Researchers Study Babies’ Sensitivity to Pain

A tiny baby flinches as a doctor inserts a tube into the prematurely born infant’s frail arm.

Is the baby pulling away in pain?

Many doctors had thought prematurely born infants were so undeveloped that they did not yet have a sense of pain, meaning they did not require anesthesia--sometimes even when they underwent surgery. Doctors also feared that the risk of using painkillers may be too great.

“Premature babies may not even cry. They have very poor muscle tone so they may not even flinch,” said Dr. Kanwaljeet S. Anand of the Children’s Hospital in Boston.

“And even if they were able to cry, since they may have tubes down their throats, sounds may not be emitted. Babies also cry to many other stimuli, such as being cold or wet,” he said.

But Anand and other scientists believe that recent research has produced strong new evidence that fetuses develop the ability to feel pain much earlier than had been previously believed.

A New Understanding

Based on this new understanding, Anand hopes to convince his colleagues to use anesthesia more often when treating premature babies with painful procedures.

“Humane considerations should apply as forcefully to the treatment of babies as they do to adult patients,” said Anand.

In a special article published recently in the New England Journal of Medicine, Anand reported the results of what he said is the most exhaustive review of the scientific literature ever conducted, documenting evidence that prematurely born infants can feel pain as early as 24 weeks into gestation.

“In the past 25 or 30 years this is the strongest statement that has ever come out in the medical literature that babies do feel pain,” said Anand in an interview. “I would say that under most conditions pain relief should be given to these babies.”

Anand said doctors’ perception of the age at which babies begin to feel pain varies considerably, depending on such factors as when they were trained. Many doctors believe babies do not feel pain until about 35 weeks into gestation, he said.

Anand stressed that his findings should not be used by those opposed to abortion because the age at which fetuses develop the ability to feel pain is long after any state allows abortion to be performed.

Elective abortions are permitted in the first trimester, which lasts about until 16 weeks into gestation, he said.

“It could be misused by the right-to-lifers, but I would be very upset if that happened. The evidence is not there. It’s just not available, speaking from the scientific point of view,” he said.

“The pathways are not developed. The nerves are not meshed up properly. I really don’t think this article has much applicability to the earlier fetus and the whole question of abortion,” he said.

But the findings should encourage doctors treating very premature babies to use anesthesia more often, especially since there are newer, safer anesthetic drugs available, he said.

In his review, Anand outlined more than 200 studies that showed that young babies and fetuses late in gestation had developed the nervous system pathways and necessary chemicals needed to transmit pain.

Anand also outlined findings that indicated these babies exhibited changes in heartbeat, blood pressure and hormone levels that indicated that they were experiencing pain.

Studies have also shown that babies respond to pinpricks and display facial expressions that indicate they are experiencing pain. They also cry differently when feeling pain than, for example, when they are hungry, he said.

Young newborns’ sleep patterns have also been shown to be disrupted after they undergo painful procedures, such as circumcision, he said.

In an editorial accompanying the paper, Dr. Anne B. Fletcher of the Children’s Hospital National Medical Center in Washington praised Anand’s findings and urged her colleagues to use anesthesia whenever possible.

An Outmoded Notion

“The observations cited in this review should dispel the now outmoded notion that newborns are insensitive to or immune from pain,” she said.

Fletcher noted that doctors may not have used anesthesia not because of “barbarism” or “indifference” but because much of the research Anand cited was published in journals doctors dealing with newborns do not normally read.

But she noted that anyone who has had experience caring for premature babies sensed that they felt pain.

“It has generally been assumed that the ability of the child to feel pain increases with age and that (newborns) may not perceive pain or may perceive it only minimally. Assumed by whom?” she said.

“Certainly not by those of us at the bedside of critically ill infants, who seem them flinch from procedures, startle in response to loud noises, and turn from bright lights and various other forms of stimulation.”