Deborah Padfield with John Pates from the series perceptions of pain, 2001 -2006, C-Type print
© Deborah Padfield, reproduced by kind permission of Dewi Lewis
I have spent most of my career treating and researching pain in children and infants. Initially, my research activities revolved around patients, but I soon realized that not all questions about pediatric pain management could be answered with clinical trials, and started working with animal models too.
We cannot assume that pain is the same in children as it is in adults, or indeed that older children experience the same pain as newborns. Pain is a complex, subjective experience and you can’t simply extrapolate from one group to another without adequate research, particularly when it comes to younger children, who cannot verbalize their pain experience and whose nervous system is still developing. Children at different ages respond differently to pain and we need to adapt our assessment tools to their age and clinical setting. We also need to understand how the nervous system responds to pain at different ages – an area that has driven a lot of my lab research.
On the clinical side, I am involved in long-term follow-up studies of preterm infants – the EPICure cohort. We published the initial research from when the children were 11 years old in 2009, and we’re currently assessing them again at 19, to see if preterm birth and neonatal intensive care is associated with changes in sensory processing. In the lab, we’re asking the question more directly, by looking at long-term impact of surgical injury. We make a surgical incision in the hindpaw of animals at different ages, allow the animals to grow up, then test their sensitivity to injury later in life, to see if that is influenced by their early-life experiences. What we’ve found is intriguing. In animals that underwent a single neonatal surgery, there was a generalized decrease in baseline sensitivity and an increase in pain threshold, which is borne out by studies in preterm birth cohorts. But, importantly, if there is a repeat surgical injury in later life, this unmasks increased sensitivity, modulated in part by an increased microglial response in the spinal cord.
Sex differences are another key component of my research. Interestingly, the signaling involved in microglial response is different in males and females – just one aspect of pain that varies between men and women. We are looking at the impact of sex on how we cope with pain, and how the nervous system modulates pain hypersensitivity. The fact that our work is focused on early life allows us to strip away some of the influence of sex hormones and social factors reported in adults. It’s easy to assume that sex differences are only important later on in life, after puberty, but it appears that differences emerge at a very early stage.
Our work has underlined the significance of good pain management in early life. Of course, we already knew it was important – we never want to see a child in pain – and our research shows that getting the right combination of analgesics could make a difference to our patients right into adulthood. Thankfully, there have been huge changes in how we view and treat pain in children over the past 30 years. Most major hospitals now have a pain team, made up of doctors, nurses, psychologists, and physiotherapists, that addresses the biological, social and psychological aspects of pain. We have a better understanding of how to deliver analgesics safely at different ages, and better assessment of pain allows us to titrate analgesia for individuals. However, chronic pain remains an understudied area, partly because it is difficult to conduct clinical trials in children with chronic pain conditions.
Deborah Padfield with Nell Keddie from the series perceptions of pain, 2001 -2006, Silver Gelatin Print
© Deborah Padfield, reproduced by kind permission of Dewi Lewis
Being involved in both clinical and laboratory research has been a huge advantage for me. I take the clinical observations we’re making in the preterm cohorts to the lab, to try to understand the mechanisms. Then I take that newfound knowledge back to the clinic to work out how we can treat altered sensitivity to pain in children who are coming back for further surgery – or prevent it from happening in the first place.
"Crossing the Threshold Basic and clinical researchers must join forces to fight pain" Michael Gold
"The Pain Puzzle" Roger Fillingim
"The Mouse Trap" Jeffrey Mogil
Suellen Walker is Reader in Paediatric Anaesthesia and Pain Medicine at University College London and Honorary Consultant in Paediatric Anaesthesia at Great Ormond Street Hospital for Children, London, UK.