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 Lifetime

Medical 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

In the reliability testing method accelerated life margin test is conducted at both component and system levels. By identifying the failure modes, these tests can be used for creating failures and will determine how often the device fails and how long it takes to fail. This helps to identify design weaknesses that could be improved upon.

The degradation can be determined by the reliability testing method in which an accelerated life margin test is conducted at both component and system levels.

It is used to determine the medical device 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 as High-temperature step stress, Low-temperature step stress, Vibration step stress, Rapid thermal cycling, Combined Environment.

Highly Accelerated Stress Screening (HASS)

The purpose of this test is to speed the identification of latent defects in the manufacturing process of the product lifecycle to reduce associated failures.

The acceleration factor for unbiased HAST testing is:

AFHAST = AFH . AFT = e cost.(RHn/s – RHn/0) e (Ea/k) (1/T0-1/Ts)

Where AFH is the acceleration factor for elevated humidity;
AFT is an accelerated factor for elevated temperature;
Const. is a 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.

Accelerated Weathering

The impact of damage by sunlight and weather is determined, within a compressed period of time. These tests are often used to test equipment designs intended for outdoor applications to predict how they will stand up to weather throughout their lifetime.

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.

Applicable International Standards - Medical Device Reliablity

International standards for Medical Device Reliability including Software device are:

ISO 14971 (ensures safety and reliability of medical devices)
IEC 60601-1 (safety standards for electromedical equipment)
ISO/TR 80002 (risk management requirements of Medical device Software)
IEC 62304 (life cycle requirements of software- software development and maintenance)

Medical Device Lifetime Vs. Medical Device Shelf Life

It is often confused between medical device lifetime and shelf life. Are they related? The lifetime of a medical device is its useful life of a device that is the duration of actual use before the device becomes unable to attain its intended use. In other words its stability to withstand the cleaning and sterilization during repeated use.

Shelf life explains duration of the medical device to be stabile to retain the sterility of the package and the device performance. It ends when the package is open or the shelf life claimed on the label, whichever comes first. Lifetime starts at the opening of the device package and ends until it works properly to attain its intended use.

Medical Device Lifetime - MDR and IVDR Requirments

As per article 18 of the MDR, it is a requirement that the manufacturer of an implantable device should provide together with the implantable device is any information of the expected lifetime of the device

Annex I GSPR 6 of MDR and IVDR states that the characteristics and performance of a device should not be adversely affected to such an extent that during the medical device lifetime of the health or safety of the patient or user and, where applicable, of other persons is compromised, as indicated by the manufacturer when the device is subjected to the stresses which can occur during normal conditions of use and has been properly maintained in accordance with the manufacturer’s instructions.

Annex I GSPR 18.2 of the IVDR states that devices should be sufficiently stable under the foreseen operating conditions. They should be appropriate to withstand stresses inherent in the foreseen working environment and to retain this resistance during the devices’ expected lifetime, subject to any inspection and maintenance requirements as indicated by the manufacturer.

Annex I GSPR 9.2 of the IVDR states that the performance characteristics of the device should be maintained during the lifetime of the device as indicated by the manufacturer.