How easy is your microwave to use? While you might have to read a manual to find out about advanced microwaving you’d reasonably expect the basics to be straightforward so that you could cook food safely. How easily could you reheat food for two minutes using a microwave you’d never seen before?
In ‘Microwave Racing’ four people (Rachel, Chris, Maartje and Alan) have a microwave each and try to complete a simple task: instructing their microwave to cook food on full power for three and a half minutes. It should be easy, but not all the contestants manage with ease.
Take another everyday example – changing the time on some types of clocks (eg oven clocks) can be infuriating when you want the time to say 19:32 and find you’ve got 19:33. Some clocks will let you go backwards by one minute, and the job is done, but many will force you to cycle forwards through the minutes until you reach 30, 31… and 32 again.
Fortunately most clock changing happens only twice a year but busy nurses have to change the settings for syringe pumps every day, so that patients receive the right dose of drug delivered at the correct rate (eg 5.5mL per hour). These are the devices that typically infuse chemotherapy drugs into patients over several hours through a length of plastic tubing into a vein. It’s crucial to get the dose and delivery rate right, if not it can be fatal.
If designers struggle to make it easy to use everyday devices like microwaves and clocks, what hope for medical devices?
Scientists from the CHI+MED project (a six year multi-centre EPSRC-funded study looking at making medical devices safer) are finding out about the impact of different number entry systems on the ease of use of interactive medical devices. In the second short (<2 min) video below Patrick Oladimeji, a CHI+MED scientist working at the University of Swansea, talks us through a simulation of the number entry system used by a real syringe pump; it uses chevron buttons to cycle through the numbers.
Many people are familiar with using a numeric keypad such as those found on mobile phones or cash machines where the user keys in the actual number directly. A chevron system requires the user to press up and down buttons until the correct number is reached. The chevron panel takes up less room and should be simple to understand but, as you’ll see in Patrick’s demonstration, in use it can be a little counterintuitive.
There are four chevron buttons in the panel. The ‘up’ double chevron increases the pump’s display by 0.1 and the ‘up’ single chevron increases it by 0.01. The ‘down’ chevrons decrease the number in a similar way. So it seems simple to raise and lower the number displayed on the device. Unfortunately the reality is a little different – what do you think happens when the display reads 9.80 and you press the double ‘down’ chevron button on the right hand side?
(These short clips ‘Problems with a syringe pump II‘ and ‘Microwave racing‘ are part of a 15 minute short film called ‘Man-Machine Nightmares: Chaos buttons, human error and healthcare‘ which is available on our website).
Different styles of systems for entering numbers into machines can make the process much harder and if you’re working with a piece of life-saving equipment it’s important to make it easier and so safer.
Getting the numbers into the device can be hard enough if the number entry system is difficult to use but it can be further complicated by timeouts which reset the system, sometimes without informing the user. If the system resets and the user continues entering numbers without restarting their sequence then the wrong information is supplied to the device which can result in a fatally wrong dose being given. An additional problem is that a reset medical device might require not just the sequence of numbers that the user has been trying to enter; other essential background information such as the weight of the patient might need to be re-entered as well.
In our final video, Professor Harold Thimbleby (from Swansea) demonstrates, with a device that delivers anaesthetic, how difficulty in using the machine can put lives at risk. In the example given, the machine will time out if there’s a delay between button presses resulting in wrong information being used by the machine.
For the user, the simplest way to get around this is by switching the machine off and on again – although this works because the information sequence can then be added in correctly from the beginning it adds time to the procedure. But if adjustments are needed while the machine is in use during an operation other background information needing to be entered as well after the machine has been reset, then the time delay and confusion could be extremely serious.
When buttons and the machines they’re found on don’t behave as expected errors can happen. When these devices are used in a safety-critical medical setting the errors can be fatal. Add in a high-pressured busy environment where distractions are common and it’s clear that the design of interactive medical devices that can make it easy to get things right (even when interrupted) and to mitigate errors is crucial.
Understanding device design and the context in which devices are used underpins the research done by the CHI+MED scientists at the four project sites (UCL, Queen Mary, City University and Swansea University). You can find out more about the different strands of the work and how they fit together on our website.
Designing number entry systems for medical devices: How can number entry systems for medical devices be designed so as to help prevent human error?
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