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The patient was a 62-year-old man who underwent hip replacement surgery. During his surgery, incompatible prostheses made by different manufacturers were used. The error was identified when data from the procedure was recorded in the National Joint Registry several days later. The investigation centred on how the error occurred and what safety recommendations we could make to reduce the risk of a similar event happening again. The investigation focuses on hip replacement surgery but the findings are applicable to all orthopaedic joint replacements.

Humans have not evolved to do medicine – or deal with complex machinery or systems. For the average (HF) scientist, it’s amazing how few errors occur and how a disinterested cave dweller (aka human) can work 12–18 hours, operate a machine (in many dimensions), and still get home safely at the end of the day. A short history of human factors HFs is a subdiscipline of both engineering and psychology. In respect of the psychology element, it is in the tradition of western performance measuring psychology. This measurement aims to aid productivity by identifying the best of the higher performing ‘cave dwellers’ for specific tasks. As we have all essentially evolved in the same ways and are not too far removed from our cave dweller ancestors, we should aim to design equipment that we can use now rather than waiting for evolution to enable us to use the kit. In this respect, HF is vital. In contrast to the western approach, the Soviet psychological tradition considers that all of us can be elevated to do any task. The background of this was that when the former Soviet Union industrialised rapidly in the 1920s they could not find the best of the higher performing ‘cave dwellers’ – as the majority were illiterate agrarian peasants. In the West, industrialisation was slow and there was time to find the best. A good example to illustrate this is the space programmes in the West compared to the Soviet Union. The United States tested people to find the best in the military whereas the Soviet Union advertised in the cotton mills “cosmonauts wanted”. Many say the Soviet tradition – also found in Scandinavian countries and in much of northern Europe – is a fair, humanitarian, way of thinking about humans, and the western method is there to divide the workers by exploiting them and getting them to produce more. This may explain my attachments to European medical establishments where I find everyone is happy! HFs is concerned with understanding how us ‘cave dwellers’ use our limited physiological skills and cognitive resources to achieve a task. The science is basic in that it attempts to understand, in principle, things like how our senses work, how our brain/mind filters the vast amount of information heading through those senses into the mind, and which bits are selectively attended to (or not). Humans tire easy, lose concentration, get distracted and are not exactly rational. Medication affects us in many ways, and aging and experience adds to the mix of human performance. That’s what HFs is about. If you ask in medicine, it’s about teamwork – or Crew Resource Management (CRM) – being nice to someone will stop any incident occurring. It’s non-technical skills – the idea that by watching someone’s behaviour (after expensive training) you can then understand their inner most cognitive processes and intentions. Or many different types of ‘psychobabble’, pet theories or simple weird ideas. HFs, being a science, relies on evidence and testing, and is interested in performance. HFs started not on the flight deck, or on the battlefield, but in medicine some 2000 years ago. The first HFs scholar was most likely a Greek doctor – him of the oath you all swear. He discusses how, for efficiency, tools and equipment are laid out in a way that is easy to use – that’s HFs or, as we have also borrowed from the Greek, ergonomics! Most likely one cave dweller preferred one rock over another. Of course, the one that preferred the apple as a communication tool was way ahead of their time! Subdisciplines of human factors There are subdivisions within HFs worthy of note as useful to medicine. These were hinted at in my last blog. These are human computer interation (HCI) and human machine interaction (HMI). Each group has its specialists. Often you don’t need a HFs generalist, you want an expert fully trained in one of these areas. An example of the difference in these subdisciplines can be illustrated in a crash involving a plane and a tug (thing that drags a plane around an airport). An HCI person looked at the screen bolted to the tug where information to the driver was displayed. Incidentally, HCI people are sometimes called UX (User Experience) designers. The theory was that the tug driver was distracted by the screen. It was fine. The HMI specialist said it must be the whole machine – the controls, the visibility from the driver’s seat – but all was fine. The HF person asked the tug driver, after doing the first two lots of tests again (HF people do things twice), when did you last see a medical professional? The answer was the day before; that he had ”some jabs ready for his holiday”. The HF person was shown the leaflet given to the driver after the jabs, telling him that he might feel dizzy or tired and not to operate heavy machines. The driver did not think an aircraft under tow was a heavy machine. HFs is, therefore, the study of the man, and the system, and the built environment which she is working. To relate this to the above about western psychology, HCI is often based on Soviet psychological testing. Rapid onset of computer and screen technology meant everyone was a naïve peasant again, with no clue how to operate the machine, or to get the Bluetooth to connect in the car! The answer of course is to use both traditions. The senses Let’s make a start about thinking about HFs. The history is important as it frames the study. Let’s think about the senses. Seeing hearing, feeling, tasting and smelling. If we start with the basics, then perhaps we can think a little about all those higher cognitive levels that the medical profession thinks HF is. Perhaps a bit on fatigue and attention as well. The senses tell us: What is out in the environment. How much is out there. Is there more or less of it than before. Where is it. Is it changing in time or place. Seeing We have evolved to operate in daylight, not at night; unlike almost all other animals we have detailed colour vision. But there is no zoom lens – we need to get closer to see the detail. Our vision is perhaps optimised to find ripe fruit in trees. Our field of view is extremely limited – or more precisely our ‘useful field of view’ is limited and in general we can only ‘see’ things we are directly looking at. Although our vison is very limited, it’s further reduced as the signal from each eye is split and sent off down different channels into the mind where it arrives as a blurred upside-down image, via the retina, and the brain has to interpret what’s going on. Vison is more about conception than perception. That’s to say the mind controls what we see to such an extent – and this control is based on experience and expectation – that vision is limited. The fact that there is something in the world that can be seen and could be identified is only a tiny bit of the picture (pun intended). The scary fact is that 95% of the information we use about the world is visual, yet we don’t have good vision. Well fruit picking is fine, but dealing with neurological conditions – no. A lot of medical packaging and its very poor labelling can’t be seen, let alone comprehended. Even in the test lab – let alone in the theatre with its weird lighting. Hearing The story gets worse – the good news is we don’t rely on hearing as much as vision. Humans find it difficult to discriminate sounds of voices from other voices and with noise in the background. Sound waves work in weird ways and you can have a negative (inverse) sound wave that cancels out the one you are trying to detect. Think noise cancelling headphones here! Taste, smell and touch These are minor senses when it comes to the overall picture of the world we need to form in our minds. Remember we are talking medicine rather than restaurant critique. They are useful. Warnings that use vibration (e.g. stick shake in a cockpit) work better than other audible warnings. I might do something on the psychology of warnings in a later blog. Investigators spend the majority of time trying to understand if the senses of the 'cave dweller' could have correctly detected and understood what was in the environment. Typically, the answer is no – that’s why it occurred. People rarely set out to have an accident, injure themselves or injure others for no apparent reason. Before the investigation team considers if higher cognitive factors like reasoning are to be thought about, you need to be sure the senses detected and correctly identified what was happening. Attention Psychologists since Greek times recognised the two types of attention mechanisms. One selective, the other sustained. Attention is the mechanism us cave dwellers use to filter out the overwhelming volume of information so we can attend to a bit of it over all the rest. The cat is reading this and also attending to the squirrel outside. If we were cats, I would not have had a job. Selective: Selective attention is where you rapidly need to selectively attend to one stimulus in the environment above all others. This is usually a product of visual search where we are looking for the thing to attend to – this can cause us to experience spatial uncertainly. The idea is that the ‘target’ will appear somewhere at some expected point (this relates to how our brain interpret things and based on expectations). Sustained: As the name suggests, this kind of attention investigates how long an operator can detect an event that is expected. Most of the research was conducted in the 1950s and investigated how reliably an American radar operator can watch the screen to detect a Russian aircraft. What we know about vigilance and monitoring tasks is that humans are very poor at it – we miss things very easily. Fatigue At the very first medical conference I went to, the A&E (ED) doctor who runs classes on HFs said he made errors due to not checking politely with his colleagues about his actions and then he spent 20 minutes talking about how pilots communicate. He then described his typical 18-hour day. At the question sessions, I asked if all his failures were not perhaps due to fatigue – and his answer was no. My second question was how often a pilot would do a shift of 18 hours and would you get on his plane if he said – “well I’m almost at 18 hours, I’ll give the landing a go”. Fatigue is time over 8 hours depending on the task. Times start from the moment you start for work – so a surgeon who drives 2.5 hours, does operations for 15, and then drives home for 3 hours has a long day. Fatigue is the hidden killer in medicine. Scheduling 12-hour days – well it keeps investigators in work. Fatigue is reduced by sleep and rest. Top tip – look at the quality of the sleep. “I’ve a young family”, “I was stationed at the end of the runway” is a good clue. Also look if the shift is ‘forward rolling’ or not. Fatigue is a very specialist area. I ask for help after the basics. Medicine is complex, tiring, difficult, challenging and us HF sleep specialists are few and far between and, in general, there has not been much done about understanding fatigue in the area of medicine (sorry). If you are an expert in this area – please, please, forgive the oversimplification. Summary HFs in the first sense is a study of basic processes. Investigations are always about these basic processes – seldom about how someone felt about someone else and about how these senses interacted with the environment, the equipment and the system or method of working. The downside of HF methods – more later in the 'how to do science' blog – is that many say it is eye wateringly expensive. Well, given the potential cost saving, it’s a bargain and research throughout Europe shows that it’s the most effective cost-saving intervention you can do. Research is done in situ and this takes time. The science types get involved to understand the human, the way of working, the equipment and the environment. Thinking of my recent projects concerning firearms deployment – well first get body armour, then training (pick up weapon – ask which end goes bang), then highly supervised patrols … then data collection – assuming your security clearances are all up to date. In respect of medicine, infection control training, theatre training, basic methods training in orthopaedics, come look how the saw has gone through the bone Martin… data collection. In heavy rail – well a lot more – apparently, I’m a great driver – stopping is my only problem! The point is to avoid anyone who says they can do it without the knowledge of the environment or say they developed this measurement tool in nuclear plant operations, and it will work here. The basic human processes described above are the same – but the environment is damned important. This is why a medically trained person is vital to keep the HFs person on a tight bit of rope. HFs is about understanding the limits of the cave dweller who dresses in scrubs and says trust me I’m an DPhil rather than trust me I’m an MD. Next time some slightly higher cognitive processes – memory, search, reasoning, biases heuristics. Thinking and deciding. The good news is that you will have concluded humans should not practice medicine – so how well humans’ reason or don’t will be of no surprise. Happy new year to our reader. Read Martin's other blogs Why investigate? Part 1 Why investigate? Part 2: Where do facts come from (mummy)? Who should investigate? Part 3 When to investigate? Part 5 How or why. Part 6

In this article, Dan looks back at the Donabedian Model, a framework for measuring healthcare quality, and suggests why this might be an over simplification and why we must also look at human factors when we think about patient safety. We are humans and we can, do and will make mistakes, so we have a personal responsibility to acknowledge and address this as a contributing factor for patient safety incidents and harm. How do we begin to address our individual responsibilities? How can each of us reduce the personal risks we pose for our patients? How do we begin to address the moral imperative to recognise and then overcome any professional complacency that may interfere with our performance? Dan believes by enhancing human performance within healthcare settings this will serve as the ultimate key to improving quality and safety. Recognition by clinicians of their own tendencies toward complacency and their own vulnerabilities toward making mistakes is to encompass a mandate for personal professional commitment and improvement. If patients are harmed on the frontlines in healthcare settings, then it is on the frontlines that many of the solutions can be found and safety improvements nurtured. First recognising, and then modulating, the human factors liabilities that exist on the frontlines and overcoming the challenges of professional complacency will be necessary steppingstones towards sustained improvements in providing patient safe care. Clinicians, managers and leaders need to work collaboratively to understand and overcome the challenges that human factors pose when addressing individual performance.