Understanding Anesthesiology - The Global Regional Anesthesia ...

SECTION 2
Anesthetic Equipment and
Monitoring
In This Section
1. The Anesthetic Machine
2. Monitoring
The Anesthetic Machine
The purpose of the anesthetic machine is to deliver
gases to the patient in precise, known concentrations.
Although the anesthetic machine has
evolved substantially over the years, the essential
features have remained remarkably constant.
Some of the important components of a modern
anesthetic machine are depicted in Interactive 2.
1. (Tap the labels for a close-up view as well as a
brief description of each component.)
Gases (oxygen, air and nitrous oxide) come from
pipelines entering the operating room through
the wall (Figure 9). Tanks on the back of the anesthetic
machine provide an alternate source of
those gases should the wall supply fail. Although
100% oxygen can be delivered to the patient, usually
a mixture of oxygen (with air or nitrous oxide)
is selected. The relative concentrations of the
gases to be delivered are controlled by flowmeters
(one flowmeter for each gas) found on the
left hand side of the anesthetic machine.
The anesthetic machine also allows the delivery
of a precise concentration of volatile agent. The
volatile anesthetic gases, such as sevoflurane and
desflurane, are contained in liquid form in the vaporizers
mounted on the machine. The gas mixture
from the flowmeters flows through the vaporizer
and the volatile anesthetic agent is added
to the mixture in gaseous form. The concentration
of the volatile gas in the final mixture is determined
by a dial on or near the vaporizer. For
safety reasons, only one volatile agent can be delivered
at a time.
The ventilator allows positive pressure ventilation
of the anesthetized patient. The ventilator
can be set to deliver a specific tidal volume (in
which case pressure varies according to lung
compliance) or to achieve a certain peak inspiratory
pressure (in which case volume varies ac-
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