Psychosomatics 44:283-289, August 2003
© 2003 The Academy of Psychosomatic Medicine
Use of the Cognitive Test for Delirium in Patients With Traumatic Brain Injury
Richard E. Kennedy, M.D.,
Risa Nakase-Thompson, Ph.D.,
Todd G. Nick, Ph.D., and
Mark Sherer, Ph.D., ABPP/Cn
Presented in part at the 13th annual meeting of the American Neuropsychiatric Association, La Jolla, Calif., March 9–12, 2002. Received June 3, 2002; revision received Dec. 2, 2002; accepted Dec. 13. 2002. From the Departments of Psychiatry, Preventive Medicine, and Neurology, University of Mississippi Medical Center, Jackson, Miss.; and the Department of Neuropsychology, Methodist Rehabilitation Center, Jackson, Miss. Address reprint requests to Dr. Kennedy, Department of Psychiatry, Virginia Commonwealth University, Medical College of Virginia Campus, Box 980268, Richmond, VA 23298-0268; rkennedy{at}mail2.vcu.edu (e-mail).
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ABSTRACT
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The sensitivity and specificity of the Cognitive Test for Delirium, which was originally developed for use in intensive care units, were tested in a group of patients with traumatic brain injury who were admitted to a neurorehabilitation center. Sixty-five consecutive patients were evaluated weekly by using the DSM-IV criteria for delirium and the Cognitive Test for Delirium. Complete ratings were available for 249 of 304 weekly observations. Analysis of the receiver operating characteristic curve suggested an optimum cutoff score of less than 22 for identification of delirium by using the Cognitive Test for Delirium, with a sensitivity of 72% and a specificity of 71% compared with the DSM-IV diagnosis. The results suggest that the Cognitive Test for Delirium provides an acceptable level of differentiation between delirious and nondelirious patients with traumatic brain injury.
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INTRODUCTION
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Delirium is defined as a disturbance of consciousness, accompanied by a change in cognition or the development of perceptual disturbances, that is not better accounted for by a preexisting, established, or evolving dementia.1 It occurs in a variety of conditions, predominantly substance intoxication and withdrawal, problems with polypharmacy, and metabolic disturbances.2 The prevalence of delirium is approximately 20% in the general hospital population,3 with higher rates in certain at-risk groups.4 It is associated with longer hospital stays5–7 and with increased complications and functional decline.7–9
Recent investigations by our group have found a high incidence of delirium after traumatic brain injury.10,11 Delirium may result from the injury itself or from associated medical complications that predispose the patient to developing delirium.12 The diagnosis of delirium after traumatic brain injury is complicated by differences in classification among disciplines. The concept that is closest to delirium in the physiatric and neurosurgical literature is posttraumatic amnesia.13 Posttraumatic amnesia is defined as occurring between the time of injury and the return of continuous memory.14 However, the term posttraumatic amnesia is often loosely used, and conditions defined as posttraumatic amnesia may overlap with coma, stupor, delirium, and amnestic syndromes.13 Instruments designed to assess posttraumatic amnesia, such as the Galveston Orientation and Amnesia Test,15 do not adequately measure delirium.13 More recently, some experts have advocated discarding the concept of posttraumatic amnesia for that of posttraumatic confusion.16 Posttraumatic confusion includes global cognitive deficits such as impaired attention, as well as amnesia. Posttraumatic confusion closely resembles delirium, but it does not incorporate some features of delirium, such as emotional lability and perceptual disturbances. Currently, there are no brief, widely accepted cognitive scales to rate posttraumatic confusion; thus, no studies examining the adequacy of such measures for the diagnosis of delirium have been done.
The term posttraumatic agitation is also used in the physiatric literature and shares some similarities with delirium but again is not synonymous with delirium. Some experts view posttraumatic agitation as a subtype of delirium,17 while others feel it is a separate disorder.12 Although physiatrists view several of the DSM criteria for delirium as features of posttraumatic agitation, many disagree with use of the term delirium to describe the latter phenomenon.18 Physiatrists may feel that delirium omits critical characteristics of agitation,18 and some have expressed concern that the term delirium incorporates both calm and agitated confusional states.19 Standardized scales such as the Agitated Behavior Scale are used for assessing posttraumatic agitation in research reported in the physiatric literature.20 There have been no studies examining the adequacy of these measures for the diagnosis of delirium in the traumatic brain injury population, but the concerns summarized here make their utility doubtful.
Thus, although delirium is a common occurrence after traumatic brain injury, the neuropsychological instruments used in the rehabilitation setting do not adequately capture this diagnosis. The psychiatric literature includes descriptions of a number of instruments with different psychometric properties.21–23 Several of these serve as screening instruments, which allow detection of possible cases but have a low specificity. Some scales designed for accurate diagnosis of delirium do not rate symptom severity, and other scales perform both functions. The accuracy of many of these instruments can be enhanced by using standardized cognitive measures during the diagnostic assessment, although cognitive testing alone is often insufficient for making a diagnosis of delirium.2 The Mini-Mental Status Examination (MMSE)24 is widely used for such cognitive assessments, although many clinicians use a battery of tests for this purpose.2
The Cognitive Test for Delirium25 was developed as an alternative method for the diagnosis of delirium solely on the basis of cognitive performance. It was designed for use in intensive care settings, where patients may suffer from verbal and motoric impairments. The test requires only nonverbal responses in the form of pointing, nodding the head, or raising the hand. It consists of five subtests that address the areas of orientation, attention span, memory, comprehension/conceptual reasoning, and vigilance. The raw scores from each subtest are converted to scores ranging from 0 to 6, which are then summed to give a total score from 0 to 30. Lower scores indicate a greater likelihood of delirium. The original validation study compared intensive care patients with delirium (N=22), outpatients with dementia (N=26), and general psychiatric inpatients with depression or schizophrenia (N=55).25 The cause(s) of delirium were not specified, other than by excluding patients with a history of neurological conditions that might affect cognitive function. Analysis of the receiver operating characteristic curve showed an optimal cutoff score of less than 19. This cutoff value was associated with a sensitivity of 100% and a specificity of 95.1%. The Cognitive Test for Delirium completely differentiated delirious patients from general psychiatric inpatients; however, some severely demented patients were misidentified as delirious. In a follow-up study of 43 intensive care patients, 10 were unable to complete the Cognitive Test for Delirium.25 Of the remaining 33 patients, 14 were unable to complete the MMSE. Thus, the Cognitive Test for Delirium may be a valuable test of cognition for patients who are unable to complete more widely used tests. The purpose of this study was to explore the utility of the Cognitive Test for Delirium in one such population—patients with traumatic brain injury. It was expected that patients with traumatic brain injury who also had delirium would score significantly lower on this test than those without delirium.
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METHOD
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Subjects were 65 consecutive patients with traumatic brain injury who were admitted to the Brain Injury Rehabilitation Unit of Methodist Rehabilitation Center in Jackson, Miss. All participants were enrolled in the Traumatic Brain Injury Model Systems project of the National Institute on Disability Rehabilitation and Research. Written informed consent was obtained from all subjects before enrollment. Surrogate consent was obtained from proxy decision makers for subjects who were unable to provide appropriate consent. All subjects had ratings at level IV or above with the Ranchos Los Amigos Cognitive Scale26 during inpatient rehabilitation; the mean rating was 4.8. Information on participants' injury severity, medical course, and demographic characteristics was obtained by research assistants from medical records. Subjects were predominantly male (78%), single (45%), and Caucasian (66%). The average age was 36 years (range=17–87). The primary mechanism of injury was motor vehicle collision (71%), and the majority (66%) had sustained severe injuries. Table 1 summarizes the demographic and injury characteristics of the study participants.
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TABLE 1. Demographic Characteristics of Subjects (N=65) in a Study of the Sensitivity and Specificity of the Cognitive Test for Delirium in Assessing Patients With Traumatic Brain Injury
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Participants were evaluated weekly, and the diagnosis of delirium was made according to the DSM-IV criteria1 by consulting neuropsychologists who had extensive experience in the diagnosis of delirium. The Cognitive Test for Delirium was administered independently by research assistants who were trained in its use according to the standardized protocol described by the instrument's developers.25
Spearman correlation coefficients were calculated to analyze the relationship between participants' subscale scores on the Cognitive Test for Delirium and the diagnosis of delirium. Logistic regression analysis was used to identify the subscales that were predictive of a delirium diagnosis. The independence assumption of logistic regression was relaxed by treating the multiple observations from an individual subject as a cluster. A receiver operating characteristic curve was constructed for the Cognitive Test for Delirium total score, with the DSM-IV diagnosis of delirium as the gold standard. Sensitivity and specificity at various cutoff values, as well as optimal cutoff values, were determined from this receiver operating characteristic curve. Analyses were completed by using the Stata statistical package,27 with the significance level set at the 0.05.
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RESULTS
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Complete ratings (i.e., the results of the evaluation with the DSM-IV delirium criteria, as well as the Cognitive Test for Delirium subscale and total scores) for the 65 participants were available for 249 of a possible 304 weekly observations; the remainder were not completed because of scheduling difficulties, patient noncompliance, and interruptions associated with hospital routine. The diagnosis of delirium was made contemporaneously with administration of the Cognitive Test for Delirium in all instances; patients were identified as having delirium according to the DSM-IV criteria in 130 (52%) of these observations. The average time from injury to initial assessment was 28.5 days (SD=15.0). Glasgow Coma Scale28 ratings made in the emergency department did not differ between the subjects who met the DSM-IV criteria for delirium at admission to the rehabilitation center and those who did not (p=0.94, Mann-Whitney test). The median Glasgow Coma Scale score for both groups was 7. Table 2 presents median subscale and total scores for the Cognitive Test for Delirium for observations made when subjects did and did not meet the DSM-IV criteria for delirium. The Cognitive Test for Delirium was designed to be administered so that participants do not give a verbal response. This feature is useful in intensive care settings, where many patients have a tracheostomy. This feature is also useful in assessing patients with traumatic brain injury, although some patients in this study were unable to complete the subscales for a variety of reasons, including severe aphasia, hypoarousal, visual impairment, motor impairment, and severe motor restlessness resulting in inability to cooperate with testing. In 18%–22% of the 249 observations in this study, some subscales of the Cognitive Test for Delirium could not be completed in the manner described by the authors25 because of various patient impairments (Table 2). For example, the orientation subscale could not be completed in 18% of the observations. Subjects who were unable to complete a subscale were given the worst possible score, and the inability to complete the subscale was coded with the score. The rationale for this procedure was that the ability of most individuals to undergo formal cognitive evaluation was determined by the degree of confusion. Since evaluations occurred weekly, subjects' participation was monitored throughout the hospitalization.
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TABLE 2. Subscale Completion Rate and Median Subscale and Total Scores for the Cognitive Test for Delirium in 249 Observations of Patients With Traumatic Brain Injury (N=65)
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Table 3 shows odds ratios for the association of subscale and total scores on the Cognitive Test for Delirium with a delirium diagnosis in the 249 completed observations. An unadjusted odds ratio is reported for the total score, and both unadjusted odds ratios and odds ratios adjusted for scores on all other subscales are reported for the subscales. Each subscale showed a significant association with the DSM-IV delirium diagnosis. The unadjusted odds ratios for the subscale scores ranged from 1.44 to 1.54, indicating that a 1-point change on each subscale (range of scores on each subscale=0–6) results in approximately a 50% increase in the patient's odds of meeting the diagnostic criteria for delirium.
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TABLE 3. Odds Ratios Showing Relative Importance of Subscale and Total Scores of the Cognitive Test for Delirium for Identification of Delirium in Patients With Traumatic Brain Injurya
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Intercorrelations (Spearman coefficients, rs) of the Cognitive Test for Delirium subscale and the total scores are shown in Table 4. The subscale scores were all significantly correlated with each other. Multivariate regression analysis showed that only the vigilance subscale made a unique contribution to prediction of a delirium diagnosis, after adjustment for the other subscale scores. The adjusted odds ratio indicated that a 1-point change on the vigilance subscale (score range=0–6) increased the odds of not meeting the criteria for delirium by 43%. For example, individuals with a score of 5 (relatively better vigilance/attention) on the vigilance subscale demonstrated a 43% higher odds of not being delirious, compared to individuals with a score of 4 (relatively worse vigilance/attention). In a separate logistic model computed by using only the Cognitive Test for Delirium total score (range of scores=0–30), the odds of not meeting the criteria for delirium increased by 11% for each 1-point change in score (Table 3). For example, individuals with a total score of 25 (relatively better cognition) had an 11% higher odds of not meeting the delirium criteria compared to individuals with a score of 24 (relatively worse cognition).
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TABLE 4. Correlation of Subscale and Total Scores on the Cognitive Test for Delirium in 249 Observations of Patients With Traumatic Brain Injury (N=65)
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To further explore the aspects of cognitive ability that are measured by the Cognitive Test for Delirium, a principal component analysis of the five subscale scores was performed by using the 249 observations. The component coefficients for the five subscales were as follows: 0.89 for orientation, 0.89 for attention, 0.84 for memory, 0.91 for comprehension, and 0.92 for vigilance. The principal component analysis extracted only one component, indicating that the Cognitive Test for Delirium is best interpreted as a measure of general cognitive ability in patients in early recovery from traumatic brain injury. This component accounted for 79% of the total variance.
Receiver operating characteristic analysis was conducted by using the serial observations reflecting cognitive status across the course of early recovery after traumatic brain injury. A cutoff value of less than 22 indicated delirium, with an area under the curve of 0.79 (95% confidence interval=0.74–0.85). (An area under the curve of 0.80 or greater is considered to reflect good predictive ability.) A cutoff value of less than 22 provided a sensitivity of 71% and specificity of 72% for identification of delirium. Greater sensitivity could be obtained with a higher cutoff value, but the specificity would be lower. For example, with a cutoff value of 25, sensitivity increased to 85%, but specificity decreased to 61%. Use of a lower cutoff value such as 19, as suggested by Hart and colleagues,25 decreased sensitivity to 62% and increased specificity to 75%.
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DISCUSSION
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To our knowledge, this study provides the first examination of the performance on the Cognitive Test for Delirium of patients with traumatic brain injury. Prior investigation of this series of patients has established that delirium is common among traumatic brain injury inpatients referred for inpatient rehabilitation.10,11 The present study demonstrated that the Cognitive Test for Delirium is useful for detecting delirium among inpatients with traumatic brain injury. It is noteworthy that some subjects were unable to complete some subscales for various reasons (e.g., hypoarousal, aphasia resulting in inability to understand task instructions, and motor impairments limiting pointing responses). This finding suggests that the Cognitive Test for Delirium has some limitations for use with traumatic brain injury patients. Patients who met the criteria for delirium demonstrated greater cognitive impairment than individuals who did not. Poor performance on the Cognitive Test for Delirium vigilance subscale and total score for individuals with delirium was expected, since attentional disturbance and impaired cognition are features of the DSM-IV diagnosis of delirium.
Principal component analysis of the patients' performance across the Cognitive Test for Delirium subscales yielded one component, suggesting that various manifestations of delirium likely affect performance across the instrument's subscales despite the potential presence of preserved or intact cognitive domains. Individuals who have motor restlessness and who are unable to focus on testing tasks may score poorly across all subscales for reasons other than the impairments the subscales are intended to measure. Since attentional impairments are one of the criteria for the DSM-IV diagnosis of delirium, inability to focus on testing was likely one of the most common reasons for poor performance across the cognitive domains assessed by the Cognitive Test for Delirium. The finding of a single cognitive factor in the principal component analysis suggests the difficulty of discriminating specific cognitive impairments in acutely confused traumatic brain injury inpatients.
The Cognitive Test for Delirium demonstrated acceptable sensitivity and specificity for the diagnosis of delirium in this group of traumatic brain injury patients. The receiver operating characteristic analysis showed an optimal cutoff value of less than 22, which yielded a sensitivity of 71% and a specificity of 72% compared to the DSM-IV diagnosis of delirium. Increasing sensitivity may be achieved by using a higher cutoff value. The cutoff value of less than 22 is slightly higher than the original cutoff value reported by Hart and colleagues,25 and the sensitivity and specificity in this study are both lower than those reported by Hart et al. These differences may reflect the inherent limitations of using the Cognitive Test for Delirium for the detection of delirium in the traumatic brain injury population. Delirium encompasses a broad array of symptoms in addition to cognitive abilities, although the Cognitive Test for Delirium only measures the latter. Two other studies have focused on cognitive tests for the detection of delirium, with similar results. Bettin and colleagues29 tested 22 delirious elderly subjects and 15 elderly comparison subjects with the forward digit span and similarities tests and found a correlation of 0.50 between performance on the tests and fulfillment of the DSM-III-R criteria for delirium. O'Keeffe and Grosney30 found that scores on a global rating of attentiveness, the backwards digit span test, and a cancellation test distinguished patients with delirium from those with dementia but that scores on the MMSE, the forward digit span test, and a vigilance test did not. Thus, it is unlikely that cognitive tests alone can adequately assess the severity of delirium and distinguish delirium from other conditions.22 Combining cognitive tests with other assessment methods may provide a more reliable diagnosis. Ely and colleagues31,32 recently used this strategy in an intensive care setting. They modified the Confusion Assessment Method by including certain elements from the Cognitive Test for Delirium to form the Confusion Assessment Method for the Intensive Care Unit. This instrument, administered by critical care nurses and intensivists, had a sensitivity of 95%–100% and a specificity of 89%–93%, compared to the DSM-IV diagnosis of delirium.
Alternatively, the lower sensitivity and specificity found in the present study may reflect differences between the characteristics of delirium in the intensive care unit, where the Cognitive Test for Delirium was originally tested, and in other settings, such as inpatient rehabilitation settings. To our knowledge, no studies have compared results from administration of the Cognitive Test for Delirium in different settings. Patients with delirium after traumatic brain injury may have a different profile of cognitive deficits than intensive care unit patients with delirium, and the Cognitive Test for Delirium may be more sensitive to the cognitive deficits in the latter group. Finally, the differences in sensitivity and specificity may reflect differences in the prevalence of delirium between settings. The prevalence of delirium in the intensive care unit has been reported to be as high as 80%,33 compared with approximately 69% among traumatic brain injury patients.10 The higher prevalence in the intensive care settings may contribute to the higher positive predictive value reported for the Cognitive Test for Delirium in those settings.
The Cognitive Test for Delirium has several potential advantages in the rehabilitation setting, including the advantages described by the developers of the instrument.25 Like the MMSE, it is a brief examination, taking only 10–20 minutes to administer in this group of traumatic brain injury patients. It also provides alternate forms to avoid the practice effects that can limit the utility of instruments such as the MMSE. Since sections of the Cognitive Test for Delirium are derived from standard neuropsychological tests, rehabilitation staff will be familiar with procedures for administering the test and will find it easy to incorporate the test into their evaluation of patients. Finally, the Cognitive Test for Delirium was designed to be used with intensive care unit patients with verbal and some motor impairments. Such difficulties are common in patients with acute traumatic brain injury and can complicate the evaluation of cognition. In this study, the nonverbal format of the Cognitive Test for Delirium allowed standard administration of the test in approximately 80% of the 249 observations. Individuals who were aphonic or aphasic were able to respond to the test by pointing to answers. Our study did not include evaluation with the MMSE, so we do not know the percentage of patients who could complete the Cognitive Test for Delirium but not the MMSE. However, the initial studies in the intensive care setting suggested that the Cognitive Test for Delirium can be used to evaluate cognition in a significant number of patients who cannot complete other measures.25 By assessing executive and nonverbal cognitive functions, the Cognitive Test for Delirium measures right hemisphere functions22 that may play a key role in the pathophysiology of delirium.33
Delirium in traumatic brain injury may represent a significant adverse event independent of other complications of injury. Studies in other populations have shown that delirium is associated with increased mortality, longer lengths of hospital stay,34 increased utilization of hospital resources,35 and poorer functional34,36,37 and cognitive8 outcomes. Use of measures such as the Cognitive Test for Delirium can enhance the detection of delirium in the traumatic brain injury population, allowing further research on the consequences of this disorder in the rehabilitation setting.
This work was supported by grant H133A980035 from the National Institute on Disability and Rehabilitation Research Traumatic Brain Injury Model Systems program.
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ABSTRACT
INTRODUCTION
