Nociception and the neonatal brain

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.

Effects of automatic heel lancet on invasiveness in neonates: A systematic review and meta-analysis

AIM

We conducted a meta-analysis comparing the invasiveness of automatic lancet devices, which can collect adequate amount of blood at shallow puncture depths, with conventional manual lance devices (lancet or needle) to statistically identify less invasive instruments for neonatal heel lance.

METHODS

We searched PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), CINAHL, and Ichushi databases for studies comparing the invasiveness between automatic lancet and manual lancet or needle in term and preterm neonates in neonatal intensive care unit.

RESULTS

This review included 9 out of 449 searched articles, with 673 neonates. Automatic lancet had significantly lower pain scores (standardised mean difference: -2.0, 95% confidence interval: -3.3 to -0.7), heart rate (mean difference: -8.0, 95% confidence interval: -13.8 to -2.1), cry duration (mean difference: -21.5, 95% confidence interval: -32.5 to -10.4), number of punctures (mean difference: -0.6, 95% confidence interval: -1.1 to -0.2), and duration of procedures (mean difference: -37.7, 95% confidence interval: -75.2 to -0.2) than manual lancet or needle. Furthermore, peripheral oxygen saturation was significantly higher in automatic lancet than in manual lancet or needle (mean difference: 4.5, 95% confidence interval: 0.5-8.5).

CONCLUSION

Automatic heel lancet devices were less invasive than manual heel lance devices (lancet or needle).

Biomarkers for assessing pain and pain relief in the neonatal intensive care unit

Newborns admitted to the neonatal intensive care unit (NICU) regularly undergo painful procedures and may face various painful conditions such as postoperative pain. Optimal management of pain in these vulnerable preterm and term born neonates is crucial to ensure their comfort and prevent negative consequences of neonatal pain. This entails accurate and timely identification of pain, non-pharmacological pain treatment and if needed administration of analgesic therapy, evaluation of treatment effectiveness, and monitoring of adverse effects. Despite the widely recognized importance of pain management, pain assessment in neonates has thus far proven to be a challenge. As self-report, the gold standard for pain assessment, is not possible in neonates, other methods are needed. Several observational pain scales have been developed, but these often rely on snapshot and largely subjective observations and may fail to capture pain in certain conditions. Incorporation of biomarkers alongside observational pain scores holds promise in enhancing pain assessment and, by extension, optimizing pain treatment and neonatal outcomes. This review explores the possibilities of integrating biomarkers in pain assessment in the NICU.

Procedural pain assessment in neonates at risk of neonatal opioid withdrawal syndrome: a scoping review protocol

OBJECTIVE

The objective of this review is to identify evidence on pain assessment during acute procedures in hospitalized neonates at risk of neonatal opioid withdrawal syndrome (NOWS).

INTRODUCTION

While all neonates are routinely exposed to various painful procedures, neonates at risk of NOWS have longer hospital stays and are exposed to multiple painful procedures. NOWS occurs when a neonate is born to a birth parent who identifies as having sustained opioid use (such as morphine or methadone) during pregnancy. Accurate pain assessment and management during painful procedures is critical for minimizing the well-documented adverse effects of unmanaged pain in neonates. While pain indicators and composite pain scores are valid and reliable for healthy neonates, there is no review of evidence regarding procedural pain assessment in neonates at risk of NOWS.

INCLUSION CRITERIA

Eligible studies will include those reporting on hospitalized pre-term and full-term neonates at risk of NOWS having pain assessments (ie, behavioral indicators, physiological indicators, validated composite pain scores) during and/or after exposure to an acute painful procedure.

METHODS

This review will follow the JBI scoping review methodology. Databases to be searched will include MEDLINE (Ovid), CINAHL (EBSCO), Embase, PsyclNFO (EBSCO), and Scopus. The relevant data will be extracted by 2 reviewers using a modified JBI extraction tool. The results will be summarized in narrative and tabular format, including the components of participants, concept, and context (PCC).

REVIEW REGISTRATION

Open Science Framework https://osf.io/fka8s .

Analgesic Electrical Stimulation Combined with Wrist-Ankle Acupuncture Reduces the Cortical Response to Pain in Patients with Myofasciitis: A Randomized Clinical Trial

OBJECTIVE

Transcutaneous electrical nerve stimulation (TENS) based on wrist-ankle acupuncture has been shown to relieve pain levels in patients with myofascial pain syndrome (MPS). However, its efficacy is highly subjective. The purpose of this study was to evaluate the feasibility and effectiveness of TENS based on wrist-ankle acupuncture for pain management in patients with MPS from the perspective of cerebral cortex hemodynamics.

DESIGN, SETTING, PARTICIPANTS AND INTERVENTIONS

We designed a double-blind, randomized, controlled clinical trial. Thirty-one male patients with MPS were randomly assigned to two parallel groups. The experimental group (n = 16) received TENS based on wrist-ankle acupuncture for analgesic treatment, while the control group (n = 15) did not. The pain was induced by mechanically pressurized at acupoint Jianjing. The multichannel functional near-infrared spectroscopy (fNIRS) equipment was utilized for measuring oxyhemoglobin (HbO) levels in the cerebral cortex during the tasks.

RESULTS

After the intervention, visual analog scale (VAS), the activation degree and activation area of pain perception cortices were significantly reduced in the experimental group compared to the baseline values (P < .05). Particularly, Frontopolar Area (FPA), and Dorsolateral Prefrontal Cortex (DLPFC) are highly involved in the pain process and pain modulation.

CONCLUSION

Compared to no intervention, TENS based on wrist-ankle acupuncture can be effective in relieving pain in patients with MPS in terms of cerebral cortical hemodynamics. However, further studies are necessary to quantify the analgesic effect in terms of cerebral hemodynamics and brain activation.

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.

Why pain hurts

We have made great strides in understanding how the human brain constructs the multidimensional experience of pain - both acute and chronic - over the past few decades. Pain wears many guises, but at its core, it hurts. How is this core component of pain represented in the brain, and how can we target it for relief?

The missing mechanistic link: Improving behavioral treatment efficacy for pediatric chronic pain

Pediatric chronic pain is a significant global issue, with biopsychosocial factors contributing to the complexity of the condition. Studies have explored behavioral treatments for pediatric chronic pain, but these treatments have mixed efficacy for improving functional and psychological outcomes. Furthermore, the literature lacks an understanding of the biobehavioral mechanisms contributing to pediatric chronic pain treatment response. In this mini review, we focus on how neuroimaging has been used to identify biobehavioral mechanisms of different conditions and how this modality can be used in mechanistic clinical trials to identify markers of treatment response for pediatric chronic pain. We propose that mechanistic clinical trials, utilizing neuroimaging, are warranted to investigate how to optimize the efficacy of behavioral treatments for pediatric chronic pain patients across pain types and ages.

Developmental Mechanisms of CPSP: Clinical Observations and Translational Laboratory Evaluations

Understanding mechanisms that underly the transition from acute to chronic pain and identifying potential targets for preventing or minimizing this progression have specific relevance for chronic postsurgical pain (CPSP). Though it is clear that multiple psychosocial, family, and environmental factors may influence CPSP, this review will focus on parallels between clinical observations and translational laboratory studies investigating the acute and long-term effects of surgical injury on nociceptive pathways. This includes data related to alterations in sensitivity at different points along nociceptive pathways from the periphery to the brain; age- and sex-dependent mechanisms underlying the transition from acute to persistent pain; potential targets for preventive interventions; and the impact of prior surgical injury. Ongoing preclinical studies evaluating age- and sex-dependent mechanisms will also inform comparative efficacy and preclinical safety assessments of potential preventive pharmacological interventions aimed at reducing the risk of CPSP. In future clinical studies, more detailed and longitudinal peri-operative phenotyping with patient- and parent-reported chronic pain core outcomes, alongside more specialized evaluations of somatosensory function, modulation, and circuitry, may enhance understanding of individual variability in postsurgical pain trajectories and improve recognition and management of CPSP.

Pain in Preterm Infants: Different Perspectives

In the last decades, there has been a tremendous change in approaching and managing neonates' pain. These changes began with rebutting the previous misconception about neonates' , particularly preterm infants' , pain. The development in neuroimaging has revealed that by 24 weeks of gestation the peripheral nervous system is mature and function fully. Researchers now know that neonates experience pain and premature infants have even lower pain thresholds. Since that time, a mounting amount of literature has addressed the issue of neonatal pain. Many pharmacological and non pharmacological pain reduction strategies have been investigated for their safety and analgesic effectiveness. Many interventions such as nonnutritive sucking (NNS), skin-to-skin contact (SSC), and facilitated tucking are effective in controlling neonates pain.

The Long-Term Effects of Neonatal Inflammatory Pain on Cognitive Function and Stress Hormones Depend on the Heterogeneity of the Adolescent Period of Development in Male and Female Rats

Exposure to stress at an early age programs the HPA axis which can lead to cognitive deficits in adults. However, it is not known whether these deficits emerge in adulthood or are expressed earlier in life. The aims of the study were to investigate (1) the immediate effects of early injury-induced stress in one-day-old (P1) and repeated stress on at P1 and P2 rat pups on plasma corticosterone levels; and (2) examine the subsequent long-term effects of this early stress on spatial learning and memory, and stress reactivity in early P26-34 and late P45-53 adolescent male and female rats. Intra-plantar injection of formalin induced prolonged and elevated levels of corticosterone in pups and impaired spatial learning and short- and long-term memory in late adolescent males and long-term memory in early adolescent females. There were sex differences in late adolescence in both learning and short-term memory. Performance on the long-term memory task was better than that on the short-term memory task for all early adolescent male and female control and stressed animals. Short-term memory was better in the late age control rats of both sexes and for formalin treated females as compared with the early age rats. These results are consistent with an impaired function of structures involved in memory (the hippocampus, amygdala, prefrontal cortex) after newborn pain. However, activation of the HPA axis by neonatal pain did not directly correlate with spatial learning and memory outcomes and the consequences of neonatal pain remain are likely multi-determined.

Effects of Temperature and Position Change on Neonatal Brain Regional Oxygen Saturation in Tub Bathing: A Prospective Study

INTRODUCTION

A major goal in neonatal medicine is to reduce stress as much as possible in routine care. Bathing is one of the important routine cares for neonates, but it makes a big environmental change for them. We aimed to examine whether water temperature, room temperature, and position changes in tub bathing serve as noxious stimuli to neonates.

METHODS

This prospective trial was performed in full-term and non-low-birth-weight neonates admitted to the hospital between July 2020 and March 2021. Those with underlying diseases, fetal distress, infection, and other medical conditions were excluded. Measurements were taken during the neonates' first tub bath since birth, which was performed by a trained nurse. Changes in regional oxygen saturation (rSO₂), determined using near-infrared spectroscopy, and water and room temperature, were examined at five different time points: upon entering the bath, head washing, position change, exiting the bath, and during the 3 min after bathing.

RESULTS

In total, 17 neonates were analyzed. No changes in rSO₂ due to head washing or position change were observed; however, rSO₂ significantly decreased upon entering (78.5 ± 4.1% vs. 75.7 ± 4.1%, p < 0.001) and exiting the bath (75.8 ± 5.7% vs. 74.4 ± 5.4%, p < 0.04). The rate change in rSO₂ upon entering the bath showed a significant inverse correlation with water temperature (r =  - 0.53, p < 0.03), and there were no significant correlations between rSO₂ and water or room temperature upon exiting the bath. There was no change in body skin temperature before and after bathing, but rSO₂ gradually decreased during the 3 min after bathing.

CONCLUSIONS

Neonates may perceive certain temperatures during bathing as noxious stimuli. Therefore, methods to minimize stress associated with bathing should be implemented to reduce the difference between water temperature and room temperature during bathing.

TRIAL REGISTRATION

This trial has been registered at UMIN repository with the trial number UMIN000041045 ( https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000046500 ). The date of the final dataset was April 01, 2021.

Effect of glucose and non-nutritive sucking on puncture pain in premature infants: a crossover clinical trial

OBJECTIVE

To compare the effect of non-nutritive sucking, 25% oral glucose and 25% oral glucose combined with non-nutritive sucking in pain relief in premature infants submitted to heel puncture for blood glucose monitoring.

METHOD

This is a randomized crossover clinical trial with 34 preterm infants who randomly received interventions: non-nutritive sucking, 25% oral glucose and the two interventions combined for three consecutive days in heel puncture for blood glucose monitoring. Assessment by the Premature Infant Pain Profile for 30 seconds before the intervention, called the baseline period and for 5 minutes after puncture.

RESULTS

The combination of interventions made the premature infants return to baseline, with 1 minute and 30 seconds after heel puncture, promoting a 2.2% percentage reduction in the scale.

CONCLUSION

Comparing the effect of isolated and combined interventions showed that, when offered in combination, preterm infants were able to return to baseline parameters more quickly. Brazilian Clinical Trials Registry: RBR-3gm6w5.

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.

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.

Pain Control with Lavender Oil in Premature Infants: A Double-Blind Randomized Controlled Study

Objectives: Aromatherapy has become popular in pain control in recent years compared with other complementary methods. Lavender (Lavandula angustifolia Miller) is a fragrant essential oil used in aromatherapy for its antibacterial, antifungal, muscle-relaxing, and analgesic effects. The smell of lavender oil, known for its soothing effect on adults, has not been adequately investigated in regards to pain control in premature infants. The purpose of our study was to assign the effect of the scent of lavender oil on pain in preterm infants during heel lancing. Design: A double-blind randomized controlled clinical study. Settings/Location: The study was conducted in a third-level neonatal intensive care unit of Bezmialem Vakif University Hospital from March 2019 to November 2019. It consisted of two groups. Subjects: Sixty-one premature babies (24-37 weeks of gestation) were enrolled in the study. Interventions: Heel stick sampling for metabolic screening was used for both study groups. The interventions were performed by two experienced nurses. Heart rate, oxygen saturation, and the baby's facial expression were recorded by a camera 3 min before the intervention, during the sampling, and 3 min after the procedure. After collecting the data, the head researcher and the assistant researcher separately watched the videos and scored them by using the Premature Infant Pain Profile-Revised (PIPP-R). Outcome measures: The difference of pain scores (PIIP-R) between two groups. Results: There was a statistically significant difference between the two groups in terms of PIPP-R scores during and after the sampling (p = 0.008 and p = 0.03 respectively). The PIPP-R scores at the beginning of the procedure were not found to be significantly different between the groups (p > 0.05). Conclusions: Inhalation of lavender scent is effective in pain control in premature infants. It is safe and low cost; it does not interfere with medical care.

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.