Insights · Human factors and equipment design
Designing for High Performance : Visual hierarchy in clinical equipment
Disclosure. I co-designed the airway bag used as an example in Part 3 and have a commercial interest in it.
Concept illustration. Not a commercial device.
Before you read a word of this article, try something. Glance at the panel below for one second, the way you would in a hurry.
Look here.
Then your eye drops to this line.
Longer text, set smaller and lighter, is read last, if at all. It is easy to skim past. The designer chose the order you just read in, and you followed it without thinking. That is visual hierarchy at work.
The patient needs a size 4 tube.
Did you reach the last line?
It was the only one that mattered. The patient needs a size 4 tube, and the design made it the easiest line to miss.
Now let the task set the hierarchy.
Size 4 tube.
The patient needs it now.
Longer text, set smaller and lighter, is read last, if at all. Here that is fine, because nothing in it is urgent. The order you read in now matches the order the task needs.
Look here.
Same task. This time, the size is clear.
Why it matters
A child needs intubating. Someone reaches into a pouch holding eight tube sizes and has to find the right one, and check it, quickly.
The light may be poor. They may be kneeling in a cramped space, gloved, with someone talking to them. The labels, colours and layout of that pouch were decided long before, by people who were not in the room. Each of those decisions either helps that search or gets in its way.
Whatever a design makes stand out, it is telling you matters most.
The question for anyone who designs, buys or teaches with clinical equipment is whether it is telling the truth at the moment it matters.
Hierarchy is a claim about importance.
Size, colour, contrast, position and spacing decide what gets seen first. The question is whether that matches what the user needs.
Visual hierarchy is the order in which a design asks to be seen. Used well, it does quiet work. A large number makes a setting easy to find. Space separates one group of controls from another. A consistent position makes a label quick to check. Used badly, a bright border pulls the eye away from the thing that matters.
Two things shape where we look
Some things pull attention
A different colour or strong contrast can be spotted rapidly among otherwise similar items.1
The task guides attention too
A clinician searching for a drug uses its name, expected position, appearance and previous experience.2
Eye-tracking research shows that what something means can guide where we look, not just what stands out most.3
The test: does what stands out match what the person is looking for? When the two agree, search is quick. When they compete, the design works against the user.
Try it: find adrenaline
Here is that test in miniature. Three rounds, six labels, one task. Only the emphasis changes.
Your task: find adrenaline.
Compare your three times. How did it feel when the highlight sat on the wrong drug?
The timing is illustrative, not a test of ability.
A few taps on a screen prove nothing on their own; practice and chance both play a part. The point is how it felt when the highlight sat on the wrong drug. That is what it is like to use a design whose emphasis does not match the task.
The same emphasis can help one task and hinder another. Highlighting midazolam is right if midazolam is what you need next.
Check the hierarchy where it will be used
A layout can look clear on its own. It still needs checking in the setting where it will be used. Lighting, viewing position and surrounding equipment all matter.
Lighting
Can users still distinguish the colours and read the markings in the lighting they will work in?
Glare
Do reflections hide a label, a number or part of the display?
Position and obstruction
Check the view from where the user will stand, sit or kneel. What is hidden by a hand, cable or open flap?
Competing information
With other equipment, displays and activity around it, is the information needed for the task still easy to find?
And under pressure, can people still find and check what they need?
Put the equipment where it will be used, with the people who will use it. Check whether what stands out still matches the task.
Roughly one in twelve men
8%
of European ancestry have a red–green colour-vision deficiency.
When researchers looked at anaesthetic syringe labels as a colour-deficient clinician would see them, some colour pairs became hard to tell apart.5
Colour can support a message. It should never be the only way the message gets through.
A hierarchy that follows the task
Good equipment groups what belongs together, and changes what stands out as the task moves on.
Grouping: the law of proximity
Things placed close together are seen as belonging together. This is known as the law of proximity.6 It means the layout itself starts to tell you which controls belong together, before you have read the labels.
The Tempus LS manual defibrillator uses it well. The controls needed to deliver a shock sit together in one strip, apart from the buttons beside the screen, numbered in the order they are used, with the shock button last.7 The grouping shows which controls belong together. The numbers show the order. Each control also has its own colour and symbol, so no single cue has to carry the identification.
One group, used in order
- 1 On
- 2 Energy
- 3 Charge
- Shock
When charged, three cues arrive at once:
- An audible tone
- “Ready to shock” on screen
- The shock button illuminates
Position and numbering show the sequence. Sound, text and light show the moment.
The message does not depend on someone watching the screen, and the clinical decision and safety checks stay with the team.
The defibrillator switched off
In one simulation exercise, doctors accidentally switched a defibrillator off in 5 of 192 attempts to shock, delaying the shock by 24 seconds on average.8
Adding sound did not help
In a patient-monitoring experiment, adding sound to a visual display did not speed up detection, and made a second task harder.9 Extra cues only help when each one says something the user needs, at the moment they need it. On the defibrillator, the tone has one job: it says the device is ready.
Colour groups, words decide
Anaesthetic syringe labels take a different approach. The international standard, ISO 26825, sets their colours, lettering and layout.10 Colour groups drugs by class; the printed name identifies the drug. The standard is clear that colour is an aid and does not replace reading the label.
Alarms are a good example. Medical equipment uses combinations of colour, light and sound to signal different levels of priority.11 Those cues already carry meaning, so reusing them for something else can create confusion. Before using colour, light or sound to draw attention, check what they already mean in that setting.
Change the design, change the result
Three studies, three kinds of redesign.
24 → 0
critical dosing errors in simulated paediatric cardiac arrest (62 and 59 doses).12
The syringes also removed the dose calculation, so the share due to colour is unknown.
13.0 → 11.1 s
to find a drug error, with faster checks of correct trays too. A follow-up found better detection under memory load.13,14
A laboratory task, not clinical practice.
Where clinicians looked
Tracking clinicians’ gaze drew attention to packaging, labels and the way drawers and kits are organised.15
A simulation study.
The design question is bigger than colour. It includes how items are grouped and labelled, and how much preparation is left for the worst possible moment.
When the right hierarchy is a flat one
When every option matters as much as the next, none should shout.
This example comes from a paediatric airway bag I co-designed, so read it with that in mind. The bag matters less than the decision.
Back to the pouch from the start of this article. It holds eight tube sizes, from 2.5 to 6 mm, in size order. Whole sizes have numbered tabs in different colours; the four half sizes share one colour and a printed “½”.
The colours help separate neighbouring whole sizes, but the number and position carry the identification.
The task is to find the requested size, and any size could be the one requested. So we aimed for a flat hierarchy: no size given more emphasis than another, with the markings carrying the decision. Three colours were considered for the half sizes.
Your task: find the tube.
Did any tab pull your eye before you read it?
The timing is illustrative, not a test of ability.
No size is deliberately given priority over another. A whole size is read by its number. A half size is read by its “½” and its place between two numbers: proximity again, doing the work colour cannot. Wherever the requested size sits, the search works the same way, and the tube’s printed size is the final check.
- Colourgroups
- Markingsidentify
- Sequenceconfirms
A flat hierarchy is still a choice about emphasis. It suits a task where every option matters as much as the next. Where one item must not be forgotten, the opposite choice is the right one: make it loud.
The Performance by Design review
Pick one piece of equipment you used, bought or designed this month. Run it through these six questions.
These six questions are a place to start, not the whole job. Medical-device usability engineering goes much further: understanding who will use the device, where they will use it, what could go wrong, and testing whether the design actually works. BS EN 62366-1 and MHRA guidance set out that wider process.16,17
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What is the priority at each moment of use?
Pick a specific task and follow it all the way through, including preparation and putting the kit back into service. Check that the design shows which stage the task has reached.
-
Does the emphasis match that priority?
Look at what stands out first. If it is not what the user needs at that moment, it is competing with them. Keep emphasis flat where any option could be the one needed, and make it loud only for what must not be forgotten.
-
What does this colour already mean?
Check across the whole kit, and against colours users already know from other devices. A familiar colour brings its old meaning with it, whether you intended that or not.
-
Are the cues working together?
Sound, light, text and position can reinforce each other, as they do on the Tempus. Added without thought, they compete for the same attention.
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Does it work where it will be used?
Try it in real light, with gloves, partial obstruction and interruptions, and with people who do not know it well. Check what is left when colour cannot be relied on.
-
How will you know it works?
Compare options on the same task. Record correct selections, errors, corrections and time, then ask users what got in their way.
The same questions apply to a drug label, a monitor screen, a trolley layout or a whole kit. For educators, they also show where teaching can help and where the design itself needs to change.
Seeing where the eye goes
Ask people what they noticed and you learn what they remember. Eye-tracking shows where they actually looked, in what order and for how long. It has already been used to study how clinicians find neonatal resuscitation equipment.15
For visual hierarchy, four measures do most of the work:
- How fast the eye gets there. How long before someone first looks at the thing they need.
- Where it lands first. The right item, or something louder.
- What holds attention. How long the eye stays on things the task does not need.
- The route it takes. Whether the eye moves through the layout in the same order as the task.
Researchers call these measures time to first fixation, first fixation, dwell time and scan path.18 Run the same task on two layouts and they show whether a change in emphasis helped the search, not just whether the user got there in the end. Pair them with errors and time to act: looking at the right item is not the same as picking it up.
Wearable eye-trackers allow this in simulation, with gloves on, in poor light and under time pressure, which is where hierarchy matters most.
Performance by Design: design the conditions before the pressure arrives.
Visual hierarchy in clinical equipment: common questions
What is visual hierarchy?
Visual hierarchy is the order in which a design asks to be seen. Size, colour, contrast, position and spacing decide what the eye reaches first. In clinical equipment, that order should match what the user needs at each moment of the task.
Why does visual hierarchy matter in clinical equipment?
Clinicians often search for equipment and information under pressure, in poor light and with interruptions. When what stands out matches what they are looking for, the search is quick. When the two compete, the design works against them.
What is a flat hierarchy?
A flat hierarchy gives options of equal importance equal emphasis, so none pulls the eye ahead of the others. It suits tasks where any option could be the one needed, such as choosing a tube size. An item that must not be forgotten needs the opposite: deliberate prominence.
Should clinical equipment rely on colour coding?
Colour is useful for grouping, but it should never be the only cue. Around 8% of men of European ancestry have a red–green colour-vision deficiency, and lighting changes how colours look. Words, numbers, shape and position should carry the identification.
How can eye-tracking test clinical equipment design?
Eye-tracking shows where people look, in what order and for how long. Comparing two layouts on the same task, using measures such as time to first fixation and time spent on distractors, shows whether a change in emphasis helps the search. Pair it with errors and time to act.
What is Performance by Design?
Performance by Design is my approach to clinical performance: design the conditions before the pressure arrives. It treats equipment layout, labelling and workflow as part of how a team performs, not just as the things the team uses.
Some of these questions are easier to ask from the outside.
References
- Treisman AM, Gelade G. A feature-integration theory of attention. Cognitive Psychology. 1980;12(1):97–136. doi:10.1016/0010-0285(80)90005-5.
- Wolfe JM, Horowitz TS. Five factors that guide attention in visual search. Nature Human Behaviour. 2017;1:0058. doi:10.1038/s41562-017-0058.
- Henderson JM, Hayes TR. Meaning-based guidance of attention in scenes as revealed by meaning maps. Nature Human Behaviour. 2017;1:743–747. doi:10.1038/s41562-017-0208-0.
- Birch J. Worldwide prevalence of red–green color deficiency. Journal of the Optical Society of America A. 2012;29(3):313–320.
- Thomas PBM, Mollon JD. Syringe labels seen through the eyes of the colour-deficient clinician. British Journal of Anaesthesia. 2018;121(6):1370–1373. doi:10.1016/j.bja.2018.07.023.
- Wagemans J, Elder JH, Kubovy M, et al. A century of Gestalt psychology in visual perception: I. Perceptual grouping and figure–ground organization. Psychological Bulletin. 2012;138(6):1172–1217. doi:10.1037/a0029333.
- Tempus LS-Manual Defibrillator: User/Operator Manual. Part number 41-3007EN-04. Issued 14 October 2024. Sections 3.1.5 and 3.1.6.3; pp. 44, 47. Operator manual.
- Høyer CS, Christensen EF, Eika B. Adverse design of defibrillators: turning off the machine when trying to shock. Annals of Emergency Medicine. 2008;52(5). doi:10.1016/j.annemergmed.2007.11.037.
- Seagull FJ, Wickens CD, Loeb RG. When is less more? Attention and workload in auditory, visual, and redundant patient-monitoring conditions. Proceedings of the Human Factors and Ergonomics Society Annual Meeting. 2001;45(18):1395–1399. doi:10.1177/154193120104501817.
- British Standards Institution. BS EN ISO 26825:2022. Anaesthetic and respiratory equipment — User-applied labels for syringes containing drugs used during anaesthesia — Colours, design and performance (identical to ISO 26825:2020). London: BSI; 2022.
- British Standards Institution. BS EN 60601-1-8:2007+A2:2021. Medical electrical equipment — General requirements for basic safety and essential performance — Collateral standard: General requirements, tests and guidance for alarm systems in medical electrical equipment and medical electrical systems. London: BSI; 2021.
- Stevens AD, Hernandez C, Jones S, et al. Color-coded prefilled medication syringes decrease time to delivery and dosing errors in simulated prehospital pediatric resuscitations: a randomized crossover trial. Resuscitation. 2015;96:85–91. doi:10.1016/j.resuscitation.2015.07.035.
- Laxton V, Maratos FA, Hewson DW, Baird A, Stupple EJN. Standardised colour-coded compartmentalised syringe trays improve anaesthetic medication visual search and mitigate cognitive load. British Journal of Anaesthesia. 2023;130(3):343–350. doi:10.1016/j.bja.2022.11.012.
- Laxton V, Maratos FA, Hewson DW, Baird A, Archer S, Stupple EJN. Effects of colour-coded compartmentalised syringe trays on anaesthetic drug error detection under cognitive load. British Journal of Anaesthesia. 2024;132(5):911–917. doi:10.1016/j.bja.2023.12.033.
- Chen LGR, Law BHY. Use of eye-tracking to evaluate human factors in accessing neonatal resuscitation equipment and medications for advanced resuscitation: a simulation study. Frontiers in Pediatrics. 2023;11:1116893. doi:10.3389/fped.2023.1116893.
- British Standards Institution. BS EN 62366-1:2015+A1:2020. Medical devices — Application of usability engineering to medical devices. London: BSI; 2020.
- Medicines and Healthcare products Regulatory Agency. Guidance on applying human factors and usability engineering to medical devices including drug-device combination products in Great Britain. Version 2.0. January 2021. GOV.UK page updated 15 January 2025. GOV.UK.
- Holmqvist K, Nyström M, Andersson R, Dewhurst R, Jarodzka H, van de Weijer J. Eye Tracking: A Comprehensive Guide to Methods and Measures. Oxford: Oxford University Press; 2011.