Expected Lifetime Analysis for Medical Devices

Unlike today’s “throw-away” consumer electronic devices, most medical devices are designed to provide a lengthy expected service life –– typically 5, 10 or even 15 years.   IEC 60601-1 defines expected service life as the time period during which the device is expected to remain suitable for its intended use, and all risk control measures remain effective.

In order to attain a desired service life, the reliability verification of the device needs a multi-pronged approach.  Reliability testing approaches must include accelerated life margin testing at both the component and system levels and destructive life testing methods such as HALT.  However, testing alone is not sufficient.  Reliability analysis methods are also needed.  One very effective reliability analysis method that is not yet commonly used is expected life analysis.

Most medical devices have components and accessories with built-in wear-out mechanisms.  For example, the electrical contacts of a connector will lose their conductivity after excessive insertion/removal cycles.  Similarly, the charge capacity of a rechargeable battery degrades with each charge cycle.  Components with intrinsic wear-out mechanisms must be analyzed based on the use model for the device.   For example, if a connector is rated for 1,500 insertion cycles, and an insertion occurs every day, the connector is expected to last 4.1 years (=1,500/365) which might be significantly less that than the expected service life of the device.

The expected life analysis follows the following process:

  • Develop a Use Model for the device
  • Identify components and accessories with intrinsic wear-out mechanisms
  • Determine the expected life of each of these parts
  • Select longer life parts or generate appropriate labeling, expected life requirements, verification procedures, and safety risk analysis and risk control measures for the part (to mitigate failure of the part)

For some components, the expected life analysis is a simple calculation as shown above.  However, many types of wear mechanisms are not specified or easily characterized.  An example is micro-vibration wear on a connector–– especially when the device is subjected to harsh environments like ambulances and helicopters.   Reliability testing methods must be used to characterize the expected life.

Andrews-Cooper has extensive experience developing medical devices with long expected lifetimes.

Process

Andrews-Cooper’s approach toward Product Definition, Product Development and Product Delivery ensures predictable schedule, cost, regulatory approval and quality outcomes throughout a product’s lifecycle. Our approach is a coordinated combination of:

  • Specific adaptation of process necessary for each project
  • Cross functional team collaboration
  • Appropriate project management
  • Systems Engineering
  • Design & implementation
  • Verification & validation
  • Regulatory support
  • Transfer to manufacturing
  • Quality Management