Biomedical Engineering Reference
In-Depth Information
In the past, the use of combustible anesthetic gases
(e.g., cyclopropane and ether) created a volatile envi-
ronment that demanded additional safety measures. It
was essential to reduce the likelihood of a static discharge
(spark) that could lead to an explosion in the operating
suite. Although the risk of explosion is not typically an
issue today, it has played an important role in the design
of electrical power systems in many existing OR. For
example, power outlets have typically been installed
approximately 4 feet above floor level because volatile
explosive agents tend to settle in the air. Special plugs,
termed ''explosion-proof,'' were also commonly installed
on power cords that, when plugged in, created an airtight
seal. Conductive flooring is also commonly found in ORs.
This technology was installed to eliminate the electrical
isolation of equipment and personnel in an operating
suite. Electrical isolation between objects is conducive to
the build-up and potential discharge of static electrical
charge. Isolated ungrounded power systems, line iso-
lation monitors (LIMs), and ground-fault circuit in-
terrupters (GFCIs) are further examples of technologies
employed in ORs to reduce the risk of explosion in the
presence of combustible anesthetic agents. These tech-
nologies also serve to reduce the risk of explosion from
electrical shocks resulting from stray (leakage) current.
An isolated ungrounded power system is an electrical
power distribution system in which all of the current-
carrying conductors are isolated from ground (and earth)
by a high impedance (Feinberg, 1980). The most common
and economical method of isolation is to use an isolating
transformer. In a properly installed system, no hazardous
current will flow fromeither conductor to ground, but the
two conductors will function as though they were
connected directly to a ground. This is especially useful in
a ''wet environment'' such as the OR, where liquid spills
and standing water increase the risk of electrical hazards.
An LIM displays the degree of electrical isolation in an
isolated ungrounded power system. It provides an early
warning system of possible leakage or fault currents from
either of the current-carrying conductors to ground.
AGFCI also serves to protect patients and staff members.
This technology monitors the ground fault current and
interrupts the power to the electrical receptacle when the
current exceeds a preset limit. Although LIM technology
is more expensive, one advantage over the GFCI is that
the LIM will alarm when a fault is detected, but will not
interrupt electrical service.
gases are stored either in metal cylinders or in the reser-
voirs of bulk gas storage and central supply systems. The
central supply system is the source of medical gases that
are distributed via the facility pipeline system. The
number and location of wall outlets in the OR varies,
depending on facility design and surgical specialty.
Figure 4.3-2
shows a wall outlet for nitrogen commonly
used to power pneumatic tools such as saws and drills.
The method of storage for the central supply of
oxygen depends on the demands of the facility. Smaller
facilities tend to store oxygen in a series of cylinders
connected by a manifold or high-pressure header
systems. Larger facilities store their bulk oxygen in
pressurized liquid form, which enables the hospital to
store more oxygen in a smaller space. The central supply
of medical air is most commonly generated by air com-
pressors, stored in a reservoir, and delivered to the piping
system. Other sources include pressurized cylinders or
a proportioning system that mixes the appropriate
amount of oxygen and nitrogen from central sources. The
nitrous oxide supply systems include the cylinder mani-
fold system or a bulk liquid storage system similar to the
one used for oxygen system. All central supply systems
for medical gases must be designed with a separate re-
serve system. Details concerning the use of medical gases
in anesthesiology are discussed in Chapter 4.4.
Nitrogen and carbon dioxide can be piped into the
OR, as well. Nitrogen, primarily used for gas-powered
equipment, is stored as a series of pressurized tanks
connected by a manifold. Carbon dioxide is also typically
stored as a cylinder manifold system.
Vacuum
The central vacuum system is another essential utility
that must be piped into the OR. The system is vital to
both surgery and anesthesia. It provides pressure for
drainage, aspiration, suction during surgical procedures,
Gas pipelines
Pressurized gases must be distributed to locations through-
out the health care facility. Medical gases such as oxygen,
nitrous oxide, and medical air are particularly important
for the administration of anesthesia in the OR. Medical
Figure 4.3-2 OR wall outlet for nitrogen gas.
