PEDIATRICS Vol. 122 No. 4 October 2008, pp. e848-e853 (doi:10.1542/peds.2007-2545)
ARTICLE |
Skin Conductance Versus the Modified COMFORT Sedation Score as a Measure of Discomfort in Artificially Ventilated Children
a Skills Training Center
b Department of Anesthesiology, Pediatric Intensive Care Unit, Rikshospitalet University Hospital, Oslo, Norway
c Department of Pediatrics, Ullevål University Hospital, Oslo, Norway
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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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.
Key Words: artificially ventilated children • pain detection • skin conductance • modified COMFORT sedation score
Abbreviations: SC—skin conductance • NSCF—number of skin conductance fluctuations • ASCF—amplitude of skin conductance fluctuations • HR—heart rate • ABP—arterial blood pressure • PCICU—pediatric cardiac ICU
Skin conductance (SC) shows increased stress as reflected in changes in the sympathetic nervous system.1 Each time the skin nerves are activated, the palmar and plantar sweat glands fill. This leads to a diminished skin resistance, and the SC increases before the sweat is reabsorbed and the SC decreases.2 Efferent skin nerve bursts occur in a rather random manner, but both the amplitude and the number of bursts rise when triggered by arousal stimuli. An increase in the number of SC fluctuations (NSCF) and the amplitude of SC fluctuations (ASCF) can therefore be interpreted as increased activity in this part of the sympathetic nervous system.2,3
SC fluctuations have been used to evaluate pain response in preterm infants.4 When the pain stimulus was induced, an immediate increase in emotional sweating and SC fluctuations occurred, and when the pain stimulus was terminated, the SC fluctuations immediately decreased4; however, unlike heart rate (HR) and arterial blood pressure (ABP) changes, nociseptive-induced sweating is not influenced by circulatory changes in alert patients, because no correlation to spontaneous fluctuations in ABP was found, neither was there arterial baroreflex modulation of skin sympathetic activity.5,6 In addition, skin sympathetic activity is without relationship to HR under resting conditions, and the discharges are not inhibited during apnea.5 The sweat glands in the skin are innervated by sympathetic fibers that induce the sweat secretion. A specific character connected to this innervation is that acetylcholine is the transmitter acting on muscarine receptors.5,6 The NSCF are therefore not influenced by hypovoluminous or adrenergic receptor active agents. The assessment of sedation in critically ill patients by various scoring systems produces insufficient information, although the COMFORT score was found to be a useful tool in assessing postoperative pain in infants.7 The modified COMFORT sedation score has its benefits in pediatric patients in its utility for all ages (0–18 years) and all levels of neurodevelopment, as well as the absence of a needed arousal stimulus to determine the adequacy of sedation.8 Significant changes in the modified COMFORT sedation score were also found earlier during endotracheal suctioning.9
Hemodynamic changes in sedated patients are influenced by circulatory changes and temperature and therefore have low specificity as a sign of adequate or inadequate anesthesia and sedation.10 NSCF may be a more sensitive method and more specifically linked to noxious stimulation. This may be attributable to the fast reaction time, 1 to 2 seconds,2 and the short-lasting response time down to 0.7 seconds of the NSCF. We wanted to study how changes of SC fluctuations, ABP, and HR were associated with the changes in the modified COMFORT sedation score during endotracheal suctioning in artificially ventilated and circulatory-stable children.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Instruments
SC activity was measured by alternating current at 88 Hz. Low-frequency electrical conductance reflects the ionic conduction in the stratum corneum, which is largely determined by the sweat duct filling.11 Resistance and conductance are 2 related quantities in measuring voltage changes in SC. The siemens is the unit of electrical conductance in the same way as the Ohm is the unit of electrical resistance. Conductance was preferred to resistance because of the parallel nature of the electrical polarization and conductance in the skin. A frequency of 88 Hz is sufficient to reduce considerably the requirements for low electrode polarizability but also low enough to ensure minimal influence from layers other than the stratum corneum. An applied voltage of 50 mV and a 3-electrode system were used. The 3-electrode system comprised a measuring electrode (M), a countercurrent electrode (C), and a reference voltage electrode (R), which ensured a constant applied voltage across the stratum corneum beneath the M electrode. As long as the electrodes are placed palmar and plantar at approximately the same areas, the distance between them is not important because of the high density of the sweat glands in these areas.12 The apparatus satisfied the safety regulations given in IEC 60601. Beckman electrodes (Sensormedics, Sensormedics, CA) were used. The electrodes were attached to the skin by disks of double-sided adhesive tape from 3M (Minneapolis, MN). Conductive paste from the National Hospital Pharmacy (Oslo, Norway), which contained 6 g of hydroxyethyl-cellulose 700, 0.58 g of NaCl, 0.1 g of methylparahydroxybenzene, 0.1 g of propylparahydroxybenzene, 2 g of alcohol 96%, and distilled water up to 100 g, was used to improve electrode conductance. HR and intra-arterial BP were read manually from the Siemens SC 9000 XL (Siemens Medical Systems, Inc, Danvers, MA) monitors used in the PICU and the pediatric cardiac ICU (PCICU), the National University Hospital (Oslo, Norway), and from the Hewlett Packard M 1167 A monitors used in the PICU (Ullevål University Hospital, Oslo, Norway).
Software Program
The SC data were stored online by using a portable computer and were analyzed off-line by means of a software analysis package. The sample frequency was 50 Hz, and the resolution was 12 bits. The software program for sampling and analyzing SC was developed in Labview (National Instruments, Austin, TX).12 When analyzing SC, the program counted the NSCF per second, the mean ASCF (µsiemens), and the mean SC level (µsiemens) in a preferred period after sampling the data (Fig 1). The program contained a function that enabled us to define a threshold for the minimum amplitude, the minimum width of the waves, and the maximum slope of SC (Fig 1). For enabling the counting of the NSCF and ASCF, the program established the valleys and peaks when the derivative of the wave was 0. The amplitude was calculated from the valley before the peak to the height of the peak. The slope of the SC fluctuation was defined as the mean distance valley to peak/time to reach peak. For elimination of artifacts, the slope was set at <20 µsiemens/second. The width of the waves was unlimited.12 The slope of the artifacts increases faster than the SC fluctuations. The software analysis program could also analyze smaller segments of the recorded data. This was used to sort out electronic noise and to set the minimum amplitude at 0.015 µsiemens for 4 patients and at 0.020 µsiemens for the remaining 16 patients after manual counting of the number of waves and corresponded this with a preset minimum amplitude.12 The apparatus and the software program were commercially developed by Med-Storm Innovation AS (Med-Storm Innovation AS, Oslo, Norway).
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COMFORT Sedation Score
A modified COMFORT sedation score was used (Table 1). The COMFORT score was developed and validated to assess distress in mechanically ventilated children aged 0 to 18 years.8 It consisted originally of 2 physiologic items (mean ABP and HR) and 6 behavioral items (alertness, calmness, respiratory response, physical movement, muscle tone, and facial tension). The physiologic and behavioral items are found to constitute separate components.7 In the modified version, HR and blood pressure were excluded. Crying was only included when the child was extubated before the "after" measure.
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Procedure
The study was conducted in the PICU and the PCICU at Rikshospitalet University Hospital (Oslo, Norway) and at the PICU at Ullevål University Hospital (Oslo, Norway). All of the children were artificially ventilated, and all received analgesics and hypnotics, but none of them received anticholinergic medication (Table 2) . An arterial line was used for invasive blood pressure monitoring and blood sampling. The SC electrodes were secured to the hand or to the foot at least 3 minutes before measurements. The children who were younger than 1 year had the electrodes secured to the foot. In older children, the thickness of epidermis usually increases at the foot, so the hand was preferred. The electrodes were placed according to the Edelberg guidelines for the placement of electrodes to obtain the most sensitive measurement.1 For children who were younger than 1 year, the C electrode was placed on the medial side of the foot over the abductor hallucis muscle adjacent to the plantar surface, the M electrode was placed midway between the first phalanx and a point directly beneath the ankle, and the R electrode was placed on the dorsal side of the foot. For children who were older than 1 year, the C electrode was placed on the thenar eminence, the M electrode on the hypothenar eminence, and the R electrode on the dorsal side of the hand. SC, ABP, and HR were measured for 2 minutes before endotracheal suctioning, during the procedure, and then again for 2 minutes 10 minutes after the procedure. At the same time intervals, a modified COMFORT sedation score was made by an investigator who was blinded to the SC measurements. The SC, NSCF, ASCF, and mean SC level were analyzed for a period of 30 seconds at the 3 defined moments, and the maximum values were used. The maximum score of the modified COMFORT sedation score, HR, and ABP in the same time periods was used.
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Patients
The protocol was approved by the regional Ethics Committee for Human Studies (Oslo, Norway). The 11 girls and 9 boys selected were a random sample of eligible patients in the PICU and the PCICU (Table 2). They all were artificially ventilated and circulatory stable. ABP was used. The skin temperature was >25°C. Sixteen children were intubated after major thoracic or abdominal surgery, and 4 children were intubated because of pulmonary insufficiency. Eleven children had been through surgery the same day, 7 children had been through surgery 1 to a few days before, and 2 children had not been operated on. Five of the 11 children who had been through surgery the same day were extubated within 6 hours after the end of the surgical procedure. Two of the children who had not received surgery the same day were extubated shortly after our investigation. Fentanyl was given to 9 of 11 children who had undergone surgery within the last 24 hours, versus 2 of 9 children who had not been through recent surgery (Table 2). The 3 youngest children did not receive any hypnotics or opioids, but 2 of them received a moderate dose of paracetamol; the third child did not receive any analgesia. The 17 oldest children received opioids, 8 of them also received a moderate dose of paracetamol and 15 received hypnotics, mostly midazolam or sodium thiopenthal. The analgesics and hypnotics given within the last 4 hours before the time of the measurements that could have an influence on SC, ABP, HR, and the modified COMFORT sedation score are shown in Table 2. None of the patients received neuromuscular blockers, anticholinergics, or sympatholytics before the measurements.
Statistical Analysis
To test how SC (NSCF, ASCF, and mean SC level) as well as mean ABP and HR were correlated with a modified COMFORT sedation score taken from before to during and from during to after endotracheal suctioning, a linear regression analysis was used. The modified COMFORT score was used as the independent variable and NSCF, ASCF, ABP, HR, and SC basal levels were used as dependent variables. A nonparametric Wilcoxon test was used to verify whether the difference between the variables measured before, during, and after endotracheal suctioning were significant. The test was not Bonferroni corrected because of the controversy concerning this method.13 All statistical analyses were performed by using SPSS 11.0 (SPSS, Inc, Chicago, IL). A statistically significant difference was defined as P < .05.
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Twenty children (11 girls and 9 boys) who were aged from 1 day to 11 years were included in the study (Table 2). For 17 children, an SC threshold of 0.020 µsiemens was used, for 3 patients a threshold of 0.015 µsiemens was used after manual counting of the waves. Crying was included in the modified COMFORT sedation score for 4 children who were extubated before the after measurements.
The regression analysis showed r2 = 0.61 (P < .0005) between NSCF and the modified COMFORT score from before to during suction in the trachea and r2 = 0.46 (P = .001) between NSCF and the modified COMFORT score from during to after suction from trachea. Six children had no rise in NSCF, and 6 children had no or just a slight rise in COMFORT level during suction from trachea; 4 of these 6 children overlapped. The regression analysis between the modified COMFORT and ABP during suction from trachea showed no significant changes with r2 = 0.06 (P = .32) from before to during and r2 = 0.01 (P = .73) from during to after. The same was true for the regression analysis between the modified COMFORT and HR, ASCF, and mean SC level with r2 = 0.00 (P = .98) from before to during and r2 = 0.00 (P = .86) from during to after for the HR, r2 = 0.04 (P = .41) from before to during and r2 = 0.00 (P = .99) from during to after for ASCF, and r2 = 0.13 (P = .12) from before to during and r2 = 0.05 (P = .33) from during to after for the mean SC level.
The nonparametric tests in related samples, without Bonferroni correction,13 showed that the difference between the samples was significant for NSCF, the modified COMFORT sedation score, and ABP (from before to during and from during to after endotracheal suctioning), for the mean SC level (from before to during endotracheal suctioning), and for the HR (from during to after endotracheal suctioning; Table 3). ASCF did not show any significant changes (Table 3).
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For the 11 patients who were operated on the same day the regression analysis showed r2 = 0.67 (P = .002) between NSCF and the modified COMFORT sedation score from before to during and r2 = 0.43 (P = .03) from during to after endotracheal suctioning. One of these patients was statistically an outlier (patient 19; Fig 2), and without this patient, the regression between NSCF and the modified COMFORT sedation score from before to during suction in the trachea was even stronger with r2 = 0.79 (P = .001). A great rise in the modified COMFORT sedation score and NSCF were found in the child who did not receive any kind of analgesia or hypnotics during suction in the trachea (Fig 2). According to the modified COMFORT sedation score and the NSCF, the 2 children who received only paracetamol both had a minor reaction to the suction in the trachea.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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In this study, we found that NSCF measured before to during suction and from during to after suction from trachea correlated well with the variation in the modified COMFORT sedation score. NSCF and the modified COMFORT sedation score also showed a statistically significant increase during suction from trachea. The correlation coefficient was lower after endotracheal suctioning probably because most of the children were totally calm and had a minimum score before the endotracheal suctioning in both NSCF and the modified COMFORT sedation score. After the procedure, some of the children woke up and some also were extubated. The modified COMFORT sedation score has a wide range that may have caused a higher score in these often active children (Table 1). The group of newly operated children more often received fentanyl than the group who had not been through surgery within the last 24 hours. This could be attributable to pain and distress postoperatively among these children. Bouwmeester et al14 found that plasma concentration of norepinephrine in children who were younger than 3 years was significantly above baseline values 24 hours after surgery. In our study, the 3 youngest children did not receive any analgesia or hypnotics except for paracetamol that was given to 2 of them; the 1 who did not receive any kind of analgesia or hypnotics reacted with much more stress than the 2 who received paracetamol.
NSCF might be a sensitive measure of discomfort when the patient is intubated, sedated, or too young to communicate. We found a stronger correlation between NSCF and the modified COMFORT sedation score among the children who had been operated on in the last 24 hours. This might be attributable to a rise in the general stress level after surgery. At a slightly higher stress level, the sensitivity of SC rises.
To monitor ABP and HR as signs of inadequate sedation is not very reliable,15 and among PICU patients, there are many other reasons for alterations in ABP, HR, perfusion, and body temperature. In a study by Playfor et al,16 many PICU patients (67%) had memories of their stay: 18% reported unpleasant memories, 16% remembered being ventilated, and 29% reported being in pain. Anand and Hickey17 found that there was a decreased incidence of sepsis, metabolic acidosis, and disseminated intravascular coagulation and fewer postoperative deaths among critically ill neonates who received deep anesthesia and postoperative analgesia with higher doses of opioids. Conversely, tolerance, physical dependence, and withdrawal abstinence can occur after prolonged administration of any agent that is used for sedation and analgesia in the PICU population.18 It is therefore important to find the right balance between being without discomfort and not being oversedated.
The possible movement artifacts when using this kind of equipment was not a problem in our study because of the intubation and sedation of these children. Detachment of the electrodes has become a minor problem as a result of new disposable electrodes with better attachment, mostly because of the size. The problem with losing signals has been improved by better isolation of the wires and by improving the connection between the electrodes and the cables. The software program has been improved so that the fluctuations stand out more clearly and the artifacts are warned by "bad signal quality." An index for monitoring postoperative pain in adults, on the basis of the NSCF per second has been developed in commercially available equipment. Ledowski et al19 found that a cut of value of 0.1 gave high sensitivity and a fairly good specificity for differentiating between mild and moderate pain. These results were reproduced for postoperative pain in children.20
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CONCLUSIONS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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NSCF was found to correlate with the increase in the modified COMFORT sedation score. Although the modified COMFORT sedation score is a well-established and cost-effective method, it is subjective and requires constant monitoring. This is often not possible in a busy PICU, and NSCF is a good objective supplement to assess physiologic signs of pain and works in agreement with a subjective observational scale.
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ACKNOWLEDGMENTS |
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The study was performed at the PICU and the PCICU of Rikshospitalet University Hospital and Ullevål University Hospital.
We thank the children who were included in this study and the parents who gave their support. We express our thanks to the nurses in the PICU and PCICU who made it possible to carry out this study.
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FOOTNOTES |
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Accepted Jun 18, 2008.
Address correspondence to Ann Christin Gjerstad, MD, Skills Training Center, National University Hospital, 0027 Oslo, Norway. E-mail: acg{at}online.no
Financial Disclosure: Dr Storm developed the method and has a patent on the MedStorm software. The other authors have indicated they have no financial relationships relevant to this article to disclose.
| What's Known on This Subject SC is a method that was developed to measure pain in patients who are unable to communicate it (eg, during surgery, after surgery). The method is based on the filling of the palmar and plantar sweat glands when the sympathetic nervous system is activated.
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| What This Study Adds SC is linked to the basic reaction to pain and discomfort; it reacts within 0.7 seconds, which provides the possibility of titrating the levels of analgesics and anesthetics close to optimum.
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PEDIATRICS (ISSN 1098-4275). ©2008 by the American Academy of Pediatrics
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