Introduction to measuring pain

Pain is a personal experience that can vary greatly between individuals, making it challenging to assess accurately. Measuring pain helps healthcare professionals understand its severity and impact on daily life, which in turn guides treatment decisions. There are different approaches to measuring pain, including subjective methods that rely on self-reports and behavioural methods that observe visible signs.

Pain measurement tools aim to capture both the intensity and the emotional aspects of pain. These tools can be quantitative, producing numerical scores, or qualitative, providing descriptive insights. Effective measurement considers factors like the patient's age, communication abilities, and the context of their pain, such as whether it is acute (short-term) or chronic (long-lasting).

Subjective measures of pain

Subjective measures involve patients reporting their own experiences of pain. These are valuable because pain is inherently personal, but they depend on the individual's ability to communicate effectively.

Clinical interviews

Clinical interviews are conversations between a healthcare professional and a patient to evaluate chronic pain. Chronic pain refers to discomfort that persists for three months or more, often affecting daily activities.

In these interviews, professionals observe the patient's emotional state and explore their beliefs about what causes the pain. They may incorporate psychometric tests, which are standardised tools to measure psychological aspects like pain intensity, everyday functioning, emotional distress, beliefs, and expectations.

Evaluation of clinical interviews:

• Strengths - They use standardised questions but allow patients to expand on answers, leading to personalised treatment plans that improve patient adherence and success rates.
• Weaknesses - Effectiveness relies on strong communication and trust between patient and professional, which may not always be present, limiting their usefulness for some individuals.

Psychometric measures and visual rating scales

Psychometric measures use structured questionnaires to quantify pain, while visual rating scales combine words and images to help patients indicate pain levels without relying solely on language.

McGill pain questionnaire

The McGill pain questionnaire (MPQ) is a tool developed to describe and measure different aspects of pain using adjectives. It contains 78 adjectives organized into 20 groups (subclasses), which are divided into 4 major categories.

Categories in the McGill pain questionnaire:

• Sensory (questions 1–10) - Focuses on physical sensations, where patients select words describing their pain, such as throbbing or shooting.
• Affective (questions 11–15) - Examines emotional responses, with options like tiring, sickening, or fearful, rated by number.
• Evaluative (question 16) - Assesses overall pain intensity on a five-point scale, from mild to excruciating.
• Miscellaneous (questions 17–20) - Covers other pain aspects using three-to-five point rating scales.

Key measurements from the questionnaire:

• Pain rating index (PRI) - A total score indicating overall pain levels, including sub-scores for sensory, affective, and evaluative categories, plus the number of words chosen; higher scores mean greater pain.
• Present pain intensity (PPI) - Measures pain at the exact time of completing the questionnaire.
• Number of words chosen - Counts how many descriptive terms the patient selects, contributing to the PRI.

Strengths of the McGill pain questionnaire:

• Reliability - Studies show high consistency; for example, a test-retest analysis found a correlation of +0.96 among 91 patients.
• Validity - Comparisons with prior research on back pain patients yield similar results, supporting its accuracy.

Limitations of the McGill pain questionnaire:

• The use of specific descriptive words may not match every patient's experience, or terms might be misunderstood, limiting how well it captures true pain.

Visual analogue scales

Visual analogue scales (VAS) are tools that represent pain intensity along a continuous line, often with pictures to aid understanding. They help monitor pain over time, such as during clinic visits, by avoiding complex language.

A typical VAS is a horizontal line numbered from 0 to 10, with cartoon faces showing increasing distress levels.

For instance:

• 0: Smiling face labelled "No pain".
• 2: Neutral face labelled "Mild, annoying pain".
• 4: Slightly frowning face labelled "Nagging, uncomfortable, troublesome pain".
• 6: Distressed face labelled "Distressing, miserable pain".
• 8: Crying face labelled "Intense, dreadful, horrible pain".
• 10: Face in extreme agony labelled "Worst possible, unbearable, excruciating pain".

Patients mark their pain level on the line to indicate current intensity.

Strengths of visual analogue scales:

• They are quick and simple to use.
• The continuous scale avoids gaps in measuring pain intensity.
• Patients often feel their pain is accurately represented, enhancing validity.

Limitations of visual analogue scales:

• They provide only basic intensity data, without room for patients to describe the pain's broader impact.
• No opportunity exists for elaboration on the experience.

Behavioural measures of pain

Behavioural measures focus on observable signs of pain rather than self-reports. These are useful for patients who cannot communicate verbally, such as young children or those with cognitive impairments.

UAB pain behaviour scale

The UAB pain behaviour scale assesses visible behaviours indicating pain, including verbal and non-verbal cues. An observer rates the frequency of these behaviours on a three-point scale over a three-week period.

For example, behaviours like body language (clutching or rubbing the pain site) are scored as:

• None: 1 point.
• Occasional: 1/2 point.
• Frequent: 0 points.

Observations are recorded daily, often in a table format tracking multiple days.

Strengths of the UAB pain behaviour scale:

• It is straightforward to score and apply.
• Suitable for large groups, including those unable to self-report, leading to more generalisable results.

Limitations of the UAB pain behaviour scale:

• Accuracy depends on the observer's skill in recording behaviours.
• There is often low correlation between UAB scores and self-reports from tools like the MPQ, questioning its reliability.

Key study: Brudvik et al. (2016)

This study investigated how well parents and doctors assess children's pain compared to the children's own reports, highlighting underestimation issues in medical settings.

Aims

• To explore relationships between children's self-reported pain and ratings by parents and doctors.
• To examine how age, medical condition, and pain severity influence these estimates.
• To assess whether pain evaluations affect pain relief administration.

Method

This was a field study using correlational analysis and questionnaires in a natural hospital environment. It involved an opportunity sample of 243 children aged 3–15 years (mean age 10.6), their parents, and 51 doctors.

Procedure:

• Children aged 3–8 used two visual analogue scales; those aged 9–15 used a single scale with a green-to-red colour gradient.
• Parents and doctors rated the child's pain numerically.
• Additional data included demographics, doctors' experience, pain relief given, diagnoses (e.g., infection, fracture, wound, soft tissue injury), and waiting times.
• Parents provided written consent, and support was available for participants, ensuring the right to withdraw.

Results

• Only 42% of children rated as having severe pain by doctors received pain relief.
• Just 14.3% of children who self-reported severe pain were given medication.
• Doctors significantly underestimated pain, with parents being better but still not fully accurate.
• Anxiety was found to heighten pain perception.

Conclusions

• Doctors often undervalue children's pain reports.
• Greater emphasis should be placed on parental and child inputs for better pain management.

Strengths of the study:

• Reliability - Standardised procedures and tools like the MPQ ensured consistency.
• Validity - Conducted in a real emergency department, reflecting typical routines and time constraints.

Limitations of the study:

• Generalisability - Limited to one Norwegian emergency department with non-specialist doctors; results may differ in other countries or specialist settings.
• Validity - Parents and children could see each other's responses, potentially influencing answers.

Issues and debates in pain measurement

Pain measurement raises broader questions about research approaches and practical applications.

Idiographic versus nomothetic approaches

The nomothetic approach seeks general laws through quantitative data, such as numerical pain ratings and statistical correlations, as seen in Brudvik et al.'s (2016) study. This allows for broad comparisons but may overlook individual differences.

In contrast, an idiographic approach focuses on unique experiences, using qualitative methods like open-ended questions to explore why pain varies between people. This could provide deeper insights into personal factors affecting pain but is less generalisable.

Application to everyday life

Research on pain measurement has real-world value, such as improving paediatric care in places like Norway. It supports training for doctors to better heed children and parents' reports, recognising that identical conditions can cause different pain levels. This is important because unmanaged pain can prolong recovery and lead to issues like hypersensitivity, where the nervous system becomes overly sensitive to stimuli.