Modulation of developing dorsal horn synapses by tissue injury

The role of time interval elimination on pain control of preterm infants by sucrose administration

PURPOSE

The 2-min time interval of sucrose administration given before minor painful procedures in preterm infants is based on a few limited studies. We aimed to assess availability of sucrose analgesia in emergency states of minor procedural pain by eliminating the 2-min time interval prior to heel lance in preterm infants. The primary outcome was Premature Infants Pain Profile-Revised (PIPP-R) at 30 and 60 s.

METHODS

Healthy 69 preterms undergoing a heel lance, who were assigned randomly to 1 of 2 groups, i.e., group I, with the 2-min time interval of per oral 24% sucrose given prior to heel lance, or group II, without a time interval of per oral 24% sucrose, were recruited. Premature Infants Pain Profile-Revised, crying incidence, duration, and heart rate at 30 and 60 s following heel lance were the outcome measures in this single-center, randomized, prospective study.

RESULTS

The 2 groups did not differ significantly in PIPP-R scores at 30 s (6.63 vs. 6.32, p = .578) and 60 s (5.80 vs. 5.38, p = .478). The crying incidence was similar between the 2 groups (p = .276). The median crying duration was 6 s (range: 1-13 s) in group I and 4.5 s (range: 1-18 s) in group II (p = .226). No significant differences in the heart rates between the 2 groups and the proportion of adverse events by time interval elimination were recorded.

CONCLUSIONS

Eliminating the time interval did not decrease the analgesic effect of orally administered 24% sucrose given prior to heel lance. In emergency states of minor procedural pain, eliminating the 2-min time interval following sucrose administration is safe and efficacious in preterm infants.

Does noninvasive electrical stimulation of acupuncture points reduce heelstick pain in neonates?

AIM

Noninvasive electrical stimulation at acupuncture points (NESAP) for analgesia is used in children, but has not been widely studied in neonates. The purpose of this study was to determine whether NESAP alone or in combination with sucrose relieved heelstick pain in neonates.

METHODS

Term neonates (n = 162) receiving routine heelsticks for newborn screening were enrolled following parental consent. All infants received facilitated tucking and non-nutritive sucking. Neonates were randomised to standard care, sucrose, NESAP or sucrose plus NESAP. NESAP (3.5 mA, 10 Hz) or sham was administered over four acupuncture points. The Premature Infant Pain Profile (PIPP), heart rate variability (HRV) and salivary cortisol were used to measure heelstick pain.

RESULTS

PIPP scores among all four treatment groups increased during heelstick, F (9,119) = 1.95, p = 0.05 and NESAP therapy had no significant effect on PIPP scores. However, PIPP scores from baseline to heelstick increased the most in the two groups not receiving sucrose (p < 0.01). Mean PIPP scores remained below five during the heelstick in all four groups, indicating minimal or no pain. Differences in HRV and salivary cortisol among groups were insignificant.

CONCLUSION

NESAP at 3.5 mA, 10 Hz is not effective in relieving pain during heelsticks in neonates.

Exposure to Early Life Pain: Long Term Consequences and Contributing Mechanisms

From an evolutionary perspective, adaptations of an organism to its early environment are essential for survival. The occurrence of early life perturbation, coincident with increased developmental plasticity, provides a unique opportunity for such adaptations to become programmed and persist throughout life. However, adaptations that are beneficial to maintaining homeostasis in one's early environment may result in extreme response strategies that confer vulnerability or dysfunction later in life. This review summarizes recent findings in human and animal studies demonstrating that early life pain results in a hypo-/hyper-sensitive phenotype in response to acute and persistent pain and stress later in life. Changes in cognition and immune function in response to early life pain have also been observed. Recent data on the neural mechanisms underlying these long-term changes are discussed, as well as potential strategies to minimize the impact of early life pain.

Neonatal sensory nerve injury-induced synaptic plasticity in the trigeminal principal sensory nucleus

Sensory deprivation studies in neonatal mammals, such as monocular eye closure, whisker trimming, and chemical blockade of the olfactory epithelium have revealed the importance of sensory inputs in brain wiring during distinct critical periods. But very few studies have paid attention to the effects of neonatal peripheral sensory nerve damage on synaptic wiring of the central nervous system (CNS) circuits. Peripheral somatosensory nerves differ from other special sensory afferents in that they are more prone to crush or severance because of their locations in the body. Unlike the visual and auditory afferents, these nerves show regenerative capabilities after damage. Uniquely, damage to a somatosensory peripheral nerve does not only block activity incoming from the sensory receptors but also mediates injury-induced neuro- and glial chemical signals to the brain through the uninjured central axons of the primary sensory neurons. These chemical signals can have both far more and longer lasting effects than sensory blockade alone. Here we review studies which focus on the consequences of neonatal peripheral sensory nerve damage in the principal sensory nucleus of the brainstem trigeminal complex.

Electrical maturation of spinal neurons in the human fetus: comparison of ventral and dorsal horn

The spinal cord is critical for modifying and relaying sensory information to, and motor commands from, higher centers in the central nervous system to initiate and maintain contextually relevant locomotor responses. Our understanding of how spinal sensorimotor circuits are established during in utero development is based largely on studies in rodents. In contrast, there is little functional data on the development of sensory and motor systems in humans. Here, we use patch-clamp electrophysiology to examine the development of neuronal excitability in human fetal spinal cords (10-18 wk gestation; WG). Transverse spinal cord slices (300 μm thick) were prepared, and recordings were made, from visualized neurons in either the ventral (VH) or dorsal horn (DH) at 32°C. Action potentials (APs) could be elicited in VH neurons throughout the period examined, but only after 16 WG in DH neurons. At this age, VH neurons discharged multiple APs, whereas most DH neurons discharged single APs. In addition, at 16-18 WG, VH neurons also displayed larger AP and after-hyperpolarization amplitudes than DH neurons. Between 10 and 18 WG, the intrinsic properties of VH neurons changed markedly, with input resistance decreasing and AP and after-hyperpolarization amplitudes increasing. These findings are consistent with the hypothesis that VH motor circuitry matures more rapidly than the DH circuits that are involved in processing tactile and nociceptive information.

Acute pain management in infants and children-Part 1: Pain pathways, pain assessment, and outpatient pain management

The field of pediatric pain management continues to evolve, with ongoing changes in our appreciation of the impact of pain on our fragile patients, a better understanding of how to assess pain, and refinements of the medications and techniques used to provide analgesia to patients with acute pain of various etiologies. The following article reviews the techniques for the assessment of pain, including various age-specific pain scoring systems. The pharmacological management of pain is discussed, including the use of agents that inhibit prostaglandin formation-nonsteroidal anti-inflammatory agents and acetaminophen-as well as the "weak opioids" that are commonly used when oral administration is feasible for the treatment of mild to moderate pain.

Altered nociceptive, endocrine, and dorsal horn neuron responses in rats following a neonatal immune challenge

The neonatal period is characterized by significant plasticity where the immune, endocrine, and nociceptive systems undergo fine-tuning and maturation. Painful experiences during this period can result in long-term alterations in the neurocircuitry underlying nociception, including increased sensitivity to mechanical or thermal stimuli. Less is known about the impact of neonatal exposure to mild inflammatory stimuli, such as lipopolysaccharide (LPS), on subsequent inflammatory pain responses. Here we examine the impact of neonatal LPS exposure on inflammatory pain sensitivity and HPA axis activity during the first three postnatal weeks. Wistar rats were injected with LPS (0.05mg/kg IP, Salmonella enteritidis) or saline on postnatal days (PNDs) 3 and 5 and later subjected to the formalin test at PNDs 7, 13, and 22. One hour after formalin injection, blood was collected to assess corticosterone responses. Transverse spinal cord slices were also prepared for whole-cell patch clamp recording from lumbar superficial dorsal horn neurons (SDH). Brains were obtained at PND 22 and the hypothalamus was isolated to measure glucocorticoid (GR) and mineralocorticoid receptor (MR) transcript expression using qRT-PCR. Behavioural analyses indicate that at PND 7, no significant differences were observed between saline- or LPS-challenged rats. At PND 13, LPS-challenged rats exhibited enhanced licking (p<.01), and at PND 22, increased flinching in response to formalin injection (p<.05). LPS-challenged rats also displayed increased plasma corticosterone at PND 7 and PND 22 (p<.001) but not at PND 13 following formalin administration. Furthermore, at PND 22 neonatal LPS exposure induced decreased levels of GR mRNA and increased levels of MR mRNA in the hypothalamus. The intrinsic properties of SDH neurons were similar at PND 7 and PND 13. However, at PND 22, ipsilateral SDH neurons in LPS-challenged rats had a lower input resistance compared to their saline-challenged counterparts (p<.05). These data suggest neonatal LPS exposure produces developmentally regulated changes in formalin-induced behavioural responses, corticosterone levels, and dorsal horn neuron properties following noxious stimulation later in life. These findings highlight the importance of immune activation during the neonatal period in shaping pain sensitivity later in life. This programming involves both spinal cord neurons and the HPA axis.

Neonatal pain

Effective management of procedural and postoperative pain in neonates is required to minimize acute physiological and behavioral distress and may also improve acute and long-term outcomes. Painful stimuli activate nociceptive pathways, from the periphery to the cortex, in neonates and behavioral responses form the basis for validated pain assessment tools. However, there is an increasing awareness of the need to not only reduce acute behavioral responses to pain in neonates, but also to protect the developing nervous system from persistent sensitization of pain pathways and potential damaging effects of altered neural activity on central nervous system development. Analgesic requirements are influenced by age-related changes in both pharmacokinetic and pharmacodynamic response, and increasing data are available to guide safe and effective dosing with opioids and paracetamol. Regional analgesic techniques provide effective perioperative analgesia, but higher complication rates in neonates emphasize the importance of monitoring and choice of the most appropriate drug and dose. There have been significant improvements in the understanding and management of neonatal pain, but additional research evidence will further reduce the need to extrapolate data from older age groups. Translation into improved clinical care will continue to depend on an integrated approach to implementation that encompasses assessment and titration against individual response, education and training, and audit and feedback.

A meta-analysis of the use of nonsteroidal antiinflammatory drugs for pediatric postoperative pain

BACKGROUND

Opioid side effects are a great concern during the postoperative period in children. Nonsteroidal antiinflammatory drugs (NSAIDs) have been shown to effectively decrease postoperative pain, but their opioid-sparing effect is still controversial. In this present meta-analysis, we investigated the postoperative opioid-sparing effect of NSAIDs in children.

METHODS

A comprehensive literature search was conducted to identify clinical trials using NSAIDs and opioids as perioperative analgesic compounds in children and infants. Outcomes measured were opioid consumption, pain intensity, postoperative nausea and vomiting (PONV), and urinary retention. All outcomes were studied during postanesthesia care unit (PACU) stay and the first 24 postoperative hours. Data from each trial were combined to calculate the pooled odds ratios (ORs) or standardized mean difference (SMD) and their 95% confidence interval.

RESULTS

Twenty-seven randomized controlled studies were analyzed. Perioperative administration of NSAIDs decreased postoperative opioid requirement (both in the PACU and during the first 24 postoperative hours; SMD = -0.66 [-0.84, -0.48] and -0.83 [-1.11, -0.55], respectively), pain intensity in the PACU (SMD = -0.85 [-1.24, -0.47]), and PONV during the first 24 postoperative hours (OR = 0.75 [0.57-0.99]). NSAIDs did not decrease pain intensity during the first 24 postoperative hours (OR = 0.56 [0.26-1.2]) and PONV during PACU stay (OR = 1.02 [0.73-1.44]). Subgroup analysis according to the timing of NSAID administration (intraoperative versus postoperative), type of surgery, or coadministration of paracetamol did not show any influence of these factors on the studied outcomes except the reduction of pain intensity and the incidence of PONV during the first 24 postoperative hours, which were influenced by the coadministration of paracetamol and the type of surgery, respectively.

CONCLUSION

This meta-analysis shows that perioperative NSAID administration reduces opioid consumption and PONV during the postoperative period in children.