Pain in babies

Do babies and children before they can speak or express feelings hurt the same as adults? Do they hurt more easily, or do they feel less pain? Up until the last 30 years medicine seems to have been unable to make up its mind about this. Doctors followed whatever the prevailing expert opinion was, and until the late nineteenth century it was generally considered that babies hurt more easily than adults. Then the opinion changed, and until the mid 1970s doctors “knew” that babies do not feel much pain. For much of the history of modern scientific medicine children and babies were therefore denied the benefits of the steadily improving medical techniques of treating pain. Fortunately for the linguistically challenged young human, having nothing but a fierce cry with which to convey hurt, science has in the last quarter of the 20th century established beyond reasonable doubt that neonates and babies definitely do experience pain – probably more than adults.

This article sets out to review the main difficulties involved in assessing and treating pain in children. It aims to dispell those social, medical, and scientific myths and fallacies which have caused whole generations of children to suffer unnecessarily, and to help in empowering caregivers to approach the hurting child with more confidence.

However could we think babies don’t hurt?

Before the late nineteenth century babies were considered to be more sensitive to pain than adults. That this should be so was patently obvious, by virtue of everyday observations and logic. The baby had a thinner skin, and an adult knows that the thin skin of a healing wound is more sensitive than the thick skin on a finger. Doris Cope quotes from The Children's Book, by Felix Wurtz, published in 1656, to illustate this logic: "If a new skin in old people be tender, what is it you think in a newborn Babe? Doth a small thing pain you so much on a finger, how painful is it then to a Child, which is tormented all the body over, which hath but a tender new grown flesh?" The ease with which an apparently trifling hurt can set off a piteous crying spell in the young child had made its impression on Mr Wurtz, and set him a-wondering, as it has turned out, on the right path.

But then the whole idea did a turn-about. Suddenly, in the late nineteenth and first half of the twentieth century, doctors were being taught that babies did not experience pain, and they were treating their young patients according to this unproven idea. From needle sticks to tonsillectomies to heart operations were done with no analgesia or even anaesthesia, other than muscle relaxation for the surgery.

When one realises that a horse lover is prepared to put his beloved mount “out of its misery” when it sustains an incurable injury, this callous attitude of humans towards their young seems inexplicable. Doris Cope thinks it possible that this was a result of a scientific misinterpretation of the findings of the new science of embryology – which considered that the non-myelinisation of much of a baby’s nervous system indicated that it did not yet function – taken together with the writings of Charles Darwin in his book The Expression of Emotions in Man and Animal (1872), that babies (as well as “animals, savages and the insane”) were incapable of experiencing pain. Whatever the real cause for the myth was, doctors were taught that in babies the expression of “pain is merely reflexive and … owing to the immaturity of the infant brain, the pain could not really matter.” At the same time there was the unscientific belief that use of opiates would lead to addiction, that babies would not remember any pain that they happened to feel, and that lack of conscious memory meant lack of long-term harm. Scientific studies on animals with various brain lesions were interpreted as supporting the idea that the reponses seen in babies were merely spinal reflexes. Furthermore, the whole effort of relieving pain was considered futile since it was thought to be impossible to measure the child's pain. No doubt the perceived risk of opiates, and the time and effort needed to provide adequate analgesia to the newborn, contributed to the doctor clinging to the doctrine of “carry on regardless of the crying”, rather than worrying about the ethics of not providing pain relief.. The “sensible and safe” approach was therefore to get on with the job and ignore the child’s crying.

While there were always doctors who treated young patients’ pain at face value, the revolution towards studying and treating pain in babies gained momentum in the 1980s. Publications on the hormonal and metabolic responses of babies to noxious stimuli began to appear, in the face of which the arguments about an “inadequate” cerebral response to pain could not be sustained. Studies on the measurement of pain in young children, as well as ways of reducing the injury response began to be done. The medical opinion about the significance of pain in the neonate has come a full circle. We now know that the very young respond more extensively to pain than the adult does, and that exposure to severe pain, without adequate treatment, can have long-term consequences. Recent writers have even suggested that inadequate treatment of painful events in the newborn may be related to violence and self-mutilation, even suicide, in later life. In spite of the difficulty of assessing how much pain a baby has, and the problem of finding the correct dosage or technique for treating a feeling which can be gauged but indirectly, modern medicine is firmly committed to improving the quality of pain relief for the very young. Science is catching up with what the caring mother has always known about her child, by the tone of her offspring’s cry.

The developmental neurobiology of pain

Ethically, one cannot take biopsies of babies’ nerves or brain tissue in order to study the neuronal anatomy and chemistry. If it were to become practical to turn the powerful tools of functional neuro-imaging to use in the study of neonates, it may well mean a second revolution in our understanding of pain in the newborn, but this has not yet been done. The reader has therefore to interpret this section in the light of the fact that beliefs about the development of the nociceptive component of the human nervous system frequently are deduced from findings in animal models of neonatal nociception.

One of the critical scientific events which lead to the present improved understanding of pain in the newborn was the realisation that the fetal and newborn unmyelinated nerve fibres are quite capable of relaying information, albeit slower than would be the case with myelinated fibres. The dictum that “babies don’t feel pain because their nerve pathways are not yet completely myelinated” originated in the nineteenth century, but was eventually, almost a century later, shown by experiment in animal models to be false.

At birth a human has developed the neural pathways for pain perception, but the pain responses of a newborn baby is not simply a miniaturised or immature version of that of an adult. There are a number of differences in both nerve structure and in the quality and extent of nerve responses which are considered to be pertinent to understanding neonatal pain.

For one, the nerves of young babies respond more readily to noxious stimuli (lower threshold to stimulation), than those of adults. Secondly, their threshold for sensitisation is also decreased. Sensitisation refers to to the phenomenon that a spinal neuron which senses a noxious event activates connections to adjacent neurons in the spine, increasing their sensitivity to noxious stimuli. In practice this means that an area of hypersensitivity to stimulation develops in the normal (unharmed, or not infected) tissue around a site of injury. This happens in adults and babies, but in babies this occurs more quickly and the sensitised area is larger than in an adult, for the same initial stimulus. A third factor which deserves mention is the fact that the pathways that descend from the brain to the spinal cord are not well developed in the newborn, so that the ability to reduce pain via central brain mechanisms is limited. Finally, the distribution of certain pain receptors is different in the newborn, compared to the adult. Specifically, the sensitivity to morphine and some anaesthetics seems to be quite different, and this is explained by the difference in the neuronal receptors for the specific drugs. For all these known reasons, and probably many which still need to be discovered, a noxious event which appears minor to adults (for instance, an intramuscular injection) can have unexpectedly widespread effects in the nervous sytem; it is sensed more intensely and potentially more diffusely than it would be in the adult.

As important as the basic increased sensitivity, it is important that the neonate's nervous system seems much more active than that of an adult in transforming its connections and central nerve pathways in response to stimuli. This reshaping - also called plasticity - involves both structural and chemical changes of the nervous system. It has been shown to occur in response to noxious events in the short term, and there are indications that such changes, once established, can persist until adult life. What precisely this implies for later childhood and adult life is as yet unclear, but the present feeling is that this potential for long term harm is yet another reason for working towards more effective management of neonatal pain.

Why treat pain at all?

Why, in general, is it necessary to treat pain (in anyone of any age)? What do different cultures say about pain and its treatment. Attitudes and beliefs. Are there consequences – immediate, delayed? Are these consequnces undesirable or harmful?

Consequences of pain

What does untreated pain do in adults? What do we know of children:

Diagnosis

The problem of assessing pain in the child – factors different from adult. Nociceptive activity vs emotional response. Problem if latter is used as criterium.

Pain assessment

the problem of no language dependence

Ways of trying to get past these difficulties

observations, forms, scales, pictures. Reliability – can one treat on these results?

Treatment

Decisions about when to treat - Specific ways of treating - difference from adults - dosage implications. Parents/family/caregiver education

Pharmacologic treatment

”Placeboid”

pacifier +- sucrose, coddling, etc.

Analgesics

Paracetamol and NSAIDs Opiates

Topical, local and regional anaesthesia

What is topical / local / regional? How does it work? What are the risks / benefits?

Physical treatments

That relieve pain That cause pain (see also specific conditions)

Environment

A place of rest and peace vs a place of conflict

Psychological

Parents and caregivers. The babies intuition. Truth and trust. Confidence and love.