Researchers looked at 56 newborn babies in the postnatal ward and special care unit at the Elizabeth Garrett Anderson Obstetric Wing at University College Hospital in the United Kingdom. They measured the stress levels of the babies using salivary levels of the stress hormone cortisol and heartbeat patterns in the babies, prior to and after the traditional and clinically significant heel lance.
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Simultaneously, they used EEG machines to measure the babies' pain responses based on brain activity and facial expression. The results showed that in babies with high stress, when compared to lower stress, the amplitude of pain the brain waves showed was higher.
In babies with the lowest stress levels, behavior and brain activity were related in that the greater the brain activity, the longer the period of crying or making pained expressions. But in the babies with the highest stress levels, this was not the case. Babies who had the highest stress levels did not have behaviors (grimaces, prolonged crying) that matched the pain levels their brain activities indicated.
This led the researchers to conclude that there is a disconnect in the behavior of newborn babies who are already stressed, and their brain activity and behaviors. They may feel pain more than previously thought based on external behaviors.
The researchers from University College London theorize that stress is an important factor when considering how babies perceive and react to pain levels. Dr. Laura Jones led the study and said that newborn babies who experience painful procedures have marked and significant increases in their brain activity and their behavioral responses, like crying.
Dr. Jones says that babies who are stressed have larger responses in their brains following painful procedure, but they do not have increased behavioral response, and it's important we understand babies who may already be stressed to alleviate excess pain.
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She says that we need to question whether assessing behaviors (crying, moaning, grimacing) in newborns and infants is an accurate assessment of their pain level, particularly if they are stressed to begin with from birth or trauma.
She says that adults experience greater pain often as the result of a stressful situation and this study suggests that to be true for babies.
Doctors and parents rely on indirect measures such as facial expressions to tell if infants are experiencing pain because they cannot express this in words. Dr. Judith Meek is a co-author of the study and says these findings are critical for people who care for newborn babies, as pain scores for babies often are based on crying or facial responses.
As the research indicates that this may not be an appropriate way to measure a stressed baby's pain, we need to look into better ways to monitor pain and reduce stress when intervening as best we can.
Dr. Jones says that repeated stressful experiences and painful procedures early in life can negatively affect the central nervous system's development. These results suggest that if we can better control stress levels of hospitalized babies, we may be helping their development and reducing their pain at the same time.