Medical Device Lifetime
Medical Device Lifetime or lifespan is the maximum time period specified by the manufacturer during which the medical device or the IVD devices is expected to maintain safe and effective use.
Determination of Medical Device Life Time
Device lifetime could be determined under risk management provisions. For active and non-sterile devices, the lifetime is evolved by following methods
- listing out the individual component lifetime
- general degradation due to the ageing and exposure to the operating environments.
The degradation can be determined by
- RELIABILITY TESTING
- RELIABILITY ANALYSIS METHOD
Reliablity Testing Method
It is used to determine the lifetime expected for the wear out of test materials by undergoing accelerated potential problems and three such methods are:
Highly Accelerated Life Test (HALT)
This method is used for identifying weak links of a product. The impact of high and low temperature and vibration is determined to precipitate failure modes faster than normal testing approaches. It is not a pass/fail test and it requires root cause analysis and corrective action to achieve optimum value from testing. It creates the ability to learn more about the design and material limitations of the product and provides opportunities for continuous improvement of the design before marketing the product. A HALT testing program includes 5 individual tests such as High temperature step stress, Low temperature step stress, Vibration step stress, Rapid thermal cycling, Combined Environment.
Highly Accelerated Stress Screening (HASS)
- Where, AFH is acceleration factor for elevated humidity;
- AFT is accelerated factor for elevated temperature;
- Const. is value that normally goes from 0.1 to 0.15,
- RHs is the stressed humidity, RHo is the operating-environment humidity, and n is an empirically derived constant (usually 1 < n < 5);
- Ea is the activation energy for the temperature-induced failure (most often 0.7 eV for electronics), k is Boltzmann’s constant, To is the operating temperature in kelvins, and Ts is the stressed temperature.
Reliability Analysis Method
In the Reliability Analysis method (expected life analysis) method following are the process
- a use model of the device is developed,
- identification of components with intrinsic wear-out mechanism, then,
- the expected life of each part is determined,
- selection of longer life parts or generation of labeling expected life requirements, safety risk analysis and risk control measures for those parts.
Based on these calculations and with literature reviews on the life expectancy, the expected device lifetime can be determined.