Qulaity

Evaluation of Medical Devices

Dr. K.V.Jogi Director, DCTL Mumbai

Medical devices are very diverse in their size, design, and application from a small implantable inert material to complex computer controlled robotic machines, from those which do not come into contact with human body to those implanted deep inside, controlling vital functions, for several years. Their complex and multi component designs lend themselves innovative changes and improvements by individual manufacturers.

Hence specifications for most devices are developed as a part of design control and many differ from manufacturer to manufacturer.

Evaluation of medical devices, generally cover 3 areas viz.

1. Quality/reliability

2. Safety

3. Efficacy

When a device is the result of changes in design, evaluation also involves risk benefit analysis compared to other currently available devices in the same category. As pointed out earlier, development of specifications and test methods is a part of design development and design control.

Design development among other things, addresses the following:

1. Fitness for purpose

2. Reliability

3. Durability

4. Serviceability and

5. Biocompatibility

At a later stage, it also considers and incorporates, appropriate mechanism to minimize or obviate foreseeable abuse and mishandling.

Involvement of Medical and biometric specialists at the stage of conceptual design, ensures conformance to input. The investigational device when used in volunteers would lead to further inputs for ease of use and discomfort in using.

Reliability of a device is measured by the failure rate (mean time between failures). If the components are tested separately, sudden death is used with Weibull Plots to calculate failure rate of each component.

Failure of a device or its component to perform its expected or intended function under specified conditions can only be evaluated against specified parameters or values.

Systematic failures are often a result of poor quality assurance operations, allowing some parameters to fall outside specified limits. This results in production of defective components which increase the probability of device failure. Random failures, as the name implies, are difficult to predict and require a statistical approach for analysis.

While hardware failure could be random, software failure is always systematic, unless it could be linked to hardware.

A system with good diagnostic software helps predict or avoid failure.

When an unacceptable rate of failure occurs, HACCP helps improve design or take precautions to avoid or minimize failure.

Failure mode and Effect Analysis, FEMA, which determines the relation between element failure and system failure, helps formulating inspection tests during manufacture and installation and acceptance criteria

Testing is done mainly to verify the claims or to validate the system to meet product specifications.

Test results are functions of operating environment and procedure adopted and the data generated should be interpreted in these contexts.

Tests may be categorized as:

1. Time testing to determine long-time reliability by estimating failure rate and mean time between failures and can show which part or component cause failure and also, mechanism of failure.

2. Event Testing is repeated testing, till failure.

3. Stress Test done by applying limiting stress that may be encountered in normal usage as well as possible (usual) mishandling. Cause of failure may be investigated by step by step evaluation.

4. Environmental Testing is done by exposing the device to environmental and transport conditions (temperature,