Cause of Device-Related Incident
*Not stated

Clinical Specialty or Hospital Department
Clinical/Biomedical Engineering

Device Factors
*Not stated

Document Type
Guidance Articles

External Factors
Electromagnetic or radio-frequency interference (EMI and RFI)

Mechanism of Injury or Death
*Not stated

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
*Not stated

Electromagnetic Interference and Medical Devices: An Update on the Use of Cellular Telephones and Radio Transmitters in Healthcare Facilities



Guidance [Health Devices Feb-Mar 1996;25(7):263]

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.

Attempting to Define the Risks

Historical Perspective

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 impact.

EMI from Cellular Telephones:

Summary of Seven Clinical Reports Received by ECRI, 1992 to 1995

Affected Device

Effect

Potential Serious Consequences?

Monitoring system

Central station alarms and printouts suppressed

Yes—However, no adverse clinical consequence occurred in this incident, which was associated with multiple cellular telephones being used in one room

Monitoring system

Waveform artifact observed

No—Waveform interference occurred, but reverted to normal when transmission ceased

Monitoring system

High blood pressure readings displayed

No—Erroneous data was displayed, but reverted to normal when transmission ceased

ECG telemetry monitoring system

Waveform artifact observed

No—Waveform interference occurred, but reverted to normal when transmission ceased

ECG telemetry monitoring system

Unknown

No

Infusion pump

Alarm sounded (rate also may have changed)

No

Ventilator (operated in a car)

Inappropriate activation of low-pressure alarm

No

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 reports.

Identifying EMI Sources: High- versus Low-Power Technologies

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.

Identifying Susceptible Devices: Ad hoc Testing

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 devices.

What Are the Limitations of and Considerations for Testing?

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 restriction.)

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.

When Is Testing Appropriate?

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.

Developing and Implementing a Policy

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.

Interactions between Cellular Telephones and Cardiac Pacemakers

Overview

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.

Analog- versus Digital-Mode Cellular Telephones

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.

Minimizing Risks

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.

ECRI Recommendations

General Comments

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.

ECRI Advises Institutions to Implement the Following:

  • 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.

ECRI Suggests that Institutions Adapt the Following as Appropriate for Their Particular Circumstances and Perceived Needs:

  • 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.

Notes

  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.


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