The next several chapters are dedicated to teaching trainees about pediatric pain and the various options for pain management in children. In this first of five chapters, we introduce the topic of pediatric pain assessment. Because expression of pain is related to age and development, practitioners must use specially developed and validated tools for assessing and measuring pain in different age groups. You cannot manage what you cannot measure.
Pediatric pain is often not recognized and not effectively managed. Perhaps this is caused by the inability of children to effectively describe the location and severity of their pain, especially those with cognitive impairment. But health care workers may also unknowingly contribute to the inadequate treatment of pain in children. The basis for this is speculative and may include a lack of knowledge about pathophysiology of pediatric pain or pharmacology of analgesics in pediatric patients. Other possible explanations include ignorance of appropriate pediatric pain assessment tools and available treatment options and an inability to recognize the large variability in pain experienced by different patients with similar types of pain.
Many health care professionals still believe that pain is an inevitable, expected consequence of illness and injury, and that pain is less harmful than the risks associated with the analgesic interventions. Many parents believe that their child’s pain is unavoidable or they fear side effects of analgesics. Inflexible prescribing practices that use PRN regimens with inappropriately low or infrequent analgesic doses still occur. Fear of side effects such as nausea, vomiting, respiratory depression, and fear of long-term sequelae (e.g., drug dependence and addiction) also cause inadequate treatment of pain in children. The fact is, however, that a variety of analgesic therapies can be provided safely to children, even prematurely born neonates.
Lack of adequate pain treatment in children is partially caused by the lack of approved labeling of potent analgesics. Pharmaceutical companies have been unwilling to fund necessary studies to obtain pediatric labeling because the market size is limited. This has resulted in a paucity of pharmacokinetic and pharmacodynamic data and a lack of information about adverse effects.
At What Age are Children Capable of Experiencing Pain?
To experience pain, one must possess the ability to perceive a peripheral noxious stimulus via a functioning nociceptive system and to develop a motor, autonomic, metabolic, psychological, behavioral, or emotional response. Neonates sense noxious stimuli and routinely demonstrate all these responses. In the developing fetus, cutaneous sensation begins in the 7th week of gestation in the perioral region and soon spreads to the face, hands, feet, and trunk. By the 15th week of gestation, cutaneous sensation has spread to the extremities, and by the 20th week of gestation, sensory perception is present in all cutaneous and mucosal regions. Substance P appears in fetal nerve tissue by the 10th week and endogenous opioids are detected at the 22nd week of gestation. Synapses begin to form between peripheral sensory neurons and dorsal horn neurons by this time. Myelination of nerve tracts in the spinal cord and brainstem begins during the 22nd week of gestation and is complete by the third trimester. Peripheral nerve myelination is not fully completed until after birth. However, one of the major nociceptive neurons is unmyelinated (C-fibers) and the other is thinly myelinated (A-δ fibers). This does not mean that noxious signals are not transmitted, but that they are transmitted more slowly.
Centrally, the cerebral cortex begins to develop at 8 weeks and will contain 10 billion neurons by the 20th week of gestation. Fetal electroencephalographic patterns, though intermittent and unsynchronized, appear by the 22nd week; by the 27th week, signals are synchronized in both hemispheres. By the 30th gestational week, cortical evoked potentials can be detected. At the beginning of the third trimester, all elements of the nociceptive system required to process noxious stimulation are present. The only component of the nociceptive system that is not present at birth is the descending inhibitory pathway, which develops during the first 6 months of antenatal life. Thus the neonate is not capable of attenuating nociceptive signals. The dorsal horn cells of the neonate that are responsible for transmitting nociceptive signals centrally have wider receptive fields and lower excitatory thresholds than in older subjects. These properties mature quickly in the postnatal period. Excitatory thresholds of dorsal horn neurons are further lowered by repetitive minor injuries such as daily heel lancing. Neonates may experience more pain in response to a given noxious stimulus than older children or adults.
Some practitioners erroneously assume that, because neonates cannot remember a painful event, it is of no consequence. But the metabolic and behavioral stress response that accompanies neonatal pain is associated with increased morbidity and mortality. This response can be reduced by using regional anesthesia, opioids, or general anesthesia before painful procedures.
Though little is known about neonatal consciousness and the perception of pain, there is evidence of complex, integrated cortical responses to nociceptive stimulation. Neonates that are subjected to noxious events (circumcision, repeated heel lancing, phlebotomy, etc.) demonstrate abnormalities in short-term behavior such as periods of increased crying, and feeding and sleeping abnormalities. Furthermore, painful experiences during early infancy affect future responses to painful events. In some instances, physiologic responses are enhanced, while behavioral responses are blunted. Opposite changes may occur under different circumstances. For example, infants who were circumcised at birth without anesthesia will demonstrate an exaggerated pain response to immunizations in the first year of life compared with infants who received some form of pain control during newborn circumcision.
To summarize, neonates may not be able to interpret or remember painful events but even premature newborns are capable of perceiving noxious events and mounting a variety of physiologic and behavioral responses. These responses may translate into short- and long-term behavioral changes during subsequent painful stimuli. Because these stress responses and adverse outcomes can be reduced by the judicious use of analgesics, pain should be anticipated whenever possible, recognized when present, and treated appropriately.
Assessing Pain in Children
One of the challenges of pediatric pain management is the assessment and treatment of pain in preverbal children and patients with neurologic or cognitive impairment who cannot communicate their experience of pain.
Pain assessment is most accurate when the child can describe its location, nature, and severity. With appropriate words and tools, children over 3 years of age can reliably communicate their pain and may be able to relate their pain to a number or face on a scale (see below). In children under 3 years, one must rely on a combination of behavioral clues and physiologic signs. Many of these signs are also seen in conditions other than pain, such as parental separation, hunger, fear, and anxiety. Thus misinterpretation is common. Parents can often determine whether their child is in pain by learning specific behaviors in their child that distinguish pain from distress or anxiety.
Piaget described four developmental stages of childhood. During the initial sensorimotor stage (up to approximately 2 years of age), children have little or no understanding of pain and no language ability. During this stage, we rely on behaviors (posture, activity, crying, feeding, sleeping, etc.) and physiologic signs (e.g., tachycardia, hypertension, diaphoresis, and oxyhemoglobin saturation) to determine the severity of an infant’s pain. We primarily rely on five different types of pain scales that are used in different age groups. For the neonatal population (up to approximately 3 months of age), we use the Neonatal Infant Pain Scale ( Table 32.1 ). It is primarily used to assess pain associated with medical procedures and includes assessment of facial expression, severity of crying, breathing patterns, movement of arms and legs, and state of arousal.
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