Biomedical Engineering Reference
In-Depth Information
Examples of proactive mitigation include consulting
services provided by the Biomedical Engineering De-
partment and the Television Services Group during the
latest expansion of Texas Children's Hospital. These
services, which involved the expertise of all groups
within the biomedical engineering department, included
not only space design, but the design, implementation,
and expansion of wireless paging and communications
systems. Through the use of a distributed energy antenna
systems, (i.e., leaky coax-radiax) radio frequency (RF)
power levels were maintained at levels deemed safe for
clinical devices while providing the required coverage
area for a nurse call-specific paging system. Safe wireless
telephonic communications were implemented using
low-power microcellular systems. Infant abduction sys-
tems were reviewed for specifications including emission
characteristics, and a system was selected based in part
on its low electromagnetic radiation levels.
The use of portable radio communication devices in
a large campus environment is a basic requirement for
security, engineering, and guest services. As part of the
mitigation process, instruction in the safe use of two-
way radio equipment in the clinical environment is
mandatory for all personnel who use this equipment
(ECRI, 1993).
Correction
Correction of victim/culprit relationship(s) can take
many forms, some practical, some impractical. Correction
may be part of a process to ensure that the victim device
meets all specifications that can affect its susceptibility
to electromagnetic radiation. For example, hospital staff
should ensure that proper case-to-case contact is made in
coated conductive coatings and that the coatings have not
been worn or abraded. In some instances, the victim
device can and should be removed from the environment
where it is at risk. If the culprit is local, removal may be
one practical solution to the problem. Instances of elec-
tromagnetic radiation emanating from abandoned wiring
(passive reradiation) have occurred that dictated removal
of the wiring. Interference to clinical devices originating
from active (nonfiberoptic) wiring, such as networking
trunk conduits, mandates rerouting of the wiring. The
same can apply to modern in-plant telephone systems,
usually digital in nature. Experiences at Texas Children's
Hospital support the work of researchers (ECRI, 1988) in
finding that shielded rooms rarely correct problems when
the source of electromagnetic radiation is contained
within the local environment. In extreme cases, the
existing shielded room must be disassembled or the
victim equipment (and department), moved to other
quarters within the institution.
Detection
Prevention
Detection is implemented upon the report of a device
malfunction. A preliminary analysis of the incident may
indicate that the cause of the malfunction, intermittent
or permanent, may have been EMI. In the case of con-
tinuing or continuous device malfunction not otherwise
attributable to defects within the device itself (e.g., no
problem found [NPF] service reports), a careful in-
vestigation begins, using various test equipment, some of
which may require specialized construction. This section
presents a more detailed description of the basic equip-
ment necessary to locate and identify sources of EMI and
some of the basic techniques, referred to as ''ghost
hunting.'' Once the type and source of the interference is
detected and analyzed, the next step is to reduce or
eliminate the interference to the victim device. How-
ever, the victim device is removed in some cases, because
of an intensely hostile electromagnetic environment.
Replacement of the victim device with an equivalent
device that may have other, less sensitive responses is an
option.
The detection phase can eliminate the possibility of
EMI as the culprit and cause of improper operation of
a specific device. Indeed, subsequent investigation can
reveal technical problems within a device that were
previously attributed to EMI.
Sustainable EMI prevention must include institution-
wide compliance with guidelines and with those policies
created within an institution to limit possible sources,
EMI as well as the selection and deployment of medical
devices that offer more effective immunity from EMI.
Overall, observance of this two-pronged policy will have
the effect of reducing the risk of EMI to the proper op-
eration of clinical devices and therefore reducing the risk
to the institution. At Texas Children's Hospital, EMI
prevention takes several forms (David, 1993). A pro-
active policies and procedures manual that, guided by the
biomedical engineering department, defines allowable
sources of radiation within the institution and mandates
training procedures for employees of the institution that
are required by job necessity to carry sources of electro-
magnetic radiation, i.e., intentional radiators. As an ex-
ample, signage mandated by the policies and procedures
manual directs that all cellular telephones be turned off.
Their use within the institutional campus is not allowed.
The policies and procedures manual further mandates
that all employees using radio equipment, especially
handheld devices, be trained in their safe use within the
institution. Additionally, a stipulation that clinical devices
must be EMI compatible is incorporated into the
