Transcript EMI and medical devices

EMI and medical devices







The problem: the EMI environment; why?
Device types emitting EMI
Devices affected
Stakeholders
Historical development and issues
Solutions
Standards
The problem



EMI—causes potential malfunctions of
medical devices
--near misses
In USA, most medical devices are exempt
from FCC emission requirements
The problem..continued


1979-93: 100 reports FDA
Now FDA re-evaluating 400,000
malfunctions (1984-94) to see if EMI
involved– expect 1000 to be related
EMI environment

Changes with time

Expensive to monitor

Can behave differently in a lab
Why problems can be
common





Physiological & biological signals are
typically very low (mV or microV)
Use high gain amplifiers
Leads, cables, body, act as antennas
Coupling signals and rectification signals
at electrode interfaces
Home devices
Typical devices that emit EMI








Local high power AM/FM & TV transmitters
Paging systems
Cellular phone base stations & repeaters
Two way radios
Amateur or CB radio
Wireless communication devices
Microwave ovens
Static discharge (people)
Others (medical)





Electrosurgical generators
Diathermy machines
Ultrasound therapy machines
Interferential therapy machines
Electrical drills
Devices frequently affected









Patient monitors
Infusion devices
Pacemakers and implantable defibrillators
Infusion pumps
Ventilators
Pulse oximeters
Apnea monitors
Hearing aids
Incubators and radiant warmers
Who are the stakeholders?





Users
Manufacturers
Voluntary standards organisations (ex.
AAMI, )
Regulators (ex. FDA, Medical Device
Bureau in Canada)
Test laboratories and researchers
Historical perspectives (30
years)



In the 1970s: Main sources AM/FM, elevators,
microwave ovens
Examples: EEG signals to confirm brain
death; EMG and evoked potential signals;
pacemakers
Solutions: Separation, Isolation, or Faraday
cage? Education? Better cover (Titanium),
bipolar leads, stronger signals
Continued….





Apnea monitors (the NB experience)
Infusion pumps and wheel chairs out of
control
Incubators shut off or re-programmed
Dialysis re-programmed
Today: More sources than ever but
more EMC protection
Solutions







Policy for safe zones (ex. Moncton H. in 1979
(ban equipment in ICU, etc)
Policy for home care devices in 1980
Policy for use of insulation (gloves) to
manipulate sensitive equipment
Policy to manage equipment and EMI sources
Document all malfunctions & investigate
Use low power devices, better EMC
Move patient or move the source!
Other issues





Lack of appropriate standards
Proliferation of medical equipment
Potential interaction between devices
Awareness level of users/manufacturers
Intermittent sources of emission
Types of incidents



True positives—replication of incident at a site
and /or a lab—increases degree of confidence
on nature of incident
False positives– attributed to EMI but
probably is NOT– perhaps a software problem
or other malfunction
False negatives– not attributed to EMI but is
likely from EMI—often happens if reporter
NOT familiar with EMI—sometimes confirmed
by alert from manufacturer
Types of malfunctions








Operation out of specifications
Operator intervention needed
Fault—needing repair
Operation out of control
Silent malfunction-- Not functioning at all
Discrepancy between clinical reality and
readout
Impossibility of reading signals
Note: Some devices are unreasonably
susceptible
Standards




MDS-201-0004 (1979) voluntary –inadequate
and not harmonized IEC
IEC.601-1-2 Collateral to IEC.601-1 (general
safety of medical equipment)—determined
that tests in BW significant for labelling of
medical devices
Recommendation: testing at 3V/m (pulse
modulation or 80 % sine wave modulation at
0.5 Hz, over 26 MHz to 1 GHz, with standard
placement of cables
Quasi-static field: 2000V/m at 0.5 Hz
Sources of information

http://www.fda.gov/cdrh/ost/reports/fy98/ELE
CTRO_MAG.HTM

http://www.fda.gov/cdrh/emc/persp.html

http://www.fda.gov/cdrh/ost/ostannrpfy98.pdf

http://www.fda.gov/cdrh/ost/emi.html