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Proceedings for Pain Management and Humane Endpoints

Pain Assessment in Children

Charles Berde, MD, PhD
Boston Children's Hospital, Harvard Medical School

Pain assessment and measurement is a feasible in infants and children, with certain limitations and sources of error. Pain measures may involve patient self-report, observation of behavior, and physiologic measures. Where feasible, self-report measures are generally the most useful of these three types of measures. In adults, visual analog scores (VAS) are widely used to record pain intensity or pain relief. These measures are useful for acute pain studies, and for assaying responses to treatment. VAS pain scores or VAS pain relief scores can be summed over multiple time points to produce summed pain intensity difference (SPID) and total pain relief (TOTPAR) scores. SPID and TOTPAR scores may improve the statistical power of repeated measures. Multidimensional scales, such as the McGill Pain Questionnaire, were developed to gain information about pain quality and impact of pain on daily living. Adults and children generally report pain honestly, though in selected situations they may over-report or under-report if there are perceived consequences from reporting in terms of attendance at work or school, disability determinations, lawsuits, receiving injections, etc.

Outcome studies of pain treatments for both adults and children should not be limited to pain scores alone. Ideally, outcome studies should assess side-effects (e.g. nausea, constipation, sedation, urinary retention, respiratory depression...), measures of mood and well-being, and functional quality of life measures, including return to work (adults) and attendance at school (children).

Many children ages 8 and above can perform VAS scoring successfully. For children ages 3-8, a variety of self-report scales have developed. These can be grouped into three major classes: (1) scoring of pain relative to a series of cartoon faces or photographs with a range of facial expressions, (2) ranking of pain by selection of number of objects, e.g. poker chips, and (3) rating of pain by a color intensity analog scale, where more intense red color is scored as more pain.

Face scales are widely used, but have several limitations: (1) scoring differs according to the choice of the "no pain" anchor of the scale (neutral versus happy expression), (2) photos appear to have some bias according to gender and ethnic or racial background, (3) the scales are discontinuous, and require nonparametric statistical analyses, and (4) adolescents may not like to use them. Scales based on selection of objects have received limited study, and it is not certain how they converge to VAS scales in older children. Color analog scales have the merit that they converge to VAS scales in older children, are usable in adolescents, are continuous measures, and the zero pain anchor appears understandable to most children. In my opinion, color analog scales are the most versatile pain measures for children ages 4 and above.

Behavioral pain measures have been developed both for very young infants, for children ages 2-8, and, in preliminary fashion, for children with neurological disabilities. In younger infants, analyses of facial expression seem particularly useful, sensitive and specific for pain. These may be used by themselves, as in Grunau et al's studies, or may be combined with assessments of body posture, movement and hemodynamic measures, as in Johnston and Stevens et al's studies. For children ages 2-8, several behavioral scales have been developed and tested primarily for children undergoing brief painful procedures, e.g. bone marrow aspiration and lumbar puncture. In general, behavioral scales in toddlers and school-aged children have two limitations: (1) they are overly sensitive to fear and anxiety with acute procedures, and (2) they under-report persistent pain when compared with self-report measures.

Physiologic measures of pain seem attractive because they are "objective" and record "hard" numbers, but in general they are nonspecific as indices of pain. Heart rate, blood pressure, and a series of stress hormones (e.g. cortisol, epinephrine, norephinephrine, glucagon, growth hormone, beta-endorphin) and metabolites (e.g. glucose) are secreted during intensive care or during surgical stress under light anesthesia. High dose opioids or epidural analgesia can suppress both autonomic and hormonal-metabolic signs of stress responses in infants and children undergoing surgery or intensive care. Nevertheless, these measures are nonspecific, since autonomic arousal and stress hormone secretion can be triggered by a number of processes unrelated to pain per se. Heart rate variability can be analyzed by several computer algorithms to estimate parasympathetic and sympathetic modulation. This method is under study by several groups, but there remain unresolved questions regarding the specificity of "vagal tone" as a measure of pain, stress, behavioral state, response to medications, or temperament.

In adults, there is considerable interest at present in using positron emission tomography (PET) scanning and functional magnetic resonance (fMRI) imaging of patients with acute and chronic pain conditions. This remains a fascinating but controversial area, and there is an ongoing need for better designs and controls. Imaging studies in children are limited by issues of consent and assent, by the requirement for isotopes in PET studies, and by the fact that many children require sedation or anesthesia to remain immobile in a scanner. Sedatives and anesthetics are likely to confound these measurements.

Placebo and nocebo effects are common, and their magnitude varies widely among studies. Placebo groups and no-treatment (natural history) groups help differentiate the specific from the nonspecific aspects of treatment, as well as the impact of natural history and regression to the mean. Nevertheless, there is often great resistance to having no-treatment or placebo groups in pediatric pain studies, because of ethical concerns regarding withholding effective treatments, and because parents and children are often unwilling to have the children tolerate a period of time with pain relief. One commonly used approach has been to assign patients in a randomized, blinded fashion to active drug versus placebo and then to use requirements for rescue analgesic dosing as an outcome measure.

Outcome studies in pediatric pain treatment should also assess safety, cost, risk, and applicability at different ages. Developmental pharmacology and toxicology models in infant animals may be helpful in preclinical studies.

Measures of side-effects (e.g. sedation, nausea, constipation, respiratory depression, ...) are often imprecise in current pediatric analgesic studies. There is a need for better standardization of these measures. For example, in studies of postoperative nausea and vomiting, there is a wide variation in how an "episode" is scored. Surrogate markers for respiratory risk deserve further study: for example, does brief episodic oxygen desaturation or a moderately low respiratory rate predict clinically important endpoints, such as apnea, respiratory arrest, clinically important atelectasis, or other complications?

In summary, outcome studies of analgesics or other forms of pain treatment in children (e.g. biobehavioral treatments) should involve self-report pain scores when feasible for children ages 4 and older, and behavioral scores for infants and younger children or those unable to report. Physiologic measures may contribute, but should not be used in isolation. Pain scores should be accompanied by measures of side-effects, mood, quality of life, and functioning in activities of daily living.


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