were required. Consequently the associated sideeffects
were frequent and severe.
In current practice, we have many different
agents (both intravenous and inhaled) at our disposal.
The intravenous agents in particular have
specific effects such as analgesia or muscle relaxation
and therefore can be used to achieve the desired
effect in a dose-related fashion.
The practice of using combinations of agents,
each for a specific purpose, is what is termed
“balanced anesthesia”. An example of a balanced
technique would be the use of propofol for
induction of anesthesia; the administration of desflurane
and nitrous oxide for maintenance of unconsciousness;
sufentanil for analgesia; and rocuronium
for muscle relaxation.
The anticipated benefits of a balanced technique
as compared to “ether anesthesia” of the past include:
• improved hemodynamic stability
• more effective muscle relaxation
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