Measurement of pain

'Measuring' pain may seem to be a strange idea but it's only when we can assess the patient's pain accurately that we can treat it effectively. Measurement of pain implies trying to assess not only its intensity but its quality and type.

Problems of pain measurement

Because pain is a personal experience there are many problems in trying to measure it. These include:

• varying baseline - the experience of pain will be different if the patient has previously been free of pain or has been subject to another painful condition
• lack of signs - the patient in extreme pain may show no observable signs, except perhaps in facial expression
• patient coping strategies - patients adapt their behaviour so as to minimise pain. For example, the patient with painful arthritis of the knees may learn to walk without bending the knees
• pain tolerance - people have different pain thresholds. What is unpleasant to one person may be unbearable to another
• stoicism - some people - especially the elderly - bear pain stoically because it is an expected part of the ageing process.

Measurement of intensity

Measuring the intensity of the pain is very difficult. It must always be remembered that what is important is the experience of severity, not the observer's assessment. 'Pain is what the patient says it is'.

Various techniques are used to try to gain an understanding of pain intensity:

• simple words such as 'mild', 'moderate' or 'severe' give a rapid categorisation
• visual analogue scales (VAS) are often used. With adults the scale will use words (eg. 'no pain' to 'unbearable pain'); with children, pictures of painful situations or faces may be used. VAS data can be used to measure progression or remission of pain as the patient's mark moves on the scale day by day.

The figure below shows average pain scores as rated by patients for different kinds of pain syndromes.

Clinical pain syndromes

Measurement of quality

Quality of pain can be best determined by encouraging patients to talk about their pain. The language of pain (types of words used by the patient) is very important in diagnosis. Non-verbal signals are also important, a patient may point to the source of a sharp, acute pain but use a flat hand to describe a dull, aching pain. Many patients use a closed fist to describe the crushing pain of angina.

Studying words

Some words give very accurate descriptions of painful conditions.

Skilled pain specialists can often differentiate functional and organic pain by the words used to describe them.

Gate theory of pain

Psychological factors are known to be of great importance in the sensation of pain. People who are anxious or afraid often consider the same pain stimulus to be much more severe than those who are not afraid. By contrast, soldiers in battle have been known to suffer great injury without feeling any pain at the time.

The gate theory attempts to explain these phenomena. It is thought that there is a neural mechanism in the spinal cord which regulates referred transmission of pain impulses to the brain: when the 'gate' is open pain impulses reach the brain; when the 'gate' is closed they are blocked.

The gate seems to be controlled by complex neurophysiological mechanisms. Pain perception is known to be raised by anxiety or fear but lowered in states of excitement or extreme concentration.

The gate theory is a means of integrating the sensory, emotional, cultural and behavioural dimensions of pain.

Summary

• Several disciplines have contributed to the study of pain yet many people suffer unrelieved pain
• Pain is a complex subjective phenomenon. It is important to realise that everyone is different
• A definition of pain is 'pain is what the patient says it is and exists when he says it does'. Judgemental attitudes are not helpful
• There are three types of pain, superficial, deep and referred
• Acute pain and chronic pain are different entities and their management is therefore different
• Pain measurement is a complex process utilising both quantitative and qualitative measures
• The gate control theory of pain attempts to explain the variation in perception of identical stimulation