Skin conductance and the stress response from heel stick in preterm infants

Nociceptive stimuli responses at different levels of general anaesthesia and genetic variability

BACKGROUND

Changes in skin conductance (SC), clinical stress score (CSS), the bispectral index spectroscopy (BIS) index and the variation in the BIS index may be used to monitor responses to nociceptive stimuli. We wanted to examine these methods during noxious stimulation during general anaesthesia and if the responses were associated with variability in genes related to pain.

METHODS

Sixty patients, given propofol to a BIS level of 40-50, were stimulated with standardised tetanic electrical stimuli during propofol infusion, plasma level of 3 μg/ml alone, or together with remifentanil target plasma level of 3 ng/ml or 10 ng/ml. The CSS, SC, BIS index and the variability of the BIS index were registered. The inter-individual variation in nociceptive responses was analysed for co-variation with genotypes of 89 single nucleotide polymorphisms from 23 candidate genes.

RESULTS

During tetanic stimuli, CSS and SC increased significantly and were attenuated with increasing level of remifentanil, different from the BIS index and the variation in the BIS index. Polymorphisms in the P-glycoprotein (ABCB1), tachykinin 1 receptor (TACR1), dopamine receptor D3 (DRD3) and beta arrestin 2 (ARRB2) genes were associated with the co-variation in SC variables or CSS response or both during standardised nociceptive stimuli (P < 0.05). Because of no corrections for multiple testing, the genetic analyses are explorative, and associations must be tested in further studies.

CONCLUSION

This exploratory study suggests genes that may be tested further with relation to nociceptive response during anaesthesia. SC and CSS may be useful tools for monitoring nociceptive response during general anaesthesia.

Outcomes in pain medicine: a brief review

Pain, and particularly chronic pain, is a difficult outcome to measure due to its subjective and multidimensional nature. The Institute of Medicine estimates that 100 million Americans have chronic pain with a cost exceeding half a trillion dollars per year. There is a pressing need to identify appropriate outcome measures to better select and evaluate treatment modalities for these patients. It is also important that we demonstrate an evidence basis for these decisions given the current practice standard. Appropriate selection and implementation of these outcome measures can help accomplish both goals. The purpose of this review is to explore the difficulties and opportunities unique to pain outcome measures. The scope of the problem and impetus for implementation of appropriate measures is initially discussed, followed by requisite evaluation criteria for any measurement instrument. The authors then review frequently employed tools for measuring pain outcomes ranging from univariable and single domain scales to multidimensional instruments. A discussion of possible behavioral and objective measures is pursued, as well as measures of statistical and treatment efficacy. The article closes with a review of recent and ongoing efforts to validate and standardize pain outcome measures and suggests directions for future clinical and research assessment.

Combined esophageal intraluminal impedance, pH and skin conductance monitoring to detect discomfort in GERD infants

BACKGROUND

The clinical significance of weakly acidic reflux in infants is unclear. Skin conductance is a novel not-invasive method to evaluate discomfort. The aim of our study was to evaluate reflux-induced discomfort in infants with gastroesophageal reflux disease using simultaneously combined skin conductance and esophageal multichannel intraluminal impedance and pH monitoring.

METHODOLOGY/PRINCIPAL FINDINGS

Infants with gastroesophageal reflux symptoms were investigated for almost 20 hours divided into 120-second intervals. Temporal relationships between refluxes and discomfort were evaluated calculating the symptom association probability. Twelve infants aged 17-45 days were studied. Out of 194.38 hours of adequate artifact-free MII/pH and skin conductance monitoring, 584 reflux events were observed; 35.78% were positive for stress, of which 16.27% were acid and 83.73% weakly acidic. A significant association between refluxes and discomfort (p<0.05) was present in all infants. The intervals with reflux events showed increased skin conductance values compared to reflux-free intervals (p<0.001); SC values were similar for acid and weakly acidic reflux events. CONCLUSION/SIGNFICANCE: Discomfort was significantly associated with reflux events and did not differ between weakly acidic and acid refluxes. Our results may raise concerns about the over-prescription use of antacid drugs in the management of gastroesophageal reflux symptoms in infancy.

Acute pain therapy in postanesthesia care unit directed by skin conductance: a randomized controlled trial

Background

After surgery, effective and well-directed acute pain therapy is a necessary and integral part of the overall treatment plan. Generally, the assessment of pain intensity depends on a patient’s self-evaluation using scoring systems such as numeric rating scales (NRS, 0 to 10). Recently, a “Pain Monitor” was commercially provided which is based on measurements of fluctuations of skin conductance (NFSC). In this randomized, controlled, single-blind trial, possible benefits of this certain device were studied.

Methods

Postoperative patients (n = 44) were randomly assigned to a test or a control group during their stay in the postanesthesia care unit (PACU). All patients were treated and monitored according to internal hospital standards. Whereas all patients systematically evaluated their pain each 15 min, test group patients were additionally addressed when NFSC exceeded a predefined level. In cases of NRS≥5 during a routine elevation or in between, pain relief was achieved by standard procedures irrespective of group allocation.

Results

During their stay in PACU, both test and control groups experienced a significant decrease in NRS as a consequence of pain therapy. No significant differences in mean NRS or in NFSC values were found between the test and control groups. No correlation was observed between NRS and NFSC.

Conclusion

Postoperative patients experience diverse stressors, such as anxiety, disorientation, shivering, sickness and pain. Although the application of continuous pain monitoring would be meaningful in this clinical setting, the tested device failed to distinguish pain from other stressors in postoperative adult patients.

Trial Registration

German Clinical Trials Register DRKS00000755.

Heart rate, oxygen saturation, and skin conductance: a comparison study of acute pain in Brazilian newborns

Heart rate variability (HRV), oxygen saturation variability (OSV) and skin conductance activity (SCA) are recognized physiological markers of acute pain. In order to verify which of them has the best correlation with psychophysical parameters of pain (intensity, reactivity, direction, regulation and slope), an observational prospective study was performed, including 41 healthy full term newborns. The measurements studied were the HRV, the OSV, and the following SCA variables: number of waves per second (NWps) and relative area under the curve of waves (AUC). The measurements were performed in periods labeled before, during, and after a heel prick. The variation measured for intensity between periods was significant for the NWps (p=0.001), AUC (p=0.03), HRV (p=0.001) and OSV (p=0.004). Also, the reactivity and direction were significant for all variables, except AUC. The regulation parameter was significant for the variables NWps (p<0.01), AUC (p<0.05), HRV (p<0.01) and OSV (p<0.01). The slope was statistically significant only for the OSV variable (p=0.000). We concluded that the responses of the SCA, HRV and OSV to painful events fit the psychophysical parameters of a physiological marker and serve as valuable measures for pain diagnostic working the use in accordance with the needs of the context.

Skin conductance measurements as pain assessment in newborn infants born at 22-27 weeks gestational age at different postnatal age

BACKGROUND

To assess pain or stress in newborn infants submitted to intensive care is important but difficult, as different observational pain scales are not always reliable in premature infants. As an indicator of pain, skin conductance (SC) measurements have detected increased sweating in newborn infants >28 gestational age (GA) submitted to heel lancing.

OBJECTIVE

To measure SC during heel lancing and routine care in newborn infants, born at 22 to 27 GA, with special relation to postnatal age (PNA).

METHODS

In six infants <28+0 GA and 4 infants ≥28+0 GA spontaneous SC activity and behavioural state (Neonatal Pain Agitation and Sedation Scale (N-PASS)) was measured before, during and after each intervention. Measurements were repeated in each patient at different PNA.

RESULTS

Baseline SC prior to intervention took longer time to stabilise and was higher in <28 than in ≥28+0 PNA. The combination of heel lancing and squeezing gave an increased SC in <28 PNA, whereas heel lancing alone gave the same SC response in ≥28+0 PNA. A possibly continued immature response in SC measurements was not observed. Oral glucose admission prior to heel lancing increased SC. Routine care did not give any changes in SC. Except during orogastric tube placement no signs of discomfort or pain could be detected by the neonatal pain, agitation and sedation scale (N-PASS) in <28 PNA.

CONCLUSION

Changes in SC could be detected in infants at <28+0 PNA and related to the combination of heel lancing and squeezing. A maturational development of the SC was observed in infants born <28 GA. SC seems to be able to differentiate between pain and discomfort.

Towards a physiology-based measure of pain: patterns of human brain activity distinguish painful from non-painful thermal stimulation

Pain often exists in the absence of observable injury; therefore, the gold standard for pain assessment has long been self-report. Because the inability to verbally communicate can prevent effective pain management, research efforts have focused on the development of a tool that accurately assesses pain without depending on self-report. Those previous efforts have not proven successful at substituting self-report with a clinically valid, physiology-based measure of pain. Recent neuroimaging data suggest that functional magnetic resonance imaging (fMRI) and support vector machine (SVM) learning can be jointly used to accurately assess cognitive states. Therefore, we hypothesized that an SVM trained on fMRI data can assess pain in the absence of self-report. In fMRI experiments, 24 individuals were presented painful and nonpainful thermal stimuli. Using eight individuals, we trained a linear SVM to distinguish these stimuli using whole-brain patterns of activity. We assessed the performance of this trained SVM model by testing it on 16 individuals whose data were not used for training. The whole-brain SVM was 81% accurate at distinguishing painful from non-painful stimuli (p<0.0000001). Using distance from the SVM hyperplane as a confidence measure, accuracy was further increased to 84%, albeit at the expense of excluding 15% of the stimuli that were the most difficult to classify. Overall performance of the SVM was primarily affected by activity in pain-processing regions of the brain including the primary somatosensory cortex, secondary somatosensory cortex, insular cortex, primary motor cortex, and cingulate cortex. Region of interest (ROI) analyses revealed that whole-brain patterns of activity led to more accurate classification than localized activity from individual brain regions. Our findings demonstrate that fMRI with SVM learning can assess pain without requiring any communication from the person being tested. We outline tasks that should be completed to advance this approach toward use in clinical settings.

Evidence for the need for anaesthesia in the neonate

Neonates are both capable of experiencing pain and memory formation, albeit implicit memory. During surgical procedures, insufficient ablation of the stress response and possible implicit memory formation of intra-operative events might result in adverse early and long-term outcomes. Neonates deserve the same respect as adult patients. It is thus the responsibility of the anaesthetist to provide sufficient anaesthesia for neonates undergoing surgery. A critical approach in weighing the risks and benefits of exposing a neonate to anaesthesia is prudent, and truly elective surgery should be delayed.

Skin conductance variability between and within hospitalised infants at rest

BACKGROUND

Various methods of pain assessment in infants have been trialled in the search for objective, specific, physiologic measures of responses to pain. Skin conductance (SC) measured in the palm of the hand or on the plantar aspect of the foot may be one such measure. SC in these sites reflects the emotional sweating due to sympathetic nerve activity. The skin conductance response (SCR), which results from filling and reabsorption of sweat in the sweat glands, has previously been suggested to be the most sensitive SC parameter of sympathetic nerve activity in response to painful stimulation.

AIM

To study SCRs within and between medically stable hospitalised infants while at rest.

METHODS

SCRs were measured in infants during at least six periods of monitoring in a maximum 48-h period. Behavioural state was recorded throughout the data collection periods.

RESULTS

SC recordings (n=91) from 15 infants during sleep showed that frequency of SCRs varied between 0 and 0.04 SCRs per second (SCRs/s), median 0.002 SCRs/s. 73% of the total variation was within-infant variation, with the remaining 27% of variation due to variation between the mean SCR values of different infants.

CONCLUSION

This pilot study contributes to establishing baseline phasic SC activity in hospitalised infants at rest by measuring SCRs. These data can be used as a reference for future studies to determine the validity and reliability of SC measurement in infants exposed to painful or stressful interventions within a neonatal unit.

Recent advance in patient monitoring

Recent advance in technology has developed a lot of new aspects of clinical monitoring. We can monitor sedation levels during anesthesia using various electroencephalographic (EEG) indices, while it is still not useful for anesthesia depth monitoring. Some attempts are made to monitor the changes in sympathetic nerve activity as one of the indicators of stress, pain/analgesia, or anesthesia. To know the balance of sympathetic and parasympathetic activity, heart rate or blood pressure variability is investigated. For trend of cardiac output, low invasive monitors have been investigated. Improvement of ultrasound enables us to see cardiac structure and function continuously and clearer, increases success rate and decreases complication of central venous puncture and various kinds of nerve blocks. Without inserting an arterial catheter, trends of arterial oxygen tension or carbon dioxide tension can be monitored. Indirect visualization of the airway decreases difficult intubation and makes it easier to teach tracheal intubation. The changes in blood volume can be speculated non-invasively. Cerebral perfusion and metabolism are not ordinary monitored yet, but some studies show their usefulness in management of critically ill. This review introduces recent advances in various monitors used in anesthesia and critical care including some studies of the author, especially focused on EEG and cardiac output. However, the most important is that these new monitors are not almighty but should be used adequately in a limited situation where their meaning is confirmed.

Preterm infants' sympathetic arousal and associated behavioral responses to sound stimuli in the neonatal intensive care unit

PURPOSE

To evaluate the utility of skin conductance (SC) as a measure of autonomic arousal to sound stimuli in preterm infants.

DESIGN

A pilot cross-sectional, correlations study.

SUBJECTS

Eleven preterm infants with a mean gestational age of 31.6 weeks without anomalies or conditions associated with neurodevelopmental delay composed the sample.

METHODS

On days 5-7 of life, the following infant responses were simultaneously recorded in response to naturally occurring sound stimuli in the NICU: real-time measurements of heart rate, respiratory rate, and oxygen saturations; sympathetic-mediated sweating via SC; and behavioral responses using the Newborn Individualized Developmental Care and Assessment Program naturalistic observation. Baseline sound levels (BSL, <55 dBA) and high sound levels (HSL, >65 dBA) were measured to index patterns of response during a nonhandling period preceding care.

RESULTS

Mean heart rate during precare was directly associated with higher SC increases to sound stimuli (r[10] = 0.697, P = .017). The SC during HSL was significantly higher than that during BSL (P < .0001). Males demonstrated higher SC increases to sound stimuli than females (P = .030). Changes in SC induced by increases in sound intensity were associated with lower attention responses (r[10] = -0.92, P < .0001) and lower summated behavioral responses (r[10] = -0.59, P = .054).

CONCLUSION

SC provides a noninvasive, sensitive measure of sympathetic arousal that may not be apparent in behavioral cues or states, or determined by standard physiological responses alone.

Functional skin adaptation in infancy - almost complete but not fully competent

Early postnatal life is a period of active functional reorganization and cutaneous physiological adaptation to the extrauterine environment. Skin as the outermost organ of mammalians is endowed of multiple functions such as protection, secretion, absorption and thermoregulation. Birth stimulates the epidermal barrier maturation and the skin surface acidification especially in premature infants. In full-term infants the developed stratum corneum accomplishes competent barrier function, in contrast to prematures. Complete barrier maturation in preterm infants is fulfilled by 2-4 weeks of the postnatal life. However, in preterms with 23-25 weeks gestational age this process takes longer. Versatile regulatory mechanisms, namely skin surface acidity, calcium ion gradient and nuclear hormone receptors/ligands are interrelated in the complex postnatal newborn adaptation. The skin of newborns is adjusting quickly to the challenging environmental conditions of the postpartum. However, certain functions, for example, microcirculation, continue to develop even beyond the neonatal period, that is, up to the age of 14-17 weeks. Different environmental factors (for instance, dry and cold climate, diapers and cosmetic care procedures) influence the postnatal development of skin functional parameters such as stratum corneum hydration and the permeability barrier especially in premature infants. The aim of this article is to summarize the current knowledge on skin physiology in newborn and infants with a practical approach and to discuss the possible clinical consequences. This review offers the readership a critical and practical overview of skin physiology in newborns and infants. It emphasizes possible new research fields in neonatal and infantile skin physiology.

Pain outcomes: a brief review of instruments and techniques

Pain is a difficult outcome to measure due to its multifaceted and subjective nature. The need for selecting proper outcome measures is high because of the increasing demand for scientifically valid demonstrations of treatment efficacy. This article discusses some basic topics in the measurement of pain outcomes and addresses issues such as statistical versus clinical significance, daily home data collection, appropriate length of outcome measurement packets, and the possibility of objective pain measurements. This article also reviews some of the more commonly used tools for measuring pain and pain-related disability. By selecting the proper tools and employing them correctly, we can obtain highly reliable and valid measures of pain outcomes in research and clinical care.

Measuring preterm cumulative stressors within the NICU: the Neonatal Infant Stressor Scale

BACKGROUND

Stress experiences, while pervasive, are less likely than painful experiences to be managed in still-hospitalised preterm infants.

AIM

We aimed to quantify the severity of common stressors for preterm infants with a view to providing a tool to manage presumed accumulated infant stress.

METHODS AND SUBJECTS

Seventeen doctors and 130 nurses who work in Neonatal Intensive and Special Care Nurseries rated the perceived stress severity of 44 acute events and 24 chronic living conditions for preterm infants at three ages (<28 weeks, 28-32 weeks, >32 weeks post-conceptional age) and for themselves. Acute items (such as heel lance) were organised into nursing, peripheral venous access, peripheral arterial access, central vascular access, ventilation, nutrition, medical procedures, surgery, radiology and miscellaneous categories. Chronic living conditions included items such as receiving intranasal oxygen and having a systemic infection.

RESULTS

Doctors and nurses perceived nearly all items to be stressful to infants to some degree and to be equally stressful across ages. The degree of stress experienced by clinicians themselves was generally low and moderately correlated with presumed infant stress for the same items. Presumed infant stress was inversely related to clinician age.

CONCLUSION

Based on these results we developed the Neonatal Infant Stressor Scale to help track, measure and manage presumed accumulated stress in preterm neonates.

A procedure for the measurement of infant skin conductance and its initial validation using clap induced startle

Studies examining psychophysiologic markers of infant emotional development abound. However, few studies have used skin conductance (SC), though it measure's sympathetic activity, and none have measured SC on infants sitting up and actively engaged with another person, a significant challenge given the measures sensitivity to movement artifact. In this pilot/feasibility study, we present a procedure for measuring infant SC during active engagement with another person who executes a series of startling claps to elicit an SC response. We measured SC on the plantar surface of the foot of seventeen 5-month-old infants. We found unconditioned SC responses that were related to the intensity of physical startle reactions for each clap trial. We also found anticipatory, conditioned SC responses that occurred within 5 s before each clap that occurred when the researcher raised his clasped hands. These conditioned SC responses grew linearly in intensity over trials. We conclude that SC may be a useful addition to the infant researcher's armamentarium and may indeed be used to measure physiologic reactivity in infants even when actively engaged with another person. Addition of SC measurement to research on infant emotion and emotional communication is likely to advance our understanding of the psychophysiologic foundations of infant emotional development.

Skin conductance versus the modified COMFORT sedation score as a measure of discomfort in artificially ventilated children

OBJECTIVE

We wanted to use skin conductance as a measure of increased stress in artificially ventilated children. The aim was to examine how changes in skin conductance, arterial blood pressure, and heart rate are associated with changes in the modified COMFORT sedation score during suction from the trachea. Nociceptive stimulation induces an outgoing sympathetic nervous burst to the skin and the palmar and plantar sweat glands are filled, which creates a skin conductance fluctuation.

METHODS

Twenty children who were 1 day to 11 years of age were studied. All patients were artificially ventilated and circulatory stable. The data were obtained before, during, and 10 minutes after endotracheal suction. The number of skin conductance fluctuations, the amplitude of skin conductance fluctuations, the mean skin conductance level, arterial blood pressure, heart rate, and the modified COMFORT sedation score were recorded and tested from before to during and from during to after suction in the trachea. RESULTS. The number of skin conductance fluctuations, mean skin conductance level, arterial blood pressure, and the modified COMFORT sedation score increased during suction in the trachea, in contrast to heart rate and amplitude of skin conductance fluctuations. The number of skin conductance fluctuations from before to during and from during to after endotracheal suctioning correlated with changes in the modified COMFORT sedation score. This was in contrast to the other variables that did not.

CONCLUSIONS

The number of skin conductance fluctuations during endotracheal suctioning showed better correlation with the increase in the modified COMFORT sedation score than heart rate and arterial blood pressure. Thus, the number of skin conductance fluctuations seems to be an objective supplement to the modified COMFORT sedation score for monitoring increased stress in artificially ventilated and circulatory stable children.

Developmental changes in the responses of preterm infants to a painful stressor

The purpose of this investigation was to examine longitudinally gestational age and developmental differences in preterm infants' self-regulatory abilities in response to a painful stressor, as well as associations between behavioral and cardiovascular responses. Participants included 49 healthy premature infants. Behavioral and cardiovascular responses to a heel stick blood draw were compared between infants of 28-31 and 32-34 weeks' gestation age at birth. Both gestational age groups displayed behavioral and cardiovascular indications of stress in response to the blood draw. However, both shortly after birth and several weeks later, infants born at younger gestational ages (28-31 weeks) were more physiologically reactive. Evidence that the behavioral stress responses of 28-31 weeks' gestation age group preterm infants do not reflect their physiological responses suggests that evaluation of preterm infants' experiences and risk require assessments of both physiology and behavior. The greater stress vulnerability of the 28-31 weeks' gestation group relative to the 32-34 weeks' gestation group and the implications of this for subsequent development are discussed.

Skin conductance compared to a combined behavioural and physiological pain measure in newborn infants

AIM

To assess the ability of galvanic skin response (GSR) to differentiate between tactile and painful stimulation in newborn infants, and to compare this with the ability of the premature infant pain profile (PIPP).

METHODS

Thirty-two healthy full-term infants undergoing routine blood sampling were recruited. In a randomized order they were subjected to tactile and painful stimulation. The three GSR variables conductance baseline level, number of waves per second and mean amplitude of the waves were recorded together with the behavioural and physiological variables of PIPP.

RESULTS

The GSR variables number of waves and amplitude of the waves increased more during painful stimulation than during tactile stimulation, as did also the PIPP score. Receiver operating characteristic curves analysis revealed no significant differences between the studied methods.

CONCLUSION

GSR can differentiate painful from tactile stimulation, but more research is needed to achieve a clinically useful application.

Comparison of skin conductance with entropy during intubation, tetanic stimulation and emergence from general anaesthesia

BACKGROUND

The number of skin conductance fluctuations (NSCF) expresses sympathetic skin nerve activity. The response entropy (RE) measures electromyographic and electroencephalographic activity in the forehead. The state entropy (SE) measures mainly electroencephalographic activity. When the suppression of frontal muscular activity is complete, RE is equal to SE. RE-Delta is defined as SE minus RE. The purposes of this study were to examine whether NSCF and RE-Delta correlate with signs of clinical stress during intubation and tetanic noxious stimulation and to elucidate how rapidly and accurately entropy and NSCF react during emergence from general anaesthesia.

METHODS

Twenty women scheduled for gynaecological laparotomy were studied. During intubation in remifentanil and propofol general anaesthesia, NSCF and RE-Delta were correlated with the clinical stress score. After a wash-out period, two series of tetanic stimuli were given, the first with (R+) and the second without (R-) remifentanil infusion. The tetanic pre-stimuli periods were compared with the tetanic post-stimuli periods, and R+ was compared with R-. During emergence, the responses of entropy and skin conductance were related to the time of extubation.

RESULTS

NSCF correlated well with the clinical stress score during intubation (r(2)= 0.73, P < 0.0005). RE-Delta showed a weaker correlation (r(2)= 0.33, P= 0.007). During tetanic stimuli, the NSCF pre-stimuli level was lower than the post-stimuli level (P < 0.001), and the NSCF R+ response was lower than the NSCF R- response (P= 0.002). RE-Delta did not show similar differences. During emergence, RE reacted before NSCF and SE (P= 0.003).

CONCLUSION

NSCF was better than RE-Delta for the measurement of clinical stress during intubation, and was sensitive to tetanic stimuli at different opioid analgesic levels, by contrast with RE-Delta. Both modalities were able to predict emergence at the end of anaesthesia, but RE was more rapid.

Monitoring of skin conductance to assess postoperative pain intensity

BACKGROUND

Pain is known to alter the electrogalvanic properties of the skin. The aim of this pilot study was to investigate the influence of postoperative pain on skin conductance (SC) readings.

METHODS

After obtaining ethical approval and written informed consent, 25 postoperative patients were asked to quantify their level of pain on a numeric rating scale (NRS, 0-10) at different time points in the recovery room. As a parameter of SC, the number of fluctuations within the mean SC per second (NFSC) was recorded. Simultaneously, the NRS was obtained from patients by a different observer who was blinded to the NFSC values.

RESULTS

Data from 110 readings of 25 patients (14 female, 11 male; 21-67 yr) were included. NFSC showed a significant correlation with the NRS (r=0.625; P<0.01), whereas heart rate and blood pressure showed no or very weak correlation with the NRS. NFSC was significantly different between patients with no (NRS=0), mild (NRS=1-3), moderate (NRS=4-5) and severe (NRS=6-10) pain (no: 0.047, mild: 0.089, moderate: 0.242, severe: 0.263; P<0.0001). Post hoc, a cut-off value for NFSC (0.1) was calculated above which a pain score >3 on the NRS was predicted with sensitivity of 89% and specificity of 74%.

CONCLUSIONS

The severity of postoperative pain significantly influences SC. Using cut-off values, NFSC may prove a useful tool for pain assessment in the postoperative period.

Skin conductance as a measure of pain and stress in hospitalised infants

BACKGROUND

Reliable and valid methods of measuring pain responses in infants continue to be sought as a means of evaluating the effectiveness of pain reduction strategies. Skin conductance has recently been shown to be a promising physiological indicator of pain and stress in premature and term infants.

AIM

To evaluate changes in skin conductance in hospitalised infants under different environmental conditions and during both painful and non-painful procedures.

METHODS

Measurements of skin conductance activity were made in infants under three different environmental temperature conditions (open cot, incubator and overhead radiant heater), during the routine non-painful nursing procedure of either nappy change or oral feeding, and whilst undergoing the painful procedure of heel lancing for blood sampling.

RESULTS

Skin conductance activity in 21 infants was studied on 43 separate occasions. Skin conductance activity was highly variable between infants but did not differ significantly under the three environmental conditions. Routine nursing care did not result in a significant increase in skin conductance activity above baseline; however, on cessation of care there was a significant reduction to levels below baseline (p < 0.05). Conversely, during the heel lance procedure, skin conductance activity significantly increased upon lance (p < 0.05) and remained elevated following completion of the procedure. There were no statistically significant differences between skin conductance activity changes from baseline as a result of routine nursing care compared to that of the heel lance procedure.

CONCLUSION

Due to large variability in skin conductance activity further studies are needed before this technology can be recommended as a clinically useful indicator of pain and stress in neonates.

Summary proceedings from the neonatal pain-control group

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

Analgesia and anesthesia for neonates: Study design and ethical issues

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Skin conductance changes during the first year of life in full-term infants

Skin conductance changes (SCC) reflect the activity in the sympathetic postganglionic cholinergic fibers, which innervate the sweat glands located in the palm of the hand and the sole of the foot. The purpose of this study was to measure the changes in the number of waves per second, the wave amplitude, and the mean skin conductance level during the 1st year of life. During SCC elicited by an auditory stimulus we measured the percentage of infants that responded, the amplitude, latency and recovery times, and any habituation pattern. Thirty-nine full-born, healthy infants were investigated during their 1st and 3rd days of life, at 3 and 10 wk of life, and at 6 and 12 mo of life. The mean skin conductance level (p < 0.001), the number of waves with an amplitude threshold higher than 0.5 and 1.0 micro siemens (p < 0.001), and the amplitude of the waves (p < 0.001) all increased during the first 10 wk of life. The percentage that responded to stimuli increased from 8% to 50%, and the amplitude of the response increased during the first 10 wk of life (p < 0.001). The level of arousal influenced the mean skin conductance level, the number of waves per second, and the amplitude of the waves during the 1st year of life. In conclusion, these results indicate that the part of the sympathetic nervous system associated with arousal develops during the first 10 wk of life.

Skin conductance and behaviour during sensory stimulation of preterm and term infants

AIM

To investigate the responses to painful and tactile stimulation in preterm and term infants in terms of changes in the plantar skin conductance activity (SCA) and behavioural state. Plantar SCA reflects activity in the sympathetic nervous system.

DESIGN

The plantar SCA and behavioural state in response to nociceptive (the heel prick for blood samples, or immunization) and tactile (routine nursery handling) simulation was recorded in four different groups of infants (n=71): Preterm and term neonatal infants (defined here as up to 1 week old), and preterm and term infants in the postneonatal period.

RESULTS

The preterm infants had significant increases in all skin conductance variables during both tactile and nociceptive stimulation (p<0.02), except for wave amplitude when newborns were heel pricked. The term infants displayed a more varied picture, but both the number and amplitude of the waves increased significantly during both procedures in the newborn groups, while the postneonatal groups only showed significant increases in wave amplitude during nociceptive stimulation (p<0.05). Tactile stimulation of the preterm newborn infants produced significantly higher increases in SCA than nociceptive stimulation (p<0.01), while the behavioural state was highest during nociceptive stimulation (p<0.05). A gradual change in this relation was seen with advancing total age.

CONCLUSION

Non-painful sensory stimulation of infants, especially the newborn and preterm ones, can produce equal or higher levels of physiological stress activation than painful stimulation. Repeated nociceptive stimulation probably sensitises the infants to pain.

Skin conductance correlates with perioperative stress

BACKGROUND

Skin conductance (SC) as a measure of emotional state or arousal may be a tool for monitoring surgical stress in anaesthesia. When an outgoing sympathetic nervous burst occurs to the skin, the palmar and plantar sweat glands are filled up, and the SC increases before the sweat is removed and the SC decreases. This creates a SC fluctuation. The purpose of this study was to measure SC during laparoscopic cholecystectomy with propofol and remifentanil anesthaesia and to evaluate whether number and amplitude of SC fluctuations correlate with perioperative stress monitoring.

METHODS

Eleven patients were studied nine times before, during and after anaesthesia. SC was compared to changes in stress measures such as blood pressure, heart rate, norepinephrine and epinephrine levels. SC was also compared to changes in Bispectral index (BIS).

RESULTS

The blood pressure, epinephrine levels and norepinephrine levels were positively correlated with both the number (P < 0.001) and amplitude (P < 0.01) of the SC fluctuations. Moreover, the BIS was positively correlated with the number (P < 0.001) and amplitude (P < 0.001) of the SC fluctuations. Furthermore, during tracheal intubation, the mean levels of the number of SC fluctuations from the 11 patients had the same stress response as measured in changes of the mean levels of norepinephrine. The mean BIS did not show any stress response during tracheal intubation.

CONCLUSION

Number of SC fluctuations may be a useful method for monitoring the perioperative stress.

The development of a software program for analyzing skin conductance changes in preterm infants

OBJECTIVES

Changes in palmar and plantar skin conductance (SC) are due to outgoing bursts in the postganglionic efferent sympathetic cholinergic fibres, which respond to changes in the central arousal state. An apparatus that measures SC by applying an alternating voltage is sensitive enough to measure SC changes in preterm infants. The purpose of this study was to develop a software program for analyzing SC in premature infants.

METHODS

The software program was designed to calculate the number and mean amplitude of the waves and the mean SC changes during a given period. Different pre-set values for minimum amplitude, maximum slope and minimum width of the waves were used in the program and the results were compared with manually counted waves.

RESULTS

For SC waves, the optimal minimum amplitude was found to be 0.015 microS, the maximum slope of the waves could, with the same result, be 1, 2 or 5 microS/s and the optimal width of the waves was found to be unlimited.

CONCLUSIONS

SC in preterm infants is easily analyzed by this software program.

Development of emotional sweating in preterms measured by skin conductance changes

Skin conductance shows the emotional state, as reflected in changes in the sympathetic nervous system. Skin conductance changes (number and amplitude of the waves, as well as mean skin conductance level) were measured in connection with heel prick from 29 weeks gestational age. The purposes of this study were to examine the development of emotional sweating in preterm infants, and to correlate the changes in emotional sweating with the changes in behavioural state. Fifty infants' behavioural state and skin conductance changes were measured for 2 min before, 2 min during, and 2 min after heel prick. Half of the infants were between 29 and 31 weeks gestational age. They were divided into three sub-groups; 0-10, 11-20 and 21-30 days postnatal age. The other half of the infants were between 32 and 34 weeks gestational age and they were divided into three similar sub-groups. They changed their behavioural state 114 times. Infants from 29 weeks gestational age and more than 10 days old showed emotional sweating as measured by the number and amplitude of the waves that were lowest in sleep and highest during crying (p<0.05). The mean skin conductance level mirrored the behavioural state from 34 weeks gestational age (p<0.05).To conclude, skin conductance changes increased with the level of behavioural state from 29 weeks gestational age and more than 10 days postnatal age.