New Method Looks into Babies' Brains to Measure Pain

(Inside Science) -- Pain is highly subjective and personal -- a bonk on the elbow could be merely an annoyance for one person, while it could drive another to tears. For babies, pain is even more mysterious.

“Babies can’t talk, so it’s difficult for doctors or nurses to know if they’re even in pain,” said Caroline Hartley, a pediatric researcher at the University of Oxford in the U.K.

But soon, there may be new ways to get the inside story of how infants feel pain. Hartley and her colleagues have uncovered a common pain pattern in brain scans of newborns.

According to Hartley, one in nine newborn babies will receive hospital care. During their hospital stay, they may receive on average 10 painful procedures per day, from common things like a needle prick in the heel to draw blood to more invasive procedures like inserting a breathing tube.

The accepted way to test if a baby is in pain is to use physiologic signals: increases in heart rate, decreases in blood oxygen saturation, or the twisted, furrowed facial expressions of discomfort. But those measures aren’t specific to pain.

“Babies cry if they are hungry, or need a nappy change,” said Hartley. “Those measures aren’t accurate enough to test pain-relieving drugs.”

To determine how pain looks in babies' brains, Hartley and colleagues taped electrical sensors to babies’ heads and did a number of studies using electroencephalograms -- also known as EEGs -- which measure electrical activity in the brain. They monitored the brain activity of 72 newborn babies while the infants received routine (and medically required) but painful experiences like a heel prick. Then, the researchers compared the scans with babies who received a heel touch or listened to a sound.

The researchers were able to find a defined pattern of pain from the group data. They also looked at scans from babies who received a numbing analgesic gel before the blood test, and found that the gel did reduce the brain’s pain signature.

All of this points to the need for better ways to tell if an infant is in pain. Around 39 percent of the babies didn’t grimace or cry when they had the blood draw -- but their brains showed they were indeed in pain.

Hartley said the most important use, in the short-term, is to identify pain-relieving drugs that work for babies. For example, it would be helpful to know whether morphine is effective for reducing pain during procedures on preterm infants. “Babies aren’t just small adults, so drugs might not work in the same way,” Hartley said. The paper was published today in Science Translational Medicine.

Could this system determine if an individual baby is in pain, say, due to an ear infection or a stomachache? Hartley said this method works at the group-level at the moment, since pain is such a subjective experience.

For babies who are born before they’re ready for the world, pain can have real and long-term consequences. Ruth Grunau, a neonatology researcher at the University of British Columbia in Canada, has found in past studies that in babies born between 24 and 32 weeks, pain is associated with altered brain structures, altered brain function, lower IQs and behavioral problems -- even beyond the typical problems of prematurity.

That’s one reason why this new work is so exciting to her. “This work is extremely important to start quantifying analgesic response and hopefully understanding the pain state of the baby through brain measures,” said Grunau.

Although the new work didn’t look at the early preemies that Grunau has studied, she hopes that this is just the start of a new way to understand infant pain. “It’s just the beginning, but a big one: a groundbreaking beginning to capture brain activity as a measure of pain.”

Grunau would like to see some common practices, like giving babies sugar water while they undergo uncomfortable procedures, get scrutinized in a quantifiable way. It’s also very important to differentiate between stress and pain. Often, babies cry because their legs are being stretched out or their heel is being squeezed. “You don’t want to treat stress with sugar or pharmaceuticals,” said Grunau.