Delirium is described in the DSM IV-TR as an acute confusional state characterized by fluctuating mental status, inattention, and either altered level of consciousness or disorganized thinking [17
]. Delirium is common, particularly in the ICU, where it has been shown to occur in 60% to 80% of ventilated patients [2
] and 40% to 60% of nonventilated patients [20
]. For the last few decades, delirium has been recognized, yet it has been described with inconsistent terminology, such as ICU syndrome, acute brain dysfunction, acute brain failure, and septic encephalopathy [22
], depending on geographic location and specialty training. Delirious patients can present in a number of ways, and the general consensus is to subcategorize the delirium of a patient according to their level of alertness (hyperactive, hypoactive, and mixed delirium) [23
]. Although the hyperactive subtype of delirium is the easiest to detect, pure hyperactive delirium (i.e., without hypoactive component) only represents approximately 5% of delirium in the ICU [24
]. The hypoactive subtype of delirium is the most common (60%) and the mixed subtype is also frequently found.
Risk factors for the development of delirium in the critical care and postoperative settings have been previously described in the literature [25
]. Broadly, risk factors can be divided into 3 categories: 1) characteristics of the acute illness itself, 2) patient or host factors, and 3) environmental or iatrogenic factors. There are 3 popular mnemonics for consideration of risk factors of delirium, which include THINK, IWATCHDEATH, and ICUDELIRIUMS (Table ) (see: http://www.mc.vanderbilt.edu/icudelirium/terminology.html
). A couple of very common risk factors are of particular importance. First, in addition to the intrinsic illnesses of patients, such as severe sepsis or congestive heart failure, iatrogenic medications (or the combination of multiple medications) must be considered as a contributing and modifiable factor in the emergence of delirium. Medications notoriously associated with delirium include opiates (especially meperidine), sedatives including benzodiazepines, anticholinergics, antihistamines, antibiotics, corticosteroids, and metoclopramide. Lorazepam and midazolam (benzodiazepines commonly used in the ICU for sedation) were shown to be independent risk factors for transitioning into delirium (odds ratio, 1.2, 95% confidence interval (1.1, 1.4); p
]. Recently, genetic predisposition to delirium was demonstrated, as the apolipoprotein E4 (APOE4) genotype was found to be a strong predictor of delirium duration after adjusting for age, severity of illness, duration of coma, and admission diagnosis of sepsis, acute respiratory distress syndrome, or pneumonia (odds ratio, 7.32; p
]. Conflicting reports related to the apolipoprotein E4 (APOE4) genotype [34
] reinforce the need to study this association further.
Mnemonics for risk factors, causes, differential diagnosis for delirium
The comatose patient is distinguishable from the delirious patient in that the comatose patient does not respond to verbal commands. The delirious patient can be aroused through vocal commands, although they may not be able to follow them. The cardinal feature of delirium is inattention. Other symptoms (such as hallucinations or delusions) can be present and associated with delirium, but they are not required for the diagnosis. Patients with some, but not all, of the clinical symptoms of delirium are described as “subsyndromal,” and their associated outcomes are intermediate between normal and clinically delirious patients [35
]. One may think of subsyndromal delirium as an “intermediate state of badness” lying between full delirium and no delirium.
Recognition and management of delirium in critical care have progressed rapidly during the last decade due to clinical tools that have proven valid, reliable, and easy to replicate. The Society of Critical Care Medicine (SCCM) has recommended two validated tools to monitor for delirium in the ICU [36
]. One clinically validated system is the Intensive Care Delirium Screening Checklist (ICDSC) [37
]. This screening checklist, based on DSM criteria and delirium features, evaluates patients on an 8-point scale, including altered level of consciousness, inattention, disorientation, psychomotor changes, sleep/wake cycle disturbances, and symptom fluctuation. Patients with greater than 4 points on the scale are said to be delirious, allowing for dichotomous measurements and analysis, with a sensitivity of 99% and specificity of 64% [37
]. In 2001, the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) was shown to have high sensitivity (93–100%), high specificity (98–100%), and high inter-rater reliability (kappa
]. In multiple other investigations since that time, the sensitivity and specificity of the CAM-ICU in high severity of illness and in patients on mechanical ventilation have been repeatedly shown to be high [4
]. In lower severity of illness states, situations of infrequent in-servicing or re-calibration of staff, or non-ICU settings, the specificity has remained high (>90%), although the sensitivity may be sacrificed by use of this instrument (shown to be near 50% in some studies) [42
]. In such circumstances, it is best to spend longer than just the average 1 minute that it takes to do the CAM-ICU, and, instead to generate higher sensitivity, it should be considered necessary to invest upward of 10 minutes with the evaluation, as is often done with other instruments, such as the full CAM or DRS-R98 [44
]. The CAM-ICU is used in combination with an “arousal scale,” such as the Riker Sedation-Agitation Scale (SAS) [46
], or the Richmond Agitation-Sedation Score (RASS) [48
] to create a “sister-instrument” 2-step approach to the examination of consciousness, summarized as a CAM-ICU flowsheet or algorithm that has a number of advantages [12
- This algorithm provides a framework for assessing sedation and delirium that can be performed rapidly, in less than 2 minutes.
- This protocol has its greatest usefulness in tracking changes in the neurological status of the patient with the duration of time, and by comparing the current RASS or SAS score alongside the stated target RASS or SAS score for adjusting potent sedative and narcotic medications.
- Use of delirium assessment tools, such as the CAM-ICU, have been shown to result in shorter duration and lower doses of drugs, such as haloperidol used in the ICU .
- The assessment can be performed by all members of the treatment team (i.e., nurses, technicians, Doctors of Pharmacy, and physicians alike).
- This sedation and delirium assessment has been successfully implemented and replicated in medical, surgical, trauma, burn, cardiovascular, neurological, and pediatric ICU settings across medical centers [42, 51–53].
- The RASS and CAM-ICU assessments have been used in multiple high-profile randomized prospective trials [18, 54, 55]. The CAM-ICU instrument, which has been translated into many languages, can be accessed online at: http://www.mc.vanderbilt.edu/icudelirium/docs/CAM_ICU_flowsheet.pdf.
By combining an arousal scale and a delirium monitoring tool, the managing team can develop a “brain road map” that asks the following questions for each patient: 1) Where is the patient going? 2) Where is the patient currently? and 3) How did the patient get to their present state? These questions can then be answered with 4 simple indicators:
- Target the RASS. Where is the patient going?
- Determine the actual RASS. Where is the patient now?
- Determine the CAM-ICU. Where is the patient in thought content now?
- Assess the current drugs. How did the patient get to his or her present state?
Using a standardized, systematic approach on a daily basis to follow this critical “sixth vital sign” [56
] can assist the treatment team in tracking the progress of the patient with the duration of time.