Premature infants who need intensive care or surgery are less sensitive to thermal (hot and cold) sensations later in life, according to research conducted at UCL (University College London). The study, published in the journal Pain, suggests that pain and injury related to major medical interventions in early development may alter how children respond to painful stimuli much later in life. 

In the study, 43 eleven-year-old children born at less than 26 weeks of gestation (14 weeks premature) who are being followed up by the EPICure study group, were tested for their responses to different sensations – temperature and light touch – using quantitative sensory testing. Compared to a group of children who had been born at full term, the premature children were less sensitive to temperature (cool, cold, warm and hot) but not to light touch, and this was most marked in those who had also undergone a surgical operation as a baby.

The researchers also found a more marked decrease in sensitivity to temperature and to touch close to scars relating to major chest surgery, again suggesting that the severity of injury in early life influences the degree of sensory change. A questionnaire survey showed that the children's everyday pain experiences were similar, but there were some minor differences between the two groups in the way children coped with pain.

Dr Suellen Walker, UCL Institute of Child Health, says: "Our study shows that babies who are born premature and need intensive care or surgery develop long-term changes in their responses to hot and cold sensations. As the same nerve fibres transmit temperature and pain, changes in thermal sensitivity may also be associated with altered responses to pain in later life. In our laboratory studies, we have also shown that surgical incisions in early life reduce sensitivity to temperature and pressure, and alter pain responses to future surgery. These effects appear to be specific to early life, as seen in the premature children who were operated on as babies." 

"The pain mechanisms in our bodies are plastic – that is, injury and nerve activity can alter them, but this is particularly true in early life when the nervous system is still developing. Our research aims to understand how responses to injury change, and how best to treat pain, at different stages of development. We are currently testing different types and doses of analgesics to prevent the long-term changes we have discovered, and this will help doctors to choose the most effective painkillers for preterm babies."

Professor Neil Marlow, UCL Elizabeth Garrett Anderson Institute for Women's Health, says: "The rate of preterm birth is rising, and improvements in intensive care mean that babies are surviving from very young gestational ages. Many of the procedures necessary to monitor and treat such babies are painful and even in the most premature babies, can trigger responses in pain-sensing areas of the brain. In some cases, major surgery may be needed to treat complications of prematurity or to correct congenital defects. It is therefore important for us to understand not only how these interventions at the earliest stages of development may affect the body's sensory functions later in life, but also how we can minimise exposure to painful stimuli."