Pain – does it measure up?

In medical research, we have a problem with studying physical pain. It is difficult to find a way of measuring it that is not subjective.

How do we measure how people feel pain? The most common way is by asking them. “Rate the pain you are feeling on a scale of 0 to 10, with 1 being no pain and 10 being severe pain or the worst pain you can imagine.” If asked to do this on a numbered line, it is called a visual analog scale or a VAS.

Unfortunately, our ability to rate pain is dependent on the pain we or those close to us have already felt, our “pain history” if you like. If we have had a devastating accident, given birth, been burnt badly or suffer a chronic illness, the pain scale will contract towards the low end accordingly (rather than inventing an 11 or 12, or, if it’s really bad, 1000).

As well as this problem of pain subjectivity, this fluidity of measurement introduces a second problem of a scale being ordinal but non-numerical, meaning a scale that is not really numbers, but just ordered categories named after numbers. Even though we have just said “0 to 10”, we may have just a legitimately said “Rate pain as none (=0), slight (=1), mild (=2), moderate (=3), severe (=4), very severe (=5), enormous (=6), kick-arse (=7), unbearable (=8), kill-me-now (=9) or worse than you could ever imagine (=10)”.

When working with these “numbers” we have to remember that they are not really numbers but names. We can’t manipulate these numbers the way we usually do. For example, 9 – 2 = 7 here would mean “If you take a kill-me-now pain level and drop two units, you have a kick-arse pain level”. The problem is the unit, or the distance between 1 and 2, 2 and 3, 3 and 4 etc. We cannot define it, it doesn’t actually exist and it is not the same between each level as we have defined them nor the same between persons. The question “How much more pain would I have to feel before my pain was no longer severe and became very severe?” is unanswerable.

While doing my honours project in biochemistry at university, I was carefully rounding the ends of some glass rods using a blue Bunsen burner flame. I finished one end of a dozen or so, and then started to work on the other ends of the rods. Lapsing in concentration for a second, I picked up the rod I had just done, by the red hot end. The pain was so enormous that I could feel throbbing a foot away in a sphere around my hand*. I could not speak and it was with great effort that I did not scream, though I may have gasped a few particularly noxious words out loud. I had two fingers and a thumb in ice for a full two hours before I could bear these second degree burns without the numbing cold.

That is my pain level 9. On a personal conversational pain scale (of my own invention), this would be wild constant shrieking inside my head. And I only burnt the tips of two fingers and the thumb of one hand. I can imagine a 10 would be doing this to a greater skin surface area. It is interesting to note that third degree burns give less pain than second degree because the nerve endings are destroyed except at the margins, where the burns are not as deep. Severe burn patients are often kept in a coma for good reason.

In comparison, muscle pain 24 hours after finishing a marathon was a 3 (quiet talk, with shouting outburst of protest on movement or attempts to walk down stairs). Giving birth with no pain relief was a 5 (The pain is bad but it is cyclic and predictable, like having a one-sided conversation). Having a fallopian tube explode due to an ectopic pregnancy was a 6 (constant loud talking, bit panicky). A full-blown head-splitting migraine could reach an 8 (constant frightened screaming, no breaths).

We would like to do be able to measure the effects of new  treatments on osteoarthritis pain. Unfortunately, the error of pain measurement is as great or greater than any difference we are able to detect. So far, no physical measurement (range of motion, nervous potential, functional abilities) can replicate how we “feel”.

I would be interested in how you rate your pain on the above scale and whether you think burns cause the worst pain. Feel free to comment.

* planning another post about this – awareness of physical self.