Most pain assessment tools currently used in neonatal intensive care are at least partially based on behavioral responses, such as the facial grimace. New research supports the assertion that behavioral changes might not be reliable in the assessment of pain.1
Because infants are unable to express their experience of pain, we have relied on measures such as physiologic and behavioral changes associated with procedures or events believed to be painful. Untreated pain has both immediate and long-term effects on the central nervous system. Gauging how much pain infants feel is a significant clinical challenge.1 To determine whether current pain assessment tools adequately measure pain in vulnerable infants, investigators studied 12 clinically stable preterm infants during a heel lance for blood procurement. A clinical pain score (the Premature Infant Pain Profile [PIPP]) was administered and brain activity in the somatosensory cortex was measured noninvasively using near-infrared spectroscopy (NIRS). The NIRS measures brain regional changes in oxygenated and deoxygenated hemoglobin concentrations.1
Brain activity changed in response to a painful stimulus and was related to the PIPP score. Brain activity changes were more strongly linked to the behavioral components of the PIPP (such as facial expression) than the physiologic components (such as heart rate). However, the study also revealed that a positive brain response could occur in the absence of any facial expression. Pain can be processed at the cortical level without producing detectable behavioral changes, suggesting that an infant with a low pain score based on pain assessment tools alone may not be pain free.1
The absence of facial activity in response to a noxious stimulus could be a consequence of immature motor circuitry failing to produce a synchronized and coordinated muscle contraction, or it may indicate a true absence of emotion. Either way, investigators concluded that pain assessment based on behavioral tools alone should be interpreted with caution because these scores could underestimate the total pain response.1
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