Measuring pain

Karoly (1985) - we should focus on all of the factors that contribute to pain

1. 1.      Sensory - intensity, duration, threshold, tolerance, location, etc
2. 2.      Neurophysiological - brainwave activity, heart rate, etc
3. 3.      Emotional and motivational - anxiety, anger, depression, resentment, etc
4. 4.      Behavioural - avoidance of exercise, pain complaints, etc
5. 5.      Impact on lifestyle - marital distress, changes in sexual behaviour
6. 6.      Information processing - problem solving skills, coping styles, health beliefs

Site of  pain: where is the pain?

•    Type of pain: what does the pain feel like?

•    Frequency of pain: how often does the pain occur?

•    Aggravating or relieving factors: what makes the pain better or worse?

•    Disability: how does the pain affect the patient’s everyday life?

•    Duration of pain: how long has the pain been present?

•    Response to current and previous treatments: how effective have drugs and other treatments been?

An important item to add to this list is the emotional and cognitive effect of the pain—in other words, how does the pain make patients feel and how does it affect their thought processes and attitudes?

Physiological measures of pain

Muscle tension is associated with painful condi­tions such as headaches and lower backache, and it can be measured using an electromyograph (EMG).

This apparatus measures electrical activity in the muscles, which is a sign of how tense they are.

Some link has been established between headaches and EMG patterns, but EMG recordings do not gen­erally correlate with pain perception (Chapman et al 1985) and EMG measurements have not been shown to be a useful way of measuring pain.

Another approach has been to relate pain to autonomic arousal.

By taking measures of pulse rate, skin conductance and skin temperature, it may be possible to measure the physiological arousal caused by experiencing pain.

Finally, since pain is perceived within the brain, it may he possible to measure brain activity, using an electroencephalograph (EEG), in order to deter­mine the extent to which an individual is experienc­ing pain.

It has been shown that subjective reports of pain do correlate with electrical changes that show up as peaks in EEG recordings. Moreover, when analgesics are given, both pain report and waveform amplitude on the EEG are decreased (Chapman et al, 1985). 

Observations of pain behaviours

People tend to behave in certain ways when they are in pain; observing such behaviour could provide a means of assessing pain.

Turk, Wack and Kerns (1985) have provided a classification of observable pain behaviours.

•   Facial /audible expression of distress: grimac­ing and teeth clenching; moaning and sighing.

•   Distorted ambulation or posture: limping or walking with a stoop; moving slowly or carefully to protect an injury; supporting, rubbing or hold­ing a painful spot; frequently shifting position.

•   Negative affect: feeling irritable; asking for help in walking, or to be excused from activities; asking questions like ‘Why did this happen to me?’

•   Avoidance of activity: lying down frequently; avoiding physical activity; using a prosthetic device.

One way to assess pain behaviours is to observe them in a clinical setting (although pain is also assessed in a natural setting as the patient goes about his or her everyday activities). Keefe and Williams (1992) have identified five elements that need to be consid­ered when preparing to assess any form of behav­iour through this type of observation.

•   A rationale for observation: it is important for clinicians to know why they are observing pain behaviours. One reason is to identify ‘problem’ behaviours that the patient may be reluctant to report, such as pain when swallowing, so that treatment can be given. Another is to monitor the progress of a course of treatment.

•   A method for sampling pain behaviour techniques for sampling and recording behaviour include continuous observation, measuring dura­tion (how long the patient takes to complete a task), frequency counts (the number of times a target behaviour occurs) and time sampling (for example, observing the patient for five minutes every hour).

•   Definitions of the behaviour: observers need to be completely clear as to what behaviours they are looking for.

•   Observer training: in most clinical situations, there will be different observers at different times and it is important that they are consistent.

•   Reliability and validity: the most useful meas­ure of consistency in observation methods is inter-rater reliability, but test-retest reliability can also be useful.

Three types of validity that could be assessed are: concurrent validity (are the results of the observation consistent with another measure of the same behaviour?), construct valid­ity (are the behaviours being recorded really signs of pain?) and discriminant validity (do the obser­vation records discriminate between patients with and without pain?).