Cell Phones and Other RF Transmitters May Interfere with Medical Devices
Case example: Staff reported problems with patient monitors,
but the equipment worked properly when tested in the biomedical
engineering department. Problem tracking found that patient
monitors experienced intermittent malfunctions mostly on one
particular side of one particular floor, located above a loading
dock. Citizens’ band (CB) or other mobile radio transmissions
from vehicles arriving at the loading dock were strongly
suspected to have been the cause of the patient monitor
interference. Truck drivers were asked to use house phones on
arriving at the hospital, and the problems were resolved.
CHPSO received several reports of equipment failure probably
related to cell phone use. In each case, the cell phone had been
placed upon the equipment. In none was the clinical engineering
department able to replicate the issue.
Radiofrequency (RF) electromagnetic interference (EMI) from cell
phones is a recognized risk. Yet, cell phones may also present a
significant benefit to health care delivery, and are increasingly
being incorporated into nursing practice at many facilities. Key
to balancing the benefits and risks is understanding how to
reduce risks and test for possible adverse effects. Also,
recognize that there are many other potential EMI sources in a
hospital, including electrocautery devices, MRIs, two-way radios,
wireless-enabled laptop computers and similar devices, RFID
readers, two-way pagers and wireless medical devices. Two-way
radios for emergency communications, in particular, may produce
Following are some key points to consider:
EMI risk decreases rapidly as distance of device to potential
EMI source increases. For two-way radios, at least three meters
separation is recommended. One-meter separation from cell phones
is generally safe, and most medical devices continue to function
normally at much closer ranges. Never place a cell phone on top
of or in direct contact with a device. Walls, excluding those
specifically built with shielding (e.g., MRI) cannot be treated
as EMI shields, so this separation distance needs to be honored
through walls, as well.
Leads and wires act as antennas. Testing for EMI should mimic
the layout encountered during the incident to replicate the
antenna structure that was present.
Cell phone transmission power varies with signal quality.
Cell tower locations and hospital design may result in markedly
varied cell phone EMI potential within the building. Improving
cell phone reception by installing microcells or other
communications infrastructure in the institution can reduce EMI
Ad hoc immunity testing of devices (Reference 2) should be
considered when EMI susceptibility is unknown, separation of
device from transmitter is less than the manufacturer’s
recommendation, the device will be in an uncontrolled environment
(e.g., cafeteria), or when new RF sources or devices are likely
to operate beside each other. However, if the new RF source
transmits less than 10 mW, it is unlikely to pose a problem
unless placed closer than 20 cm to a medical device.
CHPSO will be producing a full report on cell phone use, policy
considerations, and ad hoc testing methods; circulating to its
members for comment, then releasing to the general public. Look
for it in your email soon.