Abstract
BackgroundPain in infancy is poorly understood, and medical staff often have difficulty assessing whether an infant is in pain. Current pain assessment tools rely on behavioural and physiological measures, such as change in facial expression, which may not accurately reflect pain experience. Our ability to measure cortical pain responses in young infants gives us the first opportunity to evaluate pain assessment tools with respect to the sensory input and establish whether the resultant pain scores reflect cortical pain processing.Methods and FindingsCortical haemodynamic activity was measured in infants, aged 25–43 wk postmenstrual, using near-infrared spectroscopy following a clinically required heel lance and compared to the magnitude of the premature infant pain profile (PIPP) score in the same infant to the same stimulus (n = 12, 33 test occasions). Overall, there was good correlation between the PIPP score and the level of cortical activity (regression coefficient = 0.72, 95% confidence interval [CI] limits 0.32–1.11, p = 0.001; correlation coefficient = 0.57). Of the different PIPP components, facial expression correlated best with cortical activity (regression coefficient = 1.26, 95% CI limits 0.84–1.67, p < 0.0001; correlation coefficient = 0.74) (n = 12, 33 test occasions). Cortical pain responses were still recorded in some infants who did not display a change in facial expression.ConclusionsWhile painful stimulation generally evokes parallel cortical and behavioural responses in infants, pain may be processed at the cortical level without producing detectable behavioural changes. As a result, an infant with a low pain score based on behavioural assessment tools alone may not be pain free.
Highlights
One of the major barriers to providing adequate pain relief to infants and young children is gauging how much pain they are feeling and how much analgesia is required
near-infrared spectroscopy (NIRS) measures regional changes in oxygenated and deoxygenated haemoglobin concentration and, as with other techniques that use a haemodynamic approach to assess the functional activation of the brain, it is based on the assumption that increased tissue oxygenation represents an increase in regional cerebral blood flow, which is in turn associated with an increase in underlying neural activity [5]
The hypothesis was that the clinical pain score, calculated using the premature infant pain profile (PIPP), would correlate with the magnitude of evoked cortical haemodynamic activity recorded from the infant brain in response to a heel lance
Summary
One of the major barriers to providing adequate pain relief to infants and young children is gauging how much pain they are feeling and how much analgesia is required. The well-established premature infant pain profile (PIPP), for example, ascribes a value to infant behaviours such as sleep state and change in facial expression to produce a composite pain score, which is weighted for age Such scores have become the major outcome measure in recent analgesic trials of sucrose and morphine [3,4], despite the fact that they can arise from activation of subcortical somatic and autonomic motor pathways and may not be reliably linked to central sensory or emotional processing in the brain. Our ability to record infant cortical activity in response to noxious stimulation has given us the first opportunity to look at the relationship between clinical pain assessment scores, on the basis of behavioural and physiological responses, with measurements of pain processing in the brain.
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