ISO 14971 Fundamentals: Characteristics related to safety

Best practices for identifying safety characteristics and connecting them to design controls.

Analyzing risks associated with the use of a medical device requires identification of hazards that a patient or user may be exposed to in a hazardous situation. It is the exposure to one or more hazards that results in harm.

But how do you identify hazards and hazardous situations when you are just starting out in the initial phase of product development?

Once you have a fairly good idea of the intended use of your device, you can start by identifying different characteristics of the device and its use that could affect safety. That is why, ISO 14971¹ requires manufacturers to identify and document characteristics related to safety in sub-clause 5.3 as part of risk analysis:

For the particular medical device being considered, the manufacturer shall identify and document those qualitative and quantitative characteristics that could affect the safety of the medical device. Where appropriate, the manufacturer shall define limits of those characteristics. This documentation shall be maintained in the risk management file.

At the most basic level, any feature of a device or the way it is used in the clinical environment, may be considered as a characteristic related to safety if it can be associated with one or more hazards that can potentially cause harm.

Consider the following examples from recent Class I recalls:

1. An incompatible syringe when used in an infusion pump system may lead to pump performance issues such as overdose, underdose, delay in therapy, and delays in occlusion alarms². In this case, syringe dimensions, shape, geometry etc. may be considered characteristics related to safety since they can affect the infusion pump function.

2. Unintended arm movement of the Laparoscope Instrument Actuator (LIA) in a robotically-assisted surgical system may lead to loss of control during surgery³. In this case, specifications of components used to control the arm movement, as well as the emergency stop functionality may be considered characteristics related to safety.

3. Overheating of a reusable return electrode used during electrosurgery causes serious burn injuries and scarring in patients⁴. In this case, surface conductivity of the electrode may be considered as one of the characteristics related to safety.

4. Potentially non-sterile angiographic catheters used to deliver contrast dye to specific places in blood vessels for visualization during surgery may lead to life-threatening infection⁵. In this case, sterilizer process control parameters and procedural steps may be considered characteristics related to safety.

5. Mislabeling on the package of a pressure injectable catheter kit used to sample blood, monitor blood pressure, or administer fluids, medications or chemotherapy may cause severe, life-threatening allergic reaction⁶. In this case, safety-critical labeling information may be considered characteristics related to safety.

These examples highlight the importance of clearly and completely identifying all relevant characteristics related to safety during the risk identification phase. These characteristics, and their qualitative/quantitative limits for safe operation, should be treated as design inputs during the design and development process. In this way, you can ensure that appropriate risk control measures are considered for implementation and verified for their effectiveness.

This exercise also helps in identifying hazards and hazardous situations that can be manifested by loss of control over these characteristics related to safety.

Here are some best practices useful for identifying safety characteristics, establishing limits and connecting them to hazards.