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PEDIATRIC ANESTHESIA

A Comparison of Observational and Objective Measures to Differentiate Depth of Sedation in Children from Birth to 18 Years of Age

Department of Anesthesiology, Section of Pediatrics, C.S. Mott Children’s Hospital, University of Michigan Medical Center, Ann Arbor, Michigan

Address correspondence and reprint requests to Shobha Malviya, MD, Department of Anesthesiology, Section of Pediatrics, F3900/Box 0211, C.S. Mott Children’s Hospital, University of Michigan Medical Center, 1500 E. Medical Center Dr., Ann Arbor, MI 48109–0211. Address e-mail to smalviya{at}umich.edu.

	Abstract

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Several observational and objective methods are available to assess sedation depth; however, data regarding their accuracy in differentiating deep sedation are limited. In this study we compared 3 sedation tools in children from birth to 18 yr of age and determined their relative value in detecting deep levels of sedation. Bispectral index monitoring (BIS®), Modified Maintenance of Wakefulness Tests (MMWT), and the University of Michigan Sedation Scale (UMSS) were used to assess sedation. Three-hundred-twenty-seven observations were recorded in 39 children. The overall validity of each measure was supported by appropriate changes after sedation administration through the observation period. There were moderate to high correlations between UMSS and BIS (rho = –0.73) and UMSS and MMWT (rho = –0.59; P < 0.01). The correlation between BIS and MMWT was significant but low (r = 0.36; P < 0.01). Measures of exact agreement supported the reliability of the UMSS and MMWT across the sedation continuum. There were significant decreases in BIS across UMSS scores except from scores 2–3. ROC curves suggested that BIS 80 and MMWT 14 min were most sensitive in delineating deep sedation. Our findings demonstrate the overall validity of these observational and objective measures of sedation depth in children <18 yr of age but show ongoing limitations distinguishing moderate from deep sedation.

	Introduction

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Children who become deeply sedated after administration of sedative-analgesic medication are at risk for adverse events (1,2). Furthermore, it has been demonstrated that children may slip into deeper than intended levels of sedation after administration of sedative drugs, placing them at higher risk (1). Recognition of such risks has led national organizations, including the American Academy of Pediatrics (AAP), American Society of Anesthesiologists (ASA), and the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) to reach consensus regarding the terminology and definitions of sedation levels (3). "Mild sedation" is now considered equivalent to anxiolysis; "moderate sedation" implies the ability to respond appropriately to physical or verbal stimulation; and "deep sedation" represents a level from which the patient is not easily aroused and may include a partial or complete loss of protective airway reflexes (3). Because sedation depth represents a continuum, the JCAHO requires practitioners to have the skills necessary to rescue patients from a level of sedation deeper than intended (3–7). Frequent and accurate assessment of sedation depth is therefore pivotal to the safety of sedated children.

Several observational and objective methods have been described as reliable and valid measures; yet data regarding their accuracy in differentiating deep sedation are limited. It is imperative that a sedation assessment tool be able to detect changes in sedation depth so deep sedation can be readily recognized and appropriate rescue measures instituted. Because of their ease of use, observational scoring systems are most commonly used to assess sedation depth in the clinical setting. The University of Michigan Sedation Scale (UMSS; Table 1) (8), is an observational tool that scores the patient’s responsiveness to stimuli in a manner consistent with nationally recognized definitions. This tool has been tested for inter-rater and test-retest reliability, and construct and criterion validity in small samples of children aged 6 months to 12 years (8–10), supporting its use during procedural sedation. Furthermore, UMSS scores of 0–1 have been shown to be sensitive and specific in determining return to baseline level of alertness and discharge readiness after sedation (9). Data regarding the tool’s reliability in differentiating moderate to deep sedation are limited.

Bispectral Index (BIS®) monitoring has recently been touted as an objective and potentially clinically useful measure to quantify depth of sedation in procedural and intensive care settings (10–12), particularly when stimulation of the child, which is necessitated by observational assessment, is considered detrimental. BIS values have been shown to correlate with sedation scores in children and adults; however, values that delineate deep sedation in children have not been well defined (11). Further data are needed to clarify the potential utility of BIS monitoring in sedation settings, where such differentiation is imperative.

Developed as an objective method to assess return to baseline status after sedation, the Modified Maintenance of Wakefulness Test (MMWT) has been shown to correlate well with UMSS scores and BIS values (9). Although observational in nature, the MMWT has an objective component in that it requires timing the child’s ability to stay awake in a somnolent environment. MMWT durations may provide an additional objective measure of sedation depth during recovery; however, the tool has not been compared with other measures in regard to differentiating levels of sedation.

Current methods of sedation assessment, in light of nationally accepted definitions of sedation levels, have not been compared for their ability to differentiate deep sedation. Yet it remains important for practitioners to understand the advantages and limitations of these assessment tools. The present study was therefore undertaken to compare the observational and objective measures of sedation described above in children aged birth to 18 yr and to determine their relative value in detecting deep levels of sedation.

	Methods

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With approval from the University of Michigan’s IRB and written informed consent from the parents and child assent when appropriate, children aged newborn to 18 yr who required sedation/analgesia or general anesthesia for a procedure were studied. Children were sedated and monitored by trained pediatric nurses under the direction of the primary care provider in accordance with institutional guidelines and national standards of practice. General anesthesia was administered by a resident physician or nurse anesthetist under the supervision of an anesthesiologist.

Before administration of sedatives or induction of anesthesia, the BIS® sensor was applied to the forehead in accordance with the manufacturer’s instructions, and data were recorded continuously from baseline through recovery. The BIS® monitor (A-2000 BIS® Aspect Medical Systems, Inc., Newton, MA) was placed out of view of care providers and observers to facilitate blinding. A trained observer assigned UMSS scores at 5- to 10-min intervals when it was possible to use graded stimulation (verbal to light tactile to deep stimulation) as described previously (9). Observations were therefore not obtained during procedures when patient stimulation was not possible. Moreover, for those children who received a general anesthetic, data from induction through discontinuation of the anesthetic were not included in the analysis. A second observer assigned UMSS scores simultaneously yet independently. After the procedure, the child’s ability to maintain wakefulness (MMWT) was timed by the same observers independently using a simple visual observation from the time the child was awakened for UMSS assignment to the time he or she appeared to fall asleep (i.e., eyes closed, relaxed facial muscles, and deepened regular respiratory pattern). BIS values were later derived from average values over the 5-min period immediately before UMSS observations by an assistant blinded to the UMSS scores. Only data with a signal quality index more than 50 were used for this averaging.

Relationships between sedation measures were evaluated using Pearson’s r or Spearman’s rho correlation coefficients and analysis of variance with repeated measures, followed by post hoc pairwise comparisons using Dunnett’s c-test when applicable. Unpaired Student’s t-tests were used to determine differences in BIS values for each UMSS score between age groups. Receiver operator characteristic (ROC) curves were generated to determine the best "cut-off" values for deep sedation. Intraclass correlation coefficients with confidence intervals (CI) and kappa statistics were used to evaluate agreement in observational scores between observers. Correlations 0.50 were considered moderate to excellent. Kappa values >0.41 were considered to represent acceptable agreement; P values <0.05 were accepted as statistically significant.

	Results

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Forty-two patients were recruited for this study; however, BIS data were unobtainable in 3. Data are therefore presented for 327 observations recorded in 39 children aged 1 mo to 17 yr (6.1 ± 5.6 yr). The distribution of observations was fairly even across age groups: 81 (25%) observations in children <2 yr of age (n = 10); 84 (26%) observations in 2- to 5-yr-olds (n = 13); 60 (18%) in the 6–11 yr age group (n = 7), and 102 (31%) in those 12–17 yr of age (n = 9). Eleven children (28%) had received a volatile anesthetic, 9 (23%) propofol, 10 (26%) chloral hydrate, and 9 (23%) midazolam and fentanyl.

The construct validity of each sedation measure was supported by appropriate changes in scores/values after sedation administration through the end of the observation period. UMSS scores increased after administration of sedative/analgesics and decreased as drug effects subsided (P < 0.05). Although there were an insufficient number of baseline BIS values to evaluate initial decreases in BIS, we found significant increases after the procedure as drug effects wore off (P < 0.02). There were similar increases in MMWT durations over time (P < 0.04).

There were moderate to high correlations between UMSS scores and BIS values (rho = –0.73) and UMSS and MMWT (rho = –0.59; P < 0.01); however, the correlation between BIS and MMWT was significant but low (r = 0.36; P < 0.01). Table 2 presents the distribution of UMSS scores for each range of BIS values as well as for MMWT durations. Because detection of deep sedation is critical to patient safety, the relationship between these observational and objective measures was further evaluated for deep sedation levels (i.e., UMSS scores 3–4, BIS values 70, and MMWT duration 10 min). Only 60% of children with UMSS scores 3–4 had BIS values 70, whereas 80% had MMWT durations 10 min. To help define the optimal BIS threshold for deep sedation, ROC curves were constructed using a UMSS score threshold 3 (Fig. 1). The optimal BIS cut-off for deep sedation was considered to be 80, given the sensitivity (93%) at this value with the least compromise of its specificity (76%). Finally, to address the accuracy of MMWT in predicting deep sedation, ROC curves were developed using the same UMSS threshold (Fig. 2). The MMWT cut-off for deep sedation appears to be between 5.5 and 14 min (sensitivity 89%; range in specificity, 71–74%).

View larger version (25K): [in this window] [in a new window]   Figure 1. Receiver operating characteristic curve for Bispectral index at University of Michigan Sedation Scale scores 3–4. Area under the curve = 0.92 (95% confidence interval = 0.89–0.95). Sens = sensitivity; Spec = specificity.

View larger version (20K): [in this window] [in a new window]   Figure 2. Receiver operating characteristic curve for Modified Maintenance of Wakefulness Tests at University of Michigan Sedation Scale scores 3–4. Area under the curve = 0.84 (95% confidence interval = 0.71–0.98). Sens = sensitivity; Spec = specificity.

The relationship between BIS values and UMSS scores for all children in the sample is further depicted in Figure 3. Analysis of variance demonstrated significant differences in BIS values across all UMSS scores except for scores 2–3. Because BIS monitoring lacks sufficient validation in children <1 yr of age, data from this age group were analyzed separately from those in older children (Fig. 4). In younger children significant differences in BIS values were demonstrated only between UMSS 0–2 and 0–3. For older children, there were significant differences in BIS values across all UMSS scores, except scores 2–3. Compared with older children, BIS values were significantly lower in infants for UMSS scores 2 and 3.

View larger version (13K): [in this window] [in a new window]   Figure 3. Box and whisker plot of Bispectral index values for each University of Michigan Sedation Scale Score.

View larger version (28K): [in this window] [in a new window]   Figure 4. Box and whisker plot of Bispectral index values for each University of Michigan Sedation Scale Score across age groups.

The intraclass correlation coefficients (ICC), exact agreement, and kappa values as presented in Table 3 demonstrate the inter-rater reliability of the UMSS for the entire sample as well as for the younger and older age groups. Inter-rater reliability was similar for age groups <2 yr, 2–5 yr, 6–11 yr, and 12–17 yr (Kappa 0.71; ICC 0.95). Lastly, the inter-rater reliability for the MMWT was supported by the ICC between observers (n = 47; ICC = 0.99; CI = 0.988–0.996).

	Discussion

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The use of sedative/analgesic drugs has increased so as to ensure the comfort and immobility of children undergoing complex medical procedures. However, variations in sedation regimens and individual responses to sedative/analgesics result in unpredictable sedation levels. Children may unexpectedly progress from mild to deeper levels of sedation, and it can be difficult to delineate subtle differences in sedation depth. It is imperative that sedation assessment methods be sensitive enough to detect transitions in sedation levels, particularly the progression from moderate to deep sedation. Findings from this study provide additional support for the reliability of the UMSS and MMWT and show that UMSS scores, BIS values, and MMWT durations vary appropriately over the sedation continuum and change as expected after sedative administration. Moreover, these data suggest that BIS values less than 80 may be more sensitive in identifying deep sedation in children.

Previous investigators reported frequent deep sedation levels in children who had received sedative/analgesics for medical procedures (1,2,13). Furthermore, these investigators reported that deeper-than-intended levels of sedation occurred inadvertently in 18% to 91% of patients studied. Hoffman et al. (1) found a 2.6-fold increase in complications associated with physiologic deterioration in children who were deeply sedated compared with those who were mildly sedated. Other investigators have similarly described frequent adverse events, including airway obstruction, oxygen desaturation, or both, at deeper levels of sedation (2,9). Moreover, adverse outcomes have been shown to be related, in part, to the lack of early recognition and failure to rescue patients from a developing adverse event (14). These data emphasize the importance of monitoring sedation depth and physiologic status at regular intervals to facilitate early detection of high-risk situations and timely interventions.

Several observational scoring systems for assessing sedation depth have been developed and tested in a variety of clinical settings (8,10,15–21). The UMSS was designed as a simple tool to assess sedation depth over the entire continuum from awake to unarousable as defined by the AAP and the ASA and endorsed by the JCAHO (3,4,6,7). This study provides further support for the reliability and validity of the UMSS over the continuum of sedation levels. Interestingly, we could not demonstrate a significant difference in BIS values between UMSS scores of 2–3. Furthermore, exact agreement between observers was only 72% for these scores. This discrepancy may be explained, at least in part, by subjective interpretation of patient response to stimuli, as well as by the overlapping BIS values, highlighting the difficulties in discriminating moderate from deep sedation. Indeed, comparisons between BIS and other observational tools have shown similar variability in mid-ranges of sedation (11,12). Moreover, we found that deep sedation defined by UMSS scores 3–4 had poor agreement (i.e., 60%) with previously suggested BIS values indicating deep sedation (i.e., BIS <70). Indeed, the ROC generated by these data suggested that BIS values <80 had the best sensitivity and specificity in identifying patients with UMSS scores 3–4. Given this cut-off value for BIS, 93% of children deeply sedated, as defined by patient responsiveness, would be correctly identified. These data suggest that while BIS monitoring provides a gross indication of sedation level, it may lack specificity in discriminating sedation depth.

Previous investigators have suggested that the BIS monitor may provide a useful, continuous method to monitor depth of sedation during procedures where stimulation of the child is undesirable (10). Although BIS values have been shown to negatively correlate with end-tidal concentrations of volatile anesthetics in children, studies have also found lower BIS values at similar clinical levels of anesthesia in infants compared with older children (22,23). The present data similarly suggest that BIS values are lower in sedated infants compared with older children. Such differences may be explained by known age-related differences in electroencephalogram activity (24). Interpretation of existing data that address age-related differences in BIS value is confounded, however, by small sample sizes and variable definitions of age groups. Until further data are available, observational tools perhaps remain the most reliable and feasible method to assess sedation depth in infants. During times when patient stimulation is undesirable, it is prudent to assume that children are deeply sedated and to monitor accordingly.

Previous investigators have alluded to the variable effects of sedative/analgesic drugs on BIS (10,25). The interpretation of data in our study may be partially confounded by such variability because a variety of sedative regimens were used in our sample. A specific evaluation of the effects of sedative drugs on BIS was beyond the scope of this study. However, the importance of these data lies in their comparison of the ability of the available clinical tools to detect transitions in sedation depth regardless of the drug used.

We have previously demonstrated the potential usefulness of the MMWT to evaluate return-to-baseline status during recovery from sedation (9). Although the MMWT was not intended to be a measure of sedation depth per se, we incorporated it in the present study as an additional tool against which to compare the UMSS and BIS and we found significant correlations. Moreover, data demonstrated that MMWT durations <14 minutes were 89% sensitive in delineating deep sedation. These data suggest that incorporation of this simple test into routine sedation assessment may provide an additional objective and sensitive measure of sedation depth to ensure patient safety.

This study compared the UMSS observational tool, BIS, and the MMWT in their ability to discriminate sedation depth in children aged newborn to 18 years. Although each of these measures correlated over the spectrum of sedation, our data suggest potential difficulties in distinguishing moderate from deep sedation with observational and objective measures. Because deep sedation levels place children at higher risk for adverse events, it remains imperative to assess sedation depth routinely and to err on the conservative side when caring for patients who appear, by any measure, to be moderately sedated.

The authors would like to thank the following persons for their invaluable contributions toward this work: Connie Burke, BSN, RN, Melissa Doettl, BS, Megan Anson, and Julie Conley. We also thank Aspect Medical Systems for providing BIS® sensors for our continuing study of sedation in children.

	Footnotes

 
Supported, in part, by a grant provided from Purdue Pharma.

Accepted for publication May 31, 2005.

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999