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Numbers on a scale: How bad did you say your pain was?


ResearchBlogging.org
Have you ever been asked to give your pain rating on a scale of 0 – 10 (where 0 = no pain at all and 10 = most extreme pain you can imagine)? Have you ever tried to work out whether today’s pain is worse than yesterdays? What does a pain rating tell us?

I’ve struggled to work out how “bad” my pain is many times, is it the pain intensity that makes it troublesome? Or, in the case of a migraine, is it the quality of the pain that makes it bad (or the nausea?). Health professionals often ask people to summarise their pain experience into a form that (hopefully) we can all understand – but just what does a pain that’s around 4/10 on a VAS actually mean?

Why do we use rating scales?

We know that pain is subjective, just like taste and colour. While we might be able to agree that both of us are tasting something we call “banana”, we don’t know whether the banana taste I experience is the same as the banana taste you experience. We can see that both of us are eating the same fruit, but we don’t know how our body/brain processes that experience. Instead we assume, or infer, that we’re experiencing it in a similar way because of the similarities in context.

With pain, the situation is even more complex: we can’t determine whether the pain I feel is similar to the pain another person feels, and we don’t even have the benefit of similar “tissue damage” in the case of a migraine headache.

So, we have to infer something about the experience through some sort of common mechanism. Mostly that’s language. We hope that someone can understand that a higher number means greater pain. We hope the person can recognise what “no pain” feels like and where it might be represented on a scale. We ask the person to remember their current pain intensity, translate it into a number that in turn represents to us some kind of common understanding of what pain given that number might feel like.

Of course, there are problems with numbers on a scale. For a child who doesn’t understand the association between numbers on a scale and intensity, we use the “Faces” scale. For a person with cognitive problems (brain injury, stroke, dementia), we observe their behaviour (and hope we can translate well enough). For a person who doesn’t speak the same language as us, we might try a sliding scale with green at the bottom and red at the top, to represent increasing intensity – appealing, perhaps, to a common understanding that green = OK and red = not OK.

Worse than the difficulty translating from experience to a number is the common misunderstanding that pain severity alone represents the “what it is like” to experience pain. We know personally that it doesn’t – after all, who has had a toothache that represents “Oh no, I need a root canal and that’s going to cost a bomb!”, or “Ouch! That lemon juice in the paper cut on my finger is really annoying”, or “I feel so sick, this migraine is horrible”.

Hopefully most health professionals are taught that to use just one measure of pain is not enough. It’s important to also include other aspects of pain such as quality, how it affects function (interference), how confident we are to deal with life despite the pain (self efficacy).

So we use rating scales as a shorthand way to get to understand a tiny bit of what it is like to have pain. But the Visual Analogue Scale (VAS) is used many times to estimate whether “this person’s pain is so bad they need medication”, or “this person’s pain means we can’t expect her to help move herself from the ambulance trolley to the wheelchair”. The VAS can be used in many ways it shouldn’t be.

Studying the relationship between VAS pain intensity and disability (SF36)

The study by Boonstra, Schiphorst Preuper, Balk & Stewart (in press) aimed to identify cut-off points on the VAS to establish “mild”, “moderate” and “severe” using three different statistical approaches.  They measured pain using a Verbal Rating Scale (mild, moderate and severe), the VAS, and used several scales from the SF36 (a measure of general health quality) to establish interference from pain.

What they found was that while “mild” pain was fairly equally determined (less than or equal to 3.5), and correlated with both severity and function, when it came to “moderate” and “severe” pain, there was far less agreement. In fact, this group found that individuals could verbally rate their pain as “moderate” but at the same time report severe levels of interference. This means verbal descriptors under-represent the impact of pain on performance.

They also found that the cut-off point between “mild” and “moderate” pain in terms of interference with activity ranged between 2.5 – 4.5, and for moderate to severe pain between 4.5 – 7.4.  The associations between pain intensity and disability or interference were low to moderate and as a result these authors argue that it is “questionable” to translate VAS scores into verbal descriptors, because the different instruments measure different things.

What does this tell us?

It should be easy by now to tell that although we use numbers as a shorthand for “how bad is your pain?” in reality, they don’t directly translate the “what it is like” to have pain. Neither does the VAS correlate well with measures of disability or interference from pain. While people with mild pain might be also experiencing only a little disability, when the numbers go up the relationship between intensity and function disappear.

I think we might be trying to quantify an experience as a quick way to make clinical decisions. Really, when we ask “how bad is your pain”, depending on the context, we may be asking “do you need pain relief?”, “do you need help to move?”, “did my treatment help?” or any myriad other questions. The trouble is in research, we can’t do statistics nearly as easily on a “yes” or “really bad” or “it didn’t change much” answer. But how many of us work routinely in research settings?

I wonder whether it’s worth asking ourselves: do I need to ask for a pain rating, or should I ask a more useful question? And take the time to listen to the answer.

 

Anne M. Boonstra, Henrica R. Schiphorst Preuper, Gerlof A. Balk, & Roy E.Stewart (2014). Cut-off points for mild, moderate and severe pain on the VAS for pain for patients with chronic musculoskeletal pain Pain DOI: http://dx..org/10.1016/j.pain.2014.09.014

5 comments

  1. Bronnie, a useful question that may be directed at your clinician is: “Tell me on a scale of 1-10 just how good a pain doctor are you?”

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