In an August-September 1993 Guidance Article (Cellular telephones and
radio transmitters—Interference with clinical equipment. Health Devices 1993
Aug-Sep;22[8-9]:416-8) we discussed the potential effects of electromagnetic
interference (EMI) from various radio-frequency (RF) transmitting devices on
medical devices—a topic that continues to be of interest and concern to
many healthcare facilities. At that time, while it was clear that EMI could
interfere with the operation of clinical and other electronic equipment, the
risk of adverse clinical effects was not well understood. Thus, we recommended
that hospitals consider prohibiting the use of transmitting devices (e.g.,
cellular telephones, citizen-band radios, amateur radio transmitters) by
patients and visitors throughout the facility. However, we also noted that the
same stringent measures were not as appropriate regarding necessary
hospital-related radio communications.
Since the publication of the 1993 article, we
have encouraged others to report to us any EMI-related experiences. Although the
risks are still not clearly defined, the information we have obtained from
reporting hospitals and other sources has enabled us to relax our
recommendations. In this update, we provide our current perspectives and present
new recommendations for addressing this issue.
The ability of devices that emit radio
frequencies to interfere with the operation of electronic equipment has long
been recognized. However, recent dramatic, although not necessarily
representative, reports in the print and broadcast media have drawn significant
attention to the effect that EMI from RF transmitting devices (e.g., cellular
telephones, walkie-talkies) can have on medical devices (e.g., apnea monitors,
ventilators, powered wheelchairs). These reports frequently do not convey the
complexity of the issues to be considered when examining device susceptibility
to EMI and the likelihood or significance of any resulting clinical effects. In
reality, despite several recent technical conferences on this subject, data that
can establish a reliable estimate of risk is not available.
In a 1993 article, author Jeffrey Silberberg, from the U.S. Food and Drug
Administration's (FDA) Center for Devices and Radiological Health (CDRH),
provides information about more than 120 EMI events reported to FDA
between 1979 and 1993.(1) While mass media reports frequently focus
on cellular telephones as a major cause of EMI events, Silberberg's article
lists only 3 incidents involving cellular telephones. (And 2 of these reports
relate to the use outside North America of digital systems operating at
higher power, which have a greater potential to cause EMI ("See
Analog- versus Digital-mode Cellular Telephones," below).
Although it does not reflect an exhaustive enumeration of EMI events occurring
in the period specified, and cellular telephones were not widely used for much
of this time, Silberberg's article does appear to represent the variety of EMI
events that might occur.
Our own data, accumulated from early 1992 to the present, yields only 16
instances of interference to devices during clinical use: 7 involving cellular telephones, 5 involving
hand-held transceivers, and 4 involving other sources, including other medical
devices. (Note that all reported clinical observations are anecdotal and not
well documented.) In the 7 observations involving cellular telephones, no
adverse clinical effects on patients were reported (see the table, below). We
judged that only 1 of these 7 incidents could likely have had a serious clinical
Central station alarms and
Yes—However, no adverse
clinical consequence occurred in this incident, which was associated
with multiple cellular telephones being used in one room
occurred, but reverted to normal when transmission
blood pressure readings displayed
No—Erroneous data was
displayed, but reverted to normal when transmission
telemetry monitoring system
occurred, but reverted to normal when transmission
telemetry monitoring system
sounded (rate also may have changed)
Ventilator (operated in a
Inappropriate activation of
We also received 38 reports of EMI reflecting
tests performed by clinical engineers and biomedical technicians to determine
which devices in their inventories were susceptible. However, these reports
illustrate the complexity of the processes involved in that, where some people
have reported that they found a device to be susceptible, others have reported
that their attempts to confirm susceptibility for that same make and model of
device were unsuccessful.
In light of the apparent low incidence of
documented EMI-related problems, many print and broadcast reports appear to
overdramatize the risk, particularly in the use of cellular telephones near
medical devices. Such reports contribute to a distorted perception in the
healthcare community regarding the magnitude of the risk. In fact, some
hospitals have based policies on controlling EMI primarily on such
Two prominent, and somewhat controllable,
factors that affect the likelihood of electromagnetic interference (EMI) are
distance and power. As the distance between an RF transmitting device and
susceptible electronic equipment decreases, the likelihood of interference
increases. Also, the higher the power of an RF transmitter, the more likely
interference is to occur.
Many hospitals, concerned about reports of EMI
from cellular telephones and walkie-talkies, have expressed reservations about
incorporating lower-power wireless technologies, such as cordless telephones,
personal micro-cellular telephones, and wireless LAN-based information systems.
Many of these systems operate at or below 100 mW, with an operating frequency of
900 MHz and above. By comparison, conventional cellular telephones may operate
at maximum powers of 600 mW or higher, and hand-held transceivers operate at
powers of up to several watts.
We have not received reports of problems with
such low-power wireless technologies. Although these devices may not be widely
used in areas where they are likely to cause problems, we believe that their
potential for interference with clinical devices is substantially less than even
that associated with the use of cellular telephones. Given the advantage many of
these devices offer and their low potential for EMI, we believe it is
inappropriate to reject them out of hand.
Determining which devices among a hospital's
inventory are susceptible to EMI has been a general concern for many people who
have contacted ECRI. (For issues related specifically to cardiac pacemakers and
cellular telephones, see "Interactions between Cellular Telephones and
Cardiac Pacemakers," below.) Although thorough testing to characterize a
device's EMI susceptibility could be performed, doing so would require
sophisticated equipment and a shielded room or other appropriate space. As an
alternative, a subcommittee of the ANSI/IEEE C63 Electromagnetic Compatibility
Committee is drafting a set of ad hoc testing procedures to be used to screen
devices for susceptibility to transmissions from commonly used hand-held
While it is important that a commonly accepted
set of procedures be available, ECRI advises clinical engineers not to perform
comprehensive testing of inventory. Such testing will prove unproductive for the
time and effort expended and is not likely to conclusively establish EMI
susceptibility given the complex nature of the interference processes. Although
testing may reveal an occasional susceptible device, it will not ensure that
devices that demonstrate immunity—under the conditions of the
test—will be immune under all conditions of use.
Any testing that is
performed may require prolonged RF transmissions. Also, if testing is performed
in an unshielded space, it must be carried out within the operating requirements
under which the transmitter is licensed. Those requirements prohibit prolonged
unmodulated transmissions by transmitters licensed for land mobile service under
Part 90 of the U.S. Federal Communications Commission (FCC) regulations (47
C.F.R. § 90). (Cellular telephones are not under such a
Another consideration is that users generally
are obligated to minimize interference to the communications of others who may
be sharing a channel. If testing may interfere with other services on the same
frequency, testers should minimize transmission time and, where applicable,
advise co-users or base station operators of their intentions.
Furthermore, it is important to recognize that
even low-power transmitters can create strong electromagnetic fields at close
range. These fields may alter a device under test. During incident
investigations, particularly those with a potential for litigation, facilities
should not test for EMI susceptibility in such a way as to alter the device's
When Is Testing
Testing may be appropriate and useful to
perform when potential EMI susceptibility needs to be clarified. Such cases
could include devices reported to have had an interference problem or service
calls for which no obvious problem was found. Screening devices being considered
for purchase (or newly purchased) for which the manufacturer has not provided
adequate information to reasonably assure immunity may also be warranted.
However, if testing is to be performed, be sure to consider the limitations
Developing and Implementing a
No uniform approach to developing a hospital
policy on the use of cellular telephones and other RF transmitting devices has
emerged, and the evidence to date is insufficient to demand or justify a
"standard of care." At one extreme, we know of hospitals that have
deemed the risk so insignificant that they choose not to restrict the use of
wireless communication devices (e.g., cellular telephones). Others have
implemented a policy that severely restricts use throughout the institution by
patients, visitors, and staff. Given the uncertainty on this topic, variations
in experience with EMI, and differences in propensity for risk aversion, both
policies are reasonable.
When developing a policy, hospitals should
consider the following (which are also reflected in our Recommendations,
Although interference can occur, the rate
of occurrence and risk of significant adverse clinical impact are very low.
Medical devices can be affected by EMI for
many reasons, including electrostatic discharge and power line disturbances,
and from many sources, including other medical devices (e.g.,
electrosurgical units) and transmitting sources outside the hospital.
Cellular telephones and hand-held transceivers are but two of many sources.
Even if interference from these two sources is well managed, a significant
potential for EMI still remains.
Cellular telephones are considered an
essential tool by many. Reliance on RF systems for personal communication
and data exchange among instruments will expand and cannot be avoided.
Cellular telephones and other RF
transmitting devices pose the greatest risk when operated in the following
Where patients are in critical condition and
are highly dependent on monitoring or life-support devices
patients are receiving therapy that could be dangerous if not carefully
controlled or monitored
many instruments are in use, increasing the chance that a susceptible
device will be in proximity to an RF
Concerns may exist in general patient-care
areas as more instrumentation moves into these areas. However, risks here
may be lower if patients are less susceptible to a device malfunction. For
example, an overdose could be lethal to a patient receiving an analgesic
from an infusion pump in a general care area. However, most patients on
infusion pumps in general care areas would be less susceptible to serious
adverse effect from dose changes than patients in critical care
At present, we are not aware of any agency or
organization advocating a policy that imposes a widespread ban of the use of
wireless devices, including cellular telephones, throughout a healthcare
institution. Where such groups have spoken, the emphasis is usually placed on
management of the use of devices in such a way as to minimize risks. This can
include selective restrictions on use.
Interactions between Cellular Telephones and
Over the years, concerns, real or imagined,
have arisen about the possibility that implanted cardiac pacemaker function
might be adversely affected by nearby devices that emit electromagnetic energy.
Many readers will remember, a decade and more ago, the proliferation of signs in
public eating places warning pacemaker wearers that microwave ovens were in use
nearby. However, considerable advances have been made in shielding implanted
pacemakers, and these devices are now quite immune to environmental
electromagnetic fields. Nevertheless, questions have justly been raised as to
the possible risks associated with the use of cellular telephones by or near
people with pacemakers. These telephones are of particular concern because their
transmitting antenna can be very close to the body and the site of implantation.
Although some reports in the mass media have attempted to address these
concerns, occasionally such coverage has been unenlightened and
Research is underway to define more completely
what risks may exist. In the meantime, the Health Protection Branch of Health Canada issued an Information Letter(2)
that reflects current sound advice based on its studies, as well as those of U.S.
researchers (Carrillo in Miami, Florida, and Hayes in Rochester, Minnesota) who are
actively studying this matter in patients. The Center for the Study of Wireless
Electromagnetic Compatibility (at the University of Oklahoma) and the U.S. Food and Drug
Administration's Center for Devices and Radiological Health (FDA-CDRH) are also exploring
these issues through in vitro
According to their observations, both the Canadian agency and clinical
researchers have noted that interactions 1) do not occur in all brands and models of
pacemakers, 2) occur only with the use of telephones operating in the digital mode (see
below), and 3) are observed only when the telephone's transmitting antenna is
within a few centimeters (i.e., less than 6 cm [2.5 in] for implanted
pacemakers) and directly over the site of implantation of the pacemaker
Analog- versus Digital-Mode Cellular
In North America, the use of analog-mode
cellular telephones has been well established and continues to grow. By
contrast, telephones with a digital mode, which are a more recently emerging
technology. Digital-mode cellular telephones used in North America exist in two
forms, TDMA and CDMA; these devices can operate in the analog mode when a
digital-mode channel is not available from the nearby base station. Currently,
only about 10% of cellular telephones in North America have digital capability,
and these tend to be concentrated in metropolitan areas.
In Europe, digital cellular telephones operate
under a GSM protocol and at a higher peak power than the TDMA and CDMA devices
used in North America. Consequently, a higher susceptibility of pacemakers to
interference has been reported in Europe.
Interactions observed with digital-mode
telephones include inhibition of ventricular output, asynchronous pacing, atrial
channel tracking of electromagnetic noise, and safety pacing. Any interference
that has been observed has occurred while the telephone was transmitting; normal
pacemaker function was restored when the telephone was turned off. Currently,
there are no clinical or research reports of interference to pacemakers from
analog-mode cellular telephones.
We know of no current recommendations that
discourage pacemaker wearers from using cellular telephones. However, certain
steps are advisable to minimize any risks. The Canadian alert suggests some
practical measures, including that the cellular telephone not be carried in the
breast pocket of a coat (i.e., where it might lie directly over the implantation
site when set to the ON position). The alert also suggests that
those handsets with an integral (transmitting) antenna be used on the side of
the head opposite the site of pacemaker implantation.
Currently, common exposure concerns to warn
patients about include magnetic resonance imaging, (ionizing) radiation therapy,
and short-wave diathermy. ECRI advises that physicians implanting cardiac
pacemakers follow the results of ongoing research to define the risks, if any,
with wireless technologies. Physicians should advise their patients how to
appropriately use cellular telephones and other radio-frequency transmitting
For most hospitals, policies that concentrate on risk reduction in areas
of greatest concern; that minimize the impact on patients, visitors, and staff; and that
simplify enforcement are likely to be more acceptable. We have therefore relaxed our
previous position calling for prohibition of the use of transmitting devices (particularly
cellular telephones) by patients and visitors throughout the hospital. Our new
suggestions for a policy are based on a principle that calls for restricting the use of
transmitting devices by patients, visitors, and staff in patient areas that are characterized by
Such restrictions would be warranted in
intensive care areas; operating rooms; and emergency, labor and delivery, and
therapeutic radiology departments. Also, although we have little data to support
a concern, we suggest including clinical laboratory areas (the devices there may
be no different than patient-care devices, but with fewer alarms and displays to
permit detection of interference) and possibly certain diagnostic imaging labs
(e.g., ultrasound) and other instrumentation-intensive diagnostic labs (e.g.,
cardiac electrophysiology). Elsewhere in the hospital, restrictions may be
relaxed or lifted as appropriate for your institution.
Several hospitals that have instituted
policies constructed on this framework indicate that they believe the policies
are working successfully.
ECRI Advises Institutions to Implement the
Instruct all staff to be attentive to
unexpected performance of medical equipment and encourage them to report all
such occurrences to the clinical engineering department for investigation.
When a device is sent for service and no problem can be found, the clinical
engineering staff should inquire whether any transmitting devices were in
use at the time.
Incorporate into purchase specifications
for new equipment a requirement that manufacturers provide evidence of the
extent to which their devices conform to current electromagnetic
susceptibility performance levels (e.g., guidelines, standards). An example
of such evidence would be a certificate of compliance with IEC 601-1-2(3)
(or EN60601-1-2) or similar standards. Be aware that compliance with such
standards does not guarantee that a device will be totally immune to EMI.
For devices that have shown susceptibility
to EMI, either in clinical use or through testing or other experience, do
one of the following:
A. Move the device to another area
of the hospital where the possibility of altered performance
presents less risk.
B. Contact the manufacturer to
determine whether the device can be modified to reduce EMI
C. Schedule the device for early
When considering wireless technologies for
future communication and information handling needs, give preference to
systems for which the transmitting components operated close to patients or
critical instrumentation operate at the lowest practical power.
ECRI Suggests that Institutions Adapt the
Following as Appropriate for Their Particular Circumstances and Perceived
In highly instrumented care and diagnostic
areas, unnecessary use of cellular telephones, hand-held transceivers, and
other RF transmitting devices of similar or higher output power should be
A. Patients and visitors
should be instructed to refrain from all use of such devices and to
leave cellular telephones in the
COMMENT: When not in use,
but set to the ON
position, cellular telephones can respond to infrequent system
requests (at several-minute intervals) from the base station to
confirm their availability to receive a call. The response is
typically a short (one second or less) transmission burst. While
little recorded experience shows such bursts to be a problem, their
effect may go unnoticed because they are infrequent and short.
Turning off the telephone provides the greatest safety—and
removes the temptation to answer a call.
B. The staff should use the wired
telephone service for outgoing calls and rely on (one-way) pagers to
alert them for incoming calls.
Two-way pagers, providing answer-back
capability, have a capability to transmit. Their risk as a source of
EMI is unknown at this time.
C. The staff should take the
following measures to minimize the risk of interference when
cellular telephones and transmissions by hand-held transceivers
(using hand-held transceivers in the RECEIVE mode poses no risk) must be used:
Move to gain adequate
clearance from critical devices that may be susceptible to EMI.
One to two meters (three to six feet) has generally been
adequate for cellular telephones. Three meters (10 feet) or more
may be necessary for hand-held transceivers.
If the telecommunications
device has optional or adjustable power levels, use the minimum
power required for reliable communications.
In patient-care areas that are not
instrument-intensive, restrictions are not needed where life-support or
critical devices (e.g., ventilators, pumps administering IV-delivered
analgesics) are not routinely used.
In public-use, non-patient-care areas
(e.g., cafeterias, waiting rooms), restrictions are not needed given the low
probability of interference and the difficulty of enforcing any such
Cellular telephones are
not likely to be of concern in these areas because the distance between the
telephone and a susceptible device must be relatively short to produce an
effect. With respect to hand-held transceivers and other transmitters
operating at a few watts or higher, caution may be appropriate where such
areas are adjacent to, or directly above or below, highly instrumented
areas. However, little experience of record defines the risks in such
situations, and intervening building structures usually (but not always)
contribute some attenuation that, along with physical distance, further
reduces the risks.
Inform patients, visitors, and staff of
the hospital's policy through appropriate signage and distribution of
information. For example, the hospital's policy and restrictions may be
described in patients' preadmission packets and on visitor passes.
Silverberg JL. Performance degradation of electronic medical devices due
to electromagnetic interference. Compliance Engineering 1993 Fall;10(5):25-39.
Medical Device Alert No. 108, dated November 6, 1995; also abstracted in
Health Devices Alerts, Implants edition. as Accession No. M3988, published December 8,
- International Electrotechnical Commission (IEC). Medical electrical
equipment, Part 1: Gemeral requirements for safety, 2:
Electromagnetic compatibility--Requirements and tests. Geneva: IEC.