Defining the Expected Service Life of a Medical Device

Expected Service Life of a Medical Device

Five Critical Steps to Achieving IEC 60601-1 Compliance and Product Reliability

Hospitals, healthcare practitioners, and patients expect medical devices to be robust, remaining safe and effective throughout their expected service life.

Understanding the Standard for Expected Service Life

Though medical devices are designed to ISO standards, expected service life is actually defined by IEC 60601-1 as “the time period specified by the manufacturer during which the [device] is expected to remain safe for use.”

Reliability engineering characterizes the failure rates of finished products using the graphical representation of the bathtub curve, in which some level of random failures will occur throughout the useful life of a product. Late in the useful life, failure rates will climb rapidly, caused by physical and/or chemical deterioration with time or use. It is this “wear-out” phase of a product’s life that coincides with the expected service life.

Expected Service Life of a Medical Device

By analyzing the expected service life of a medical device, you can achieve compliance with regulatory standards while ensuring product reliability that builds customer confidence and improves brand reputation.

There is an entire field of study around reliability engineering, which we cannot cover here. However, consider these five critical steps to determine if the expected service life of a medical device meets the intended use.

Five Critical Steps to Achieving IEC 60601-1 Compliance and Product Reliability:

1) Setting a Target Requirement for Expected Service Life

As identified above, customers anticipate medical devices should have a long expected service life, so it’s important to start by setting a target (or system requirement) for expected life.

▢ Is it desirable for the new device to have a longer service life than the previous or current generation?
▢ Is it desirable for the device to outlast a competitor’s product?
▢ Are there other market conditions which would determine the product use?
▢ Is the expected life of critical components limiting the expected life of the device?

Realize that later on in the design and development cycle, you can consider refining the target requirements based on the results of analysis and testing.

2) Developing a Use Model for the Device

It is necessary to consider the intended use of the medical device and its operational and storage environment before you can determine the expected service life.

▢ How many mating cycles will there be?
▢ What are the temperature and humidity requirements of the operational and storage environments?
▢ Are there any chemical interactions?
▢ What external forces, vibrations, or impacts are anticipated?

Keep in mind that the longevity of a medical device is only as good as its subsystems and components and the quality of the interactions between them. When setting the use model for the device, consider the use models of subsystems and components as well.

3) Leveraging an FMEA to Identify the Highest Risk Systems and Components

Most medical devices have components that inevitably wear out over time or after a predictable number of cycles.

> After a certain number of mating cycles, a connector’s electrical contacts lose their conductivity.
> With each subsequent charge cycle, a rechargeable battery’s charge capacity degrades.
> After years of cleaning and disinfection, chemical degradation occurs.

For simple devices, it is often sufficient to identify the risk of failure for each component individually.

For complex medical devices, it is essential to perform a Failure Mode and Effect Analysis (FMEA) to define the structure of the assembly and quantify and prioritize the associated risks.

▢ What are the various potential failure modes of the device and its components?
▢ What is the associated severity?
▢ What is the frequency of occurrence?
▢ Can failure be detected, and how?

Through the lens of an FMEA, you can further analyze and mitigate any failure mode risks that exceed a predetermined threshold.

Because the completion of an FMEA is such a crucial step, you may want to go deeper and get support through a custom analysis.

4) Analyzing the Expected Service Life of High-Risk Components

Based on the applicable use model of the device, it’s important to perform an analysis to calculate the expected service life of each component that was identified as high risk in your FMEA.

For example, if a connector is rated for 1,500 mating cycles, and the use model indicates that a mating cycle occurs once per day, then the connector is expected to last 4.1 years (=1,500/365). As you perform the analysis, you may discover that the calculated expected life of high-risk components is significantly less than the target service life for the device. If the analysis determines that the required expected service life is not achievable, you can consider a number of potential solutions.

▢ Does there need to be a reduction in expected service life?
▢ Is it necessary to select parts or materials with a longer service life?
▢ Should the design be revised to enable the replacing or servicing of parts?
▢ If possible, can redundant components be added to the system?
▢ Are any other risk control measures needed to mitigate failure of the component?

5) Confirming Requirements are Met Through Verification Testing

Once determinations are made through the service life analysis, additional quality and regulatory activities such as verification testing can be focused on the highest risk conditions.

Reliability verification testing confirms if a product meets requirements at the beginning of life, as well as at end of life. For this purpose, expected service life performance is at the end of life and often evaluated through HALT, HAAS, or cycle testing.

Supplemental Benefits to Support Characterization and Performance Evaluation

The analysis you do to define the expected service life also provides supplemental benefits that will support your efforts to characterize and evaluate the performance of your medical device, such as:

> The steps you use here to define the device’s service life are also easily adapted to help you conduct a lifetime analysis for your medical device.
> A well-defined expected service life (and the analysis achieved through these five steps) is extremely useful when you conduct post-market surveillance to manage new safety and performance data and update the risk management of your device.

We realize there is a wealth of information that can be explored around the work of defining the expected lifetime of a medical device, starting with the IEC 60601-1 standard. The good news is you don’t have to go it alone – AC has your back. We have extensive experience designing and developing medical devices to meet stringent customer, brand, and regulatory requirements with long expected lifetimes.

To learn more about Andrews Cooper and how we may be able to assist in expected service life performance, reach out to us today. We’re here to help!



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