June 23, 2008 -- Current tools used to tell if young babies are in pain may underestimate how much they are hurting, according to a study published in the June issue of PLoS Medicine.
Properly gauging infant pain can be difficult. Health care providers rely on a clinical assessment of factors such as facial expressions and changes in heart rate to tell if a baby's in pain, and to estimate how much pain treatment is required for uncomfortable medical procedures.
However, London-based researchers have found that such behavioral and physiological measures may not accurately reflect an infant's pain experience, and infants can be in pain without making it immediately known.
"An infant with a low pain score based on behavioral assessment tools alone may not be pain free," the researchers write in the journal article.
Inadequate pain management not only means an infant feels immediate discomfort, it may also lead to long-term effects. Some believe that repeated pain in premature infants may be linked to attention deficit disorder, learning disorders, and behavioral problems in later childhood.
Rebeccah Slater of the University College of London and colleagues wanted to see how well current clinical pain assessment tools reflected pain in infants. Their study involved 12 infants with stable vital signs. The team compared brain activity responses to behavioral and physiological changes (such as facial expression and heart rate changes) on 33 occasions when the infants needed a heel stick for a medical reason. No heel sticks were done solely for the purpose of the study. Brain activity was measured using a noninvasive technique called near-infrared spectroscopy, which is widely used in neonatal research.
Researchers examined the relationship between brain activity and infant pain scores, which were calculated using the well-established premature infant pain profile (PIPP). PIPP assigns a value to infant behaviors, such as facial expressions, based on age.
In 10 heel stick occasions, infants had changes in pain-related brain activity without displaying a change in facial expression. Overall, the study showed that brain activity changes were more strongly linked to infant behavior changes (facial expressions) than physical changes, such as heart rate fluctuations.
The findings suggest that infants may process pain at the brain level without producing detectable behavioral changes. The lack of a grimace or similar facial expression may be due to immature muscle responses, or it truly could be an absence of emotion, the researchers say.
"Either way, the infants may not actually be pain free," the researchers conclude in the journal article. "As a result, pain assessment based on behavioral tools alone should be interpreted with caution as they could under estimate the total pain response."