What do babies feel?

What do babies feel? McGill University

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McGill Reporter
January 13, 2000 - Volume 32 Number 08
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What do babies feel?

| The first thing that most of us did when we entered this world was complain.

The crying of newborn babies often relieves anxious parents, and has traditionally been the sign of a strong, healthy infant. But recent research into how babies express their displeasure suggests that they are much more sensitive to pain than was previously believed.

In the early 1980s, for instance, the accepted practice of the day was to not even prescribe pain-killers for babies undergoing procedures as invasive as open-heart surgery. Conventional medical wisdom held that the myelination or conductivity of babies' nervous systems was not developed enough to register any significant amounts of pain.

Professor Celeste Johnston
PHOTO: OWEN EGAN

"Now we know better," says Professor Celeste Johnston, the School of Nursing's associate director for research, who has been studying pain response in babies for more than 15 years. Her research has shown that even babies born three months prematurely and weighing only 500 to 600 grams can feel pain.

"These babies are extremely premature, and you are able to see a differential response to pain from different stimuli," says Johnston. "But as they get older, you see a stronger, more robust pain response. They show more painful expressions to pain, they're able to sustain it longer and it's more clearly recognized as pain."

While babies may not actually become more sensitive to pain as they grow, they are better able to express themselves. To gauge those responses, researchers have developed about 15 measurements that incorporate an infant's behavioural and physiologic reactions to stimuli.

These include monitoring heart rate, oxygen saturation, facial activity, galvanic skin response and spectrographic cry analysis, which is often the most telling sign that a baby is experiencing pain. Cries of pain in term infants are usually high-pitched, longer and harsher compared to normal crying by babies.

"The human ear can hear that as a shrill kind of cry," says Johnston, who has used computer models to measure the harmonics and peak spectral energy emitted along the higher frequencies of babies' cries. "It's like a siren, a really attention-getting cry for survival."

While it is now common practice for all babies undergoing major surgery in developed countries to receive general anesthesia, giving local anesthesia for minor surgical procedures is still rare.

Adults, for example, will routinely receive injections of a local anesthetic with a lumbar puncture or the insertion of a chest tube, while babies will not. One of the confounding factors in measuring pain in infants, however, is pinpointing their responses to such procedures.

"You're going to get an increase in heart rate as soon as you touch them," says Johnston. "You might even see grimacing in these babies, but they don't sustain it. It's much more fleeting than when they are in pain and they don't show as great a magnitude of response to a non-painful stimulus as to a painful stimulus. Even squeezing the foot doesn't get the same response as when you actually do tissue damage when you do a heelstick for a blood test."

Despite the fact that there is a growing consensus that there is no medical reason to circumcise infants, if it is done, anesthetic is seldom used. Yet the small numbers of boys or adults who do need to be circumcised later in life for health reasons routinely receive general anesthetic or nerve blocks for the procedure.

One unconfirmed study even suggested that males who had been circumcised cried more at their two-month immunization than those who had not been circumcised.

"I think it's close to 50 per cent of male infants that are circumcised for non-religious reasons," says Johnston. "I've been to a briss, and at least they hold the child and let it suck on a cloth dipped in alcohol and honey, which probably elicits the endorphin system. It's a very different thing than in the hospital, when these kids are plunked down on a plastic board and strapped spread-eagled to it. Really, it's barbaric."

Johnston's past research has shown that giving infants small doses of sucrose before, during or after painful procedures such as a heelstick, through which small quantities of blood are drawn from infant feet for testing, is more beneficial than a placebo in reducing pain scores. She is now participating in an ongoing study at the Jewish General Hospital, Ste-Justine Hospital and IWK-Grace Hospital in Halifax that will examine the efficacy of reducing pain with 0.1 ml oral sucrose in 100 premature babies over a course of several weeks.

"I think that babies might in fact feel more pain than adults, and that is based on the developing nervous system of animal models," says Johnston. "We know that in animals, the ascending pathways along which pain signals move develop sooner in fetal growth than the descending pathways that help the inhibitory system. So, it seems that your endorphin system develops after your pain-awareness systems."

The past decade has seen a surge of awareness in the issue of babies' sensitivity to pain, such that Johnston regularly receives calls from local hospitals and nurseries seeking advice on pain management.

"We're definitely making progress," says Johnston. "If you stick around long enough, you actually see things changing. There's a real interest in it now, and I think that the procedural pain that I'm worried about will be attended to as well as surgical pain that few people worried about 15 years ago."

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