- To be able to recognise the importance of utilising a validated pain assessment tool
- To accurately describe a variety of validated tools and recognise when their individual use is indicated
- To discuss the advantages and disadvantages of multiple pain assessment tools
- To recognise the limitations of behavioural assessment tools
Pain Assessment Tools
A pain assessment tool requires reliability, (consistent results when performed under similar conditions or circumstances) and validity (the measurement does actually scale 'pain' and not some other quantity such as anxiety; this is problematic in assessment tools that assess behaviour in those unable to respond). Precision is necessary and the tool cannot be too cumbersome to use by the patient as they may give up or give inaccurate responses if tired and in pain.
It is important to utilise an appropriate pain assessment tool having ensured that staff and patients are educated in its use. In order to evaluate the effectiveness of the intervention, assessment should also be made post intervention. In order to demonstrate trends, documentation is important, preferably in a graphical format.
The point in time at which pain is assessed also needs consideration. In the case of post-operative pain management assessment should commence pre-operatively as it can valuable to establish the patient’s expectation of pain relief . Furthermore it is important to determine any pre-existing chronic pain and long term analgesia that needs to be taken into account when considering a postoperative regimen. Postoperative pain is relatively easily controlled at rest, however pain should be assessed on movement and where appropriate on deep breathing. In the quickly changing acute setting, frequent pain assessment is required if pain is to be managed effectively. Undertaking occasional assessment on a retrospective basis (‘what has your pain been like over the last 24 hours?’) does not provide meaningful data. Pain assessment should also, where possible, be undertaken verbally. This is the principal method unless patient’s age and cognitive status makes it impossible . Most assessment systems tend to yield numerical values either on a continuous or interval scale, since statistically these are more powerful, but behavioural methods also exist.
Approaches to the measurement of pain include verbal and numeric self-rating scales, behavioural observation scales and physiological responses. The complex nature of the experience of pain suggests that measurements from these domains may not always show high agreement. Because pain is subjective, the patient’s self-report provides the most valid measure of the experience. The visual analogue scale and the McGill Pain Questionnaire appear to be the most frequently used self-rating instruments for the measurement of pain in general clinical and research settings. However, the McGill is rather time consuming and would be impractical in the acute setting unless the health professional was dealing with a patient who had a complex pain problem. Factors that affect the choice of tool to be used include ease of use and the time it takes to administer to the patient . The staff using the tool need to be cognizant in pain assessment and understand how the tool should be applied. Other factors include the ability of the assessor when faced with complex assessment problems such as assessing pain in preverbal children, in cognitively impaired older adults and sedated patients; the subjectivity of the assessor and the time lag between the assessment and acting on the assessment.
The ideal pain assessment tool would have the following attributes but when you consider these attributes and measure them against the tools available you realise that no one tool has all attributes:
- Sensitive and free from bias;
- Immediate information about accuracy and reliability;
- Distinguishes between pain, unpleasantness and emotion;
- Assesses experimental and clinical pain;
- Absolute rather than relative scales;
- Estimates confidence of predictions.
Methods used for pain measurement, have until recently, measured pain as if it was a single unique quality that only effects intensity. Time constraints and patient requirement, however, may prevent more ambitious tools from being used in the acute pain setting. Verbal rating scales (VRS), numerical rating scales (NRS), and visual analogue scales (VAS) have been used extensively in the acute and research setting to measure pain. They provide simple, efficient and minimally intrusive measures of pain intensity .
Verbal rating scales
The VRS consists of a list of adjectives describing different levels of pain intensity. An adequate VRS of pain intensity should include adjectives that reflect the extremes of this dimension; from 'no pain' to 'extremely intense pain' and sufficient additional adjectives to capture gradations of pain intensity that may be experienced between these two extremes. Patients are asked to read over the list of adjectives and select the word or phrase that best describes their level of pain on the scale. Many different VRS lists have been created (, , ). The one used in University Hospital of Wales NHS Trust is a 4 point scale of no pain = 0, mild = 1, moderate = 2 or severe = 3. VRSs are usually scored by listing the adjectives in order of pain severity and assigning each one a score as a function of its rank.
VRSs are easy to administer, score and comprehend. Therefore, compliance with use are as good if not better than other scoring systems (, ). They are also valid and related positively and significantly to other measures of pain intensity (, , , ). The VRS also consistently demonstrates sensitivity to treatments that are known to have an impact on pain intensity .
A criticism raised with respect to the rank-scoring method is that it assumes equal intervals between the adjectives, even though it is extremely unlikely that it is perceived to be equal. That is, the interval between no pain and mild pain may be much smaller than that between moderate pain and severe pain, yet the interval is scored as if the difference were equivalent .
Other issues are that:
- patients have to be familiar with the terms before they select one that most closely resembles their pain and for a four point scale this is not that problematic, but for a 15 point scale this can be time consuming;
- patients may not find a descriptor that accurately describes their perceived pain intensity;
- in patients who are illiterate, they are less reliable than other pain intensity measures.
Visual analogue scales and graphic rating scales
A VAS consists of a line, usually 10cms long whose ends are labelled as the extremes of pain - 'no pain' to 'worst pain'. A VAS may have specific points along the line that are labelled with intensity denoting adjectives or numbers. Those scales that use adjectives are called graphic rating scales. Patients are asked to rate their pain along the line that best represents the intensity of their pain. This distance between the no end and the mark provided by the patient is measured and this gives the pain intensity score.
There is much evidence to support the validity of VAS for pain intensity. Such scales demonstrate positive relations to other self-report measures of pain intensity (, ), to observed pain behaviour  and are sensitive to treatment effects .
The VAS is also more sensitive than other measures especially those with a limited number of response categories because there are in fact 101 response levels (0 to 100mm) . Mechanical VAS have been developed and these usually look like a ruler with a red line on a slide that can be moved by the patient on one side of the ruler, and scored by the nurse on the other side. The problems with VAS include:
- scoring is more time consuming and involves more steps (and more opportunity for error) than scoring for other measures of pain intensity;
- they require the patient to have the ability to make a mark along the line or move the slide on a ruler;
- patients find them difficult to understand than other measures especially in patients with cognitive problems e.g. older adults and patients on high dose opioids;
- requires careful explanations and reinforcement for the patients to use them accurately.
Numerical rating scale
A NRS involves asking the patient to rate his or her pain from 0 to 10 (11 point scale) or from 0 to 100 (101 point scale) with the understanding that 0 is equal to no pain and 10 or 100 is equal to worst possible pain. This does not require the patient to write or use a ruler and he or she provides a verbal response which the healthcare provider can then document. A number of written response NRS exist. Jensen et al ,  describes one where patients are asked to record the number that best represents their pain intensity. The Brief Pain Inventory  utilises a NRS but presents the numbers in ascending order with the endpoint descriptors near the 0 and the highest number of the scale, it asks patients to circle the number that best represents their pain intensity.
NRS are valid and demonstrate positive and significant correlations with other measures of pain intensity . They have also demonstrated sensitivity to treatments that are expected to have an impact on pain intensity . The NRS is extremely easy to administer and score and therefore can be used with a greater variety of patients (e.g. older adults and patients with motor problems) than with a VAS. It is also useful for telephone assessments. The simplicity of the measure means that individuals comply better than with other tools. The only real drawback is, as for the other rating scales, that it assesses only pain intensity.
Picture or Face Scales
Picture or face scales employ photographs or drawings that illustrate facial expressions or persons experiencing different levels of pain severity (, ). Patients are asked to indicate which one of the illustrations best represents their pain experience. Each face has a number representing the rank order of the pain illustrated and the number of the picture chosen by the patient represents that patient's pain intensity score. These types of scales do not require patients to be literate and provide an option for those patients who have problems with written language. They are particularly useful in the paediatric population where scales have demonstrated validity through their association with other measures of pain intensity (, ) and through their ability to detect the effects of analgesics . Children also seem to prefer face scales . There is also evidence that they are valid for use in adults .
There are problems with face scales in clinical practice and these include:
- they have to be explained to the patient implying a degree of comprehension that may be lacking in the very young, for instance;
- the faces could convey misery, discomfort, depression or anxiety etc rather than pain
- no evidence regarding relative compliance rates.
Descriptor Differential Scale of Pain Intensity (DDSI)
The DDS-I consists of a list of 12 descriptors describing different levels of pain intensity . Patients are asked to rate the intensity of their pain as being more, or less than each descriptor on the list. If their pain is worse than the descriptor, they place a mark to the right of the word in proportion to how much greater their pain is. If their pain is less than the descriptor, they place a mark on the left of the chart. If the descriptor exactly describes their pain, they place a mark directly below the descriptor. There are 10 points along which patients can rate their pain intensity to the right and left of each descriptor, so the pain is rated on a 21 point scale for each descriptor. Pain intensity is defined as a mean of the ratings and can range from 0 to 20. The scale is valid and reliable and is associated with other measures of pain intensity  and is sensitive to treatment effects . However, the DDSI:
- is complex, especially in relation to other existing measures and those who have motor, or cognitive impairment may find it difficult;
- is time consuming in that is takes far longer to complete than other measures mentioned previously;
- has limited research on its validity and sensitivity.
The acute pain model suggests that if a patient has pain, visible signs of discomfort, behavioural and/or physiological will be present. Examples of behaviour usually expected of patients with pain include grimacing, rigid body posture, limping, frowning or crying. Vital signs are also expected to be elevated. However, it may not be appreciated that both physiological and behavioural adaptation occurs leading to periods of minimal, or no signs of pain. Absence of signs does not necessarily mean absence of pain.
When pain is sudden or severe, behavioural and physiological indicators may be present, but only for a brief time. However, very quickly the patient may make an effort to cease behaviours, such as crying or moaning, because it may be seen as unacceptable. This is especially true within Western cultures. The patient may also be exhausted. Physiological indicators, such as increased blood pressure and pulse rate may also disappear as the body seeks to maintain homeostasis. The patient may have a medical condition or may be undergoing treatment, which may prevent physiological reactions (e.g. Beta-blockers, hypothyroidism).
The guidelines from the American Pain Society  offer the following advice on using behavioural and physiological assessments:
- Observations of behaviour and vital signs should not be used instead of self report;
- Physiological measures (e.g. heart rate, blood pressure) are neither sensitive nor specific as indicators of pain;
The lack of objective signs (behavioural and physiological) may prompt the inexperienced clinician to say that the patient does not ‘look’ like he or she is in pain and withhold analgesia as a result. Therefore, behavioural and physiological indictors should not be used for patients who are able to self-report and indicate to the health carer that they are in pain. However, there are some patients who may not be able to tell you that they are in pain yet we need to try and assess their pain in some meaningful way. Cognitively impaired adults, children, and the very young fall into this category and nonverbal communication can be a source of information in this instance .
To sum up, no ideal pain assessment tools exists so it is important to use pain tools that are valid and reliable. There are many myths and misconceptions that need to be confronted to ensure that when a patient is reporting his or her pain, it is believed. Behavioural tools, while useful for those who are unable to self report, can assess fear, anxiety and depression also so care is needed when interpreting them in clinical practice. Where possible, self report pain tools should be used and pain scores documented as the 5th vital sign.
- Pain : creative approaches to effective management. Macmillan, Basingstoke., 2000.
- Clinical pain management : acute pain. Arnold, London., 2003.
- Textbook of pain, 4thth ed. Churchill Livingstone, Edinburgh., 1999.
- Comparison of fixed interval and visual analogue scales for rating chronic pain.. Eur J Clin Pharmacol, Eur J Clin Pharmacol 8, 415-20., 1975.
- The use of pain scales in assessing the efficacy of analgesics in post-operative dental pain. European Journal of Clinical Pharmacology, European Journal of Clinical Pharmacology 23, 441-444., 1982.
- A comparison of three ways of measuring pain.. Rheumatol Rehabil, Rheumatol Rehabil 21, 211-7., 1982.
- The measurement of clinical pain intensity: a comparison of six methods.. Pain, Pain 27, 117-26., 1986.
- The subjective experience of acute pain. An assessment of the utility of 10 indices.. Clin J Pain, Clin J Pain 5, 153-9., 1989.
- Measurement of pain: patient preference does not confound pain measurement.. Pain, Pain 10, 241-8., 1981.
- Validity of a verbally administered numeric rating scale to measure cancer pain intensity.. Cancer Nurs, Cancer Nurs 20, 88-93., 1997.
- Handbook of pain assessment, 2ndnd ed. Guilford Press, New York., 2001.
- Efficient pain assessment in clinical settings.. Behav Res Ther, Behav Res Ther 30, 71-3., 1992.
- Comparison of group progressive-relaxation training and cognitive-behavioral group therapy for chronic low back pain.. J Consult Clin Psychol, J Consult Clin Psychol 50, 757-65., 1982.
- Responsiveness of pain scales: a comparison of three pain intensity measures in chiropractic patients.. J Manipulative Physiol Ther, J Manipulative Physiol Ther 21, 1-7., 1998.
- Pain assessment: global use of the Brief Pain Inventory.. Ann Acad Med Singapore, Ann Acad Med Singapore 23, 129-38., 1994.
- Reliability and validity of the Faces and Word Descriptor Scales to measure procedural pain.. J Pediatr Nurs, J Pediatr Nurs 11, 368-74., 1996.
- Construct validity estimation for the African-American and Hispanic versions of the Oucher Scale.. J Pediatr Nurs, J Pediatr Nurs 13, 20-31., 1998.
- Pain in children: comparison of assessment scales.. Pediatr Nurs, Pediatr Nurs 14, 9-17., 1988.
- The Faces Pain Scale: reliability and validity with mature adults.. Appl Nurs Res, Appl Nurs Res 11, 84-9., 1998.
- The contribution of job satisfaction to the transition from acute to chronic low back pain.. Arch Phys Med Rehabil, Arch Phys Med Rehabil 79, 366-74., 1998.
- A placebo-controlled randomized clinical trial of nortriptyline for chronic low back pain.. Pain, Pain 76, 287-96.1998.
- Principles of Analgesic Use in the Treatment of Acute Pain and Cancer Pain., 3rd ed. American Pain Society, Skokie, Ill., 1992.