By: Michael Wiklund and Jonathan Kendler

For more than half a century, the airline industry has relied on checklists to help improve safety. Prior to every flight, a pilot visually inspects the outside of the aircraft and executes a preflight checklist from within the cockpit. These checklist reviews and enhancements have helped pilots avoid use errors, such as forgetting to configure a plane properly for takeoff.

 

In The Checklist Manifesto, Atul Gawande, a practicing surgeon who writes about his efforts to ensure good patient outcomes, extols the virtues of checklists used in multiple domains, including in his hospital’s operating rooms. He cites promising studies that show how a checklist can reduce the rate of postsurgical complications, such as infection by 36% and deaths by 47%, as compared with normal medical practice.¹ Could a checklist help medical device developers produce user interface designs that are less likely to induce the use errors that lead to patient injury or death?

 

To date, user interface design flaws have been implicated in a disconcerting number of adverse outcomes.² A checklist could help avoid the most common and readily detectable flaws, particularly when quality checking is followed up with comprehensive usability testing. With this in mind, we’ve put together a four-part checklist. It is unquestionably off-the-cuff compared with those developed in a more comprehensive manner involving contributions from multiple subject matter experts, peer reviews, and validation studies. Therefore, if you question the checklist’s validity, you are exercising good judgment. However, the listed items are based on findings from thousands of hours spent observing people succeed and struggle to use medical devices when performing clinical work and participating in usability tests. The checklist is also generally consistent with the applied design guidance found in ANSI/AAMI HE75:2009, “Human Factors Engineering—Design of Medical Devices.”

 

Research suggests that shorter checklists are often more effective than longer checklists, helping pilots quickly obtain critical information in emergencies, for example.³ Although product designers do not normally encounter the immediate stresses faced by pilots, this article opts for brevity with four 10-item checklists. Each checklist addresses a different aspect of a medical device’s user interface, including its hardware, software, and printed elements (i.e., documentation), as well as its integrated performance.

 

1. Controls Provide Positive Feedback. People want controls to be responsive to inputs, and they readily notice delayed responses. For example, most people will notice a delay greater than 200 milliseconds between pressing a keyboard key and seeing the associated character appear on the display screen. People are also sensitive to the effects of their actions, such as the clicking noise produced by moving a rotary control from one position to another. Therefore, designers should ensure that all control actions provide definitive, distinctive, and nearly immediate feedback. Such feedback helps users detect control input errors (e.g., the absence of the second “0” in a dose rate of “200” or the lack of a clicking noise associated with a secure tube connection).

 

2. Controls Have the Appropriate Degree of Precision. Controls can be insufficiently precise or too precise (see Figure 1). For example, a control might have so little travel (i.e., range of motion) and so few markings (e.g., 0, 25, 50, 75, 100) that it is difficult to set an exact value, such as 65, which would require interpolation. Conversely, a control might have too much travel and too many markings (e.g., 1, 2, 3, 4, 5…96, 97, 98, 99, 100), providing too many choices when low, medium, or high designations might be sufficient.

3. Handles Enable a Comfortable and Secure Grip. Good handles are easily accessible and located where users expect to find them. They are shaped to accommodate various hand sizes and angled so that users can apply as much force as necessary with minimal strain, which usually means enabling a power grip (i.e., with the thumb and fingers placed on opposite sides of a handle). Good handles also have a nonslip texture, which may be achieved by knurling or adding a soft-touch plastic coating, such as Santoprene.

 

4. Components Are Clearly Labeled. Because clinicians typically use dozens of medical devices during the average work week, it helps to label a device’s interactive components. Although the purpose of individual components should be intuitive, text or symbolic labeling is generally a welcome affordance, because it provides extra protection against users mistaking one component for another. Labeling with abbreviations and acronyms other than those that have become ubiquitous (e.g., ECG) reduces the benefit.

 

5. Controls Are Shape Coded. Certain environments or use scenarios require users to operate a device without looking at it. For example, anesthesiologists might need to titrate the gas flow on their anesthesia machine while carefully watching the patient’s fluctuating breathing rate on a monitor. To help users avoid activating an incorrect control, the controls should be shape coded to distinguish them by touch alone.

 

6. Critical Controls Are Protected. Recessing a control or placing a cover over it are straightforward ways to protect controls from inadvertent actuation (i.e., being bumped into and accidentally pressed). Patient-controlled analgesia pumps feature even stricter protection, requiring clinicians to enter a special code before enabling control access, thereby guarding against both inadvertent and unauthorized use.

 

7. Controls and Related Displays Are Adjacent. Users often look to adjacent displays to obtain visual feedback after a control action (e.g., moving a lever). It’s a lot simpler for users if there is one obvious display to scan. Placing the display above the control is optimal, because it reduces the likelihood that the user’s hand will block the control during operation.

 

8. Matched Components Only Connect to Each Other. The list of patient injuries and deaths caused by misconnections is alarmingly long. For example, gas lines have been forced into IV ports, and IV lines have been forced into enteral feeding tubes. Therefore, matched and mated components should be redundantly coded (e.g., shaped, keyed, colored, labeled) to clarify the appropriate and compatible connection. Such coding also eliminates the potential for misconnections.

 

9. Controls Are Sufficiently Large and Spaced Apart. Users with larger-than-average fingers might struggle to access small controls, such as a push button with a diameter of less than 0.5 in. Similarly, if controls are spaced too close to each other, users might inadvertently actuate one control when attempting to use another.

 

10. Critical Components Are Visible. Some medical devices require users to regularly inspect or observe parts of the machine. For example, dialysis nurses regularly inspect a hemodialysis machine’s tubing set to ensure proper blood flow, and critical care nurses might look for a green status light atop an infusion pump to verify that the infusion is active.

 

1. Alarm Indicators Are Informative. A good visual alarm indicator coherently and concisely describes the alarm condition and how to resolve it. The indicator should not require users to look up alarm codes in a user manual to understand the alarm condition and what action they should take. Requiring such intense searching wastes time and might compromise the patient’s stability and well-being.

 

2. Interactive Objects Are Self-Evident. Some graphical user interfaces do not distinguish interactive content (i.e., controls) from nonselectable elements. For example, a static status indicator might have the same appearance as a button used to access a parameter adjustment screen. A clear visual language (e.g., making buttons look 3-D and informational fields look flat) can help users differentiate between static and dynamic elements.

 

3. On-Screen Information Is Legible. Safe device use often hinges on a user’s ability to read information on a display and respond quickly and appropriately (see Figure 2). Therefore, on-screen content (e.g., text, numbers, symbols) should be adequately sized to ensure legibility under all expected viewing conditions (e.g., various lighting conditions and distances) and by all intended users. When it comes to sizing information, such as vital signs or an important status message on a patient monitor, it’s a mistake to cut it close. Some users might need to view the information from a considerable distance, an acute angle, or with slightly impaired vision—possibly as a result of forgetting to carry along reading glasses.

 

4. Screens Have Unique Identifiers. Identifiers such as titles, icons, and background colors help users distinguish among different screens, thereby ensuring that users gather information effectively and efficiently, exercise control on the correct screen, and foster a better sense of their location within a screen hierarchy.

 

5. Screens Guide User Actions. Provide an appropriate level of prompting and procedural guidance to suit the intended use scenarios and associated user needs. Such guidance can reduce the likelihood that the user will not know what to do when quick action is essential to preventing or correcting problems.

6. Screens Tell Users When and How Long to Wait. When devices are performing a procedure that requires the user to wait (e.g., priming the tubing set on a dialysis machine or calibrating air-in-line sensors on an infusion pump), they should indicate the remaining procedure time through text such as a numeric countdown or graphics (e.g., a filling progress bar). Providing such status information helps ensure that users give devices the required attention at the right time and that their actions do not outpace a slow-responding device.

 

7. Displays Draw Attention to Critical Content. Many medical device user interfaces contain an abundance of information, only some of which might be critical to the user. Ways to make the critical information stand out include surrounding it with blank space, enlarging it, and adding more color.  Flashing the information also works, but this highlighting method is best reserved for drawing attention to alarms.

 

8. Screens Include a “Back” Option. Providing undo, back, or cancel options enables users to quickly correct their mistakes (presuming the mistakes are detectable). It also allows them to explore user interfaces with greater confidence that they can take the wrong path and go back if needed.

 

9. Input Errors Are Readily Detectable. Rapid error detection is a tenet of safety engineering. A use error is not usually a hazardous event, but rather can open the door to one. The goal is to prevent a hazardous event by some means. For example, a morphine overdose could be prevented by visually indicating that the entered medication dose exceeds the infusion pump’s dosing recommendations.

 

10. Users Must Confirm Critical Software Actions. Carpenters are fond of the expression “measure twice, cut once,” acknowledging that double-checking can mitigate common errors. The same principle applies to medical devices that call for irreversible user actions. For example, many software user interfaces present a particularly effective way to administer double checks and have a confirmation dialog or pop-up box. Employing a means of confirmation can boost the end-user’s confidence when interacting with a device, because they know that they can undo mistakes.

 

Documentation
1. Employ Active Voice Construction. Use active voice constructions that clearly indicate who does what. The active voice typically produces more concise sentences that clearly tell readers what to do.

 

2. Text Is Syntactically Consistent. Readers can get easily distracted by arbitrary differences in a document’s writing style and occasionally ascribe inappropriate meaning to such unintended differences.

 

3. Images Replace Text When an Image Is Clearer Than Words Alone. Pictures can be an effective replacement for words (see Figure 3). This is particularly true in documents that provide procedural instructions (e.g., instructions for installing a cartridge in an insulin pump) or describe a device’s physical components (e.g., an overview of a ventilator’s hardware components).

 

4. Illustrations Focus on Key Details and Exclude or Subdue Extraneous Details. Whereas technical illustrations intended for engineers typically feature exhaustive detail for the sake of technical accuracy, illustrations intended for device users should omit noncritical details for the sake of clarity. For example, an illustration depicting the connection of a patient blood lines to a hemodialysis machine might feature grayed-out drawings of the machine’s many other tubes and components behind the machine’s blood lines and patient access lines, which should be presented in bright, bold colors. 

 

5. Procedural Steps Are Numbered. It’s a basic but effective way to organize information—numbering steps in a series of instructions helps users estimate the effort involved in the associated task as well as track their progress as they work through it.

 

6. Headings and Subheadings Are Helpful. Users who are hurrying to complete a critical task with a new medical device are unlikely to read through paragraphs of instructions when seeking a quick answer to a specific question. However, if the paragraphs are preceded by headings that describe key content, users are more likely to find sought-after information.

 

7. Long Documents Have Helpful Location Aids. Documents longer than about five pages benefit from location aids that give readers an overview of the document’s contents and facilitate jumping from one section to another. Examples of such aids include a table of contents, an index, and tabs that enable readers to quickly access content of interest.

 

8. Document Stays Open During Use. Although a document’s binding method might seem like a trivial production-quality detail, it can affect a document’s usability. So-called perfect bind documents are difficult to keep open, which could cause users to lose their place when following step-by-step instructions to perform a task. Conversely, a wire-bound document can lie on a flat surface while remaining open to a specific page.

9. Presents Warnings in the Context of Related Procedural Guidance. Given the myriad of risks associated with the most basic medical device, typical device documentation has plenty of warnings. To increase the positive effects of the warnings, integrate them with related content as opposed to placing them only in a section dedicated to all warnings.

10. Language Is Clear. A medical device’s designers and users often speak very different languages (figuratively and literally). To help users avoid language-related confusion, instructional documents should use terms likely to be familiar to and understood by the device’s intended users.

 

1. Enables Users to Set the Pace. People get frustrated and make more mistakes when a device requires them to perform tasks at a particular pace. Accordingly, it’s best to let the user set the pace and for the device to keep up or tolerate delays. This method ensures that users can acquire and process all necessary information before taking action.

 

2. Uses Consistent Terminology, Graphics, and Dynamic Effects. Confusion and use errors arise from design inconsistencies, such as using different terms to describe the same thing. Users trying to sort out inconsistencies (e.g., buttons with different names performing the same action) sometimes draw the wrong conclusions.

3. Accommodates Inexperienced and Experienced Users. Some users might spend countless hours gaining expertise with a device. But others might spend little to no time studying or using the device, resulting in a marginal level of operational knowledge and skill. A device’s design should support both ends of this spectrum, enabling novice users to obtain detailed guidance and step-by-step instructions while allowing expert users to skip instructional steps and possibly access advanced features.

 

4. Enables Users to Apply Preestablished Knowledge and Skills. Although innovative design solutions can give a device a wow factor, designers should be cautious to implement interaction schemes that stray too far from conventions. Designs should enable users to apply their established skills, some of which might have developed over years of medical device experience. This is especially true of devices such as endoscopes and laparoscopic instruments, which users might only master after a long period of use.

 

5. Enables Good Situational Awareness. Signs and maps are often used to help individuals navigate through complex environments, such as airports. Similarly, certain product design elements can increase a user’s situational awareness of a medical device’s status and the user’s progress while completing a given task. Examples of design elements that increase situational awareness include indicator lights and labels on hardware components, status messages and prompts in software user interfaces, and headings in instructional documents.

 

6. Excludes Extraneous Information. Increasingly large displays enable designers to provide users with what is usually more than enough information to perform a task. However, there is a tipping point at which supplemental information loses its value due to information overload. Designers need to determine what information is essential versus extraneous and eliminate the latter. 

 

7. Fails Gracefully. To maximize a medical device’s use safety, designers and engineers must consider scenarios involving system failures, such as a software crash or a power outage. Ideally, a failing device will provide diagnostic and recovery information that enables users to understand the cause of the failure, perform the recovery steps, and contact the appropriate individuals or organizations for technical support.

 

8. Prevents Unauthorized Use. In addition to considering a device’s intended users, designers need to consider unintended users. For example, a critical care unit visitor might attempt to silence an alarming ventilator and inadvertently change a ventilation parameter by pressing the wrong button. To prevent such adverse events, medical devices should feature sufficient hardware and software protection mechanisms, such as a physical lockout and password protection, respectively.

 

9. Ascribes to User Population Conventions. Population conventions—product characteristics that match established design features common among similar products—help users learn to use and adapt to a new device. The telephone keypad layout is a classic hardware example (top row = 1-2-3, second row = 4-5-6, third row = 7-8-9, and 0 in the center of the bottom row). 

 

10. Is Satisfying to Use. While producing a safe and usable device might seem like a sufficient achievement, designers should go farther down the path toward optimizing a device from an emotional standpoint. In ideal cases, medical devices are satisfying to use, giving users the sense they are using a high-quality, aesthetically appealing product that enables them to perform their task with an appropriate level of comfort and control.

 

A device that satisfies the above checklists is on the right path toward user-friendliness. However, the best way to determine a device’s true usability and use safety is to evaluate its performance when representative users perform representative tasks with the device in a representative use environment. Therefore, you can add an overarching item to the set of checklists—design validated by means of usability testing.

 

Good user interfaces arise from a structured design process that starts with research and leads to appropriate user interface requirements; continues with an iterative design process, prototype development, and user-based evaluations (e.g., formative usability tests); and culminates with a summative (i.e., validation) usability test. This process is detailed in ANSI/AAMI HE74:2001, “Human Factors Design Processes for Medical Devices,” and the related international standard ISO/IEC 62366:2007, titled “Medical Devices—Application of Usability Engineering to Medical Devices.”

 

The four checklists in this article highlight specific user interface design characteristics that are particularly important to a device’s ultimate usability and safety. Meanwhile, developers have an authoritative source of detailed guidance on user interface design. Recently, AAMI released AAMI HE75:2009, “Human Factors Engineering—Medical Devices,” which is essentially a 465-page encyclopedia of good user interface design practices that apply to medical devices.

 

Conclusion
Conducting a usability test is the most effective way to detect user interface design strengths and shortcomings. However, performing a design inspection prior to usability testing can be a productive exercise, revealing opportunities to fix user interface design flaws so users don’t have to cope with them. Apply these checklists and you will be on the path toward designing a device that is easier to use and safer (in terms of preventing dangerous user errors) than it might be otherwise.

 

References
1.    Atul Gawande, The Checklist Manifesto–How to Get Things Right (New York: Metropolitan Books, 2009).
2.    Suzanne Rich, “How Human Factors Lead to Medical Device Adverse Events,” Nursing 38, no. 6 (2008): 62–63; available from Internet: www.fda.gov/MedicalDevices/Safety/
AlertsandNotices/TipsandArticlesonDeviceSafety
/ucm070185.htm.
3.    John Turner and Stephen Huntley, The Use and Design of Flight Crew Checklists and Manuals, (Springfield, VA: National Technical Conformance Information Service, 1991).