Measurement and Assessment of Pediatric Pain
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:
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).
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 (Varni et al 1987, Savedra and Tesler 1989, Abu-Saad 1990, McGrath 1990) that are modeled on the McGill Pain Questionnaire (Melzack 1975). 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 (McGrath et al 2008), 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:
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.
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” (Wall 1989), 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.
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 (Bieri et al 1990), most pain measures in children are ordinal-level measurements.
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.
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.
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 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
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 (McGrath et al 2008) accepted their recommendations. For children 3 to 4 years old, the Pieces of Hurt Tool (Hester et al 1990) was preferred. The Faces Pain Scale (Revised) (Hicks et al 2001) 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 (Melzack 1975), 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. Wilkie and colleagues (1990) 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.
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 (O’Hara et al 1987). Ratings also correlate with behavioral measures of pain (McGrath et al 1985).
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. Maunuksela and colleagues (1987) 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.
Category scales consist of a series of words along a continuum of increasing value (e.g., no pain, mild pain, medium pain, severe pain). The Pieces of Hurt Scale, sometimes referred to as the Poker Chip Tool (Hester 1979), a type of category scale, requires the child to evaluate the intensity of pain by choosing one to four poker chips, which represent the “pieces of hurt” experienced. Children’s ratings correlate with overt behavior during immunization. In comparing child, nurse, and parental ratings of pain, Hester and associates (1990) demonstrated convergent validity and partial support for discriminant validity in children between the ages of 4 and 8 years.
Faces scales, another form of category scale, use faces expressing varying amounts of pain. The Oucher scale (Beyer 1984) is a variant of the faces scale that is designed to measure pain intensity in children aged 3–12 years. The scale is displayed in a poster format and consists of a vertical numerical scale (0–100) on the left and six photographs of children in varying degrees of pain positioned vertically to the right. Validity studies indicate that children are able to classify the pictures in the correct sequence and that scores correlate highly with the VAS and results from the Poker Chip Tool (Beyer and Aradine 1987). Scores on the Oucher scale are sensitive to analgesia-induced reductions in pain (Aradine et al 1988). Variants of the Oucher have been designed and validated for African American and Hispanic children (Beyer and Knott 1998).
Bieri and co-workers (1990) developed a faces scale to assess pain intensity in children aged 6–8 years that used children’s drawings of faces and the facial action coding literature in its development. Strong agreement among children was demonstrated on rank ordering of the faces according to pain severity, as well as their perception of the faces as representing equal intervals. A newer version of this scale has been developed and validated (Hicks et al 2001). It can be converted to a 0–10 rating and entered into the child’s chart. In summary, faces scales are easily understood by children and inexpensive, and several have excellent psychometric characteristics.
NRSs use numbers (i.e., 0–5, 0–10, or 0–100) to reflect increasing degrees of pain. Children must understand number concepts to use this type of scale. The intervals along the scale cannot be assumed to be equal, and a change between 0 and 3 is not necessarily the same as a change between 6 and 9. Recent work on the psychometric properties of NRSs ( Miró et al 2009, von Baeyer et al 2009) has shown excellent psychometric properties for 0–10 scales (NRS-11). von Baeyer (2009) examined what needs to be done with NRSs. One of the most important issues is standardization of anchors. NRSs are the most commonly used scales and have the major advantage of requiring no equipment and being easy to chart. Diaries are a specific type of NRS in which repeated ratings of pain are recorded. Pain diaries have been used for the measurement of headache, abdominal pain, and limb pain. In a typical format, ratings range from 0–5, and each number corresponds to a verbal description of pain severity. The scale requires a minimum of instruction and has satisfactory inter-rater reliability when comparisons are made between parent and child ratings (Richardson et al 1983). Pain diaries may also be used to encourage self-management strategies. Electronic pain diaries such as those on the Internet or on personal digital assistants (PDAs) have been found to be more reliable than paper diaries in adults (Stone et al 2004) but are more expensive. Palermo and colleagues (2004) demonstrated in a randomized trial that children older than 8 years, especially boys, were more likely to complete a diary on a PDA than a paper diary. The electronic diary also had fewer errors than the paper diary. Similarly, Stinson and co-workers (2006b) demonstrated that electronic diaries are useful for adolescents with arthritis to record their pain and other symptoms. Electronic diaries can be programmed to prompt responses and to ask specific follow-up questions.
Primarily non-verbal methods have also been used to measure the self-report of pain. These methods include asking children to describe the color of their pain or to draw pictures of their pain. Children are reported to typically describe severe pain as being red or black (Unruh et al 1983). Red and black appear to be the preferred colors for all pain drawings, even for drawings of low intensities of pain (Kurylyszyn et al 1987). Children’s pain drawings are rich in detail, are emotively powerful, and provide a basis for discussion about pain. Although they can be reliably classified by raters and may show developmental differences, it is not clear that drawings can tell us much about the intensity or origin of the child’s pain.
In summary, several self-report measures of pain that are easy to perform and use in clinical situations have been developed. However, the lower limits of these measures have not been sufficiently investigated, nor has it been clearly established that one measure is superior to another. Some measures have been translated into other languages (e.g., the Pain Faces Scale is now available in 47 languages) ( Hicks et al 2001, von Baeyer 2010).
The second component of pain that can be measured is pain behavior. Behavior such as vocalization, facial expression, and body movement is often associated with pain. Anand and Craig (1996) suggested that behavior should be considered the equivalent of self-report for preverbal children. There is, however, the ever-present challenge of distinguishing behavior caused by pain from that caused by other forms of distress (e.g., hunger, thirst, and anxiety). The best evidence of the reliability and validity of behavioral measures is based on studies of short painful stimuli such as venipuncture, heelstick, or bone marrow aspiration, but there is emerging evidence from postoperative and chronic pain. von Baeyer and Spagrud (2007) systematically reviewed behavioral measures of pain in children 3 to 18 years of age as part of the PedIMMPACT process. They recommended the FLACC (Face, Legs, Activity, Cry, and Consolability) (Merkel et al 1997) or the CHEOPS (Children’s Hospital of Eastern Ontario Pain Scale) (McGrath et al 1985). For postoperative pain they recommended the FLACC. The recommended measure for postoperative pain at home is the Parents’ Postoperative Pain Scale (Chambers et al 2003). For pain measurement in critical care settings, the COMFORT Scale (Ambuel et al 1992) was recommended. von Baeyer and Spagrud (2007) could make no recommendations for behavioral measures in children with chronic pain.
Facial behavioral scales have been developed for measuring pain in infants, children, and adults. Grunau and Craig (1987) developed the Neonatal Facial Action Coding System (NFACS), which consists of 10 facial actions that trained coders can identify from review of videotapes, and a Child Facial Action Coding System (CFACS) has also been developed and validated ( Gilbert et al 1999, Breau et al 2001). Facial movements observed in response to heel lance (the “pain face”) were brow bulge, eye squeeze, nasolabial furrow, lip part, taut tongue, stretched mouth, and chin quiver (Grunau and Craig, 1987). The results indicated that facial response to heel lance was greater in babies who were quiet and awake than in babies who were sleeping. Facial expressions are interesting because they are relatively free of learning bias and may represent the infant’s innate response to pain.
To date, the facial coding systems have been used primarily for short, sharp pain in a research context. They require video recording and time-consuming scoring of responses. Facial action may be difficult to record in babies who have their faces obstructed because of medical interventions. As a result, the full NFACS and CFACS are not appropriate for routine clinical use. A modified approach does have clinical utility. Stevens ( Stevens et al 1996, Stevens 1998) has successfully used facial actions in the Premature Infant Pain Profile in the clinical context. Grunau and colleagues (1998) have also shown that facial action can easily and accurately be coded at babies’ bedside.
Several researchers ( Craig et al 1984, Johnston and Strada 1986) have observed gross body movements associated with pain in infants and young children. Commonly observed behavior includes general diffuse movements in newborns, withdrawal of the affected limb in 6-month-old infants, and touching the affected area in 12-month-old infants. The Infant Pain Behavior Rating Scale (Craig et al 1984), a time-sampling scale, rates expressive body responses (rigidity, kicking), as well as vocalizations and facial expressions, in infants and young children. The scale has satisfactory inter-rater reliability for most of the items, as well as validity. In a survey of neonatal nurses’ perceptions of pain, similar behavior was identified as being indicative of pain in neonates, but their specific behavior did not indicate more or less pain as measured by nurses’ ratings (Pigeon et al 1989).
The Procedural Behavior Rating Scale (Katz et al 1980) and the Observational Scale of Behavioral Distress (Jay et al 1983) were developed to measure distress in pediatric oncology patients as a result of bone marrow aspiration and lumbar puncture. Types of behavior include crying, screaming, physical restraint, verbal resistance, requests for emotional support, muscular rigidity, verbal pain expression, flailing, nervous behavior, and information seeking. The scales have satisfactory inter-rater reliability above 0.75 ( Katz et al 1980, Jay et al 1983), and distress behavior on the Observational Scale of Behavioral Distress correlates with children’s self-report of pain and anxiety scores (Jay et al 1983).
Crying has received considerable attention as a pain measure. Investigators have attempted to differentiate the pain cry in infants in terms of its psychoacoustic properties ( Johnston and Strada 1986, Grunau and Craig 1987). Grunau and Craig (1987) found that both gender and psychological state affected crying behavior. Specifically, in response to heel lance, boys cried sooner and had more crying cycles than girls did. Also, sleeping babies cried less quickly than alert babies. Although some characteristic cry patterns have been identified during medical procedures, a cry pattern or cry template unique to painful stimuli has not been identified.
The CHEOPS (McGrath et al 1985) consists of six types of behavior (crying, facial expression, verbal expression, torso position, touch position, and leg position). The scale has inter-rater reliability above 0.80, is sensitive to changes after the intravenous injection of opioids, and correlates with independent pain ratings by nurses. Several variations of this scale have been developed. Beyer and associates (1990) established that gross behavior such as grimacing and body movements occurs very rarely in children with postoperative pain once they are out of the recovery room.
The FLACC scale (Merkel et al 1997) is an acronym for the components that are rated: Face, Limbs, Activity, Cry, and Consolability. Behavior is rated by a trained rater using a 0–2 scale. It has extensive reliability and validity data.
The COMFORT Scale reports on alertness, calmness or agitation, respiration, physical movement, change in blood pressure, change in heart rate (HR), muscle tone, and facial tension. There are extensive validity data for the COMFORT Scale (van Dijk et al 2000)
The Postoperative Pain Measure for Parents (Chambers et al 1996) was developed from parents’ reports of behavior that they used to determine whether their child was in pain (Reid et al 1995). The scale is highly correlated with self-report and has high sensitivity and specificity in detecting clinically significant pain. Moreover, it clearly measures pain rather than anxiety and has been validated in children as young as 2 years of age (Chambers et al 1996, 2003; Finley et al 2003).
The Non-Communicating Children’s Pain Checklist (McGrath et al 1998) measures pain in children who cannot communicate about their pain because of physical and cognitive handicap. Similar scales have been developed in France and England ( Giusiano et al 1995, Stallard et al 2002). Breau and colleagues (2002) conducted an extensive series of studies validating this scale in its use by parents and professionals for both longer-lasting pain and postoperative pain and have shown the scale to be valid and sensitive to pharmacological interventions.
In summary, there has been extensive work on measures of short, sharp pain and increasing work on long-term pain. The scales range from measures of gross behavior to measures of small changes in facial response. The behavioral measurement of long-term pain and the development of measures for special populations, such as children with disabilities, have made important strides.
Biological measures of pain in children suffer from many of the same problems as behavioral measures do. In particular, it is often difficult to determine whether the perturbation being measured is due to causes other than pain (e.g., hunger). Some authors (e.g., Porter 1993) have argued that discrimination between pain and other distress may be meaningless for infants and that a search for a pain-specific measure in this age group should be abandoned in favor of a biological measure of distress. Much like behavioral measures of pain, it appears that biological indices of pain habituate in the face of longer-term pain.
Sufficient data on HR, transcutaneous oxygen, sweating, and the stress response have accumulated to argue for their validity as measures of pain in some circumstances. Less evidence is available for using endorphins, respiration, and blood pressure. However, further research may elucidate their validity.
HR is the most widely used biological measure of pain in infants and children. In general, HR increases in response to more invasive procedures. However, depending on the length of period sampled, slowing of the HR may occur as the first response to pain (Johnston and Strada 1986). There appear to be major differences between healthy and ill neonates and between full-term and premature neonates, with generally weaker, more variable, disorganized responses occurring in ill and premature babies ( Field and Goldson 1984, Porter 1993). Porter (1993) described the use of vagal tone as a direct measure of parasympathetic control and a possible index of pain and distress. However, no studies have demonstrated the superiority of this measure over simple HR. Indeed, no studies have adequately attempted to evaluate HR as a measure of longer-term pain, although it is clear that HR is not substantially elevated by postoperative pain in older children (O’Hara et al 1987).
Transcutaneous measurement of the oxygen saturation of hemoglobulin is reduced during painful procedures such as circumcision (Williamson and Williamson 1983), lumbar puncture (Porter et al 1987), and intubation (Kelly and Finer 1984). This may be due to changes in ventilation or to stress-induced vasoconstriction because it also occurs during non-painful handling of neonates. This is a frequently available measure in the intensive care unit, although measurements of peripheral hemoglobulin oxygenation are heavily influenced by a host of factors, particularly in critically ill patients.
Harpin and Rutter (1983) demonstrated that in full-term babies (but not in preterm babies), palmar sweating, as measured by an evaporimeter, was a sensitive index of pain from heel lance. Gedaly-Duff (1989) reviewed the use of a simpler measure, the palmar sweat index, which measures the number of active sweat glands rather than the extent of sweating. Palmar sweating has been used primarily as a measure of distress rather than pain. Recently, Hullett and colleagues (2009) proposed that fluctuations in skin conductance be used to measure postoperative pain. Berde and McGrath (2009) noted that there are serious limitations to adoption of this measure in clinical practice but that it warrants further examination. Choo and co-workers (2010) confirmed these limitations.
Surgery or trauma triggers the release of stress hormones (corticosteroids, catecholamines, glucagon, and growth hormone). This leads to a cascade of events that may have the positive effect of facilitating healing but, in a sick neonate, can have disastrous results. Anand and colleagues detailed the stress response of premature and full-term infants to surgery (Anand et al 1987a, 1987b; Anand 1993). The response generally consists of marked increases in plasma catecholamines, glucagon, and corticosteroids and suppression of insulin secretion with subsequent hyperglycemia and lactic acidosis. The reaction to anesthesia indicates the validity of the measures, but it is clear that the stress response is more than a measure of pain. Though useful in the research context, these measures have limited use as clinical pain measures in individual patients. Cortisol release has been studied widely in adults and quite frequently examined in infants and children (Gunnar 1986). Cortisol release is not specific to pain and occurs in many aversive situations. Changes in cortisol level from a resting baseline are significant in response to circumcision (Gunnar et al 1981). However, sick premature babies may have very unstable levels. Thus, small perturbations as a result of specific painful procedures may not be detectable. Lewis and Thomas (1990), in their cross-sectional study of healthy infants 2, 4, and 6 months of age, provided insight into the complexity of the response even in healthy infants at different ages. They used diphtheria-tetanus-pertussis inoculations and found that the strongest increase in cortisol levels, as measured by salivary assay, occurred in the 2-month-old children. There was little change in cortisol levels in the 4-month-old children and only a moderate response in the 6-month-old children. The age differences in cortisol response were eliminated if the behavioral response was used as a covariate. In addition, baseline levels of cortisol were important in interpreting the cortisol response to painful stimulation. There have been recent developments involving advanced imaging techniques in measuring changes in the central nervous system during pain in adults. Although these measures provide greater understanding of the central representation of pain, the research has not been replicated in children because of the invasiveness of the measurement. Moreover, these measures are not yet clinically useful.
Biological methods of measuring pain provide important information about the body’s response to insult. These measures are particularly important to the clinician when they provide warning about responses affecting the medical stability of the child. However, biological measures are not specific to pain, often habituate, and are frequently not available in the clinical setting (Sweet and McGrath 1998). At this time, although there is some evidence of their validity, biological measures are not as well validated as behavioral and self-report measures of pain.
Because pain is a multidimensional phenomenon and no single pain measure has sufficient reliability and validity, composite measures of pain have been developed (Stevens 1998). Combining items can enhance the reliability and validity of instruments. Several scales have been developed for both neonates and children and have been reviewed by Stevens (1998). Two of the most widely used and extensively validated scales are the Premature Infant Pain Profile (PIPP) (Stevens et al 1996) and the COMFORT Scale (Ambuel et al 1992).
The PIPP consists of six items that vary in value with gestational age at the time of the observations: behavioral state, change in HR, change in oxygen saturation, brow bulge, eye squeeze, and nasolabial furrow. The scale has excellent psychometric properties and is now in clinical use (Ballantyne et al 1999). The COMFORT Scale (Ambuel et al 1992) is an eight-item scale designed to measure distress (including pain) in pediatric intensive care units. The items included are movement, calmness, facial tension, alertness, respiratory response, muscle tone, HR, and blood pressure. The scale has excellent psychometric properties and takes only minutes to administer. A study (Carnevale and Razack 2002) involving intubated, mechanically ventilated children in a pediatric intensive care unit found that 97% of the variance was accounted for by the first six items and that HR and blood pressure had little validity and reliability. They suggest that the COMFORT Scale be revised by eliminating the HR and blood pressure variables.
Mounting evidence and pressure by professionals and parents for the need to measure pain have led to the development of policy statements and guidelines for pain by professional associations and public policy organizations (Jacox and Spengler 2003). The American Society of Anesthesiologists (1994) advised that infants be given adequate pain relief during surgery following landmark research by Anand and colleagues (1987a, 1987b) and publicity about Jill Lawson’s efforts for better pain relief for neonates (Scanlon 1985). A joint statement by the American Academy of Pediatrics and the Canadian Paediatric Society (2000) summarized the extant literature and made clear recommendations on pain in neonates. In the United Kingdom, the Royal College of Paediatrics and Child Health (1997) published Prevention and Control of Pain in Children: A Manual for Health Professionals, and in 2002 the Royal College of Nursing developed clinical practice guidelines for the recognition and assessment of acute pain in children. In the United States, between 1992 and 1996 the Agency for Health Care Policy and Research (now the Agency for Healthcare Research and Quality) sponsored the development of clinical practice guidelines, including guidelines for acute pain, cancer pain, and chronic pain. These documents had careful and detailed sections on pain in children. These statements and documents increased professional pressure to improve the standards of care for management of pain in infants and children.
Accreditation standards followed. The first were those by the Commission on Accreditation of Rehabilitative Facilities (1983). In 2000 the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) adopted pain standards that were implemented in 2001. These standards required that pain be assessed, a plan developed, and pain outcomes monitored. The impact on pain management in children has not yet been carefully assessed, but it appears that they have resulted in increased effort to measure and treat pain in children. Similar accreditation standards were implemented in Canada.
In the United States, a further development for implementing pain measurement and management is attention to pain as a marketing tool to attract patients in a competitive market. Weisman (2001) detailed the development and implementation of The Comfort Zone at the Children’s Hospital of Wisconsin. This program includes extensive hospital policy development and protocols, staff training, and monitoring of pain outcomes.
The major impediment to the measurement of pain in children is failure to implement what is already known. All children who are at risk for pain, including those who have undergone surgery and children who are in the active phase of potentially painful diseases or disorders such as cancer, sickle cell disease, migraine headache, or juvenile arthritis, should have their pain monitored routinely. Hospitalized children’s pain should be recorded on pain flow sheets on a regular basis every few hours (McGrath and Unruh 1987). Stevens (1990) has shown that pain flow sheets decrease pain by improving pain management. Pain diaries, completed by the child or by the parent, can be used with children who are at risk for significant recurrent pain. We believe that routine measurement should be used in quality assurance programs to ensure the adequacy of pain control in hospitals. Our belief is that adequate pediatric pain measurement is an ethical imperative that all health care professionals are obligated to implement. However, there is, at this time, little evidence to show that routine measurement will bring about less pain in children (Franck and Bruce 2009).
There is an emerging literature aimed at developing a threshold for treating pain in children. Children themselves believe that not all pain should be treated. For example, Gauthier and colleagues (1998) and Demyttenaere and co-workers (2001) found that children believe that only pain higher than about 3 on a 10-point scale should be treated pharmacologically. Eradication of all pain is seldom a realistic goal of clinical pain management; however, pain that interferes with activity and limits participation in social roles should be managed appropriately.
Voepel-Lewis and colleagues (2010), in a sophisticated study of 113 hospitalized children after surgery, attempted to determine the clinical meaningfulness of pain measures by using an NRS from 0–10. They found that pain scores were reliably related to perceived need for medication, perceived satisfaction, and pain relief. However, they found that the number of false-negative and false-positive results made determination of a single common threshold for treatment of pain in all patients inappropriate.
Limitation of activity as a result of pain is often measured as disability and has received little systematic attention in the pediatric literature. Varni’s pain assessment questionnaire ( Thompson and Varni 1986, Varni et al 1987) and Patricia McGrath’s (1990) assessment tool contain a measure of disability. Unfortunately, the validity of the measures and the extent of disability in different populations are unknown. Walker and Greene (1991) developed and validated the Functional Disability Inventory. This 15-item scale was developed carefully and shows excellent construct, concurrent, and predictive validity. The instrument was stable over time and also sensitive to medical treatment. The Functional Disability Inventory is one of the most widely used scales for pediatric chronic pain (Eccleston et al 2005).
The major social roles of children are as peers, as students, and as family members. Consequently, restriction in social role participation is focused on restriction in educational and social activities, sometimes also referred to as handicap. Despite limited data on the topic, school absence because of pain may be relatively infrequent in children (Collin et al 1985), whereas the impact of pain on family life and quality of life appears to be more significant (Hunfeld et al 2002a, 2002b). Hershey and associates (2001) developed and validated the PedMIDAS to measure the impact of headache on role functioning in children and adolescents with headache. This measure is useful for other types of pain as well.
Pain is a frequent complaint by children with school phobia. In these situations the pain symptom is usually so transparent that it is quite readily (and quite appropriately) given little attention. The prevalence of restriction in social role participation because of pain in children may be lower than that in adults. Children whose social roles become restricted are particularly troubling to the health care system, and appropriate assessment may lead to more effective treatment. Little work has been done on the correlates of restriction in social roles. In a small study we found that mothers of adolescents who were missing school because of pain became overinvolved when supervising an exercise task that might elicit pain in their adolescent (Dunn-Geier et al 1986).
Measures have been developed to measure coping with pain. The most widely used (Eccleston et al 2005) was developed by Reid and colleagues (1998). The 39-item Pain Coping Questionnaire has major subscales on approach-focused, problem-focused, and emotion-focused avoidance. Crombez and co-workers (2003) developed and provided preliminary validation of a 13-item catastrophizing scale that had three subscales: rumination, magnification, and helplessness. The exact role that coping plays in pain in children and adolescents is not clear, but coping measures may be particularly useful in directing the focus of cognitive–behavioral interventions. Catastrophizing may be particularly important in pain avoidance and thus increase restriction of social roles.
Because the family is the crucible in which children learn about pain (McGrath et al 2008), how parents cope with or react to their children when in pain has been examined by several groups. Huguet and colleagues (2008) developed a 37-item inventory with three interrelated scales: solicitousness (n = 15 items), discouragement (n = 10 items), and promotion of well behavior and coping (n = 12 items). Hermann and associates (2008) and Van Slyke and Walker (2006) have developed a similar measure.
Self-report measures of pain have been developed and well validated in children. Behavioral measures are becoming more widely used and well validated. Physiological measures are not well validated except for short, sharp pain. Only a few instruments for the measurement of specific types of behavior or activity that are restricted because of pain or measures of role restriction have been developed and validated.
The references for this chapter can be found at www.expertconsult.com.
Abu-Saad H.H. Toward the development of an instrument to assess pain in children: Dutch study. In: Tyler D.C., Krane E.J., eds. Advances in pain research and therapy: pediatric pain. New York: Raven Press; 1990:101–106.
Ambuel B., Hamlett K.W., Marx C.M., et al. Assessing distress in pediatric intensive care environments: the COMFORT scale. Journal of Pediatric Psychology. 1992;17:95–109.
American Academy of Pediatrics and the Canadian Paediatric Society. Prevention and management of pain and stress in the neonate. Pediatrics. 2000;105:454–461.
American Society of Anesthesiologists, Practice guidelines for acute pain management in the perioperative setting, 1994. (Approved by the House of Delegates, October 16, 1994). Accessed at, www.asahq.org October 1, 2004
Anand K.J.S. The applied physiology of pain. In: Anand K.J.S., McGrath P.J., eds. Pain in the neonate. Amsterdam: Elsevier; 1993:39–66.
Anand K.J.S., Craig K.D. New perspectives on the definition of pain. Pain. 1996;67:3–6.
Anand K.J.S., Sippell W.G., Aynsley-Green A. Randomized trial of fentanyl anaesthesia in preterm babies undergoing surgery: effects on the stress response. Lancet. 1987;1(8526):234.
Anand K.J.S., Sippell W.G., Schofield N.M., et al. Does halothane anaesthesia decrease the stress response of newborn infants undergoing operation? British Medical Journal. 1987;296:668–672.
Aradine C., Beyer J., Tompkins J. Children’s pain perceptions before and after analgesia: a study of instrument construct validity. Journal of Pediatric Nursing. 1988;3:11–23.
Ballantyne M., Stevens B., McAllister M., et al. Validation of the Premature Infant Pain Profile in the clinical setting. Clinical Journal of Pain. 1999;15:297–303.
Berde C., McGrath P. Pain measurement and Beecher’s challenge: 50 years later. Anesthesiology. 2009;111:473–474.
Beyer J.E. The Oucher: a user’s manual and technical report. Evanston, IL: Hospital Play Equipment; 1984.
Beyer J.E., Aradine C.R. Patterns of pediatric pain intensity: a methodological investigation of a self-report scale. Clinical Journal of Pain. 1987;3:130–141.
Beyer J., Knott C.B. Construct validity estimation of the African–American and Hispanic versions of the Oucher Scale. Journal of Pediatric Nursing. 1998;13:20–31.
Beyer J.E., McGrath P.J., Berde C. Discordance between self-report and behavioral pain measures in 3–7 year old children following surgery. Journal of Pain and Symptom Management. 1990;5:350–356.
Bieri D., Reeve R.A., Champion G.D., et al. The Faces Pain Scale for the self-assessment of the severity of pain experienced by children: development, initial validation, and preliminary investigation for ratio scale properties. Pain. 1990;41:139–150.
Breau L.M., McGrath P.J., Camfield C.S., et al. Psychometric properties of the Non-communicating Children’s Pain Checklist–revised. Pain. 2002;99:349–357.
Breau L.M., McGrath P.J., Craig K.D., et al. Facial expression of children receiving immunizations: a principal components analysis of the Child Facial Coding System. Clinical Journal of Pain. 2001;17:178–186.
Carnevale F.A., Razack S. An item analysis of the COMFORT scale in a pediatric intensive care unit. Pediatric Critical Care Medicine. 2002;3:177–180.
Chambers C.T., Finley G.A., McGrath P.J., et al. The parents’ postoperative pain measure: replication and extension to 2–6-year-old children. Pain. 2003;105:437–443.
Chambers C.T., Reid G.J., McGrath P.J., et al. Development and preliminary validation of a postoperative pain measure for parents. Pain. 1996;68:307–313.
Choo E.K., Magruder W., Montgomery C.J., et al. Skin conductance fluctuations correlate poorly with postoperative self-report pain measures in school-aged children. Anesthesiology. 2010;113:175–182.
Collin C., Hockaday J.M., Waters W.E. Headache and school absence. Archives of Disease in Childhood. 1985;60:245–247.
Commission on Accreditation of Rehabilitation Facilities, 1983. Retrieved from, http://www.carf.org/. Accessed October 1, 2004
Craig K.D., McMahon R.J., Morison J.D., et al. Developmental changes in infant pain expression during immunization injections. Social Science in Medicine. 1984;19:1331–1337.
Crombez G., Bijttebier P., Eccleston C., et al. The child version of the Pain Catastrophizing Scale (PCS-C): a preliminary validation. Pain. 2003;104:639–646.
Demyttenaere S., Finley G.A., Johnston C., et al. Pain treatment thresholds in children following major surgery. Clinical Journal of Pain. 2001;17:173–177.
Dunn-Geier B.J., McGrath P.J., Rourke B.P., et al. Adolescent chronic pain: the ability to cope. Pain. 1986;26:23–32.
Eccleston C., Jordan A.L., Crombez G. The impact of chronic pain on adolescents: a review of previously used measures. Journal of Pediatric Psychology. 2006;31:684–697.
Field T., Goldson E. Pacifying effects of nonnutritive sucking on term and preterm neonates during heelstick procedures. Pediatrics. 1984;74:1012–1015.
Finley G.A., Chambers C.T., McGrath P.J., et al. Construct validity of the Parents’ Postoperative Pain Measure. Clinical Journal of Pain. 2003;19:329–334.
Fradet C., McGrath P.J., Kay S., et al. A prospective survey of reactions to blood tests by children and adolescents. Pain. 1990;40:53–60.
Franck L.S., Bruce E. Putting pain assessment into practice: why is it so painful? Pain Research & Management. 2009;14:13–20.
Gauthier J.C., Finley G.A., McGrath P.J. Children’s self-report of postoperative pain intensity and treatment threshold: determining the adequacy of medication. Clinical Journal of Pain. 1998;14:116–120.
Gauvain-Piquard A., Rodary C., Rezvani A., et al. Pain in children aged 2–6 years: a new observational rating scale elaborated in a pediatric oncology unit—preliminary report. Pain. 1987;31:177–188.
Gedaly-Duff V. Palmar sweat index use with children in pain research. Journal of Pediatric Nursing. 1989;4:3–8.
Gilbert C.A., Lilley C.M., Craig K.D., et al. Postoperative pain expression in preschool children: validation of the Child Facial Coding System. Clinical Journal of Pain. 1999;15:192–200.
Giusiano B., Jimeno M.T., Collignon P., et al. Utilization of a neural network in the elaboration of an evaluation scale for pain in cerebral palsy. Methods of Information in Medicine. 1995;34:498–502.
Grunau R.V.E., Craig K.D. Pain expression in neonates: facial action and cry. Pain. 1987;28:395–410.
Grunau R.E., Oberlander T., Holsti L., et al. Bedside application of the Neonatal Facial Coding System in pain assessment of premature neonates. Pain. 1998;76:277–286.
Gunnar M.E., Fisch R.O., Korsvik S., et al. The effects of circumcision on serum cortisol and behaviour. Psychoneuroendocrinology. 1981;6:269–275.
Gunnar M.R., Human developmental psychoneuroendocrinology: a review of research on neuroendocrine response to challenge and threat in infancy and childhood. Lamb M.E., Brown S.L., Rogoff B., eds. Advances in developmental psychology, vol. 9. Hillsdale NJ: Erlbaum; 1986:51–103.
Harpin V.A., Rutter N. Making heel pricks less painful. Archives of Disease in Childhood. 1983;58:2216–2228.
Hershey A.D., Powers S.W., Vockell A.L., et al. PedMIDAS: development of a questionnaire to assess disability of migraines in children. Neurology. 2001;57:2034–2039.
Hester N.K. The preoperational child’s reaction to immunization. Nursing Research. 1979;28:250–255.
Hester N.K., Foster R., Kristensen K. Measurement of pain in children: generalizability and validity of the pain ladder and the poker chip tool. In: Tyler D.C., Krane E.J., eds. Advances in pain research and therapy: pediatric pain. New York: Raven Press; 1990:79–84.
Hicks C.L., von Baeyer C.L., Spafford P.A., et al. The Faces Pain Scale–revised: toward a common metric in pediatric pain measurement. Pain. 2001;93:173–183.
Huguet A., Miró J., Nieto R. The Inventory of Parent/caregiver Responses to the Children’s Pain Experience (IRPEDNA): development and preliminary validation. Pain. 2008;134:128–139.
Hullett B., Chambers N., Preuss J., et al. Monitoring electrical skin conductance: a tool for the assessment of postoperative pain in children? Anesthesiology. 2009;111:513–517.
Hunfeld J.A., Perquin C.W., Bertina W., et al. Stability of pain parameters and pain-related quality of life in adolescents with persistent pain: a three-year follow-up. Clinical Journal of Pain. 2002;18:99–106.
Hunfeld J.A., Perquin C.W., Hazebroek-Kampschreur A.A., et al. Physically unexplained chronic pain and its impact on children and their families: the mother’s perception. Psychology and Psychotherapy. 2002;75:251–260.
Jacox A.K., Spengler C.D. Health centre policies and accreditation. In: McGrath P.J., Finley G.A., eds. Pediatric pain: biological and social context. Seattle: IASP Press; 2003:183–199.
Jay S.M., Ozolins M., Elliott C., et al. Assessment of children’s distress during painful medical procedures. Journal of Health Psychology. 1983;2:133–147.
Johnston C.C. Pain assessment and management in infants. Pediatrician. 1989;16:16–23.
Johnston C.C., Strada M.E. Acute pain response in infants: a multidimensional description. Pain. 1986;24:373–382.
Joint Commission on Accreditation of Healthcare Organizations. Pain assessment and management: an organizational approach. Washington, DC: Joint Commission on Accreditation of Healthcare Organizations; 2000.
Katz E.R., Kellerman J., Seigel S.E. Distress behavior in children with cancer undergoing medical procedures: developmental considerations. Journal of Consulting and Clinical Psychology. 1980;48:356–365.
Kelly M.A., Finer N.N. Nasotracheal intubation in the neonate: physiologic responses and effects of atropine and pancuronium. Journal of Pediatrics. 1984;105:303–309.
Kurylyszyn N., McGrath P.J., Cappelli M., et al. Children’s drawings: what can they tell us about intensity of pain? Clinical Journal of Pain. 1987;2:155–158.
Lewis M., Thomas D. Cortisol release in infants in response to inoculation. Child Development. 1990;61:50–59.
Maunuksela E.L., Olkkola K.T., Korpela R. Measurement of pain in children with self-reporting and behavioral assessment. Clinical Pharmacology and Therapeutics. 1987;42:137–141.
McGrath P.A. Pain in children: nature, assessment, treatment. New York: Guilford; 1990.
McGrath P.J., Johnson G., Goodman J.T., et al. The CHEOPS: a behavioral scale to measure postoperative pain in children. In: Fields H.L., Dubner R., Cervero F., eds. Advances in pain research and therapy. New York: Raven Press; 1985:395–402.
McGrath P.J., Rosmus C., Camfield C., et al. Behaviour caregivers use to determine pain in non-verbal, cognitively impaired individuals. Developmental Medicine and Child Neurology. 1998;40:340–343.
McGrath P.J., Unruh A.M. Pain in children and adolescents. Amsterdam: Elsevier; 1987.
McGrath P.J., Walco G.A., Turk D.C., et al. Core outcome domains and measures for pediatric acute and chronic/recurrent pain clinical trials: PedIMMPACT recommendations. Journal of Pain. 2008;9:771–783.
Melzack R. The McGill Pain Questionnaire: major properties and scoring methods. Pain. 1975;1:227–299.
Merkel S.I., Voepel-Lewis T., Shayevitz J.R., et al. The FLACC: a behavioral scale for scoring postoperative pain in young children. Pediatric Nursing. 1997;23:293–297.
Miró J., Castarlenas E., Huguet A. Evidence for the use of a numerical rating scale to assess the intensity of pediatric pain. European Journal of Pain. 2009;13:1089–1095.
O’Hara M., McGrath P.J., D’Astous J., et al. Oral morphine versus injected meperidine (Demerol) for pain relief in children after orthopedic surgery. Journal of Pediatric Orthopedic Surgery. 1987;7:78–82.
Palermo T.M., Valenzuela D., Stork P.P. A randomized trial of electronic versus paper pain diaries in children: impact on compliance, accuracy, and acceptability. Pain. 2004;107:213–219.
Pigeon H., McGrath P.J., Lawrence J., et al. Nurses’ perceptions of pain in the neonatal intensive care unit. Journal of Pain and Symptom Management. 1989;4:179–183.
Porter F. Pain assessment in children: infants. In: Schechter N.L., Berde C.B., Yaster M., eds. Pain in infants, children and adolescents. Baltimore: Williams & Wilkins; 1993:87–96.
Porter F., Miller J.P., Marshall R.E. Local anaesthesia for painful medical procedures in sick newborns. Pediatric Research. 1987;21:374.
Reid G.J., Gilbert C.A., McGrath P.J. The Pain Coping Questionnaire: preliminary validation. Pain. 1998;76:83–96.
Reid G.J., Hebb J.P.O., McGrath P.J., et al. Clues parents use to assess postoperative pain in their children. Clinical Journal of Pain. 1995;11:229–235.
Richardson G.M., McGrath P.J., Cunningham S.J., et al. Validity of the headache diary for children. Headache. 1983;23:184–187.
Royal College of Nursing. Clinical practice guidelines. The recognition and assessment of acute pain in children: audit protocol. London: Royal College of Nursing; 2002.
Royal College of Paediatrics and Child Health. Recognition and assessment of acute pain in children. London: Royal College of Paediatrics and Child Health; 2001.
Savedra M.C., Tesler M.D. Assessing children’s and adolescents’ pain. Pediatrician. 1989;16:24–29.
Scanlon J.W. Barbarism (editorial). Perinatal Press. 1985;9:103–104.
Stallard P., Williams L., Velleman R., et al. The development and evaluation of the Pain Indicator for Communicatively Impaired Children (PICIC). Pain. 2002;98:145–149.
Stevens B. Development and testing of a pediatric pain management sheet. Pediatric Nursing. 1990;16:543–548.
Stevens B. Composite measures of pain. In: Finley G.A., McGrath P.J., eds. Measurement of pain in infants and children. Seattle: IASP Press; 1998:161–178.
Stevens B., Johnston C.C., Petryshen P., et al. Premature Infant Pain Profile: development and initial validation. Clinical Journal of Pain. 1996;12:13–22.
Stinson J.N., Kavanagh T., Yamada J., et al. Systematic review of the psychometric properties, interpretability and feasibility of self-report pain intensity measures for use in clinical trials in children and adolescents. Pain. 2006;125:143–157.
Stinson J.N., Petroz G.C., Tait G., et al. e-Ouch: usability testing of an electronic chronic pain diary for adolescents with arthritis. Clin J Pain. 2006;22:295–305.
Stone A.A., Broderick J.E., Shiffman S.S., et al. Understanding recall of weekly pain from a momentary assessment perspective: absolute agreement, between- and within-person consistency, and judged change in weekly pain. Pain. 2004;107:61–69.
Sweet S.D., McGrath P.J. Physiological measures of pain. In: Finley G.A., McGrath P.J., eds. Measurement of pain in infants and children. Seattle: IASP Press; 1998:59–81.
Thompson K.I., Varni J.W. A developmental cognitive–biobehavioral approach to pediatric pain assessment. Pain. 1986;25:283–296.
Unruh A., McGrath P.J., Cunningham S.J., et al. Children’s drawings of their pain. Pain. 1983;17:385–392.
van Dijk M., de Boer J.B., Koot H.M., et al. The reliability and validity of the COMFORT Scale as a postoperative pain instrument in 0 to 3-year-old infants. Pain. 2000;84:367–377.
Van Slyke D.A., Walker L.S. Mothers’ responses to children’s pain. Clinical Journal of Pain. 2006;22:387–391.
Varni J.W., Thompson K.L., Hanson V. The Varni/Thompson Pediatric Pain Questionnaire. 1. Chronic musculo-skeletal pain in juvenile rheumatoid arthritis. Pain. 1987;28:27–38.
von Baeyer C.L. Numerical rating scale for self-report of pain intensity in children and adolescents: recent progress and further questions. European Journal of Pain. 2009;13:1005–1007.
von Baeyer C.L., Faces Pain Scale–Revised, 2010. Retrieved from, http://www.usask.ca/childpain/fpsr/. Accessed December 30, 2010
von Baeyer C.L., Spagrud L.J. Systematic review of observational (behavioral) measures of pain for children and adolescents aged 3 to 18 years. Pain. 2007;127:140–150.
von Baeyer C.L., Spagrud L.J., McCormick J.C., et al. Three new datasets supporting use of the numerical rating scale (NRS-11) for children’s self-reports of pain intensity. Pain. 2009;143:223–227.
Voepel-Lewis T., Burke C.N., Jeffreys N., et al. Do 0-10 numeric rating scores translate into clinically meaningful pain measures for children? Anesthesia and Analgesia. 2011;112:415–421.
Walker L.S., Greene J.W. The Functional Disability Inventory: measuring a neglected dimension of child health status. Journal of Pediatric Psychology. 1991;16:39–58.
Wall P.D. Introduction. In: Wall P.D., Melzack R., eds. Textbook of pain. 2nd ed. Edinburgh: Churchill Livingstone; 1989:1–18.
Weisman S.J. Toward a pain-free hospital. In: Finley G.A., McGrath P.J., eds. Acute and procedure pain in infants and children. Seattle: IASP Press, 2001.
Wilkie D.J., Holzemer W.L., Tesler M.D., et al. Measuring pain quality: validity and reliability of children’s and adolescents’ pain language. Pain. 1990;41:151–159.
Williamson P.S., Williamson M.L. Physiologic stress reduction by a local anesthetic during newborn circumcision. Pediatrics. 1983;71:36–40.