Date Published: June 24, 2008
Publisher: Public Library of Science
Author(s): Rebeccah Slater, Anne Cantarella, Linda Franck, Judith Meek, Maria Fitzgerald, A. David Edwards
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.
Partial Text: One of the major barriers to providing adequate pain relief to infants and young children is gauging how much pain they are feeling and therefore how much analgesia is required. While adults can use visual analogue scales to report their pain, infants cannot report subjective pain intensity, and clinical pain scoring systems are based upon behavioural, physiological, and metabolic signs [1,2]. 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.
The hypothesis was that the clinical pain score, calculated using the PIPP, would correlate with the magnitude of evoked cortical haemodynamic activity recorded from the infant brain in response to a heel lance. The primary outcome measures were (i) cortical activity measured as the change in total haemoglobin (HbT) concentration using NIRS and (ii) a clinical pain score, calculated using the PIPP.
The difficulty in accurate measurement of pain in infants is a major impediment in providing effective analgesia for infants undergoing neonatal intensive care. Here, for the first time, we have measured the cortical haemodynamic activity evoked by noxious stimulation in infants while simultaneously scoring their responses with a validated clinical behavioural and physiological assessment tool. Studies were undertaken when hospitalised infants underwent noxious procedures as part of their routine medical care. The results show that while observable behaviour and physiological changes are in general well correlated with cortical activation, it is possible to record significant cortical activity with no concomitant behavioural response.