Measurement and Assessment of Pediatric Pain

SUMMARY

Appropriate management of pain in children depends on valid and reliable assessment and measurement that is implemented regularly and responded to appropriately. Significant improvements in pediatric pain measurement have been made in the past 25 years, and many acceptable measures of “short, sharp” pain are now available for all children and excellent measures of pain for children who can self-report. At this time there are promising measures of longer-term pain for children who cannot self-report.

Routinely, behavioral scales can assess pain in children younger than 6 years. Children older than 6 years can use self-report “faces” scales. Above about age 8, children can rate their pain on a 0–10 scale and can indicate descriptors of pain. At all ages and in children who have serious cognitive impairment, behavioral scales are useful to measure pain.

Because of the requirements of accreditation bodies, many health centers in Canada and the United States routinely measure pain in inpatient settings, but it is not clear how well measurement is being carried out and whether it changes pain management. Overall, much less attention has been paid to measurement of the impact of pain, which is particularly important in chronic and recurrent pain. We propose the use of a schema that includes the pain event, the impact of pain on specific behavior (activity restriction), and the impact of pain on social roles. Such a schema can help pinpoint problem areas for patients who require direct assistance.

Introduction

There have been major advances in the measurement of pain in children, and appropriate research attention is being paid to the reliability and validity of pediatric pain measures. Pain measures appear to be used widely in hospital inpatient settings but much less so in outpatient settings. Pain is a subjective, private event that can be measured only indirectly by one of three strategies:

What children report about their experience (self-report measures)
The way that children react in response to pain (behavioral measures)
How children’s bodies respond to pain (biological measures)

Because neonates, preverbal children, and children with significant handicaps cannot describe their experiences, behavioral and biological measures must be used. Even with verbal children, self-report is not always possible (e.g., when affected by an anesthetic).

Assessment and Measurement

Measurement refers to the application of some metric to an aspect of pain, usually its intensity. Measurement is like using a ruler to determine the height of something, whereas assessment is deciding whether it is height, weight, volume, or tensile strength that is important to measure. Assessment is much broader and should be tailored to the purpose of the investigation.

Although measurement of pain has become increasingly sophisticated, assessment has lagged behind. At least four groups have developed standardized pediatric pain assessment packages ( , , , ) that are modeled on the McGill Pain Questionnaire ( ). Each package measures location and intensity of pain and some factors that may be related to the pain, but none are used extensively in research or practice.

The PedIMMPACT ( ), a consensus group of leading researchers in pediatric pain, in conjunction with representatives from industry and regulatory agencies made suggestions regarding pain assessment and measurement to be considered for use in clinical trials. They suggested that pediatric acute pain clinical trials should consider assessing pain intensity, global judgment of satisfaction with treatment, symptoms and adverse events, physical recovery, emotional response, and economic factors. For chronic and recurrent pain, they suggested measuring pain intensity and physical functioning, emotional functioning, role functioning, symptoms and adverse events, global judgment of satisfaction with treatment, and sleep.

Pain and its impact can be conceptualized as occurring on four levels:

1.
With the abnormality or disease that is causing the pain.
2.
Development of the symptom of pain.
3.
Restriction of activity emerging with the lack of ability to perform in the normal manner.
4.
Social role limitation in the individual’s social context. Limitations in social role are concerned with the social disadvantages experienced as the result of pain and restriction of activity.

Extensive abnormality or disease may or may not result in much pain. For example, some children with juvenile rheumatoid arthritis have pain, but others do not. Similarly, pain may not result in restriction of activity. Some children persist in their activities despite pain, whereas others stop activity with relatively minor pain. Restriction of activity may not limit social roles. For example, a child who cannot engage in one sport may develop other interests and continue to interact with friends and peers. Many children make successful adaptations when pain from recurrent injury limits participation in their favorite sport; others do not. The direction of causality may be from limitation in social roles to pain. For example, a child who becomes socially isolated and bedridden (social role limitation) because of pain may significantly exacerbate the underlying problem and pain by decreasing physical fitness. It is critical to consider each level because the cause of problems at each level may be different and interventions can be designed for problems at each level. Thus, for example, when a child is evaluated at a pain clinic because of pain and school absence, as much effort should be focused on having the child return to school as on treating the child’s pain. What is causing and maintaining the pain may not be the same as what is causing and, perhaps more importantly, maintaining school absence. Successful treatment will probably not occur if the only target is the pain symptom or the school absence. Although there are relationships among disease, pain, activity restriction, and social role limitations, there is, by no means, perfect correlation.

Interventions that will ameliorate the underlying disease process are important, but often the underlying disease cannot be determined or is not amenable to change. Interventions that alter pain are indicated whenever pain is present, but most children with limitations in activity or social roles will also need treatment targeting these problems.

Discordance in Pain Assessment

Concordance and discordance in pain measures and assessment can occur both within and between levels. Few problems are caused by concordance, so attention will be focused on discordance. When a child functions beyond the level that is expected, it not only is accepted but may also be seen as admirable, and the child’s behavior may be encouraged. Such behavior can be a problem if a child’s activities exacerbate damage from the disease or tissue injury. So, for example, children in competitive sports may wish to compete or be encouraged by some coaches or by their peers to compete while injured despite pain and cause themselves significant damage.

The most problematical discordance occurs when the child has more activity restriction or limitation in social roles than expected on the basis of the underlying disease or disorder. A common reaction to this discordance is the “leap to the head” ( ), in which malingering or psychogenicity is assumed even when no positive evidence of psychological causation is present.

Discordance within levels may occur across behaviors, settings, or time. Discordance between the child’s self-report of pain and observers’ evaluation of the child’s pain based on behavior is not unusual. For example, children who report moderate levels of pain when asked may be observed to be playing and seem to be unaffected. This behavior can best be seen as a normal way for a child to cope with pain. A clinician faced with conflicting information about the amount of pain that a child is experiencing may have difficulty deciding on a course of action and view discordance with alarm or as evidence of malingering or psychogenicity. Indeed, the diagnostic category of somatization disorder is based primarily on discordance between the underlying disorder and symptoms. An assumption of malingering or psychogenicity is unwarranted, but discordant findings do indicate the need for further assessment.

Psychometrics of Pain Measurement

The essence of pain measurement is to assign a value to pain. The simplest level of measurement is nominal or, in the case of pain, dichotomous (i.e., ascertaining the presence or absence of pain). This level of measurement can be useful in screening or triage situations. So, for example, we use a dichotomous judgment if one’s own young child is in pain and needs comforting. The second level, ordinal, occurs when pain severity is ranked. Ordinal measures can determine whether a pain is more or less severe than another pain. Ordinal measurement is the level that is required for decision making with patients. For example, we need to know whether the pain is sufficient to warrant intervention and whether the pain is reduced with intervention. The third level is interval measurement, in which measures have equal intervals between values. The final level is ratio, in which there is a true zero point. Ratio and interval measures have psychometric benefits and may give more information about the meaningfulness of a change. Although there may be some debate ( ), most pain measures in children are ordinal-level measurements.

Reliability and Validity

Two of the most important psychometric properties of a pain measure are its reliability and validity. Reliability refers to the consistency or reproducibility of the measure. Internal reliability refers to the degree of similarity between different items in a measurement scale. For example, if a scale uses three items to measure facial response, one would hope for a moderately high degree of interrelationship or reliability among the items. Perfect reliability would suggest that fewer items would be needed, and low reliability would indicate that a single concept (pain) was not being measured. Inter-rater reliability refers to how well two observers would rate the same behavior.

Many self-report measures of pain in children, such as facial scales or numerical rating scales (NRSs), are single-item measures using a number or a face, and thus internal reliability cannot be calculated. Additionally, because pain often varies over time, there has been little interest in stability over time or test–retest reliability.

Validity refers to how well the measure actually measures what it is supposed to measure. Face validity refers to whether the measure makes sense. For example, using facial response makes sense as a measure of pain and thus has high face validity. Construct validity refers to any evidence that adds to the credibility of the measure. For example, increases in a measure immediately following an invasive procedure or decreases with analgesics suggest construct validity of a measure of pain. Because pain is a subjective measure and there is no direct measure of experience, it can be measured only indirectly by self-report, behavior, and physiology. Thus in both children and adults, there can be no real “gold standard” of pain. In younger children, self-report is not available and thus behavior and physiology are all that can be used.

Utility

The utility of a measure refers to its usefulness in research or clinical care. One aspect of utility is ease of use; another is versatility. A measure that requires a trained observer 10 minutes to complete and can be used only with adolescents in acute pain is less useful and less versatile than a measure that can be carried out by anyone in a few seconds across a wide age range for both acute and chronic pain. Some pain measures are used in research settings but may be too expensive or too demanding in terms of skills or time needed for clinical use. Moreover, some pain measures, such as a child’s retrospective report of average headache intensity over the previous week, may not be sufficiently precise or detailed for making clinical decisions but may be very useful in an epidemiological study.

Strategies of Pain Measurement

The three most frequently considered aspects of pain are the subjective (measured by self-report), the behavioral (measured by sampling of observation and coding or rating of behavior), and the biological (measured by sampling of physiological or electrical potentials and assaying body fluids or other biological responses). All measures of pain are indirect because there is no direct measure of the pain experience, and all measures are subject to bias in collection and interpretation. There is no evidence that children older than 6 or 7 years are less accurate in self-report than adults. Nor is there any evidence that children are more or less likely than adults to be biased in their self-report or behavioral or physiological responses.

Self-Report Measures of Pain

Self-report measures depend on the child’s own report of the subjective pain experience. This report can include descriptions of pain-relevant feelings, statements, and images, as well as information about the quality, intensity, and temporal and spatial dimensions of the child’s pain. Self-report measures, when they can be obtained, can be regarded as the gold standard. Self-report measures require the child to have a certain level of cognitive and linguistic development, which excludes all preverbal children and possibly many other young children. Children at the earliest levels of language development may be able to respond to the least demanding questions, such as those about the existence of pain.

Bias can occur in self-report measures. Following surgery, children may deny having pain when asked because the needle that they may receive is more feared than the pain itself. If children are asked to describe pain to their mothers, they may give different answers than if they are asked to describe pain to an authority figure such as a physician. In addition, the type of question and the response options (e.g., open-ended questions versus a checklist) may also substantially alter the child’s answers.

Methods used to measure self-report of pain include direct questioning, pain adjective descriptors, self-rating scales, NRSs, and non-verbal methods. Spontaneous reports (e.g., “My tummy hurts”) or direct questioning about pain can be useful with verbal preschoolers and school-age children as a prompt to initiate more assessment. Reliance on spontaneous reports alone will seriously underestimate pain because many children who have pain will not mention it. Direct questioning may include

Asking the child to make comparisons with previous pain experiences (“Is this pain like the stomachache you had last week?”)
Providing the child with temporal anchors for measuring the duration of pain (“Has the pain been going on since you woke up?”)
Facilitating communication through the use of objects and gestures (“How much pain do you have—a little bit or a lot?”)

Although this type of questioning is useful, it is not a measure and has shortcomings. Questions such as “How is your pain today?” may function more as conversation prompts than pain measures and are particularly open to bias because of demand characteristics. Additionally, there are no numbers associated with the answers. Furthermore, even if specific questions are asked about pain frequency, intensity, and duration, retrospective questions may be inaccurate. Asking the child’s mother or father global questions about the child’s pain may, in some cases, produce sufficient information to guide diagnosis and treatment but will be insufficient in many situations, especially where there is significant variability in the expression of pain. More precise measures of pain will be obtained from the child when prospective, well-validated measures are used. Stinson and colleagues (2006a) systematically reviewed self-report measures for pain in children as part of the PedIMMPACT process. They reviewed 36 single-item self-report measures to examine their psychometric properties, interpretability, and feasibility and found no clear winner but made recommendations. The PedIMMPACT consensus group ( ) accepted their recommendations. For children 3 to 4 years old, the Pieces of Hurt Tool ( ) was preferred. The Faces Pain Scale (Revised) ( ) was recommended for children 4–12 years old and the visual analog scale (VAS) for use in children 8 years and older. The Ped IMMPACT group also considered the NRS because it is widely used and easy to use and chart but did not recommend it. There were no data on the reliability and validity of the NRS for children at that time. Since then several papers have demonstrated the reliability and validity of the NRS-11 (i.e., 0–10 scale, see later).

Pain adjective lists, such as the McGill Pain Questionnaire ( ), have been used successfully in older adolescents to measure pain. A major strength of this type of scale is that it is not restricted to the intensity dimension of pain but also measures the affective and evaluative aspects of pain. developed and tested lists of words that included sensory, affective, and evaluative words that can be completed by children older than 8. As yet, the meaning of different patterns of words has not been determined. Although these methods are appealing because the richness of the pain experience is described, children younger than about 8 cannot use these methods. In addition, they have not been shown to be clinically superior to simpler methods that focus on the intensity of pain. Self-rating scales of the intensity of pain vary according to the type and number of anchor points provided and include VASs, category rating scales, and NRSs.

Visual Analog Scales

VASs have either a vertical or a horizontal line, usually 10 cm in length, with verbal or pictorial anchors indicating a continuum from no pain to severe pain. Children are asked to indicate on the line how much pain they are experiencing. Children older than 5 or 6 years can reliably and validly use a VAS. Children’s ratings of their pain on a VAS correlate with parents’, nurses’, and physicians’ ratings ( ). Ratings also correlate with behavioral measures of pain ( ).

Some have suggested that a vertical scale is more appropriate than a horizontal scale because children may find it easier to conceptualize the notion of greater or lesser intensity of pain with up and down rather than left or right. developed and validated a variant of a VAS in the form of a red and white wedge; other wedges have also been used. To use a VAS, a child must have the cognitive ability necessary to translate the pain experience into an analog format and to understand proportionality. Care must be taken when repeatedly reproducing the scale to ensure that the process does not alter the length of the line and confound scoring.

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