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 : 100 reports FDA Now FDA re-evaluating 400,000 malfunctions ( ) 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 (1979) voluntary –inadequate and not harmonized IEC IEC Collateral to IEC (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 CTRO_MAG.HTM