Behavioural discrimination of noxious stimuli in infants is dependent on brain maturation

Clinical rating scales for assessing pain in newborn infants

BACKGROUND

Six to nine per cent of all newborn infants require admission to a neonatal intensive care unit (NICU) due to either illness or prematurity. During their stay, these infants are often subjected to many painful procedures that can cause negative long-term consequences. To reduce the negative effects of pain exposure and ensure optimal and safe pain treatment, accurate assessment of pain is necessary. To achieve this, clinicians are dependent on the use of reliable, objective, and standardised clinical rating scales of pain, henceforth referred to as 'rating scales'. Numerous rating scales have been published; however, discrepancies in validity limit their overall applicability in clinical practice and research. Such limitations may lead to an over- or underestimation of pain, resulting in unnecessary sedation or inadequately treated pain, potentially jeopardising infant safety through treatment side effects, including withdrawal symptoms or prolonged discomfort. To date, the majority of rating scales have been developed to assess procedural pain, whilst fewer scales for prolonged pain are available. Premature infants further complicate matters, as they often have a reduced ability to display robust pain behaviour due to their immaturity. Research has also shown that the use of rating scales in clinical practice is suboptimal, due to both inadequate and infrequent implementation alongside inappropriate choice of scale for the specific pain, population, or setting under evaluation. Despite numerous studies investigating the burden of pain in newborn infants, little work has been done to summarise the current evidence on the appropriateness of rating scales for specific types of pain or infant conditions. This has likely been limited by the subjectivity of pain assessment and further complication of assessing such a non-verbal and immature patient population. The immense burden of neonatal pain worldwide has also led to the development of numerous rating scales in various languages, further hindering evidence summation.

OBJECTIVES

To systematically review the literature to compile and describe the development, content, and measurement properties of clinical rating scales for the assessment of pain in newborn infants.

SEARCH METHODS

An Information Specialist systematically searched CENTRAL, PubMed, Embase, and CINAHL. The latest update search is current to July 2023.

SELECTION CRITERIA

We included all study designs that involved the development or testing of a rating scale for assessing pain in newborn infants. We included preterm (born before week 37) and term (born at week 37 or beyond) infants undergoing pain assessment for any medical indication. We also included studies that included healthcare professionals.

DATA COLLECTION AND ANALYSIS

We evaluated clinical rating scales assessing pain in newborn infants using the Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) methodology evaluating content validity, structural validity, internal consistency, reliability, measurement error, hypothesis testing, and cross-cultural validation. We used a modified GRADE approach to assess risk of bias, inconsistency, imprecision, and indirectness.

MAIN RESULTS

We included 79 studies involving a total of 7197 infants, 326 nurses, and 12 physicians. Twenty-seven clinical rating scales were used in 26 countries, with 14 studies evaluating preterm infants, 11 on term infants, 46 on both preterm and term infants, four solely on medical staff, and four on preterm and/or term infants plus medical staff. Following the COSMIN checklist, we found all rating scales to be of very low-certainty evidence, raising concerns regarding their validity, reliability, and applicability in this vulnerable population across diverse clinical settings.

AUTHORS' CONCLUSIONS

Clinical staff should be vigilant when applying the currently available neonatal rating scales. Further development of rating scale content and testing for structural validity are necessary and should be prioritised. Together, they determine the content and structure of rating scales, underpin further testing, including reliability, and their prioritisation will make the greatest contribution to the evidence base for rating scales to assess neonatal pain. Collaborative efforts between clinicians and methodology experts will prevent methodological pitfalls and contribute to improving the validity and reliability of pain-rating scales in neonatology.

The Influence of Postmenstrual Age and Neurological Impairments on the Modified Pain Assessment Tool Score in Infants Admitted to Neonatal Intensive Care: A Retrospective Medical Record Review

Repetitive and prolonged experience of pain by infants in neonatal intensive care units (NICUs) may adversely affect growth and alter pain responses. The degree of infant prematurity and/or presence of neurological impairment (NI) may impact an infant's ability to behaviorally respond to pain. This study aimed to determine whether the scores on the mPAT, a widely used pain assessment tool, is impacted by postmenstrual age (PMA) at assessment, irrespective of neurological impairment. Data from medical records were collected on infants admitted to the NICU who underwent a pain assessment with the modified Pain Assessment Tool (mPAT) between March 2019 and September 2021. Total mPAT, behavioral, and physiological pain scores were independently analyzed using logistic regression to detect differences based on PMA categories (< 33 weeks, 33-36 weeks, ≥ 37 weeks) and presence of NI. Significant differences were indicated when p < 0.05. Of 204 infants sampled, 62% were male, and 71% were born at term-age (i.e., ≥ 37 wks). Thirty-six (18%) infants had a queried or confirmed NI and 28 (14%) infants were postsurgical. Logistic regression analysis showed that neither PMA nor presence of NI predicted pain for total mPAT scores (χ 2 (3) = 3.9, p > 0.05) or physiological scores (χ 2 (3) = 2.7, p > 0.05). Higher behavioral scores were 3.7 times (OR 0.27, 95% CI 0.10-0.77, p = 0.01) more likely in extremely-to-very preterm (< 33 weeks) infants when compared to term (≥ 37 weeks) infants. The mPAT may be suitable for clinicians to utilize when assessing infants in NICUs regardless of PMA or NI status. The higher behavioral responses in younger infants require further investigation in a future prospective study.

Behavioral and physiological pain structures of PIPP-R and parental stress: structural equation modeling approach

BACKGROUND

Although most non-acute pain assessment tools are multi-dimensional (behavioral and physiological measures) in their approach, the outputs of such tools are considered unidimensional. This study aimed to explore and determine the behavioral and physiological pain structures of Premature Infant Pain Profile-Revised (PIPP-R) for neonates and its association with parental stress.

METHODS

This cross-sectional study was conducted in 2022-2023 in Isfahan, Iran. We recruited 400 pre-term infants, i.e. with gestational age (GA) of less than 37weeks who were admitted to the NICU of educational hospitals. PIPP-R and Parental Stressor Scale: Neonatal Intensive Care Unit (PSS: NICU) were used for data gathering. The latent structures of pain and its association with parental stress were explored using latent variable modeling approach.

RESULTS

A two-factor model, i.e. behavioral and physiological pain factors, was extracted, explaining 65% of the total variance. The results of confirmatory factor analysis showed that the identified structures in the exploratory factor analysis could be nearly replicated (CFI = 0.99، TLI = 0.98, RMSEA = 0.001). Behavioral pain structure, independent from gestational age had a significant direct association with parental stress score (β = 0.005, SE = 0.002, p = 0.026).

CONCLUSIONS

The PIPP-R assesses both behavioral and physiological pain factors. We also found that behavioral pain factor was associated with parental stress.

IMPACT

These results may provide a potential clue for physicians, nurses, and parents to manage the pain in preterm infant. The PIPP-R scores in preterm infants consist of "Behavioral and Physiological" pain factors. Single dependence on behavioral indicators (such as facial expression) has some limitations. Multidimensional tools may be the optimal method in detecting pain in preterm infants. Parental stress can affect behavioral pain structure in preterm infants. Intensive care nurses play an effective role in reducing the parental stress and pain severity of these preterm infants by including the help of mothers in procedures and providing them with psychological support.

On the relation of injury to pain-an infant perspective

ABSTRACT

Forty-five years ago, Patrick Wall published his John J Bonica lecture "On the relation of injury to pain."90 In this lecture, he argued that pain is better classified as an awareness of a need-state than as a sensation. This need state, he argued, serves more to promote healing than to avoid injury. Here I reframe Wall's prescient proposal to pain in early life and propose a set of different need states that are triggered when injury occurs in infancy. This paper, and my own accompanying Bonica lecture, is dedicated to his memory and to his unique contribution to the neuroscience of pain. The IASP definition of pain includes a key statement, "through their life experiences, individuals learn the concept of pain."69 But the relation between injury and pain is not fixed from birth. In early life, the links between nociception (the sense) and pain (the need state) are very different from those of adults, although no less important. I propose that injury evokes three pain need states in infancy, all of which depend on the state of maturity of the central nervous system: (1) the need to attract maternal help; (2) the need to learn the concept of pain; and (3) the need to maintain healthy activity dependent brain development.

Brain health in preterm infants: importance of early-life pain and analgesia exposure

"Everyday" exposures in the neonatal period, such as pain, may impact brain health in preterm infants. Specifically, greater exposure to painful procedures in the initial weeks after birth have been related to abnormalities in brain maturation and growth and poorer neurodevelopmental outcomes in preterm infants. Despite an increasing focus on the importance of treating pain in preterm infants, there is a lack of consensus of optimal approaches to managing pain in this population. This may be due to recent findings suggesting that commonly used analgesic and sedative medications in preterm infants may also have adverse effects of brain maturation and neurodevelopmental outcomes. This review provides an overview of potential impacts of pain and analgesia exposure on preterm brain health while highlighting research areas in need of additional investigations for the development of optimal pain management strategies in this population.

Establishing a standardised approach for the measurement of neonatal noxious-evoked brain activity in response to an acute somatic nociceptive heel lance stimulus

BACKGROUND

Electroencephalography (EEG) can be used in neonates to measure brain activity changes that are evoked by noxious events, such as clinically required immunisations, cannulation and heel lancing for blood tests. EEG provides an alternative approach to infer pain experience in infants compared with more commonly used behavioural and physiological pain assessments. Establishing the generalisability and construct validity of these measures will help corroborate the use of brain-derived outcomes to evaluate the efficacy of new or existing pharmacological and non-pharmacological methods to treat neonatal pain. This study aimed to test whether a measure of noxious-evoked EEG activity called the noxious neurodynamic response function (n-NRF), that was originally derived in a sample of term-aged infants at the Oxford John Radcliffe Hospital, UK, in 2017, can reliably distinguish noxious from non-noxious events in two independent datasets collected at University College London Hospital and at Royal Devon & Exeter Hospital. We aimed to reproduce three published results that use this measure to quantify noxious-evoked changes in brain activity. We used the n-NRF to quantify noxious-evoked brain activity to test (i) whether significantly larger noxious-evoked activity is recorded in response to a clinical heel lance compared to a non-noxious control heel lance procedure; (ii) whether the magnitude of the activity evoked by a noxious heel lance is equivalent in independent cohorts of infants; and (iii) whether the magnitude of the noxious-evoked brain activity increases with postmenstrual age (PMA) in premature infants up to 37 weeks PMA. Positive replication of these studies will build confidence in the use of the n-NRF as a valid and reliable pain-related outcome which could be used to evaluate analgesic efficacy in neonates. The protocol for this study was published following peer review (https://doi.org/10.17605/OSF.IO/ZY9MS).

RESULTS

The n-NRF magnitude to a noxious heel lance stimulus was significantly greater than to a non-noxious control heel lance stimulus in both the UCL dataset (n = 60; mean difference .88; 95% confidence interval (CI) .64-1.13; p < .0001) and the Exeter dataset (n = 31; mean difference .31; 95% CI .02-.61; p = .02). The mean magnitude and 90% bootstrap confidence interval of the n-NRF evoked by the heel lance did not meet our pre-defined equivalence bounds of 1.0 ± .2 in either the UCL dataset (n = 72; mean magnitude 1.33; 90% bootstrapped CI 1.18-1.52) or the Exeter dataset (n = 35; mean magnitude .92, 90% bootstrapped CI .74-1.22). The magnitude of the n-NRF to the noxious stimulus was significantly positively correlated with PMA in infants up to 37 weeks PMA (n = 65; one-sided Pearson's R, adjusted for site: .24; 95% CI .06-1.00; p = .03).

CONCLUSIONS

We have reproduced in independent datasets the findings that the n-NRF response to a noxious stimulus is significantly greater than to a non-noxious stimulus, and that the noxious-evoked EEG response increases with PMA. The pre-defined equivalence bounds for the mean magnitude of the EEG response were not met, though this might be due to either inter-site differences such as the lack of calibration of devices between sites (a true negative) or underpowering (a false negative). This reproducibility study provides robust evidence that supports the use of the n-NRF as an objective outcome for clinical trials assessing acute nociception in neonates. Use of the n-NRF in this way has the potential to transform the way analgesic efficacy studies are performed.

An Evidence-Based Discussion of Fetal Pain and Stress

BACKGROUND

The concept of fetal pain results from procedures conducted without anesthesia in preterm newborns and fetuses, which indicate that it is possible to examine fetal pain based on stress hormone, metabolic, and behavioral changes. Anatomical and physiological data suggest that fetuses become capable of processing nociceptive stimuli around midgestation, although the associated changes in fetal brain development remain unclear. What constitutes fetal pain remains controversial in the light of the definition of pain adopted by the International Association for the Study of Pain (IASP), which posits pain as an "unpleasant sensory and emotional experience."

SUMMARY

Here, we examine the notion that human fetuses cannot "experience" pain and potential implications of this claim. We highlight the key scientific evidence related to fetal pain, including clinical studies on pain in fetuses and preterm newborns. We argue that consistent patterns of stress hormones, metabolic changes, body movements, hemodynamic changes, and pain-related facial expressions in fetuses exposed to invasive procedures overcome the need for subjective proof of pain as articulated in the IASP definition. No study to date has conclusively proven the absence of fetal pain beyond the age of viability.

KEY MESSAGES

Based on the current evidence, we propose that all fetuses receive anesthesia regardless of the invasive procedures being performed to guarantee the least possible pain and physiological, behavioral, or hormonal responses without exposing the mother or her baby to unnecessary complications.

Sensory event-related potential morphology predicts age in premature infants

OBJECTIVE

We investigated whether sensory-evoked cortical potentials could be used to estimate the age of an infant. Such a model could be used to identify infants who deviate from normal neurodevelopment.

METHODS

Infants aged between 28- and 40-weeks post-menstrual age (PMA) (166 recording sessions in 96 infants) received trains of visual and tactile stimuli. Neurodynamic response functions for each stimulus were derived using principal component analysis and a machine learning model trained and validated to predict infant age.

RESULTS

PMA could be predicted accurately from the magnitude of the evoked responses (training set mean absolute error and 95% confidence intervals: 1.41 [1.14; 1.74] weeks,p = 0.0001; test set mean absolute error: 1.55 [1.21; 1.95] weeks,p = 0.0002). Moreover, we show that their predicted age (their brain age) is correlated with a measure known to relate to maturity of the nervous system and is linked to long-term neurodevelopment.

CONCLUSIONS

Sensory-evoked potentials are predictive of age in premature infants and brain age deviations are related to biologically and clinically meaningful individual differences in nervous system maturation.

SIGNIFICANCE

This model could be used to detect abnormal development of infants' response to sensory stimuli in their environment and may be predictive of neurodevelopmental outcome.

The fetal pain paradox

Controversy exists as to when conscious pain perception in the fetus may begin. According to the hypothesis of cortical necessity, thalamocortical connections, which do not form until after 24-28 weeks gestation, are necessary for conscious pain perception. However, anesthesiologists and neonatologists treat age-matched neonates as both conscious and pain-capable due to observable and measurable behavioral, hormonal, and physiologic indicators of pain. In preterm infants, these multimodal indicators of pain are uncontroversial, and their presence, despite occurring prior to functional thalamocortical connections, has guided the use of analgesics in neonatology and fetal surgery for decades. However, some medical groups state that below 24 weeks gestation, there is no pain capacity. Thus, a paradox exists in the disparate acknowledgment of pain capability in overlapping patient populations. Brain networks vary by age. During the first and second trimesters, the cortical subplate, a unique structure that is present only during fetal and early neonatal development, forms the first cortical network. In the third trimester, the cortical plate assumes this function. According to the subplate modulation hypothesis, a network of connections to the subplate and subcortical structures is sufficient to facilitate conscious pain perception in the fetus and the preterm neonate prior to 24 weeks gestation. Therefore, similar to other fetal and neonatal systems that have a transitional phase (i.e., circulatory system), there is now strong evidence for transitional developmental phases of fetal and neonatal pain circuitry.

The outcomes of a healing environment and clustering nursing care on premature infants' vital signs, pain, and sleeping

Our study aimed to assess the effects of creating a healing environment and clustering nursing care on premature infants' vital signs, pain, and sleeping. The study had an experimental research design for the control and study group, each with 53 premature infants. We collected the data through the Vital Signs Sheet, Premature Infant Pain Profile, and Neonatal behavioral state. We used T-tests and chi-square tests to assess the differences between groups. There was a highly statistically significant difference between the study and control groups concerning respiration (p-value<0.01) and heart rate, systolic blood pressure, and O² saturation (p-value<0.05). 90.6% of participants in the study group had a mild total premature infant pain profile, while 37.7% of the control group had a moderate total premature infant pain profile score. Applying a healing environment and clustering nursing care significantly improved respiration, heart rate, oxygen saturation, and systolic blood pressure. Furthermore, it increased sleep time and decreased wake state and pain score.

The development of descending serotonergic modulation of the spinal nociceptive network: a life span perspective

The nociceptive network, responsible for transmission of nociceptive signals that generate the pain experience, is not fully developed at birth. Descending serotonergic modulation of spinal nociception, an important part of the pain network, undergoes substantial postnatal maturation and is suggested to be involved in the altered pain response observed in human newborns. This review summarizes preclinical data of the development of descending serotonergic modulation of the spinal nociceptive network across the life span, providing a comprehensive background to understand human newborn pain experience and treatment. Sprouting of descending serotonergic axons, originating from the rostroventral medulla, as well as changes in receptor function and expression take place in the first postnatal weeks of rodents, corresponding to human neonates in early infancy. Descending serotonergic modulation switches from facilitation in early life to bimodal control in adulthood, masking an already functional 5-HT inhibitory system at early ages. Specifically the 5-HT₃ and 5-HT₇ receptors seem distinctly important for pain facilitation at neonatal and early infancy, while the 5-HT_1a, 5-HT_1b, and 5-HT₂ receptors mediate inhibitory effects at all ages. Analgesic therapy that considers the neurodevelopmental phase is likely to result in a more targeted treatment of neonatal pain and may improve both short- and long-term effects. IMPACT: The descending serotonergic system undergoes anatomical changes from birth to early infancy, as its sprouts and descending projections increase and the dorsal horn innervation pattern changes. Descending serotonergic modulation from the rostral ventral medulla switches from facilitation in early life via the 5-HT₃ and 5-HT₇ receptors to bimodal control in adulthood. A functional inhibitory serotonergic system mainly via 5-HT_1a, 5-HT_1b, and 5-HT_2a receptors at the spinal level exists already at the neonatal phase but is masked by descending facilitation.

Premature Infants Display Discriminable Behavioral, Physiological, and Brain Responses to Noxious and Nonnoxious Stimuli

Pain assessment in preterm infants is challenging as behavioral, autonomic, and neurophysiological measures of pain are reported to be less sensitive and specific than in term infants. Understanding the pattern of preterm infants’ noxious-evoked responses is vital to improve pain assessment in this group. This study investigated the discriminability and development of multimodal noxious-evoked responses in infants aged 28–40 weeks postmenstrual age. A classifier was trained to discriminate responses to a noxious heel lance from a nonnoxious control in 47 infants, using measures of facial expression, brain activity, heart rate, and limb withdrawal, and tested in two independent cohorts with a total of 97 infants. The model discriminates responses to the noxious from the nonnoxious procedure with an overall accuracy of 0.76–0.84 and an accuracy of 0.78–0.79 in the 28–31-week group. Noxious-evoked responses have distinct developmental patterns. Heart rate responses increase in magnitude with age, while noxious-evoked brain activity undergoes three distinct developmental stages, including a previously unreported transitory stage consisting of a negative event-related potential between 30 and 33 weeks postmenstrual age. These findings demonstrate that while noxious-evoked responses change across early development, infant responses to noxious and nonnoxious stimuli are discriminable in prematurity.

The impact of premature extrauterine exposure on infants' stimulus-evoked brain activity across multiple sensory systems

Prematurity can result in widespread neurodevelopmental impairment, with the impact of premature extrauterine exposure on brain function detectable in infancy. A range of neurodynamic and haemodynamic functional brain measures have previously been employed to study the neurodevelopmental impact of prematurity, with methodological and analytical heterogeneity across studies obscuring how multiple sensory systems are affected. Here, we outline a standardised template analysis approach to measure evoked response magnitudes for visual, tactile, and noxious stimulation in individual infants (n = 15) using EEG. By applying these templates longitudinally to an independent cohort of very preterm infants (n = 10), we observe that the evoked response template magnitudes are significantly associated with age-related maturation. Finally, in a cross-sectional study we show that the visual and tactile response template magnitudes differ between a cohort of infants who are age-matched at the time of study but who differ according to whether they are born during the very preterm or late preterm period (n = 10 and 8 respectively). These findings demonstrate the significant impact of premature extrauterine exposure on brain function and suggest that prematurity can accelerate maturation of the visual and tactile sensory system in infants born very prematurely. This study highlights the value of using a standardised multi-modal evoked-activity analysis approach to assess premature neurodevelopment, and will likely complement resting-state EEG and behavioural assessments in the study of the functional impact of developmental care interventions.

Toward personalized medicine for pharmacological interventions in neonates using vital signs

Vital signs, such as heart rate and oxygen saturation, are continuously monitored for infants in neonatal care units. Pharmacological interventions can alter an infant's vital signs, either as an intended effect or as a side effect, and consequently could provide an approach to explore the wide variability in pharmacodynamics across infants and could be used to develop models to predict outcome (efficacy or adverse effects) in an individual infant. This will enable doses to be tailored according to the individual, shifting the balance toward efficacy and away from the adverse effects of a drug. Pharmacological analgesics are frequently not given in part due to the risk of adverse effects, yet this exposes infants to the short‐ and long‐term effects of painful procedures. Personalized analgesic dosing will be an important step forward in providing safer effective pain relief in infants. The aim of this paper was to describe a framework to develop predictive models of drug outcome from analysis of vital signs data, focusing on analgesics as a representative example. This framework investigates changes in vital signs in response to the analgesic (prior to the painful procedure) and proposes using machine learning to examine if these changes are predictive of outcome—either efficacy (with pain response measured using a multimodal approach, as changes in vital signs alone have limited sensitivity and specificity) or adverse effects. The framework could be applied to both preterm and term infants in neonatal care units, as well as older children. Sharing vital signs data are proposed as a means to achieve this aim and bring personalized medicine rapidly to the forefront in neonatology.

Pain Behavioural Response to Acoustic and Light Environmental Changes in Very Preterm Infants

Noise and high light illumination in the neonatal intensive care unit (NICU) are recognized as stressors that could alter the well-being and development of vulnerable preterm infants. This prospective observational study evaluated the pain behaviours of very preterm infants (VPIs) to sound peaks (SPs) and light levels variations (LLVs) in the NICU. We measured spontaneously occurring SPs and LLVs in the incubators of 26 VPIs over 10 h. Their behavioural responses were analysed through video recordings using the "Douleur Aigue du Nouveau-né" (DAN) scale. We compared the maximum DAN scores before and after environmental stimuli and the percentage of VPIs with a score ≥ 3 according to the type of stimuli. A total of 591 SPs and 278 LLVs were analysed. SPs of 5 to 15 dBA and LLVs significantly increased the maximum DAN scores compared to baseline. The occurrence of DAN scores ≥ 3 increased with both stressors, with a total of 16% of SPs and 8% of LLVs leading to quantifiable pain behaviour. Altogether, this study shows that VPIs are sensitive to SPs and LLVs, with a slighter higher sensitivity to SPs. The mechanisms leading to pain behaviours induced by noise and light changes should be evaluated further in the context of VPIs brain development. Our results provide further arguments to optimize the NICU sensory environment of neonatal units and to adapt it to the expectations and sensory abilities of VPIs.

Prediction of Nociception in Children Using the Nociceptive Flexion Reflex Threshold and the Bispectral Index-A Prospective Exploratory Observational Study

OBJECTIVES

The prediction of patient responses to potentially painful stimuli remains a challenge in PICUs. We investigated the ability of the paintracker analgesia monitor (Dolosys GmbH, Berlin, Germany) measuring the nociceptive flexion reflex threshold, the cerebral sedation monitor bispectral index (Medtronic, Dublin, Ireland), the COMFORT Behavior, and the modified Face, Legs, Activity, Cry, Consolability Scale scores to predict patient responses following a noxious stimulus.

DESIGN

Single-center prospective exploratory observational study.

SETTING

Fourteen-bed multidisciplinary PICU at the University Children's Hospital, University Medical Center Hamburg Eppendorf, Germany.

PATIENTS

Children on mechanical ventilation receiving analgesic and sedative medications.

INTERVENTIONS

Noxious stimulation by way of endotracheal suctioning.

MEASUREMENTS AND MAIN RESULTS

Two independent observers assessed modified Face, Legs, Activity, Cry, Consolability and COMFORT Behavior Scales scores during noxious stimulation (n = 59) in 26 patients. Vital signs were recorded immediately before and during noxious stimulation; bispectral index and nociceptive flexion reflex threshold were recorded continuously. Mean prestimulation bispectral index (55.5; CI, 44.2-66.9 vs 39.9; CI, 33.1-46.8; p = 0.007), and COMFORT Behavior values (9.5; CI, 9.2-13.2 vs 7.5; CI, 6.7-8.5; p = 0.023) were significantly higher in observations with a response than in those without a response. Prediction probability (Pk) values for patient responses were high when the bispectral index was used (Pk = 0.85) but only fair when the nociceptive flexion reflex threshold (Pk = 0.69) or COMFORT Behavior Scale score (Pk = 0.73) was used. A logistic mixed-effects model confirmed the bispectral index as a significant potential predictor of patient response (p = 0.007).

CONCLUSIONS

In our sample of ventilated children in the PICU, bispectral index and nociceptive flexion reflex threshold provided good and fair prediction accuracy for patient responses to endotracheal suctioning.

Quantifying the pharmacodynamics of morphine in the treatment of postoperative pain in preverbal children

While the pharmacokinetics of morphine in children have been studied extensively, little is known about the pharmacodynamics of morphine in this population. Here, we quantified the concentration‐effect relationship of morphine for postoperative pain in preverbal children between 0 and 3 years of age. For this, we applied item response theory modeling in the pharmacokinetic/pharmacodynamic analysis of COMFORT‐Behavior (COMFORT‐B) scale data from 2 previous clinical studies. In the model, we identified a sigmoid maximal efficacy model for the effect of morphine and found that in 26% of children, increasing morphine concentrations were not associated with lower pain scores (nonresponders to morphine up‐titration). In responders to morphine up‐titration, the COMFORT‐B score slowly decreases with increasing morphine concentrations at morphine concentrations >20 ng/mL. In nonresponding children, no decrease in COMFORT‐B score is expected. In general, lower baseline COMFORT‐B scores (2.1 points on average) in younger children (postnatal age <10.3 days) were found. Based on the model, we conclude that the percentage of children at a desirable COMFORT‐B score is maximized at a morphine concentration between 5 and 30 ng/mL for children aged <10 days, and between 5 and 40 ng/mL for children >10 days. These findings support a dosing regimen previously suggested by Krekels et al, which would put >95% of patients within this morphine target concentration range at steady state. Our modeling approach provides a promising platform for pharmacodynamic research of analgesics and sedatives in children.

Exploration and Validation of Behavioral Pain Measures and Physiological Pain Measures Factor Structure Extracted From the Pain Assessment Tool Item Scores for Infants Admitted to Neonatal Intensive Care

OBJECTIVE

The objective of the study was to explore and then validate the factor structure of the Pain Assessment Tool (PAT).

MATERIALS AND METHODS

A retrospective medical record review was performed of all infants who were admitted to a neonatal intensive care unit between 2008 and 2018 and had 1 PAT assessment (n=2111). Scores on items of the PAT were collected. Infants were randomized to either the principal component analysis (n=1100) to explore the factor structure or confirmatory factor analysis (n=1011).

RESULTS

Infants in the 2 samples were demographically comparable. A 2-factor model, consisting of factors Behavioral and Physiological Pain Measures, was extracted, explaining 39.8% of the total variance. There was a low interfactor correlation (r=0.12), and both Behavioral (r=0.59) and Physiological Pain (r=0.37) Measures factor scores were correlated with nurses' perception of pain scores. When the frequencies in the gestational age at birth categories were compared between upper and lower quartile score infants, there was more with pain at preterm than at term (χ2(3)=44.9, P<0.001) for the Physiological Pain Measures factor, whereas Behavioral Pain Measures frequency was higher at term than at preterm (χ2(3)=8.1, P<0.043). A similar pattern was observed for postmenstrual age at assessment categories: Behavioral Pain Measures (χ2(3)=41.8, P<0.001) Physiological Pain Measures (χ2(3)=46.1, P<0.001). The 2-factor correlated model performed better at explaining the observed variances: (χ2(13)=41.6, P<0.001) compared with rival models.

DISCUSSION

The PAT assesses both Behavioral Pain and Physiological Pain Measures, and these dimensions need to be considered separately when assessing pain in infants in the neonatal intensive care unit. Behavioral item scores may be insufficient for detecting pain in premature infants if used alone.

Quantifying noxious-evoked baseline sensitivity in neonates to optimise analgesic trials

Despite the high burden of pain experienced by hospitalised neonates, there are few analgesics with proven efficacy. Testing analgesics in neonates is experimentally and ethically challenging and minimising the number of neonates required to demonstrate efficacy is essential. EEG (electroencephalography)-derived measures of noxious-evoked brain activity can be used to assess analgesic efficacy; however, as variability exists in neonate's responses to painful procedures, large sample sizes are often required. Here, we present an experimental paradigm to account for individual differences in noxious-evoked baseline sensitivity which can be used to improve the design of analgesic trials in neonates. The paradigm is developed and tested across four observational studies using clinical, experimental, and simulated data (92 neonates). We provide evidence of the efficacy of gentle brushing and paracetamol, substantiating the need for randomised controlled trials of these interventions. This work provides an important step towards safe, cost-effective clinical trials of analgesics in neonates.

The influence of breastfeeding on cortical and bio-behavioural indicators of procedural pain in newborns: Findings of a randomized controlled trial

AIMS

The objective of this study was to compare the influence of breastfeeding and 24% oral sucrose on pain-related electrophysiologic activity, bio-behavioural pain scores, physiologic recovery, and adverse events during heel lance.

STUDY DESIGN

Single-blind randomized controlled trial.

SUBJECTS

39 full-term infants were randomized to receive breastfeeding or 0.24 mL of 24% oral sucrose plus offered non-nutritive sucking 2 min prior to heel lance.

OUTCOME MEASURES

The primary outcome of pain-related potential was recorded on electroencephalogram. Secondary outcomes included Premature Infant Pain Profile - Revised (PIPP-R) score, physiologic recovery, and adverse events. Data were analyzed per protocol (ClinicalTrials.gov: NCT03272594).

RESULTS

Between November 2017 and January 2019, 20 infants were randomized to breastfeeding and 19 infants to receive oral sucrose. Infants who were breastfeeding had an appreciably smaller, yet not statistically different (F[1,15.9] = 0.58, p = 0.64, SE = 11.79), amplitude pain-related potential (peak amplitude 0.29 μV) following heel lance compared to infants who received oral sucrose (peak amplitude 8.97 μV). Mean PIPP-R scores were not statistically significantly different between groups following heel lance, however, they were indicative of low pain across groups. Mean time in seconds to physiologic recovery was faster in breastfeeding infants (M = 17.5, SD = 31.1) compared to oral sucrose (M = 70.8, SD = 144.3). There were no safety concerns.

DISCUSSION

Breastfeeding and oral sucrose both reduce bio-behavioural responses to pain, however, may differentially modulate pain response in the infant brain. Further research to understand the neurophysiologic effects of these interventions during acute painful procedures is needed.

The burden of early life stress on the nociceptive system development and pain responses

For a long time, the capacity of the newborn infant to feel pain was denied. Today it is clear that the nociceptive system, even if still immature, is functional enough in the newborn infant to elicit pain responses. Unfortunately, pain is often present in the neonatal period, in particular in the case of premature infants which are subjected to a high number of painful procedures during care. These are accompanied by a variety of environmental stressors, which could impact the maturation of the nociceptive system. Therefore, the question of the long-term consequences of early life stress is a critical question. Early stressful experience, both painful and non-painful, can imprint the nociceptive system and induce long-term alteration in brain function and nociceptive behavior, often leading to an increase sensitivity and higher susceptibility to chronic pain. Different animal models have been developed to understand the mechanisms underlying the long-term effects of different early life stressful procedures, including pain and maternal separation. This review will focus on the clinical and preclinical data about early life stress and its consequence on the nociceptive system.

Can Event-Related Potentials Evoked by Heel Lance Assess Pain Processing in Neonates? A Systematic Review

To clarify the possibility of event-related potential (ERP) evoked by heel lance in neonates as an index of pain assessment, knowledge acquired by and problems of the methods used in studies on ERP evoked by heel lance in neonates were systematically reviewed, including knowledge about Aδ and C fibers responding to noxious stimuli and Aβ fibers responding to non-noxious stimuli. Of the 863 reports searched, 19 were selected for the final analysis. The following points were identified as problems for ERP evoked by heel lance in neonates to serve as a pain assessment index: (1) It is possible that the ERP evoked by heel lance reflected the activation of Aβ fibers responding to non-noxious stimuli and not the activation of Aδ or C fibers responding to noxious stimulation; (2) Sample size calculation was presented in few studies, and the number of stimulation trials to obtain an averaged ERP was small. Accordingly, to establish ERP evoked by heel lance as a pain assessment in neonates, it is necessary to perform a study to clarify ERP evoked by Aδ- and C-fiber stimulations accompanied by heel lance in neonates.

Distinct Age-Dependent C Fiber-Driven Oscillatory Activity in the Rat Somatosensory Cortex

When skin afferents are activated, the sensory signals are transmitted to the spinal cord and eventually reach the primary somatosensory cortex (S1), initiating the encoding of the sensory percept in the brain. While subsets of primary afferents mediate specific somatosensory information from an early age, the subcortical pathways that transmit this information undergo striking changes over the first weeks of life, reflected in the gradual emergence of specific sensory behaviors. We therefore hypothesized that this period is associated with differential changes in the encoding of incoming afferent volleys in S1. To test this, we compared S1 responses to A fiber skin afferent stimulation and A + C skin afferent fiber stimulation in lightly anaesthetized male rats at postnatal day (P)7, P14, P21, and P30. Differences in S1 activity following A and A + C fiber stimulation changed dramatically over this period. At P30, A + C fiber stimulation evoked significantly larger γ, β, and α energy increases compared with A fiber stimulation alone. At younger ages, the changes in S1 oscillatory activity evoked by the two afferent volleys were not significantly different. Silencing TRPV1+ C fibers with QX-314 significantly reduced the γ and β S1 oscillatory energy increases evoked by A + C fibers, at P30 and P21, but not at younger ages. Thus, C fibers differentially modulate S1 oscillatory activity only from the third postnatal week, well after the functional maturation of the somatosensory cortex. This age-related change in afferent evoked S1 oscillatory activity may underpin the maturation of sensory discrimination in the developing brain.

Inferring pain experience in infants using quantitative whole-brain functional MRI signatures: a cross-sectional, observational study

Background

In the absence of verbal communication, it is challenging to infer an individual's sensory and emotional experience. In communicative adults, functional MRI (fMRI) has been used to develop multivariate brain activity signatures, which reliably capture elements of human pain experience. We aimed to translate whole-brain fMRI signatures that encode pain perception in adults to the newborn infant brain, to advance understanding of functional brain development and pain perception in early life.

Methods

In this cross-sectional, observational study, we recruited adults at the University of Oxford (Oxford, UK) and infants on the postnatal wards of John Radcliffe Hospital (Oxford, UK). Healthy full-term infants were eligible for inclusion if they were clinically stable, self-ventilating in air, and had no neurological abnormalities. Infants were consecutively recruited in two cohorts (A and B) due to the installation of a new fMRI scanner using the same recruitment criteria. Adults (aged ≥18 years) were eligible if they were postgraduate students or staff at the University of Oxford. Participants were stimulated with low intensity nociceptive stimuli (64, 128, 256, and 512 mN in adults; 64 and 128 mN in infants) during acquisition of fMRI data. fMRI pain signatures (neurologic pain signature [NPS] and stimulus intensity independent pain signature-1 [SIIPS1]), and four control signatures (the vicarious pain signature, the picture-induced negative emotion signature [PINES], the social rejection signature, and a global signal signature) were applied directly to the adult data and translated to the infant brain. We assessed the concordance of the signatures with the brain responses of adults and infants using cosine similarity scores, and we assessed stimulus intensity encoding of the signature responses using a Spearman rank correlation test. We also assessed brain activity in pro-pain and anti-pain components of the signatures.

Findings

Between May 22, 2013, and Jan 29, 2018, we recruited ten healthy participants to the adult cohort (five women and five men; mean age 28·3 years [range 23-36]), 15 infants to infant cohort A (six girls and nine boys; mean postnatal age 4 days [range 1-11]), and 22 infants to infant cohort B (11 girls and 11 boys; mean postnatal age 3 days [range 1-10]). The NPS was activated in both the adults and infants, and reliably encoded stimulus intensity. The NPS was activated in the adult cohort (p<0·0001) and both infant cohorts (p=0·048 for infant cohort A; p=0·001 for infant cohort B). The SIIPS1 was only expressed in adults. Pro-pain brain regions showed similar activation patterns in adults and infants, whereas responses in anti-pain brain regions were divergent.

Interpretation

Basic intensity encoding of nociceptive information is similar in adults and infants. However, translation of adult brain signatures to infants indicated substantial differences in infant cerebral processing of nociceptive information, which might reflect their absence of expectation, motivation, and contextualisation associated with pain. This study expands the use of brain activity pain signatures to non-verbal patients and provides a potential research approach to assess the impact of analgesic interventions on brain function in infants.

Funding

Wellcome Trust, Supporting the Sick Newborn and their Parents Medical Research Fund.

Methodological Issues in the Study of the Development of Pain Responsivity in Preterm Neonates: A Systematic Review

The study of the development of neonatal pain responses is of key importance, both for research and for clinical reasons, with particular regard to the population of preterm neonates, given the amount of painful procedures they are exposed to on a daily basis. The aim of this work was to systematize our knowledge about the development of pain responses in prematurely born neonates by focusing on some key methodological issues. Studies on the impact of age variables, namely gestational age (GA), postmenstrual age (PMA) and chronological age (CH), on pain responsivity in premature neonates were identified using Medline and Scopus. Studies (N = 42) were categorized based on terminological and methodological approaches towards age variables, and according to output variables considered (facial, nonfacial behavioral, physiological). Distinct multidimensional developmental patterns were found for each age-sampling strategy. Overall, each of the three age variables seems to affect pain responsivity, possibly differently across age windows. Targeted as well as integrated approaches, together with a renewed attention for methodological consistency, are needed to further our knowledge on this topic.

Acute pain measured with the modified Bernese Pain Scale for Neonates is influenced by individual contextual factors

BACKGROUND

Individual contextual factors like gestational age (GA) or previous painful experiences have an influence on neonates' pain responses and may lead to inaccurate pain assessment when not appropriately considered.

OBJECTIVES

We set out to determine the influence of individual contextual factors on variability in pain response in neonates, measured with the modified Bernese Pain Scale for Neonates (BPSN), and, if necessary, to incorporate relevant individual factors into a revised version of the BPSN.

METHODS

We videotaped 154 full-term and preterm neonates of different GAs during 1-5 capillary heel sticks in their first 14 days of life. For each heel stick, we produced three video sequences: baseline, heel stick, and recovery. The randomized sequences were rated on the BPSN by five blinded nurses. Individual contextual factors were retrospectively extracted from patient charts and from the video recordings. We analysed the data in single and multiple linear mixed models.

RESULTS

Premature birth (b = -0.721), caffeine (b = -0.302), and the behavioural states quiet and awake (b = -0.283), active and asleep (b = -0.158), and quiet and asleep (b = -0.498) were associated with changes in behavioural pain scores. Premature birth (b = -0.232), mechanical ventilation (b = -0.196), and duration of the heel stick procedure (b = 0.0004) were associated with changes in physiological pain scores. Premature birth (b = -0.907), Caffeine (b = -0.402), the behavioural states quiet and awake (b = -0.274), and quiet and asleep (b = -0.459), and duration of the heel stick procedure (b = 0.001) were associated with changes in the modified BPSN total scores.

CONCLUSIONS

Postmenstrual age, behavioural state, caffeine, and ventilation status have an influence on neonates' pain response and should be incorporated in the revised BPSN to enhance clinical pain assessment in neonates with different GAs.

SIGNIFICANCE

We identified individual contextual factors associated with dampened pain response in neonates and will incorporate them into a revised version of the Bernese Pain Scale for Neonates to provide clinicians with a tool they can use to more accurately assess and manage pain in this vulnerable population.

Early Neonatal Pain-A Review of Clinical and Experimental Implications on Painful Conditions Later in Life

Modern health care has brought our society innumerable benefits but has also introduced the experience of pain very early in life. For example, it is now routine care for newborns to receive various injections or have blood drawn within 24 h of life. For infants who are sick or premature, the pain experiences inherent in the required medical care are frequent and often severe, with neonates requiring intensive care admission encountering approximately fourteen painful procedures daily in the hospital. Given that much of the world has seen a steady increase in preterm births for the last several decades, an ever-growing number of babies experience multiple painful events before even leaving the hospital. These noxious events occur during a critical period of neurodevelopment when the nervous system is very vulnerable due to immaturity and neuroplasticity. Here, we provide a narrative review of the literature pertaining to the idea that early life pain has significant long-term effects on neurosensory, cognition, behavior, pain processing, and health outcomes that persist into childhood and even adulthood. We refer to clinical and pre-clinical studies investigating how early life pain impacts acute pain later in life, focusing on animal model correlates that have been used to better understand this relationship. Current knowledge around the proposed underlying mechanisms responsible for the long-lasting consequences of neonatal pain, its neurobiological and behavioral effects, and its influence on later pain states are discussed. We conclude by highlighting that another important consequence of early life pain may be the impact it has on later chronic pain states-an area of research that has received little attention.

Multimodal pain assessment improves discrimination between noxious and non‐noxious stimuli in infants

Infants in neonatal intensive care units frequently experience clinically necessary painful procedures, which elicit a range of behavioral, physiological, and neurophysiological responses. However, the measurement of pain in this population is a challenge and no gold standard exists. The aim of this study was to investigate how noxious‐evoked changes in facial expression, reflex withdrawal, brain activity, heart rate, and oxygen saturation are related and to examine their accuracy in discriminating between noxious and non‐noxious stimuli. In 109 infants who received a clinically required heel lance and a control non‐noxious stimulus, we investigated whether combining responses across each modality, or including multiple measures from within each modality improves our ability to discriminate the noxious and non‐noxious stimuli. A random forest algorithm was used to build data‐driven models to discriminate between the noxious and non‐noxious stimuli in a training set which were then validated in a test set of independent infants. Measures within each modality were highly correlated, while different modalities showed less association. The model combining information across all modalities had good discriminative ability (accuracy of 0.81 in identifying noxious and non‐noxious stimuli), which was higher than the discriminative power of the models built from individual modalities. This demonstrates the importance of including multiple modalities in the assessment of infant pain.

Developmental neurobiology as a guide for pharmacological management of pain in neonates

Pain in newborn children should be prevented due to negative short- and long-term consequences. A good understanding of the development of the nociceptive system in newborns is necessary to enable optimal pain assessment, and most importantly to treat and prevent pain adequately in neonates. So far, preclinical juvenile animal studies have led to a tremendous amount of information regarding the development of the nociceptive system. In addition, they have made clear that the developmental stage of the nociceptive system may influence the mechanism of action of different classes of analgesics. Age specific analgesic therapy, based on post-menstrual age, should therefore be considered by incorporating information on the developmental stages of the nociceptive system in combination with knowledge from pharmacokinetic and -dynamic studies in neonates.