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Risk Assessment for Power Supplies to Comply with IEC 60601-1 3rd Edition

For medical device OEMs seeking compliance to the 3rd Edition of IEC 60601-1 for their power supplies, what is quite clear by now are the regional dates for enforcement, the required risk management at the medical electrical equipment or system level, the new definitions of Means of Operator Protection (MOOP) and Means of Patient Protection (MOPP), and other differences as compared to the 2nd Edition. What is not clear is how to address these new definitions and requirements. Rather than simply redesigning and resubmitting for 3rd Edition certification, questionnaires and flowcharts that map out the requirements at the device or system level help to minimize the evaluation and redesign at the power supply level. By having the medical device OEM and power supply vendor answer the questionnaire concurrently, deficiencies from the equipment or power supply can be quickly assessed in order to satisfy the requirement.

IEC 60601-1 3rd Edition Standard

altThe IEC 60601-1 standard is a globally recognized standard for electromedical equipment safety, and a parent standard to more than 60 particular device standards. The next evolution in the IEC 60601-1 3rd Edition, requires a risk management file and process conforming to ISO 14971, the international standard for Application of Risk Man agement to Medical Devices. In Europe, the standard went into effect in June of 2012 for all medical products, new or existing. In North America, the FDA announced that it has adopted and recognized ANSI/AAMI 60601-1 3rd Edition and established June 30, 2013, as the mandatory transition date applicable for new medical device submissions only — existing medical devices in the market are “grandfathered” under the regulation.

Medical device OEMs are required to meet this standard for their end products and are responsible for the risk management and applications categorized as MOOP or MOPP. Even though the 3rd Edition standard really does not apply to components, a few power supply manufacturers are working closely with their medical device customers to comply with this new regulation. For next generation medical device products, it is easier to start requiring power supplies certified to the 3rd Edition. For existing electromedical devices especially those in the EU market, complying may mean re-qualifying another power supply through end-device verification and validation or doing risk assessment of the continued use of current power supply.

Risk Management

Risk Management covers risk analysis and evaluation followed by risk control to bring overall risk to an acceptable level, with continuous monitoring and feedback process. Table 1 shows a risk assessment typically used to identify hazards and conditions affecting safety and critical performance of a medical device, to gauge the severity of harm done, to identify the cause of the condition, assign probability of occurrence, and to define activities to mitigate risks.

To include the power supply in the risk assessment, the medical device product team (i.e., staff coming from regulatory affairs, engineering, marketing, quality, etc.) should consider feedback from their power supply partner in identifying the hazard conditions as well as the probability of those events occurring.

The four items listed in the table are common failure modes recorded in the FDA adverse events database as well as causes in product recalls. The probability of occurrence can be provided by the power supply partner based on their field failure data (parts per million failures on those corresponding product or family).

The nature of the clinical or therapeutic function of the electromedical device affects heavily the severity and hence the risk of each failure mode. Typically, a power failure merely causes postponing the use of the medical device until another unit comes along. However, when the need for the medical device is urgent and essential to administering therapy quickly, then any delay due to non-operation can be a real issue. The rest of the information includes generic examples and requires more detail in a true risk assessment documentation.

For some world-class power supply manufacturers, Risk Management is part of the Quality Standard processes though not in the same format or level as described above. In regards to design controls, DFMEA (Design Failure Mode and Effects Analysis) is a method for evaluating a design for robustness against potential failures. MTBF (mean time between failure) calculations and component derating are guidelines used to select appropriate components that meet the required application conditions and product life. For purchasing controls, the rigorous and disciplined use of preferred parts list and approved vendor list ensures that only those parts and suppliers that meet performance and quality metrics are considered and used. To improve production and process controls, full functional, Hipot and safety tests are 100 percent done in tandem with lot sampling for burn-in and accelerated life tests based on a standard quality plan. In addition, traceability, field failures, and failure analysis data are correlated back to production metrics performance and specific component lots or date codes when needed.

Collaboration

Beyond the risk management file, doing the gap analysis between 2nd and 3rd Editions of the IEC60601-1 is critical for those medical device OEMs intent on using their current 2nd Edition power supply for existing and/or new designs. Discussion between the OEM and power supply vendor is vital. This collaboration can help identify any obstacles in the power supply and how to properly adjust. Looking at the specifications together can go a long way in minimizing the work done to make the medical device, including the power supply component, comply to the 3rd Edition. Important discussion points include:

• MOOP or MOPP classification
• Classification of applied parts: Type B, BF or CF
• Main fuses and over-current releases
• Elevation
• Leakage current
• Safety insulation for transformers
• Y1 &Y2 capacitors
• Hipot voltage
• Creepage and clearance

Classifying the particular medical device application into MOOP, MOPP, and Type B/BF/CF are key questions since these determine the degree of evaluation the power supply and medical device need to undergo. MOOP is less stringent than MOPP. Within MOPP, Type B has the least stringent requirements, followed by BF. Type CF has the strictest specifications. These classifications have to be determined by the medical device OEMs by properly considering the device’s intended use and particular application environment.

On several occasions, forcing an existing power supply to comply with the demands of the 3rd Edition, especially on MOPP, requires a handful of component changes and a complete PCB re-spin. That entails practically repeating the power supply qualification (i.e., DVT build and QA verification), if not an abbreviated one. This, in turn, may force verification and validation on the medical device level as well using the upgraded power supply.

Also, if some of the requirements listed in the bullets above are not met by the power supply, the medical device design engineers may look at the system level if such requirements are considered outside of the power supply, but within the medical device like having redundant fuses, capacitors, and insulation.

Conclusion

While change is never easy, implementation of risk management touches not only the end-product manufacturer, but the component supplier as well. The implementation of the 3rd Edition helps to ensure performance and safety throughout the lifetime of a given device. Forward planning and upfront collaboration with suppliers will help mitigate problems later down the road. Moreover, the gap analysis of the differences between 3rd and 2nd Editions at the power supply level becomes an easier and more directed task. Sometimes, it is easier to change a component outside the power supply rather than forcing power supply to upgrade to IEC 60601-1 3rd Edition.

This article was written by Cochise Mapa, Director of Global Product Management for SL Power, Ventura, CA. For more information, visit http://info.hotims.com/45599-163.