St. Louis, July 6, 1999 -- During nursing and medical procedures in the hospital, premature infants respond to pain and can tell the difference between more and less painful procedures. They also react more to pain as they grow older. Researchers at Washington University School of Medicine in St. Louis report these findings in the July issue of Pediatrics and recommend universal pain management in newborns to reduce the acute and long-term impact of early procedural pain.
"These findings underscore just how sophisticated newborns are," said Fran Lang Porter, Ph.D., assistant professor of pediatrics and the study's lead author. "The study shows that not managing their pain, as if their early experiences don't matter, is a real mistake. We're beginning to understand that what we're doing has long-term effects."
As part of their required clinical care in a hospital nursery, infants, whether healthy or sick, can be exposed to procedures that adults consider painful. In one of Porter's previous studies, physicians and nurses reported that babies receive very little pain relief and few comfort measures during required medical procedures in the hospital and elective procedures such as circumcision. The doctors and nurses in the study believed, however, that babies can feel as much pain as adults.
There is a close relationship between how adults behave in response to pain, how painful they sense the stimulus to be and how their bodies react to the stimulus, studies have shown. Porter decided to find out if the same relationship holds true for newborns by monitoring their responses to nursing and medical procedures during hospitalization. Finding that the babies didn't react to pain and that their caregivers didn't see a change in behavior might help explain why doctors and nurses seldom manage pain in newborns during painful procedures.
Specifically, Porter set out to determine if newborns respond more as procedures become more invasive and if prematurity affects how much they respond. She also wanted to know whether premature babies become more sensitive to pain as they grow older.
Porter and colleagues recruited 152 newborns ranging in gestational age from less than 28 weeks through full-term. The babies were admitted to normal newborn, premature or intensive care nurseries at Washington University Medical Center. Of the original infants recruited, 135 were studied at least two times and qualified for the analysis.
The researchers measured the newborns' heart rates and behavior while they underwent a wide array of required or elective procedures, ranging from heel sticks to chest tube insertions to circumcision. They measured two behaviors-- the time the babies spent fussing or crying and the time they spent sleeping. The babies were observed during four periods -- baseline, preparatory, procedure and recovery -- and the invasiveness of each procedure was rated according to length of the procedure, amount of tissue damage and site of the procedure.
As expected, the newborns' heart rates increased significantly over baseline in response to the preparation and the procedure itself but declined during recovery. The infants also slept less and became more agitated during preparation and the procedure, and they slept more during baseline and recovery.
The babies were able to differentiate clearly between mildly, moderately and highly invasive procedures. The more invasive the procedure, the more their heart rates and agitation increased.
The researchers also found that, during the first week of life, prematurity does not affect how much a baby responds. Babies born prematurely and at full term responded similarly to painful procedures, as judged by heart rate, agitation and sleep.
Even very premature babies were able to judge the invasiveness of a procedure during the first week of life. Heart rate and agitation increased as the procedure became more invasive. "Even a tiny baby born around 26 or 28 weeks gestation is detecting differences in the painfulness of what we do to them," Porter said.
To determine whether premature babies react more strongly to procedures than full-term babies, the researchers followed babies born very prematurely (less than 28 weeks gestation) through their full-term age. With age, heart rates and agitation increased over baseline in response to the preparation and the procedure, signaling that these babies became more responsive as they grew older.
"In other words, if you are born earlier, you might show increasing sensitivity to pain over time," Porter said. "Even though this study didn't determine whether these effects are due to age or exposure to pain, we currently are conducting studies that will answer that question."
Porter recommends providing pain management for all babies, not only to those who appear more likely to respond to pain or to be at greater risk for long-term effects. She also believes it's important to continue to research which types of pain management are more effective and determine the downsides, if any.
"Nevertheless, with emerging reports that there may be long-term effects of early pain, we should do our best to protect babies and help ensure healthy development for those who require medical interventions early in life," Porter said.
Porter FL et al. Procedural Pain in Newborn Infants: The Influence of Intensity and Development. Pediatrics, vol.104, no. 1, p. 105, July 1999.
This work was supported by a grant from the National Institute of Child Health and Human Development.
The full-time and volunteer faculty of Washington University School of Medicine are the physicians and surgeons of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC Health System.
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