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Actigraphy in the Critically Ill: Correlation With Activity, Agitation, and Sedation

	Abstract

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Objectives To determine the feasibility of continuous measurement of limb movement via wrist and ankle actigraphy (an activity measure) in critically ill patients and to compare actigraphy measurements with observed activity, subjective scores on sedation-agitation scales, and heart rate and blood pressure of patients.

• Methods In a prospective, descriptive, correlational study, all activity of 20 adult patients in medical and coronary care units in a university medical center were observed for 2 hours and documented. Wrist and ankle actigraphy, heart rate, and systolic and diastolic blood pressure data were collected every minute. The Comfort Scale and the Richmond Agitation-Sedation Scale were completed at the beginning of the observation period and 1 and 2 hours later.

•Results Wrist actigraphy data correlated with scores on the Richmond Agitation-Sedation Scale (r = 0.58) and the Comfort Scale (r = 0.62) and with observed stimulation and activity events of patients (r = 0.45). Correlations with systolic, diastolic, and mean arterial pressures were weaker. Wrist and ankle actigraphy data were significantly correlated (r = 0.69; P < .001); however, their mean values (wrist, 418; ankle, 147) were significantly different (t = 5.77; P < .001).

• Conclusions Actigraphy provides a continuous recording of patients’ limb movement. Actigraphy measurements correlate well with patients’ observed activity and with subjective scores on agitation and sedation scales. Actigraphy may become particularly important as a continuous measurement of activity for use in behavioral research and may enhance early recognition and management of the excessive activity that characterizes agitation.

The appropriate method for measuring agitation and sedation has gained much attention recently and is clinically important.^2,9–14 In a comprehensive review of sedation-agitation scoring systems, De Jonghe et al¹⁵ found that although sedation-agitation tools have been used to measure the effectiveness of sedation in ICU patients, few of such tools have satisfactory clinimetric properties. Only a few sedation scales also include multiple levels of excessive activity and/or agitated behavior. The Sedation Agitation Scale¹⁶ and the Motor Activity Assessment Score¹⁷ have 3 levels of agitated behavior, and the recently published Richmond Agitation-Sedation Scale (RASS)¹⁸ has 4 levels of agitated behavior. These subjective scales have been tested for validity and reliability in adult ICU patients.^16–18 No physiological measure of stress has been uniformly accepted that can provide a reference standard against which agitation-sedation scales can be measured. Tools currently in use include direct observations and intermittent structured assessments by nurses and other care providers, but these tools do not provide a continuous measure of activity and/or agitation. Available continuous measures such as blood pressure or heart rate may reflect patients’ status; that is, higher blood pressure or heart rate often accompanies increased activity or agitation. However, these measures are nonspecific and include a variety of reasons for change. Because agitation is associated with excessive restlessness and physical activity, the ability to detect increased activity, especially continuously, may be an important first step in assessing agitation.

Although agitated behavior is common among patients in critical care units, objective measures can be used to continuously evaluate patients’ behavior.

 

The actigraph, which provides a continuous measure of activity, was initially developed to measure sleep activity. This small electronic device can be strapped to the wrist or ankle and can continuously sense and record minimal movements or activity (ie, accelerations, linear displacements) during predetermined "epochs" for as long as several days. Actigraphy data are expressions of the acceleration movement in numerical form. Actigraphy is easy to use and has proved reliable in noncritical populations of patients. It has been used to track circadian rest-activity cycles¹⁹ and to identify states of wakefulness and sleep.^20,21 Polysomnographic results have shown significant agreement with data from wrist actigraphy for assessing sleep-wake cycles.^22,23 More recently, wrist actigraphy provided objective indications of changes in depth of anesthesia or sedation during surgery and recovery.²⁴ Patients’ activity can represent nursing interventions, purposeful movement of patients, or nonpurposeful movement of patients.

Although wrist actigraphy has not been widely tested as a measure of agitation or sedation in critically ill patients, its use for continuous monitoring of activity may be helpful. Wrist actigraphy can help in the objective measurement of agitation by providing a numerical record of limb movement, resulting in early detection of the excessive nonpurposeful movement that characterizes agitation. Conversely, the greater the depth of sedation, the less limb movement might be expected. Therefore, the purpose of this study was to determine the feasibility of continuous measurement of limb movement via wrist and ankle actigraphy (an activity measure) in critically ill patients and to compare actigraphy measurements with patients’ observed activity, subjective scores on sedation-agitation scales (RASS and Comfort Scale), and heart rate and blood pressure. This evaluation of actigraphy will provide beneficial information for further use of the actigraph as a research tool. With further study, the benefit of actigraphy as a clinical tool may also become apparent.

Actigraphy, a continuous measure of activity used to evaluate sleep, can also provide an objective measure of agitation.

 

	Materials and Methods

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The study was conducted at the Medical College of Virginia Hospital (MCVH), the teaching hospital of the Virginia Commonwealth University Health System in Richmond, Va. MCVH is a 788-bed, tertiary care university medical center in an urban area that offers a wide range of healthcare services, including all critical care specialties. This study was conducted in 2 adult critical care units: the medical respiratory ICU and the coronary medical ICU. The study was approved by Virginia Commonwealth University’s institutional review board. All subjects or their legally authorized representatives provided written informed consent.

A convenience sample of 20 subjects was drawn from all patients more than 18 years old admitted to the medical respiratory and coronary medical ICUs during an 8-month period (October 2001–May 2002). For an initial evaluation of actigraphy in critically ill adults, we thought that this sample size would provide sufficient variability to assess the technology adequately. The presence of an indwelling arterial catheter was required for continuous monitoring of arterial blood pressure. Patients who were receiving neuro-muscular blocking agents and those with overt disease affecting the brain (eg, head trauma, intracranial hemorrhage, meningitis, stroke) were excluded.

Measurement
Actigraphy data were compared with patients’ observed activity, scores on subjective sedation-agitation scales (RASS and Comfort Scale), and heart rate and blood pressure.

  Actigraphy.   The wrist actigraph (Actiwatch 16, model 198-0101, Mini Mitter, Bend, Ore) was placed on the wrist and ankle and used to measure patients’ activity. This actigraph is a small, lightweight, limb-worn device that measures long-term gross motor activity and integrates degree and intensity of motion. It contains an accelerotometer that is capable of sensing any motion with minimal resultant force of 0.01g. Internal memory and programming allow the actigraph to store data for several days. Data are downloaded to a computer-based database through a wireless data transfer system. Time epochs from every 5 seconds to every hour can be selected. Because our observation period was relatively short, we used a 15-second time epoch, which was similar to the epoch used in the only other study of sedation in hospitalized patients.²⁴ The actigraphy data (activity level) may vary from zero (no activity) to values in the hundreds (vigorous movement). Because actigraphy measures degree and intensity of motion, maximum values are difficult to quantify.

  Researcher Observation.   A coinvestigator visually observed and documented all patients’ activity during the data collection period. Data were collected about patients’ movements and patients’ interactions with healthcare providers. Because subtle cues and causes of agitated behavior are not well documented, direct observation of patients’ activity as well as interactions with care providers may provide valuable insight into the complex response in critically ill patients. All behavior was documented, including behavior caused by healthcare providers (eg, turning, bathing, suctioning) or environmental stimulation (eg, alarms, talking) as well as independent (nonstimulated) behavior of patients (eg, movement, coughing). The total number of events (initiated by care provider or by patient) was documented and summarized as an observed stimulation/activity count. Observational data were obtained without the researcher’s knowledge of heart rate and blood pressure or actigraphy data because these data were downloaded after the observational period.

  RASS.   Members of this research team developed RASS at Virginia Commonwealth University. It is a 10-point scale, with scores ranging from +4 (combative) to 0 (calm, alert) to –5 (unarousable). The RASS score is assessed at the bedside in 3 simple steps that involve use of discrete criteria, for 30 to 60 seconds.¹⁸ The RASS has been validated against a visual analogue scale of sedation and agitation (r = 0.93) and tested for interrater reliability among nurse, physician, and pharmacist raters in 5 adult ICUs at MCVH ( = 0.73).¹⁸ It has also been validated against other published sedation-agitation scales and tested for reliability among bedside nurses compared with a nurse educator after implementation of RASS in the MCVH medical ICU ( = 0.80).¹⁸ Additional testing of the interrater reliability and validity of RASS, including testing with bispectral array electroencephalography, has been done in addition to the evaluation of sedation over time.²⁵

  Comfort Scale.   The Comfort Scale is a nonintrusive measure of behavioral and physiological factors (8 items; with scores ranging from 1 to 5) originally designed to assess distress in children in the pediatric ICU.²⁶ The scale has been used to measure both pain^27–30 and sedation^31,32 in children. Although it was developed for children, because it consists of only behavioral and physiological measures, the Comfort Scale is also uniquely suited for use in intubated, sedated adults, who, similar to children, may be unable to communicate distress clearly. Criterion validity was established by comparison with concurrent global ratings of nurses in the pediatric ICU (r = 0.75). The scale is used to measure the level of consciousness as well as other parameters such as face grimacing, muscle tone, physiological values, and level of agitation. In its original testing, the 2 correlated factors, behavioral and physiological, accounted for 84% of variance,²⁶ and assessments by 3 raters simultaneously showed good internal consistency (r = 0.84).¹⁵ Interrater reliability of the items on the Comfort Scale is also good ( = 0.63–0.93).²⁶ The Comfort Scale has been used to measure sedation, comparing favorably with another sedation scale (Hartwig)³¹ and has been used to determine a target for optimal sedation, namely, a Comfort score of 17 to 26.³²

  Heart Rate and Blood Pressure.   Heart rate and blood pressure data were collected from the bedside monitor (model 66, Hewlett Packard Co, Andover, Mass) and printed during the 2-hour data collection period. Heart rate was recorded from the digital readout on the monitor that is based on the R-R interval, averaged over several beats of the electrocardiography tracing to yield stable values on the screen. Systolic blood pressure, diastolic blood pressure, and mean arterial pressure were recorded every 1 minute from continuous monitoring of the arterial pressure via an indwelling catheter (RA 04020, Arrow, Reading, Pa) by using a disposable transducer (model 42559-01, Abbott Critical Care Systems, N. Chicago, Ill). Pressure transducers were zeroed when each patient was admitted to the study per the manufacturer’s instructions. The data were printed, entered, and stored in a spreadsheet-compatible file for analysis.

Procedures
The investigator collecting the data was trained in all aspects of the study. Training on scoring the RASS and the Comfort Scale was conducted until an inter-rater reliability with the study’s principal investigator reached 90% or better. Patients in the 2 ICUs were evaluated as potential subjects for the study. If a patient met criteria for inclusion in the study, written consent was obtained from the patient’s legally authorized representative. A 2-hour observation period was used to directly observe patients’ activity and to measure patients’ activity by using wrist and ankle actigraphy, the RASS, the Comfort Scale, heart rate, and blood pressure. Immediately before the 2-hour data collection period, 1 actigraph was placed on the patient’s nondominant wrist and 1 actigraph was placed on the right ankle and secured with the wristband provided with the instrument. The study observer (investigator) remained in the patient’s room, out of the way and unobtrusive, during the observation period. The presence or absence of a soft restraint on all limbs was noted.

For a 2-hour period, actigraphy data were compared with patients’ observed activity, results on 2 sedation scales, heart rate, and blood pressure.

 

Once the observation period began, heart rate and blood pressure were automatically recorded every minute. The Comfort Scale and the RASS data were collected at the beginning of the observation period and 1 hour and 2 hours into the observation period. In order to score the RASS, the subject must be stimulated to respond if not obviously awake and alert. Therefore, an event marker was used during the RASS data collection, so that stimulation was identified during the data recordings. In addition, the Comfort Scale was scored before the RASS so that stimulation required by the RASS did not influence scores on the Comfort Scale. Actigraphy data were recorded and later were downloaded for analysis.

Data Analysis
In order to detect associations among actigraphy data and other measures of sedation, actigraphy counts were totaled for each 15-minute period (8 periods; 2 hours total). Means for heart rate and blood pressure were also calculated for each of the eight 15-minute periods, a process similar to an evaluation of actigraphy and motor activity during anesthesia.²⁴ In all tests, a P < .05 was considered significant. Because of the descriptive nature of this study, no adjustment for multiplicity was used. Statistical analysis was performed with Spearman correlations by using JMP software (SAS Institute Inc, Cary, NC) to test for significant relationships among all major variables. A paired t test was used to compare wrist and ankle actigraphy. In addition, because of the small sample size, in order to detect trends in the data, scores on the RASS and the Comfort Scale and the observed stimulation/activity counts were categorized into 3 groups. The RASS score was classified as low, medium, or high on the basis of clinically appropriate groupings: deeply sedated (RASS score –5, –4, or –3), lightly sedated/awake (–2, –1, 0), and agitated (+1,+2, +3, +4). Results of wrist actigraphy with and without restraints were compared for each RASS group by using a 2-sample t test with the Satterthwaite approximation to adjust for unequal group variances. Because the RASS score was obtained at just 3 time points (baseline, 1 hour, 2 hours), only the 15 minutes of heart rate, blood pressure, and actigraphy data from before determination of scores on the Comfort Scale and RASS were used in the analysis.

Scores on the Comfort Scale were categorized into 3 groups on the basis of target score identification by Marx and colleagues.²⁶ However, during the testing of a target score, 5 categories were collapsed into 3 (too sedated, optimally sedated, inadequately sedated).²⁶ Because our subjects fell into 2 of their 3 categories (too sedated and optimally sedated), we subdivided the optimally sedated into the original categories optimally sedated and somewhat inadequately sedated as described by Marx and colleagues in their original work,²⁶ creating groupings of low (10–16), medium (17–21), and high (22–25) scores on the Comfort Scale. This categorization was also the same as using the upper, middle, and lower tertiles. Because the observed stimulation/activity count was an untested variable, it was categorized by using the upper and lower quartiles (low 0–7, medium >7 to 12, high >12). As with the RASS, only the heart rate, blood pressure, and actigraphy data collected in the 15 minutes before the Comfort Score was assessed (at baseline, 1 hour, 2 hours) were used in the analysis.

	Results

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Testing was completed on all 20 subjects enrolled. Table 1 shows the demographic characteristics of the subjects. Most of the subjects were receiving some type of sedation (continuous, intermittent). Mean age of the subjects was 50.5 years; there were equal numbers of men and women, they had a variety of admitting diagnoses, and most were intubated. All data collection periods occurred between 11 AM and 7 PM. Total actigraphy count for the eight 15-minute periods of analysis varied from 0 to 3593 (Table 2). An example of the actigraphy recording for a subject is shown in Figure 1. Although higher scores (ie, from 26 to 40) on the Comfort Scale were not observed, scores did vary from 10 to 25. Because the data were not normally distributed, all data are shown with mean and median with accompanying interquartile ranges (Table 2).

View larger version (13K): [in this window] [in a new window]   Figure 1 Wrist actigraphy recording for a subject during the 2-hour observation period. Actigraphy count is the total for each 15-second epoch. Examples of observed movement are noted.

View this table: [in this window] [in a new window]   Table 3 Correlation (Spearman ) of major variables

View larger version (11K): [in this window] [in a new window]   Figure 2 Box plots of actigraphy count (total for 15-minute epoch) for 3 groups of scores on the Richmond Agitation-Sedation Scale (RASS): low = –5, –4, or –3; medium = –2, –1, or 0; and high = +1, +2, +3, or +4. The box represents the interquartile range; the horizontal line, the median value; and the error bars, the upper and lower range. For each category of the RASS, box plots illustrate the increasing median and the correlation of 0.58 between wrist actigraphy data and the score on the RASS.

View larger version (12K): [in this window] [in a new window]   Figure 3 Box plots of actigraphy count (total for 15-minute epoch) for 3 groups of scores on the Comfort Scale: low = 10 to 16; medium = 17 to 21; and high = 22 to 25. The box represents the interquartile range; the horizontal line, the median value; and the error bars, the upper and lower range. For each category of the Comfort Scale, box plots illustrate the increasing median and the correlation of 0.62 between wrist actigraphy data and the score on the Comfort Scale.

View larger version (13K): [in this window] [in a new window]   Figure 4 Box plots of actigraphy count (total for 15-minute epoch) for 3 groups of observed stimulation/activity count: low = 0 to 7, medium = 8 to 12, and high = 13 to 30. The box represents the interquartile range; the horizontal line, the median value; and the error bars, the upper and lower range. For each category of the observed stimulation/activity count, box plots illustrate the increasing median and the correlation of 0.45 between wrist actigraphy data and the stimulation/activity count.

Because the presence of restraints on the same extremity used for actigraphy might alter the limb movement and thus affect actigraphy data, this variable was addressed. During the 2-hour observational period, subjects had restraints on the upper extremities 38% of the time and on the lower extremity 4% of the time. Because few subjects had leg restraints, only the effect of wrist restraints was investigated. Wrist actigraphy counts were not significantly greater in subjects who were restrained than in subjects who were not restrained (t = –0.631; P = .56). However, those subjects with greater activity level may have been more affected by restraints than were subjects with little activity. Therefore, in order to evaluate differences in actigraphy counts relative to level of agitation (Table 4), RASS scores were grouped into 3 clinically appropriate categories: low (–5, –4, –3), medium (–2, –1, 0), and high (+1, +2, +3, +4). Compared with subjects who were not restrained, only subjects in the high RASS category who were restrained showed a trend toward lower actigraphy values (t = 2.95; P = .01). The normality assumption was satisfied for the high RASS group.

	Discussion

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However, without sensitive, specific objective measures of agitation, the presence and/or severity of agitation is recognized only after overt, often dangerous behaviors by patients (eg, removal of devices). This study provides an evaluation of actigraphy as a measure of activity in critically ill patients, which may be a beginning step in quantifying agitated behavior. Actigraphy data correlated with valid and reliable measures of sedation and agitation, with both behavioral measures and physiological measures and direct observation of behavior. We found that actigraphy counts correlate strongly with scores on subjective scales of agitation and sedation (RASS, Comfort Scale) and with observed stimulation and activity of patients such that high activity levels on actigraphy are associated with increased stimulation and activity of patients, whereas low activity levels on actigraphy are associated with decreased activity of patients. Actigraphy data correlated modestly with heart rate and blood pressure, but these are insensitive measures of activity and might be influenced by underlying medical conditions and medications.¹⁷ In addition, wrist and ankle actigraphy were highly correlated; ankle actigraphy indicated decreased levels of activity as would be expected because vigorous movement is more likely for upper extremities than for lower extremities.

Actigraphy may provide a behavioral measurement of activity as a surrogate for subjective or observed behavior and may be particularly important as a continuous measurement in longitudinal research. Although critically ill patients are often observed, and obvious increases in patients’ activity may be recognized by a bedside nurse or research observer, subtle changes in activity may not be as easily detected. The level of external stimulation in the ICU environment related to alarms, monitors, ventilators, and personnel may hamper the ability of a bedside nurse to monitor patients’ activity carefully. In addition, nurse-patient staffing ratios may reduce the time spent at each patient’s bedside. Objective activity measures such as actigraphy may provide a method of monitoring activity over time and allow early recognition and management of the increased activity that may be associated with agitation. However, this evaluation of actigraphy provides only an initial assessment of the technology as a research tool in critical care. Although increased activity may have a variety of causes both purposeful and nonpurposeful (eg, pain, delirium, anxiety, nursing interventions), without additional study, specific causes of increased activity cannot be clearly identified by using actigraphy alone.

Actigraphy data were correlated with valid and reliable measures of sedation and agitation, both behavioral and physiological measures and direct observations of behavior.

 

Limitations of this study include the small sample size and the possible effect of use of restraints on actigraphy at the higher levels of agitation that may mask detection of increased activity. However, the number of subjects in these subgroups (ie, high agitation and restraint use) was small, a characteristic that limits the generalizability of these findings. Data were not collected about the timing of sedative administration (only the presence or absence of sedation). However, the goal of the study was not to determine the appropriate level of sedation or of activity among subjects, but to compare the measurement of activity by using actigraphy with other tools for assessing activity/agitation.

Further evaluation of actigraphy as a measurement tool in critical care research is needed. Future studies should focus on a description of causes of increased activity, perhaps with the use of event markers in combination with actigraphy. In addition, comparison of actigraphy with other objective measures of sedation such as the bispectral index may be beneficial, because both the bispectral index and actigraphy provide data about the continuum from sedation to agitation. Identification of an ideal tool for assessing agitation-sedation will ultimately assist healthcare providers in caring for critically ill patients by providing accurate assessment of agitation and sedation, enhancing the caregivers’ ability to determine optimal levels of sedation, and ultimately minimizing agitation among patients.

Although its clinical use is currently limited, actigraphy may provide an objective, continuous measurement of patients’ behavior in longitudinal research.

 

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Commentary by Mary Jo Grap (see shaded boxes).

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