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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

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EMI and medical devices

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  1. EMI and medical devices The problem: the EMI environment; why? Device types emitting EMI Devices affected Stakeholders Historical development and issues Solutions Standards

  2. The problem • EMI—causes potential malfunctions of medical devices • --near misses • In USA, most medical devices are exempt from FCC emission requirements

  3. 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

  4. EMI environment • Changes with time • Expensive to monitor • Can behave differently in a lab

  5. 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

  6. 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)

  7. Others (medical) • Electrosurgical generators • Diathermy machines • Ultrasound therapy machines • Interferential therapy machines • Electrical drills

  8. Devices frequently affected • Patient monitors • Infusion devices • Pacemakers and implantable defibrillators • Infusion pumps • Ventilators • Pulse oximeters • Apnea monitors • Hearing aids • Incubators and radiant warmers

  9. Who are the stakeholders? • Users • Manufacturers • Voluntary standards organisations (ex. AAMI, ) • Regulators (ex. FDA, Medical Device Bureau in Canada) • Test laboratories and researchers

  10. 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

  11. 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

  12. 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!

  13. Other issues • Lack of appropriate standards • Proliferation of medical equipment • Potential interaction between devices • Awareness level of users/manufacturers • Intermittent sources of emission

  14. 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

  15. 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

  16. 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

  17. Sources of information • http://www.fda.gov/cdrh/ost/reports/fy98/ELECTRO_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

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