“Just a little scratch”


If you’ve had a blood test, flu jab or Covid-19 vax (please do, not just for you but for the vulnerable) you’ll probably have heard those words “Just a little scratch” then the needle goes in and ouch! I’ve wondered why phlebotomists and vaccinators use those words: is it to reduce the pain? give you some warning so you don’t pull away? why use the word “scratch” when it’s not a scratch?!

I suspect, though I haven’t read up on it, that the reason people say “just a little scratch” is to influence expectancies. Expectancies are defined as “cognitions regarding the probability of future experiences, events, and behaviour” (Peerdeman, van Laarhoven, Peters & Evers, 2016). In other words, what we expect to experience, happen or do influences what we actually experience, what happens, and what we do. Expectancies are really important when we consider placebo – and nocebo. Despite commentators who don’t consider placebo to be a thing (the response to being in a treatment ritual, over and above the effects of any active therapeutic agent), in pain, it is most definitely a thing, and one we need to be aware of as clinicians.

Back to expectancies.

Mostly, what we expect is what we experience. If we expect something to REALLY HURT then it’s likely to REALLY HURT! But what happens when we don’t expect something and it happens? Or when we expect something not to really hurt, but it actually does?

Peerdeman, Geers, Porta, Veldhuijzen and Kirsch (2021) investigated this mismatch between what we expect and what actually happens. It’s fascinating because the results weren’t quite in line with what the researchers thought…

What did they do?

The authors selected 82 healthy adults, aged between 18 and 30, with no health problems (physical or psychologist), no chronic pain, no current pain, no medications, no pacemakers, and no pregnancy. The participants weren’t allowed to use any medication, alcohol or other drugs in the 24 hours before the experiment.

Two experimenters undertook the experiments – one wasn’t aware of who was getting what, while the other was unaware of what was getting what until just before she gave the verbal suggestion. The experimenter who was blinded left the room before the second one gave the suggestion, in order to remain blinded throughout.

The participants were wired up to record heart rate, skin conductance, and then thermal and nociceptive perception thresholds were identified – at least in part to give participants a chance to get used to the heat stimulus. The experimenters went in to increase the heat to identify the temperature where participants indicated the pain was “moderately high” (who volunteers for these experiments? Oh – they recruited from around the university and on social media...). Then the experimenters got to work: participants were randomised to get either a suggestion of “no pain” (they’d already had three occasions where the thermal stimulus wasn’t painful, and three where it was), or a suggestion of moderately high pain. Then the stimulus was applied four times, with participants having to rate the expected pain intensity, how certain they were of this prediction, and how afraid they were. Afterwards, they were asked to rate pain intensity and unpleasantness.

For all the details of this experiment, head to the paper itself – it’s very detailed, and could be replicated.

Results

One person dropped out before the trial began – it was too painful – leaving 81 people remaining. The average age was 22 years, but the investigators don’t report gender.

When people were told “it’s not going to hurt” participants rated the pain lower than those who were told it was going to hurt, and while the ratings changed depending on what they experienced, when it was again suggested they’d feel no pain – again their pain ratings were lower than expected. Who knew pain intensity could vary so much? Reported pain intensity in the people who were told they wouldn’t experience pain was 4/10 points lower than the other group who were told it would hurt, and a bit over 2 points lower the second time (on a 0 – 10 numeric rating scale). That’s a thumping great amount of pain reduction! Add to this, these participants also were less afraid of their pain than the other group.

BUT, and this is important, participants in the “it’s not going to hurt” group reported less trust in the experimenter (who would have thought, huh?!). So beware: if you tell someone “oh this won’t hurt a bit” – they may experience less pain, but they’ll look at you sideways and be a bit wary of you because you violated their trust.

Discussion

I haven’t described the second experiment because of space, but go ahead and read it. Essentially they added some more participants, varied the procedure a little to reduce the memory burden on participants, and added a “medium” underprediction element into the process. The results showed similar outcomes – lower ratings of pain in both the “you won’t feel a thing” and the “it’ll hurt but not much” experiments, and yet again, less trust in the experimenter suggesting that it wouldn’t hurt.

Lessons to learn?

Think carefully about inflating how much pain relief someone will experience, especially if you’re going to see that person again. While people might experience less pain, losing someone’s trust in a therapeutic setting is a serious problem. The authors point out that healthy volunteers in a lab setting, getting short-term pain, is not like a therapeutic setting where it’s probable that trust is well-established. We don’t know what effect violating trust in a longer-term relationship might have.

At the same time – it does strike me as intriguing that simply being told “it won’t hurt” can influence pain intensity rating. What’s going on? How can a communication stimulus influence an experience? How could a psychological input change the way we perceive a noxious stimulus? Perhaps the way forward might be to use neutral language or, more positively, suggest that the person can handle it? “Just a little sting and you’ll get through”

Peerdeman, K. J., Geers, A. L., Della Porta, D., Veldhuijzen, D. S., & Kirsch, I. (2021, Jul 1). Underpredicting pain: an experimental investigation into the benefits and risks. Pain, 162(7), 2024-2035. https://doi.org/10.1097/j.pain.0000000000002199

Peerdeman KJ, van Laarhoven AI, Peters ML, Evers AW. An Integrative Review of the Influence of Expectancies on Pain. Front Psychol. 2016;7:1270. Published 2016 Aug 23. doi:10.3389/fpsyg.2016.01270

2 comments

  1. Question is, what are the long term effects of this? These days if I see “you may experience some discomfort with the procedure” I mostly think “oh, bother, this one is going to be really painful, I better plan that nothing much will happen for the rest of the day”. This is because I have experienced enough medical professionals telling me something about “mild discomfort” when in reality it was worse. I didn’t necessarily think that way when I was young and didn’t have much interaction with doctors. So it seems that an attempt to influence expectancies led to an opposite effect over time, at least for me.

    1. Good question! I don’t have an answer for it, either, because the experimental (and clinical) work hasn’t been done on it. We do know that negative expectancies increase pain intensity, so I wouldn’t be at all surprised if the words someone says are over-ridden by your personal experiences especially over time.In this experiment they only manipulated verbal suggestion, but I wonder if you could manipulate other contextual factors such as other people in the vicinity, the long-term or repeated effects of this mismatch (because they only did one round of nociceptive stimulation which is nothing like a persistent pain experience), and they carefully excluded people with nociplastic mechanisms such as fibromyalgia.
      In fibromyalgia we already know that noxious stimuli are upregulated and perceived at a lower threshold than people with so-called “normal” nociceptive processing, and the conditional pain modulation experimental paradigm has the opposite effect for people with FM vs those with “normal” nervous systems. So – food for thought, and someone’s PhD?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.