Medical device use-safety: Incoporating human factors engineering into risk management

Guidance for industry from the US Food and Drug Administration (FDA). Written by Ron Kaye and Jay Crowley and issued 18 July 2000

Hazards related to medical device use should be addressed during device development as part of the risk management process. Human factors engineering is a key element in achieving the goal of ensuring users are able to use medical devices safely and effectively throughout the product lifecycle. This requires an understanding of the interaction between users, devices and the use environment.

Evidence suggests that the frequency and consequence of hazards resulting from medical device use might far exceed those arising from device failures. Some of these errors will result in fatality. Whilst direct hazards associated with devices (i.e. chemical, mechanical, electrical etc.) are often well understood, use errors can cause medical problems through misdiagnosis (i.e. assigning the wrong cause to a condition and hence providing inappropriate treatment), failure to recognise and act on information (e.g. information from a monitoring device) or provision of improper treatment (i.e. device set up incorrectly when implementing a therapy).

Use-related hazards occur for one or more of the following reasons:
* Devices used in ways that were not anticipated in design;
* Devices used in ways that were anticipated but inadequately controlled for;
* Device use requires personal abilities (e.g. physical, perceptual, cognitive) that exceed those of the user;
* Device use is inconsistent with users' expectation or intuition about device operation;
* The use environment effects device operation and this effect is not understood by the user;
* The users capacities are exceeded when using the device in a particular environment.

Whilst user trials of devices are an important part of development, it is important to be aware of their limitations. For example, unusual circumstances often represent the greatest threat to safe and effective use of a medical device because users are less able to react appropriately to situations that occur infrequently, but these are difficult to predict during early development or to test during user trials. Also, users will often have a preference for ease of use and aesthetics, whereas the safest arrangement may require some design features that can slow down use of effect aesthetics (e.g. shields over critical controls, mechanical or software-based interlocks).

Human factors engineering shows us the following apply:
* Use environment - light, noise, distraction, motion/vibration, workload;
* User - knowledge, abilities, expectations, limitations;
* Device - operation requirements, procedures, device complexity, specific user interface characteristics

User characteristics include
* General health and mental state (stressed, relaxed, rested, tired, affected by medication or disease) when using the device,
* Physical size and strength,
* Sensory capabilities (vision, hearing, touch),
* Coordination (manual dexterity),
* Cognitive ability and memory,
* Knowledge about device operation and the associated medical condition,
* Previous experience with devices (particularly similar devices or user interfaces),
* Expectations about how a device will operate,
* Motivation, and
* Ability to adapt to adverse circumstances.

A good example for the user is diabetics. They are required to monitor their blood sugar levels on a regular basis, and electronic devices are available to do this. However, diabetics often suffer from retinopathy which affects eye sight. Blood monitoring devices have in the past been provided with small displays which many of the intended users cannot use reliably.

The following list can help identify potential scenarios that could result in hazard
1. Why have problems occurred with the use of other similar products?
2. What are the critical steps in setting-up and operating the device? Can they be performed adequately by the expected users? How might the user set the device up incorrectly and what effects would this have?
3. Is the user likely to operate the device differently than the instructions indicate?
4. Is the user or use environment likely to be different than that originally intended?
5. How might the physical and mental capabilities of users affect their use of the device?
6. Are users likely to be affected by clinical or age-related conditions that impact their physical or mental abilities and could affect their ability to use the device?
7. How might safety-critical tasks be performed incorrectly and what effects would this have?
8. How important is user training, and will users be able to operate the device safely and effectively if they don’t have it?
9. How important are storage and maintenance recommendations for proper device function, and what might happen if they are not followed?
10. Do any aspects of device use seem complex, and how can the operator become "confused" when using the device?
11. Are the auditory and visual warnings effective for all users and use environments?
12. To what extent will the user depend on device output or displayed instructions for adjusting medication or taking other health-related actions?
13. What will happen if necessary device accessories are expired, damaged, missing, or otherwise different than recommended?
14. Is device operation reasonably resistant to everyday handling?
15. Can touching or handling the device harm the user or patient?
16. If the device fails, does it "fail safe" or give the user sufficient indication of the failure?
17. Could device use be affected if power is lost or disconnected (inadvertently or purposefully), or if its battery is damaged, missing or discharged?

Having identified potential hazards, it is then necessary to implement a combination of mitigation and control strategies. The following should be considered in the stated order
1. Modify device design to remove hazard or reduce its consequence;
2. Make user interface, including operating logic, error tolerant
3. Alert users to the hazard
4. Develop written procedures and training for safe operation.

Andy Brazier