Page 59 - Safety Risk Management for Medical Devices

38 Safety Risk Management for Medical Devices

While you may not have any control over the environmental factors that surround
the medical device, knowledge and awareness of such factors is critical for the proper
design of the UI of the medical device.

Tip Consider the typical workflows where your device will be used. If your device replaces an
existing device, legacy behaviors may carry over to the use of your System.

8.6 DESIGN MEANS TO CONTROL USABILITY RISKS

In most cases, changes to the design of the medical device can serve to reduce the
risks due to use failures. Some examples of such design controls are as follows:
• Keystroke debouncing—if the same key is pressed within 200 ms, ignore the sec-
ond keystroke.
• Reasonableness checks—evaluate the user input for reasonableness. If the input is
out of range or unreasonable, inform the user.
• Proper sizing—use anthropomorphic data to size the use interface such that
physical errors are less likely, e.g., buttons sized to human fingers.
• Alarm types—use IEC 60601-1-8 [19] for guidance on proper design of alarms.
• Font size—use AAMI HE75 [20] for guidance on font sizes for visual displays.

If such design means are employed to reduce risk, they should be verified for
effectiveness in risk reduction.

8.7 TASK ANALYSIS

The Standard [14] requires that the manufacturers identify UI characteristics that
could be related to the safety of medical devices. A common tool to achieve this is
task analysis. Task analysis is a formal and systematic activity that starts by creating a
detailed description of sequential and simultaneous actions of the user of the medical
device. Task analysis usually starts with high-level use-scenarios, and then adds tasks
and ultimately details down to individual steps are spelled out. The output of task
analysis is input to the UMFMEA (see Section 12.8). As such, conditions of use and
user profiles are important to know, and should be included in the task analysis. Task
analysis results are typically stored in a tabular or flowchart format.
Task analysis should begin at concept development stage at a high level, and should
progress with more details as UI design matures. Because designs iterate multiple times
during the design process, task analysis should be kept in sync with the UI design to
ensure the validity of risk management with respect to UI design.
For the purposes of risk management, what is of interest are the user-performed
steps, and how errors in performing them could result in Hazards.