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The challenges of pain assessment in infants, children and young people are well recognised. As pain is known to be a complex and subjective phenomenon that is influenced by many factors, it is clear that both the intensity and unpleasantness or suffering due to pain can only be expressed accurately by the individual who experiences it. Therefore, self-report of pain is, and is likely to always remain, the ‘gold standard’ of assessment. Nevertheless, as self-report of pain is impractical in many clinical situations, a number of proxy measures of pain, including facial expressions, behaviours and ‘biomarkers’, i.e. changes in physiological or biological parameters, have been investigated and incorporated, where appropriate, into clinical practice. To date, no measure has emerged as superior to others in all situations and consequently they are often combined or included in composite pain measurement scales that require validation for particular groups of patients in specific clinical circumstances.
Biomarkers, such as heart rate, skin conductance, plasma levels of cortisol and stress hormones, inflammatory and genetic markers and neuroimaging have the advantage that they are relatively easy to measure and generally respond rapidly and in conjunction with the autonomic arousal that occurs in response to certain types of pain. Although they tend to broadly correlate with each other and with other pain measures including behaviours and self-reported pain, their clinical usefulness has generally been limited by their lack of specificity, low to moderate sensitivity, and tendency to ‘habituate’ over time due to homeostatic mechanisms.
Interest in reflex pupillary motor activity measurement (pupillometry) has recently emerged as a potential biomarker …