Scientists have shown that newborn babies have a "unique" nervous system which makes them respond differently to pain than adults. In research that has far-reaching implications for the medical and surgical treatments of infants, the scientists have found that newborn children feel pain longer and more sensitively. In premature babies, the mechanism that allows older children and adults to "dampen down" the pain messages does not work properly.
Until recently it has been presumed that a baby's pain system was too immature to function properly, or that they reacted in a similar way to adults, but less efficiently. Researchers at University College London have now discovered that babies' sensory systems have a unique pain-signalling mechanism, which disappears, as they grow older.
In the absence of confirmatory communication because of the inability of the fetus to tell us of her pain, medical practice and science judge that pain exists when anatomical structures necessary to pain sensation are in place and when physiological responses normally associated with pain occur.
In other words, if the biological sensory machinery exists, if something causes a response like that which pain would cause, and if that something would elicit the same response from human beings generally, then we can deduct that pain occurs.
Certain neurological structures are necessary to pain sensation :
In the skin and throughout the body are free nerve endings that act as pain receptors. These pain receptive cells are called nociceptors. When a nociceptor is affected by a noxious stimulus - something harmful or potentially harmful to the cell - it discharges an electrical impulse that travels through interfacing nerve fibers to the spinal cord, and often to the brain.
However, a nociceptor may be stimulated and result in a reflex response without causing pain awareness. A reflex response in its simplest form, is a movement following a stimulus: it is an automatic reaction such as a child withdrawing her hand from a hot object.
By studying sensory nerve cells in infants, scientists discovered that their reflex to pain or harm is greater and more prolonged than that of adults. The sensory nerve cells are also linked to larger areas of skin which means that they feel pain over a greater area of their body. While adults produce pain reflexes only when they encounter harmful stimulation, newborn children respond less selectively and produce the same reflex even to a light touch
Scientists believe that this is because in babies, the sensory nerve fibres that communicate non-harmful touch - known as A fibres - end in a different part of the spinal cord than adults.
But in adults the cells are connected only to pain-transmitting C fibres. Maria Fitzgerald, Professor of Developmental Neurobiology at the Thomas Lews Pain Research Centre, based at UCL, said another contributing factor in the new born child's pain system is that the nerve pathways, which carry pain-inhibiting messages from the brain stem to the spinal cord, mature later than other parts of the system.
Prof. Fitzgerald adds: "These nerve fibres from the brain stem start to grow down the spinal cord early in fetal life, but they do not extend branches into the spinal cord for some time, and do not function fully until soon after birth." This means the premature baby cannot benefit from the natural pain-killing system which, in adults, dampens down pain messages as they enter the nervous system.
It used to be the case that preterm infants were not given anaesthetic prior to an operation. In an article in the New York Times, dated 10 February 2008, an article on fetal pain, Dr. Kanwaljeet Anand noticed that on the infants return from the theatre they were in a distressed state. Their skin was grey, their breathing shallow, their pulses weak. He would spend hours stabilizing their vital signs, increasing their oxygen supply and administering insulin to balance their blood sugar. He discovered that infants undergoing major surgery were receiving only a paralytic to keep them still. And it was common in other jurisdictions too as doctors believed that newborns’ nervous systems were too immature to sense pain.
Today, adequate pain relief for even the youngest infants is the standard of care, and the treatment that so concerned Anand two decades ago would now be considered a violation of medical ethics.