The association between physiological and behavioral pain measures in 0- to 3-year-old infants after major surgery

Reliability and validity of the pain observation scale for young children and the visual analogue scale in children with burns

The aim of this study was to assess if the pain observation scale for young children (POCIS) and the visual analogue scale (VAS) are reliable and valid instruments to measure procedural and background pain in burned children aged 0-4 years. Burn care nurses (n=73) rated pain from 24 fragments of videotaped children during wound care procedures and during periods of rest using the POCIS and the VAS. Intraclass correlations were used to assess inter-rater and intra-rater reliability for the POCIS and the VAS. Internal consistency for POCIS was assessed by Cronbach's alpha. The POCIS has shown poor to moderate inter-rater reliability, moderate to good intra-rater reliability and an acceptable internal consistency. The VAS turned out to have poor inter-rater reliability and poor to moderate intra-rater reliability. Due to poor results of inter-rater reliability in both scales, construct validation is left undone until more acceptable results are obtained. Factors explaining the results are the large number of raters, the manner they were trained and a lack of variation between pain classes in video fragments. Although not all results were satisfying, an easy to use scale as POCIS has promising qualities and deserves further reliability research.

Pediatric procedural pain

Pain is subjective. The pain response is individual and is learned through social learning and experience. Early pain experiences may play a particularly important role in shaping an individual's pain responses. Painful medical procedures such as immunizations, venipunctures and dental care, and minor emergency department procedures such as laceration repair, compose a significant portion of the average child's experience with painful events. Inadequate relief of pain and distress during childhood painful medical procedures may have long-term negative effects on future pain tolerance and pain responses. This article reviews the evidence for long-term negative effects of inadequately treated procedural pain, the determinants of an individual's pain response, tools to assess pain in children, and interventions to reduce procedural pain and distress. Future research directions and a model for conceptualizing and studying pediatric procedural pain are proposed.

The association between heart rate, heart rate variability, endocrine and behavioural pain measures in horses suffering from laminitis

The objective of this study was to compare the stress response of horses suffering from laminitis after short- and long-term treatment with the intent to evaluate power spectral analysis of heart rate variability (HRV) for pain monitoring. Data were collected from 19 horses with acute or chronic exacerbating laminitis without known primary disease before and after treatment with non-steroidal anti-inflammatory drugs (NSAID). Recordings were carried out the day after admission to the equine hospital. Measurements were repeated on day 7 of the treatment. The recorded parameters included a clinical orthopaedic index (OLPI: Obel-grade plus hoof tester score), frequency of weight-shifting between contralateral limbs, mean beat-to-beat interval (R-R) duration, standard deviation of continuous R-R intervals, low- (LF) and high-frequency (HF) components of HRV, sympatho-vagal balance (LF/HF), and plasma concentration of cortisol, adrenalin and noradrenalin. The LF represents mainly sympathetic influences on the heart whereas HF is mediated by the parasympathetic tone. Weight-shifting and OLPI decreased significantly with treatment. The LF normalized units (n.u.) decreased after NSAID from 60.41 +/- 21.42 to 51.12 +/- 19.81 and was 49.33 +/- 22.64 on day 7, whereas HF n.u. increased from 35.07 +/- 20.02 to 43.14 +/- 18.30 and was 45.98 +/- 23.00 on day 7. Hormone levels showed no tendency to change with treatment. The OLPI was only correlated with LF/HF, LF and HF (R = 0.57, 0.55 and -0.54 respectively). Significant negative correlations existed between HFn.u. and weight-shifting frequency (R = -0.37), HFn.u. and adrenalin (R = -0.47), and HFn.u. and noradrenalin (R = 0.33). The LFn.u. only correlated positively with adrenalin. Cortisol levels were poorly associated with the other parameters. Determination of the sympatho-vagal influences on cardiac function may offer complementary information for reliable assessment of pain and may represent a valuable alternative method to catecholamine measurements.

Postoperative pain assessment tools in day surgery: literature review

BACKGROUND

Postoperative pain is an expected phenomenon. However, its passage beyond acceptable limits is a common and costly experience. This is particularly the case in day surgery, partly because of the increasing demand to reduce waiting lists for elective surgery, and partly because of lack of knowledge about patients' experiences of postoperative pain and relevant published research. The latter is mainly concerned with different interpretations of the phenomenon of pain that appear to have led to a variety of often inappropriate pain measurement tools.

AIM

This paper critically reviews some of the available objective and subjective measures of pain and establishes the suitability of a Visual Analogue Scale (VAS) for measuring the intensity of pain after day surgery.

METHOD

Nursing and health care papers published since 1983 were sought using the keywords: postoperative pain, day surgery, ambulatory surgery, rating scales, VAS, severity, assessment, tool, nursing, validity, sensitivity, reliability and their various combinations. The databases used were Medline, CINAHL, Nursing Collection, Embase, Healthstar, BMJ and several on-line Internet journals, specifically Ambulatory Surgery. The search included only papers published in the English language.

FINDINGS

A range of interpretations of pain have led to the development of various measurement tools that address different components of pain. This inconsistency has led to ineffective pain management. Based on established criteria, the VAS was found to be methodologically sound, conceptually simple, easy to administer and unobtrusive to the respondent. On these grounds, the VAS seems to be most suitable for measuring intensity of pain after day surgery.

CONCLUSIONS

Common guidelines on the definition and measurement of pain are needed. In day surgery, the availability of a unified and reliable measure of pain that can address its sensory component, such as the VAS, will provide more reliable information about the pain experience and, hence, improve its overall management.

Developmental pharmacokinetics of morphine and its metabolites in neonates, infants and young children

BACKGROUND

Descriptions of the pharmacokinetics and metabolism of morphine and its metabolites in young children are scant. Previous studies have not differentiated the effects of size from those related to age during infancy.

METHODS

Postoperative children 0-3 yr old were given an intravenous loading dose of morphine hydrochloride (100 micro g kg(-1) in 2 min) followed by either an intravenous morphine infusion of 10 micro g h(-1) kg(-1) (n=92) or 3-hourly intravenous morphine boluses of 30 micro g kg(-1) (n=92). Additional morphine (5 micro g kg(-1)) every 10 min was given if the visual analogue (VAS, 0-10) pain score was >/=4. Arterial blood (1.4 ml) was sampled within 5 min of the loading dose and at 6, 12 and 24 h for morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). The disposition of morphine and formation clearances of morphine base to its glucuronide metabolites and their elimination clearances were estimated using non-linear mixed effects models.

RESULTS

The analysis used 1856 concentration observations from 184 subjects. Population parameter estimates and their variability (%) for a one-compartment, first-order elimination model were as follows: volume of distribution 136 (59.3) litres, formation clearance to M3G 64.3 (58.8) litres h(-1), formation clearance to M6G 3.63 (82.2) litres h(-1), morphine clearance by other routes 3.12 litres h(-1) per 70 kg, elimination clearance of M3G 17.4 (43.0) litres h(-1), elimination clearance of M6G 5.8 (73.8) litres h(-1). All parameters are standardized to a 70 kg person using allometric 3/4 power models and reflect fully mature adult values. The volume of distribution increased exponentially with a maturation half-life of 26 days from 83 litres per 70 kg at birth; formation clearance to M3G and M6G increased with a maturation half-life of 88.3 days from 10.8 and 0.61 litres h(-1) per 70 kg respectively at birth. Metabolite formation decreased with increased serum bilirubin concentration. Metabolite clearance increased with age (maturation half-life 129 days), and appeared to be similar to that described for glomerular filtration rate maturation in infants.

CONCLUSION

M3G is the predominant metabolite of morphine in young children and total body morphine clearance is 80% that of adult values by 6 months. A mean steady-state serum concentration of 10 ng ml(-1) can be achieved in children after non-cardiac surgery in an intensive care unit with a morphine hydrochloride infusion of 5 micro g h(-1) kg(-1) at birth (term neonates), 8.5 micro g h(-1) kg(-1) at 1 month, 13.5 micro g h(-1) kg(-1) at 3 months and 18 micro g h(-1) kg(-1) at 1 year and 16 micro g h(-1) kg(-1) for 1- to 3-yr-old children.

The challenges of pain measurement in critically ill young children: A comprehensive review

This article addresses the issues in measuring pain in critically ill children, provides a comprehensive review of the pain measures for children aged between 0 and 3 years, and discusses their applicability to this group of children. When children are critically ill, pain can only exacerbate the stress response that already exists, to the extent that homeostasis cannot be maintained. Severity of illness is thus likely to affect physiologic and behavioural pain responses that would normally be demonstrated in healthy children. The problem of differentiating pain from other constructs adds to the complexity of assessing pain in non-verbal children. A pain measure to be useful clinically must be adapted to the developmental age of the target population. Search of electronic databases and other electronic sources was supplemented by hand review of relevant journals to identify published and unpublished pain measures for use in children aged between 0 and 3 years. Twenty eight pain measures were identified in the literature; 11 for neonates only, 11 for children aged between 0 and 3 years, and six for children more than 12 months. These measures vary in relation to their psychometric properties, clinical utility and the context in which the study was performed. These measures may not be suitable for the critically ill young child, because the items included were derived from observations of healthy or moderately sick children, and may not reflect pain behaviour in those who are critically ill. It is therefore recommended to develop new pain scales for this population of compromised children.

Neonatal Facial Coding System for Assessing Postoperative Pain in Infants: Item Reduction is Valid and Feasible

OBJECTIVE

The objectives of this study were to: (1). evaluate the validity of the Neonatal Facial Coding System (NFCS) for assessment of postoperative pain and (2). explore whether the number of NFCS facial actions could be reduced for assessing postoperative pain.

DESIGN

Prospective, observational study.

PATIENTS

Thirty-seven children (0-18 months old) undergoing major abdominal or thoracic surgery.

OUTCOME MEASURES

The outcome measures were the NFCS, COMFORT "behavior" scale, and a Visual Analog Scale (VAS), as well as heart rate, blood pressure, and catecholamine and morphine plasma concentrations. At 3-hour intervals during the first 24 hours after surgery, nurses recorded the children's heart rates and blood pressures and assigned COMFORT "behavior" and VAS scores. Simultaneously we videotaped the children's faces for NFCS coding. Plasma concentrations of catecholamine, morphine, and its metabolite M6G were determined just after surgery, and at 6, 12, and 24 hours postoperatively.

RESULTS

All 10 NFCS items were combined into a single index of pain. This index was significantly associated with COMFORT "behavior" and VAS scores, and with heart rate and blood pressure, but not with catecholamine, morphine, or M6G plasma concentrations. Multidimensional scaling revealed that brow bulge, eye squeeze, nasolabial furrow, horizontal mouth stretch, and taut tongue could be combined into a reduced measure of pain. The remaining items were not interrelated. This reduced NFCS measure was also significantly associated with COMFORT "behavior" and VAS scores, and with heart rate and blood pressure, but not with the catecholamine, morphine, or M6G plasma concentrations.

CONCLUSION

This study demonstrates that the NFCS is a reliable, feasible, and valid tool for assessing postoperative pain. The reduction of the NFCS to 5 items increases the specificity for pain assessment without reducing the sensitivity and validity for detecting changes in pain.

Physiologic correlates of comfort in healthy children

Pain assessment is particularly challenging when children are unable or unwilling to provide a self-report. Although clinicians frequently use vital signs as an adjunct to pain assessment, little evidence exists to support this practice. The purpose of this study was to explore the ability of selected physiologic variables (peripheral skin temperature, heart rate, skin conductance activity [SCA], respiratory rate, electromyogram [EMG] of the frontalis and right forearm muscles, and systolic and diastolic blood pressure [BP]) to detect changes in children's autonomic arousal from baseline. A one-group, repeated measures, randomized crossover design guided the study. Chosen from a convenience sample, 100 healthy children (ages 8-17 years) served as their own controls while undergoing two levels of intervention: cold pressor pain and guided imagery. Although most physiologic responses showed changes in the expected direction, EMG, SCA, and heart rate decreased slightly during cold pressor. Few significant intercorrelations were demonstrated among the physiologic variables. SCA, forehead EMG, respiratory rate, systolic and diastolic BP detected significant changes in arousal across measures. Notably, heart rate failed to detect changes for any of the measures. Results emphasize the need for caution in interpreting heart rate as an index of comfort. Further research is needed to examine the effects of clinical pain on physiologic indices and to further examine age and sex influences. To be relevant for assessment of acute established pain, physiologic variables must also be tested for their sensitivity beyond the immediate period of autonomic arousal.

Methodological considerations for the use of heart rate variability as a measure of pain reactivity in vulnerable infants

Measures of HR and HRV offer multiple indices of reactivity to painful events. These measures are particularly helpful in preterm and ill infants where distress signals are often nonspecific and ambiguous. HR is easy to acquire, and a variety of widely used techniques are available for processing it. In general, the neuroanatomic and neurophysiologic bases for pain perception are in place even in the most preterm infant and produce patterns of HR and HRV responses that are similar across multiple settings. Developmental and experiential factors related to preterm birth, however, may affect these HR responses. Furthermore, evaluation of ill infants in an NICU setting adds multiple contextual factors that potentially influence HR and HRV and alter their specificity as measures of pain. In some cases, it may appear that pain reactivity is reduced when, in fact, HR reactivity is only an expression of the biologic capacity to produce a response, not the presence of a response itself. The nature of the setting and the infant's health, developmental stage, and behavioral state all contribute to potentially altering HR responses to painful events in this setting. Thus, the methodology used and its application must be flexible. A variety of HRV analysis techniques may be needed to identify a variety of response patterns and mechanisms that influence pain reactivity. Furthermore, careful selection of HR epochs for stationarity, an understanding of the potential discordance between biologic and behavioral measures, the effects of medication, and an accounting for developmental differences that occur during a typical NICU course are all critical factors for investigators to be aware of. Understanding cardiovascular reactivity as a measure of response to painful events in vulnerable infants requires ongoing work.

Are postoperative pain instruments useful for specific groups of vulnerable infants?

Based on the authors' review of the literature on pediatric postoperative pain assessment with special attention to groups of vulnerable infants, this article (1) reports on type of surgery and its relationship to postoperative pain intensity; (2) reviews the characteristics of existing postoperative pain instruments for neonates, infants, and toddlers; (3) discusses timing, duration, and who should assess postoperative pain; (4) reviews the specific literature on pain assessment in critically ill infants, including the extremely low birth weight and the cognitively and/or neurologically impaired infant, and (5) discusses the role of parents in postoperative pain assessment. Postoperative pain instruments are useful for specific groups of vulnerable infants, but it is important that in addition to the valuable scoring of pain, common sense is used and factors such as developmental stage, temperament and personality, number of previous painful experiences, anxiety, and environmental factors are taken into account.