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 performance.

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 described above.

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, below):

• 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 areas:

– Where patients are in critical condition and are highly dependent on monitoring or life-support devices

– Where patients are receiving therapy that could be dangerous if not carefully controlled or monitored

– Where many instruments are in use, increasing the chance that a susceptible device will be in proximity to an RF transmitter

• 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 areas.

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.

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 misleading.

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 studies.

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 unit.

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 technologies.

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 intensive instrumentation.

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.

• 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 susceptibility.

C. Schedule the device for early replacement.

• 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.

• 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 restricted.

 A. Patients and visitors should be instructed to refrain from all use of such devices and to leave cellular telephones in the OFF position.

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.

COMMENT: 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 restrictions.

 COMMENT: 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.

1. Silverberg JL. Performance degradation of electronic medical devices due to electromagnetic interference. Compliance Engineering 1993 Fall;10(5):25-39.
2. Medical Device Alert No. 108, dated November 6, 1995; also abstracted in Health Devices Alerts, Implants edition. as Accession No. M3988, published December 8, 1995.
3. International Electrotechnical Commission (IEC). Medical electrical equipment, Part 1: Gemeral requirements for safety, 2: Electromagnetic compatibility--Requirements and tests. Geneva: IEC.