Abdominal sensitivity in the first year of life: comparison of infants with and without prenatally diagnosed unilateral hydronephrosis

Evidences of emerging pain consciousness during prenatal development: a narrative review

BACKGROUND

The study of consciousness has always been considered a challenge for neonatologists, even more when considering the uterine period. Our review aimed to individuate at what gestational age the fetus, which later became a premature infant, can feel the perception of external stimuli. Therefore, the aim of our review was to study the onset of consciousness during the fetal life.

MATERIALS AND METHODS

A literature search was performed in Medline-PubMed database. We included all papers found with the following MeSH words: "consciousness or cognition or awareness or comprehension or cognitive or consciousness of pain" in combination with "embryo or fetus or fetal life or newborn." Studies were selected if titles and/or abstracts suggested an association between formation of consciousness (the basics of neurodevelopment) and preterm infant or fetus. Titles and abstracts were first screened by three independent reviewers according to Cochrane Collaboration's recommendations.

RESULTS

From the literature review, we found only 8 papers describing the onset of consciousness in the transition period from fetus to premature newborn. Therefore, according to these papers, we temporally analyzed the formation of the thalamocortical connections that are the basis of consciousness.

CONCLUSIONS

We can conclude that from a neuroanatomical point of view, it is rather unlikely that the infant can be seen as a conscious human before 24 weeks of gestational age, thus before all the thalamocortical connections are established. Further literature data have to confirm this hypothesis.

Long-term alterations in somatosensory functioning in survivors of childhood cancer

ABSTRACT

Cancer and its treatment can have lasting consequences on somatosensation, including pain, which is often underrecognized and undertreated. Research characterizing the impact of cancer on pain and sensory processing in survivors of childhood cancer is scarce. This study aimed to quantify generalized differences in pain and sensory processing in survivors of childhood cancer compared with reference data using a standardized thermal and mechanical quantitative sensory testing (QST) protocol. The association between demographic, clinical (eg, leukemia vs other cancers and treatment exposures), and psychosocial (eg, anxiety and pain catastrophizing) variables and sensitivity to pain and sensory stimuli were also evaluated. Participants were 56 survivors of various types of childhood cancer (52% male, Mage = 13.5 years, SD = 3.2, range = 8-17 years). On average, children were 7 years (SD = 4.1, range = 1.2-16.5) post treatment. Almost all participants (86%) had at least 1 abnormal QST parameter compared with age- and sex-matched reference data; however, few participants self-reported the presence of sensory abnormalities. Generally, participants exhibited reduced sensitivity across the QST parameters examined (Ps < 0.05, ds = 0.40-3.45). A significant minority (45%) also exhibited pain sensitization (P <0.001, d = 0.42). Several risk factors for changes in sensory processing were identified, including current age, history of leukemia, certain treatment exposures (eg, vincristine cumulative dose, major surgery, and bone marrow or stem cell transplant), time off treatment, and higher anxiety and pain catastrophizing scores. Overall, this study demonstrated that somatosensory changes are prevalent in survivors of childhood cancer years after the completion of treatment. Future research is needed to understand long-term implications of altered somatosensation in this complex population.

What is the definition of acute episodic and chronic pain in critically ill neonates and infants? A global, four-stage consensus and validation study

OBJECTIVES

To define and validate types of pain in critically ill neonates and infants by researchers and clinicians working in the neonatal intensive care unit (NICU) and high dependency unit (HDU).

DESIGN

A qualitative descriptive mixed-methods design.

PROCEDURE/S

Each stage of the study was built on and confirmed the previous stages. Stage 1 was an expert panel to develop definitions; stage 2 was a different expert panel made up of neonatal clinicians to propose clinical characteristics associated with the definitions from stage 1; stage 3 was a focus group of neonatal clinicians to provide clinical case scenarios associated with each definition and clinical characteristics; and stage 4 was a survey administered to neonatal clinicians internationally to test the validity of the definitions using the clinical case scenarios.

RESULTS

In stage 1, the panel (n=10) developed consensus definitions for acute episodic pain and chronic pain in neonates and infants. In stage 2, a panel (n=8) established clinical characteristics that may be associated with each definition. In stage 3, a focus group (n=11) created clinical case scenarios of neonates and infants with acute episodic pain, chronic pain and no pain using the definitions and clinical characteristics. In stage 4, the survey (n=182) revealed that the definitions allowed an excellent level of discrimination between case scenarios that described neonates and infants with acute episodic pain and chronic pain (area under the receiver operating characteristic=0.87 and 0.89, respectively).

CONCLUSIONS

This four-stage study enabled the development of consensus-based and clinically valid definitions of acute episodic pain and chronic pain. There is a need to define and validate other pain types to inform a taxonomy of pain experienced by neonates and infants in the NICU and HDU.

The neurobiology of childhood trauma, from early physical pain onwards: as relevant as ever in today's fractured world

Background: The situation in the world today, encompassing multiple armed conflicts, notably in Ukraine, the Coronavirus pandemic and the effects of climate change, increases the likelihood of childhood exposure to physical injury and pain. Other effects of these worldwide hardships include poverty, malnutrition and starvation, also bringing with them other forms of trauma, including emotional harm, neglect and deliberate maltreatment. Objective: To review the neurobiology of the systems in the developing brain that are most affected by physical and emotional trauma and neglect. Method: The review begins with those that mature first, such as the somatosensory system, progressing to structures that have a more protracted development, including those involved in cognition and emotional regulation. Explored next are developing stress response systems, especially the hypothalamic-pituitary-adrenal axis and its central regulator, corticotropin-releasing hormone. Also examined are reward and anti-reward systems and genetic versus environmental influences. The behavioural consequences of interpersonal childhood trauma, focusing on self-harm and suicide, are also surveyed briefly. Finally, pointers to effective treatment are proffered. Results: The low-threshold nature of circuitry in the developing brain and lack of inhibitory connections therein result in heightened excitability, making the consequences of both physical and emotional trauma more intense. Sensitive and critical periods in the development of structures such as the amygdala render the nervous system more vulnerable to insults occurring at those points, increasing the likelihood of psychiatric disorders, culminating in self-harm and even suicide. Conclusion: In view of the greater excitability of the developing nervous system, and its vulnerability to physical and psychological injuries, the review ends with an exhortation to consider the long-term consequences of childhood trauma, often underestimated or missed altogether when faced with adults suffering mental health problems.

Vorteile, Sicherheit und Nebenwirkungen der Tumeszenz‐Lokalanästhesie bei dermatologischen Operationen an Säuglingen

Die Tumeszenz-Lokalanästhesie (TLA) spielt bei dermatochirurgischen Eingriffen eine wichtige Rolle. Die TLA bietet etliche Vorteile, wie lang anhaltende Betäubung, reduzierte Blutung während der Operation und Vermeidung möglicher Komplikationen einer Vollnarkose. Einfache Durchführung, günstiges Risikoprofil und breites Indikationsspektrum sind weitere Gründe dafür, dass TLA zunehmend auch bei Säuglingen eingesetzt wird. Es gibt nicht nur viele Indikationen für chirurgische Exzisionen im Säuglingsalter, wie angeborene Naevi, sondern es hat auch erhebliche Vorteile, wenn diese Exzisionen in einem frühen Alter durchgeführt werden. Dazu zählen die geringere Größe der Läsionen sowie die unproblematische Wundheilung und Geweberegeneration im Säuglingsalter. Dennoch müssen hinsichtlich der Anwendung der TLA bei Säuglingen einige Aspekte berücksichtigt werden, darunter die Dosierung, eine veränderte Plasmaproteinbindung und die Notwendigkeit einer adäquaten und lang anhaltenden Schmerzkontrolle.

Benefits, safety and side effects of tumescent local anesthesia in dermatologic surgery in infants

Tumescent local anesthesia (TLA) plays an important role in dermatosurgical procedures. TLA has several benefits such as long-lasting anesthesia, reduced bleeding during surgery and the avoidance of general anesthesia-associated complications. Convenience and a favorable risk profile along with a broad spectrum of indications are further reasons why TLA is increasingly applied in infants as well. There are not only a variety of indications for surgical excisions in infancy, such as congenital nevi, but also substantial benefits when performing these excisions at an early age. These include the smaller size of the lesions as well as the unproblematic wound healing and tissue regeneration in infancy. Nevertheless, several aspects need to be considered when applying TLA in infants including dosing, altered plasma protein binding and the need for adequate and long-lasting pain control.

Defining pain in newborns: need for a uniform taxonomy?

A framework for defining pain terms such as acute, persistent, prolonged or chronic pain to newborns was derived from the scientific literature on neonatal pain assessments, previous attempts to define chronic pain and the clinical and neurophysiological features of neonatal pain. This novel framework incorporates the temporal features, localising characteristics, and secondary effects of the pain experienced, as well as the behavioural and physiological response patterns of newborns.

CONCLUSION

Although not evidence-based, this framework provides an initial starting point for defining commonly used neonatal pain terms. It will require future revision/refinement based on the accumulating evidence for non-acute pain.

Beyond Acute Pain: Understanding Chronic Pain in Infancy

This topical review presents the current challenges in defining chronic pain in infants, summarizes evidence from animal and human infant studies regarding the biological processes necessary for chronic pain signaling, and presents observational/experiential evidence from clinical experts. A literature search of four databases (CINAHL, EMBASE, PsycINFO, and MEDLINE) was conducted, along with hand searches of reference lists. Evidence from animal studies suggest that important neurophysiological mechanisms, such as the availability of key neurotransmitters needed for maintenance of chronic pain, may be immature or absent in the developing neonate. In some cases, human infants may be significantly less likely to develop chronic pain. However, evidence also points to altered pain perception, such as allodynia and hyperalgesia, with significant injury. Moreover, clinicians and parents in pediatric intensive care settings describe groups of infants with altered behavioral responses to repeated or prolonged painful stimuli, yet agreement on a working definition of chronic pain in infancy remains elusive. While our understanding of infant chronic pain is still in the rudimentary stages, a promising avenue for the future assessment of chronic pain in infancy would be to develop a clinical tool that uses both neurophysiological approaches and clinical perceptions already presented in the literature.

Changing Balance of Spinal Cord Excitability and Nociceptive Brain Activity in Early Human Development

In adults, nociceptive reflexes and behavioral responses are modulated by a network of brain regions via descending projections to the spinal dorsal horn [1]. Coordinated responses to noxious inputs manifest from a balance of descending facilitation and inhibition. In contrast, young infants display exaggerated and uncoordinated limb reflexes [2]. Our understanding of nociceptive processing in the infant brain has been advanced by the use of electrophysiological and hemodynamic imaging [3, 4, 5, 6]. From approximately 35 weeks’ gestation, nociceptive-specific patterns of brain activity emerge [7], whereas prior to this, non-specific bursts of activity occur in response to noxious, tactile, visual, and auditory stimulation [7, 8, 9, 10]. During the preterm period, refinement of spinal cord excitability is also observed: reflex duration shortens, response threshold increases, and improved discrimination between tactile and noxious events occurs [2, 11, 12]. However, the development of descending modulation in human infants remains relatively unexplored. In 40 infants aged 28–42 weeks’ gestation, we examined the relationship between nociceptive brain activity and spinal reflex withdrawal activity in response to a clinically essential noxious procedure. Nociceptive-specific brain activity increases in magnitude with gestational age, whereas reflex withdrawal activity decreases in magnitude, duration, and latency across the same developmental period. By recording brain and spinal cord activity in the same infants, we demonstrate that the maturation of nociceptive brain activity is concomitant with the refinement of noxious-evoked limb reflexes. We postulate that, consistent with studies in animals, infant reflexes are influenced by the development of top-down inhibitory modulation from maturing subcortical and cortical brain networks.

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Noxious-evoked brain activity increases in magnitude across the preterm period

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Maturation of nociceptive brain activity coincides with reflex activity refinement

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This may relate to the emergence of top-down inhibition in human infants

The relationship between nociceptive brain activity, spinal reflex withdrawal and behaviour in newborn infants

Measuring infant pain is complicated by their inability to describe the experience. While nociceptive brain activity, reflex withdrawal and facial grimacing have been characterised, the relationship between these activity patterns has not been examined. As cortical and spinally mediated activity is developmentally regulated, it cannot be assumed that they are predictive of one another in the immature nervous system. Here, using a new experimental paradigm, we characterise the nociceptive-specific brain activity, spinal reflex withdrawal and behavioural activity following graded intensity noxious stimulation and clinical heel lancing in 30 term infants. We show that nociceptive-specific brain activity and nociceptive reflex withdrawal are graded with stimulus intensity (p < 0.001), significantly correlated (r = 0.53, p = 0.001) and elicited at an intensity that does not evoke changes in clinical pain scores (p = 0.55). The strong correlation between reflex withdrawal and nociceptive brain activity suggests that movement of the limb away from a noxious stimulus is a sensitive indication of nociceptive brain activity in term infants. This could underpin the development of new clinical pain assessment measures.

Persistent changes in peripheral and spinal nociceptive processing after early tissue injury

It has become clear that tissue damage during a critical period of early life can result in long-term changes in pain sensitivity, but the underlying mechanisms remain to be fully elucidated. Here we review the clinical and preclinical evidence for persistent alterations in nociceptive processing following neonatal tissue injury, which collectively point to the existence of both a widespread hypoalgesia at baseline as well as an exacerbated degree of hyperalgesia following a subsequent insult to the same somatotopic region. We also highlight recent work investigating the effects of early trauma on the organization and function of ascending pain pathways at a cellular and molecular level. These effects of neonatal injury include altered ion channel expression in both primary afferent and spinal cord neurons, shifts in the balance between synaptic excitation and inhibition within the superficial dorsal horn (SDH) network, and a 'priming' of microglial responses in the adult SDH. A better understanding of how early tissue damage influences the maturation of nociceptive circuits could yield new insight into strategies to minimize the long-term consequences of essential, but invasive, medical procedures on the developing somatosensory system.

Neonatal analgesia: A neglected issue in the tropics

Pain control in newborns is poorly understood and often neglected in neonatal practice in many settings in our environment. Managing pain among newborns can be quite challenging and the effectiveness of various interventions used to ameliorate pain in this category of patients are either unknown or poorly understood by many a people engaged in the care of newborns in one way or the other. A search for published works on neonatal analgesia was performed using Google and PubMed. The Cochrane Database of Systematic Reviews was also searched. The areas of focus were definition, pathophysiology and management of pain in neonates. Relevant information was extracted and processed. Contrary to what is widely believed in many quarters, howbeit erroneously, there is compelling evidence that newborns do indeed feel pain. Supportive care, comprising of use of sucrose, glucose, breastfeeding, kangaroo mother care are worthwhile measures in ameliorating pain in the newborn. Novel therapies (such as sensorial saturation and swaddling) have been evaluated and proven useful. The use of sedation did not show any beneficial results.

Biological and neurodevelopmental implications of neonatal pain

Nociceptive pathways are functional following birth. In addition to physiological and behavioral responses, neurophysiological measures and neuroimaging evaluate nociceptive pathway function and quantify responses to noxious stimuli in preterm and term neonates. Intensive care and surgery can expose neonates to painful stimuli when the developing nervous system is sensitive to changing input, resulting in persistent impacts into later childhood. Early pain experience has been correlated with increased sensitivity to subsequent painful stimuli, impaired neurodevelopmental outcomes, and structural changes in brain development. Parallel preclinical studies have elucidated underlying mechanisms and evaluate preventive strategies to inform future clinical trials.

Are there long-term consequences of pain in newborn or very young infants?

Physiologic studies indicate that very early pain or stress experiences have more than immediate consequences for infants. Assessment and care of pain are complex subjects made even more complex and challenging when the individual experiencing pain is a very young infant. This review provides evidence that significant and long-lasting physiological consequences may follow painful insults in the very young, including changes in the central nervous system and changes in responsiveness of the neuroendocrine and immune systems to stress at maturity.

Neuraxial analgesia in neonates and infants: a review of clinical and preclinical strategies for the development of safety and efficacy data

Neuraxial drugs provide robust pain control, have the potential to improve outcomes, and are an important component of the perioperative care of children. Opioids or clonidine improves analgesia when added to perioperative epidural infusions; analgesia is significantly prolonged by the addition of clonidine, ketamine, neostigmine, or tramadol to single-shot caudal injections of local anesthetic; and neonatal intrathecal anesthesia/analgesia is increasing in some centers. However, it is difficult to determine the relative risk-benefit of different techniques and drugs without detailed and sensitive data related to analgesia requirements, side effects, and follow-up. Current data related to benefits and complications in neonates and infants are summarized, but variability in current neuraxial drug use reflects the relative lack of high-quality evidence. Recent preclinical reports of adverse effects of general anesthetics on the developing brain have increased awareness of the potential benefit of neuraxial anesthesia/analgesia to avoid or reduce general anesthetic dose requirements. However, the developing spinal cord is also vulnerable to drug-related toxicity, and although there are well-established preclinical models and criteria for assessing spinal cord toxicity in adult animals, until recently there had been no systematic evaluation during early life. Therefore, in the second half of this review, we present preclinical data evaluating age-dependent changes in the pharmacodynamic response to different spinal analgesics, and recent studies evaluating spinal toxicity in specific developmental models. Finally, we advocate use of neuraxial drugs with the widest demonstrable safety margin and suggest minimum standards for preclinical evaluation before adoption of new analgesics or preparations into routine clinical practice.

Neonatal tissue damage facilitates nociceptive synaptic input to the developing superficial dorsal horn via NGF-dependent mechanisms

Tissue injury during a critical period of early life can facilitate spontaneous glutamatergic transmission within developing pain circuits in the superficial dorsal horn (SDH) of the spinal cord. However, the extent to which neonatal tissue damage strengthens nociceptive synaptic input to specific subpopulations of SDH neurons, as well as the mechanisms underlying this distinct form of synaptic plasticity, remains unclear. Here we use in vitro whole-cell patch clamp recordings from rodent spinal cord slices to demonstrate that neonatal surgical injury selectively potentiates high-threshold primary afferent input to immature lamina II neurons. In addition, the increase in the frequency of miniature excitatory postsynaptic currents after hindpaw incision was prevented by neonatal capsaicin treatment, suggesting that early tissue injury enhances glutamate release from nociceptive synapses. This occurs in a widespread manner within the developing SDH, as incision elevated miniature excitatory postsynaptic current frequency in both GABAergic and presumed glutamatergic lamina II neurons of Gad-GFP transgenic mice. The administration of exogenous nerve growth factor into the rat hindpaw mimicked the effects of early tissue damage on excitatory synaptic function, while blocking trkA receptors in vivo abolished the changes in both spontaneous and primary afferent-evoked glutamatergic transmission following incision. These findings illustrate that neonatal tissue damage can alter the gain of developing pain pathways by activating nerve growth factor-dependent signaling cascades, which modify synaptic efficacy at the first site of nociceptive processing within the central nervous system.

Endpoints in pediatric pain studies

Assessing pain intensity in (preverbal) children is more difficult than in adults. Tools to measure pain are being used as primary endpoints [e.g., pain intensity, time to first (rescue) analgesia, total analgesic consumption, adverse effects, and long-term effects] in studies on the effects of analgesic drugs. Here, we review current and promising new endpoints used in pediatric pain assessment studies.

Visceral pain originating from the upper urinary tract

Pain originating from the upper urinary tract is a common problem and stone colic is one of the most intense pain conditions that can be experienced in the clinic. The pain is difficult to alleviate and often leads to medical attention. In humans, pain mechanisms of the upper urinary tract pain are still poorly understood, which often leads to a trial and error approach in clinical pain management. Pain from the upper urinary tract seems to have all the characteristics of pure visceral pain, including referred pain with or without hyperalgesia/trophic changes in somatic tissues and viscero-visceral hyperalgesia. However, further studies are needed to better understand these visceral pain mechanisms with regard to optimising pain management. This review gives an introduction to visceral pain in general and upper urinary tract pain in particular, with special reference to pain pathways and pharmacological and non-pharmacological pain modulation.

Long-term impact of neonatal injury in male and female rats: Sex differences, mechanisms and clinical implications

Over the last several decades, the relative contribution of early life events to individual disease susceptibility has been explored extensively. Only fairly recently, however, has it become evident that abnormal or excessive nociceptive activity experienced during the perinatal period may permanently alter the normal development of the CNS and influence future responses to somatosensory input. Given the significant rise in the number of premature infants receiving high-technology intensive care over the last 20 years, ex-preterm neonates may be exceedingly vulnerable to the long-term effects of repeated invasive interventions. The present review summarizes available clinical and laboratory findings on the lasting impact of exposure to noxious stimulation during early development, with a focus on the structural and functional alterations in nociceptive circuits, and its sexually dimorphic impact.

FETAL PAIN

The concept of fetal pain is becoming more and more relevant since the possibilities for invasive intrauterine treatment are increasing. However, there is much debate as to whether the fetus is mature enough to be able to perceive pain. But what is ‘pain’? One cannot determine whether a fetus feels pain unless one has a conception of what pain is. There is a difference in opinion about what pain really is and that is also the difficulty in studies on fetal pain: we cannot simply ask the fetus whether or not it feels pain. We can only give indirect evidence of possible harmful effects of stressful stimuli on the developing fetus. In this review we will first explore the meaning of ‘pain’. We will then discuss fetal anatomic, neurophysiologic and behavioural development and the responses which are thought to be required to experience pain. Finally, we discuss some ethical considerations and suggestions on fetal anaesthesia.

Increased gastrointestinal permeability and gut inflammation in children with functional abdominal pain and irritable bowel syndrome

OBJECTIVES

To determine gastrointestinal (GI) permeability and fecal calprotectin concentration in children 7 to 10 years of age with functional abdominal pain and irritable bowel syndrome (FAP/IBS) versus control subjects and ascertain potential relationships with pain symptoms and stooling.

STUDY DESIGN

GI permeability and fecal calprotectin concentration were measured. Children kept a 2-week diary of pain episodes and stooling pattern.

RESULTS

Proximal GI permeability was greater in the FAP/IBS group (n = 93) compared with control subjects (n = 52) (0.59 +/- 0.50 vs 0.36 +/- 0.26, respectively; mean +/- SD; P < .001) as was colonic permeability (1.01 +/- 0.67 vs 0.81 +/- 0.43, respectively; P < .05). Gastric and small intestinal permeability were similar. Fecal calprotectin concentration was greater in children with FAP/IBS compared with control children (65.5 +/- 75.4 microg/g stool vs 43.2 +/- 39.4, respectively; P < .01). Fecal calprotectin concentration correlated with pain interference with activities (P = .01, r(2) = 0.36). There was no correlation between GI permeability and pain related symptoms. Neither permeability nor fecal calprotectin correlated with stool form.

CONCLUSIONS

Children with FAP/IBS have evidence of increased GI permeability and low-grade GI inflammation, with the latter relating to the degree to which pain interferes with activities.

Behavioral stress is affected by the mode of tube feeding in very low birth weight infants

OBJECTIVE

To compare the effect of continuous versus bolus feeding on behavioral responses of stress in very low birth weight infants during early postnatal life.

METHODS

In a randomized, controlled trial conducted at 3 neonatal units, 70 premature infants with gestational age 24 to 29 weeks and birth weight <1200 g were randomly assigned to 1 of 3 feeding methods: continuous nasogastric feeding, bolus nasogastric feeding, and bolus orogastric feeding. Behavioral responses were video recorded during feeding at 7 and 15 days of postnatal age and at 32 weeks of postmenstrual age. The odds ratio (OR) of manifest behavioral stress was calculated by means of logistic regression.

RESULTS

A significantly higher risk of a behavioral stress response in bolus-fed infants compared with continuous-fed infants at 15 days of age was observed, [adjusted OR=4.1 (95% confidence interval: 1.1-15.4)]. A similar difference was observed at 32 weeks of postmenstrual age [adjusted OR=4.2 (95% confidence interval: 1.0-17.8)]. In addition, bolus-fed infants showed statistically significant higher need of behavioral and physiologic stabilization during feeding.

DISCUSSION

This trial suggests that continuous feeding is associated with lower behavioral stress response as compared with bolus feeding among very low birth weight infants, in early postnatal life.

Pain in children: recent advances and ongoing challenges

Significant advances in the assessment and management of acute pain in children have been made, and are supported by an increase in the availability and accessibility of evidence-based data. However, methodological and practical issues in the design and performance of clinical paediatric trials limit the quantity, and may influence the quality, of current data, which lags behind that available for adult practice. Collaborations within research networks, which incorporate both preclinical and clinical studies, may increase the feasibility and specificity of future trials. In early life, the developing nervous system responds differently to pain, analgesia, and injury, resulting in effects not seen in later life and which may have long-term consequences. Translational laboratory studies further our understanding of developmental changes in nociceptor pathway structure and function, analgesic pharmacodynamics, and the impact of different forms of injury. Chronic pain in children has a negative impact on quality of life, resulting in social and emotional consequences for both the child and the family. Despite age-related differences in many chronic pain conditions, such as neuropathic pain, management in children is often empirically based on data from studies in adults. There is a major need for further clinical research, training of health-care providers, and increased resources, to improve management and outcomes for children with chronic pain.

Bodily progression of motor responses to increasing mechanical force stimulation in the newborn infant and the effect of heel prick

BACKGROUND

The newborn infant's response to stimulation with von Frey filaments has previously been examined only at the spinal level as the flexion withdrawal response or abdominal reflex. The threshold for the spinal responses has been shown to be lower following skin damage and visceral pathology. Higher forces of mechanical stimulation elicit other body responses, which are likely to arise from higher levels in the nervous system: these have not been investigated before.

OBJECTIVE

To investigate the newborn infants' responses to increasing forces of mechanical (von Frey filament) stimulation and whether their progression is affected by repeated heel prick.

SUBJECTS AND METHODS

The study was performed in 31 full term and 77 preterm infants. Graded mechanical forces (using von Frey filaments) were applied to the heels and the abdominal skin. The thresholds for the flexion withdrawal reflex or abdominal reflex and other body responses were recorded.

RESULTS

The thresholds for the flexion withdrawal reflex and other body movements to graded mechanical force on the heel were significantly lower in preterm infants compared to full term infants. The threshold for the abdominal reflex and other body responses from graded mechanical stimulation of the abdomen was also significantly lower in preterm infants. In all infants thresholds were further reduced following sensitisation from previous heel pricks. The progression of the responses is independent of gestation or prior sensitisation.

CONCLUSION

Both preterm and full term newborn infants respond to graded mechanical stimuli by a series of body responses, which progress in response to increasing force from a simple spinal withdrawal reflex to more complex responses involving higher levels of the central nervous system.

Postnatal tuning of cutaneous inhibitory receptive fields in the rat

Spinal nociceptive processing undergoes extensive maturation in the postnatal period. The large excitatory cutaneous receptive fields and sensitivity to mechanical stimulation in the first weeks of life suggest a lack of inhibitory control in developing spinal sensory pathways, which cannot be easily explained at the synaptic level. We hypothesized that developmental changes in dorsal horn inhibition occur at the network level, and tested this by mapping the spatial and modality organization of dorsal horn cell inhibitory receptive fields (RFs) in decerebrate spinal adult and neonatal rats. We report two novel results. First, although contralateral inhibition of dorsal horn cells was well established by postnatal day 3 (P3), inhibitory RFs were significantly less spatially restricted at P3 than in the adult and the intensity of inhibition across the RF was more evenly distributed in the neonate. Second, contralateral inhibitory RFs could be activated by both low- and high-intensity stimulation in the neonate, in contrast to the situation in adult where high-intensity pinch is normally required. These results demonstrate substantial postnatal changes in the organization or 'tuning' of inhibition in the developing dorsal horn, which are likely to contribute to the maturation of tactile and nociceptive spinal processing and coordinated sensorimotor and pain behaviour.

Current controversies regarding pain assessment in neonates

Although over 40 methods of pain assessment in infants are available for use in clinical practice, unrecognized and under-treated pain remains one of the most commonly reported problems within the Neonatal Intensive Care Units. A number of factors have been found to account for differences in the robustness of the pain response in neonates of varying gestational ages. Discrepancies between behavioral and physiological pain indicators have also been reported. With newer technologies, there is an opportunity not only to verify infant pain perception, but these tools may allow an identification of which of the observed indicators are most sensitive in particular clinical situations. The current controversies regarding pain assessment in preterm and term infants are reviewed to define the most important issues and to develop a dialogue for future directions.

Chronic pain after childhood groin hernia repair

BACKGROUND

In contrast to the well-described 10% risk of chronic pain affecting daily activities after adult groin hernia repair, chronic pain after childhood groin hernia repair has never been investigated. Studies of other childhood surgery before the age of 3 months suggest a risk of increased pain responsiveness later in life, but its potential relationship to chronic pain in adult life is unknown.

METHODS

This was a nationwide detailed questionnaire study of chronic groin pain in adults having surgery for a groin hernia repair before the age of 5 years (n = 1075).

RESULTS

The response rate was 63.3%. In the 651 patients available for analysis, pain from the operated groin was reported by 88 (13.5%) patients whereof 13 (2.0%) patients reported frequent and moderate or severe pain. Pain occurred primarily when exercising sports or other leisure activities. Patients operated on before the age of 3 months (n = 122) did not report groin pain more often or with higher intensity than other patients did.

CONCLUSIONS

Groin pain in adult patients operated on for a groin hernia in childhood is uncommon and usually mild and occurs in relation to physical activity. Operation before the age of 3 months does not increase the risk of chronic pain.

Long-term alteration of pain sensitivity in school-aged children with early pain experiences

While animal studies suggest that neonatal pain experiences induce long-term alterations in pain sensitivity, no such data exist in humans. Changes in pain sensitivity in school-aged children (9-14 years) who were born preterm or fullterm, had been hospitalized for a prolonged period of time after birth and had undergone repeated painful procedures while being treated in a Neonatal Intensive Care Unit (NICU) were determined. A retrospective cohort study of 19 preterm (<or=31 weeks gestational age) and 20 fullterm children (>or=37 weeks gestational age) treated at least 3 days in a NICU at a University Hospital and 20 fullterm control children without NICU experience was performed. Perceptual sensitization to tonic heat and repetitive mechanical stimuli as well as heat pain and mechanical pain thresholds were obtained at the thenar and a trigeminal site. Length of hospitalization and NICU treatment was significantly higher in preterm than fullterm children. Nonetheless, both preterm and fullterm children with NICU experience showed greater perceptual sensitization to tonic heat and elevated heat pain thresholds at both sites. Mechanical pain threshold and perceptual sensitization did not differ between groups. Consistent with findings in animals, repeated pain experiences during the neonatal period were associated with alterations in thermal pain responsivity in school-aged preterm and fullterm children that was characterized by enhanced perceptual sensitization to prolonged painful stimulation and hypoalgesia to brief heat pain stimuli. Our findings suggest that repeated pain experiences in neonates may induce activity-induced changes in the functioning of pain pathways that persist well beyond infancy.

Assessing postoperative pain in neonates: a multicenter observational study

OBJECTIVE

A multicenter observational study was conducted to evaluate the practices of postoperative pain assessment and management in neonates to identify specific targets for improvement in clinical practice.

METHODS

Ten participating NICUs collected data for the 72 hours after a surgical operation on 25 consecutive neonates (N = 250), including demographics, principal diagnoses, operative procedure, other painful procedures, pain assessments, interventions (pharmacologic and nonpharmacologic), and adverse events in neonates who underwent minor and major surgery. Descriptive and logistic-regression analyses were performed by using SPSS and Stata.

RESULTS

The neonates studied had a birth weight of 2.4 +/- 1.0 kg (mean +/- SD) and gestational age of 36 +/- 4.3 weeks; 57% were male, and length of hospital stay was 23.5 +/- 30.0 days. Participating hospitals used 7 different numeric pain scales, with nursing pain assessments documented for 88% (n = 220) of the patients and physician pain assessments documented for 9% (n = 23) of the patients. Opioids (84% vs 60%) and benzodiazepines (24% vs 11%) were used more commonly after major surgery than minor surgery, and a small proportion (7% major surgery, 12% minor surgery) received no analgesia. Logistic-regression analyses showed that physician pain assessment was the only significant predictor of postsurgical analgesic use, whereas major surgery and postnatal age in days did not seem to contribute. Physician pain assessment was documented for 23 patients; 22 of these received postoperative analgesia.

CONCLUSIONS

Documentation of postoperative pain assessment and management in neonates was extremely variable among the participating hospitals. Pain assessment by physicians must be emphasized, in addition to developing evidence-based guidelines for postoperative care and educating professional staff to improve postoperative pain control in neonates.

Long-term consequences of pain in human neonates

The low tactile threshold in preterm infants when they are in the neonatal intensive care unit (NICU), while their physiological systems are unstable and immature, potentially renders them more vulnerable to the effects of repeated invasive procedures. There is a small but growing literature on pain and tactile responsivity following procedural pain in the NICU, or early surgery. Long-term effects of repeated pain in the neonatal period on neurodevelopment await further research. However, there are multiple sources of stress in the NICU, which contribute to inducing high overall 'allostatic load', therefore determining specific effects of neonatal pain in human infants is challenging.

Cortical pain responses in human infants

Despite the recent increase in our understanding of the development of pain processing, it is still not known whether premature infants are capable of processing pain at a cortical level. In this study, changes in cerebral oxygenation over the somatosensory cortex were measured in response to noxious stimulation using real-time near-infrared spectroscopy in 18 infants aged between 25 and 45 weeks postmenstrual age. The noxious stimuli were heel lances performed for routine blood sampling; no blood tests were performed solely for the purpose of the study. Noxious stimulation produced a clear cortical response, measured as an increase in total hemoglobin concentration [HbT] in the contralateral somatosensory cortex, from 25 weeks (mean Delta[HbT] = 7.74 micromol/L; SE, 1.10). Cortical responses were significantly greater in awake compared with sleeping infants, with a mean difference of 6.63 micromol/L [95% confidence interval (CI) limits: 2.35, 10.91 micromol/L; mean age, 35.2 weeks]. In awake infants, the response in the contralateral somatosensory cortex increased with age (regression coefficient, 0.698 micromol/L/week; 95% CI limits: 0.132, 1.265 micromol/L/week) and the latency decreased with age (regression coefficient, -0.9861 micromol/L/week; 95% CI limits: -1.5361, -0.4361 micromol/L/week; age range, 25-38 weeks). The response was modality specific because no response was detected after non-noxious stimulation of the heel, even when accompanied by reflex withdrawal of the foot. We conclude that noxious information is transmitted to the preterm infant cortex from 25 weeks, highlighting the potential for both higher-level pain processing and pain-induced plasticity in the human brain from a very early age.

A postnatal switch in GABAergic control of spinal cutaneous reflexes

GABAergic signalling exerts powerful inhibitory control over spinal tactile and nociceptive processing, but during development GABA can be depolarizing and the functional consequences of this upon neonatal pain processing is unknown. Here we show a postnatal switch in tonic GABA(A) receptor (GABA(A)R) modulation of cutaneous tactile and nociceptive reflexes from excitation to inhibition, but only in the intact spinal cord. Neonatal and 21-day-old (P21) rats were intrathecally treated with one of the GABA(A)R antagonists bicuculline and gabazine, with both compounds dose-dependently decreasing hindpaw mechanical and thermal withdrawal thresholds in P21 rats but increasing them in P3 neonates. Intrathecal gabazine also produced an increase in the cutaneous evoked electromyography (EMG) response of the biceps femoris in P21 rates but lowering the response in neonates. Injections of 3H-gabazine in the L4-L5 region at P3 confirmed that gabazine binding was restricted to the lumbar spinal cord. Spinalization of P3 neonates at the upper thoracic level prior to drug application reversed the behavioural and EMG responses to GABA antagonists so that they resembled those of P21 rats. The effects of spinalization were consistent with gabazine facilitation of ventral root potentials observed in isolated neonatal spinal cord. These data show a marked postnatal developmental switch in GABAergic control of neonatal nociception that is mediated by supraspinal structures and illustrate the importance of studying developmental circuits in the intact nervous system.

Summary proceedings from the neonatal pain-control group

Recent advances in neurobiology and clinical medicine have established that the fetus and newborn may experience acute, established, and chronic pain. They respond to such noxious stimuli by a series of complex biochemical, physiologic, and behavioral alterations. Studies have concluded that controlling pain experience is beneficial with respect to short-term and perhaps long-term outcomes. Yet, pain-control measures are adopted infrequently because of unresolved scientific issues and lack of appreciation for the need for control of pain and its long-term sequelae during the critical phases of neurologic maturation in the preterm and term newborn. The neonatal pain-control group, as part of the Newborn Drug Development Initiative (NDDI) Workshop I, addressed these concerns. The specific issues addressed were (1) management of pain associated with invasive procedures, (2) provision of sedation and analgesia during mechanical ventilation, and (3) mitigation of pain and stress responses during and after surgery in the newborn infant. The cross-cutting themes addressed within each category included (1) clinical-trial designs, (2) drug prioritization, (3) ethical constraints, (4) gaps in our knowledge, and (5) future research needs. This article provides a summary of the discussions and deliberations. Full-length articles on procedural pain, sedation and analgesia for ventilated infants, perioperative pain, and study designs for neonatal pain research were published in Clinical Therapeutics (June 2005).

The effects of early pain experience in neonates on pain responses in infancy and childhood

Iatrogenic pain is commonplace in newborn infants yet we know very little about its long-term effects. This article reviews the evidence for and against the suggestion that painful procedures experienced in the perinatal period influence subsequent pain responses in infancy or in childhood. The evidence suggests that early experiences with pain are associated with altered pain responses later in infancy. The direction of the altered response depends, in part, on the infant's developmental stage (full-term vs preterm), and his or her cumulative experience with pain. Preterm infants that are hospitalized as neonates and subjected to painful procedures appear to have a dampened response to painful procedures later in infancy. Full-term neonates exposed to extreme stress during delivery, or to a surgical procedure, react to later noxious procedures with heightened behavioral responsiveness. Studies in which analgesic agents (local anesthetics or opioids) have been administered prior to noxious procedures demonstrate less procedural pain and a reduction in the magnitude of long-term changes in pain behaviors. The precise determinants of these changes, their extent, and their permanence are not known but they appear to involve noxious stimulus-induced peripheral and central sensitization, as well as classical conditioning.

The development of nociceptive circuits

The study of pain development has come into its own. Reaping the rewards of years of developmental and molecular biology, it has now become possible to translate fundamental knowledge of signalling pathways and synaptic physiology into a better understanding of infant pain. Research has cast new light on the physiological and pharmacological processes that shape the newborn pain response, which will help us to understand early pain behaviour and to design better treatments. Furthermore, it has shown how developing pain circuitry depends on non-noxious sensory activity in the healthy newborn, and how early injury can permanently alter pain processing.

Analgesia and anesthesia for neonates: Study design and ethical issues

OBJECTIVE

The purpose of this article is to summarize the clinical, methodologic, and ethical considerations for researchers interested in designing future trials in neonatal analgesia and anesthesia, hopefully stimulating additional research in this field.

METHODS

The MEDLINE, PubMed, EMBASE, and Cochrane register databases were searched using subject headings related to infant, newborn, neonate, analgesia, anesthesia, ethics, and study design. Cross-references and personal files were searched manually. Studies reporting original data or review articles related to these topics were assessed and critically evaluated by experts for each topical area. Data on population demographics, study characteristics, and cognitive and behavioral outcomes were abstracted and synthesized in a systematic manner and refined by group members. Data synthesis and results were reviewed by a panel of independent experts and presented to a wider audience including clinicians, scientists, regulatory personnel, and industry representatives at the Newborn Drug Development Initiative workshop. Recommendations were revised after extensive discussions at the workshop and between committee members.

RESULTS

Designing clinical trials to investigate novel or currently available approaches for analgesia and anesthesia in neonates requires consideration of salient study designs and ethical issues. Conditions requiring treatment include pain/stress resulting from invasive procedures, surgical operations, inflammatory conditions, and routine neonatal intensive care. Study design considerations must define the inclusion and exclusion criteria, a rationale for stratification, the confounding effects of comorbid conditions, and other clinical factors. Significant ethical issues include the constraints of studying neonates, obtaining informed consent, making risk-benefit assessments, defining compensation or rewards for participation, safety considerations, the use of placebo controls, and the variability among institutional review boards in interpreting federal guidelines on human research. For optimal study design, investigators must formulate well-defined study questions, choose appropriate trial designs, estimate drug efficacy, calculate sample size, determine the duration of the studies, identify pharmacokinetic and pharmacodynamic parameters, and avoid drug-drug interactions. Specific outcome measures may include scoring on pain assessment scales, various biomarkers and their patterns of response, process outcomes (eg, length of stay, time to extubation), intermediate or long-term outcomes, and safety parameters.

CONCLUSIONS

Much more research is needed in this field to formulate a scientifically sound, evidence-based, and clinically useful framework for management of anesthesia and analgesia in neonates. Newer study designs and additional ethical dilemmas may be defined with accumulating data in this field.

Does neonatal surgery lead to increased pain sensitivity in later childhood?

Does pain or tissue damage in early life lead to hyperalgesia persisting into childhood? We performed a cross-sectional study in 164 infants to investigate whether major surgery within the first 3 months of life increases pain sensitivity to subsequent surgery and to elucidate whether subsequent surgery in the same dermatome or in a different dermatome leads to differences in pain sensitivity. All infants received standard intraoperative and postoperative pain management, with rescue analgesia guided by a treatment algorithm. Differences in pain sensitivity during surgery were assessed by the intraoperative fentanyl intake and by (nor)epinephrine plasma concentrations. Differences in postoperative pain sensitivity were assessed by the observational pain measures COMFORT and VAS, and by morphine intake and (nor)epinephrine plasma concentrations. Infants previously operated upon in the same dermatome needed more intraoperative fentanyl, had higher COMFORT and VAS scores, had greater (nor)epinephrine plasma concentrations, and needed also more morphine than did infants with no prior surgery. In contrast, infants who previously underwent surgery in another dermatome had only significant higher postoperative analgesic requirements and norepinephrine plasma concentrations in comparison with infants with no prior surgery. These preliminary differences may indicate the occurrence of spinal and supraspinal changes following neonatal surgery. We conclude that the long-term consequences of surgery in early infancy are greater in areas of prior tissue damage and that these effects may portend limited clinical but important neurobiological differences.

Pain, opioid tolerance and sensitisation to nociception in the neonate

Pain is commonplace in newborn infants. Opioid analgesics have become increasingly used to reduce different types of pain in neonates, including pain from surgery, medical procedures and chronic conditions. Adverse effects of opioids include respiratory depression, hypotension and tolerance. These adverse effects can be minimised by utilising specific administration techniques and constant monitoring. Recent studies have demonstrated that untreated pain can have long-term effects on infant pain behaviours months beyond the events, thus, opioid analgesics may have a beneficial role that extends beyond the immediate painful event(s).