Several delirium assessments exist, but the Confusion Assessment Method (CAM) is probably the most widely accepted by clinicians. The CAM was developed for non-psychiatrists and is based upon the Diagnostic and Statistical Manual of Mental Disorders, Revised 3rd Edition
It consists of four features: 1) acute onset of mental status changes and a fluctuating course, 2) inattention, 3) disorganized thinking, and 4) altered level consciousness.101
A patient must have both features 1 and 2 and either feature 3 or 4 to meet criteria for delirium (). The CAM training manual recommends using a cognitive screening test such as the Mini-Mental State Examination and the Digit Span Test to help determine the features of the CAM.102
Features of the Confusion Assessment Method. A patient must have both features 1 and 2, and either 3 or 4 to meet criteria for delirium.
An acute change in mental status and fluctuating course (feature 1) is a cardinal feature of delirium and must be present for a patient to be CAM positive. In the ED, this feature is determined from interviewing a proxy such as a family member. Feature 1 can be difficult to ascertain if a proxy is not readily available in the ED. If a patient comes from a long-term care facility, contacting the patient’s nurse or physician at that facility can often help establish the patient’s baseline mental status. Similarly, the patient’s primary care provider, if available, is another potential resource. In some patients, an acute change and fluctuation in mental status can be observed first hand during the ED stay.
Features 2, 3, and 4 are assessed during the patient interview and cognitive screen. Similar to feature 1, inattention (feature 2) is considered another cardinal feature of delirium and is described as a patient who is easily distractible and has difficulty maintaining focus. A patient with disorganized thinking (feature 3) may ramble, display tangential thoughts, or demonstrate an illogical flow of ideas. Patients with altered level of consciousness (feature 4) may exhibit drowsiness, lethargy, anxiety, hypervigilance, or combativeness (hyperactive).
Inouye et al. found the CAM to have excellent sensitivity (94% – 100%) and specificity (90% – 95%) in hospitalized patients.101
Subsequent validation studies have shown more variability in diagnostic performances with sensitivities ranging from 46% to 94% and specificities ranging from 63% to 100%.103
However, this variability is most likely attributable to the level of training.104
The CAM has excellent interobserver reliability (kappa 0.70 – 1.00) when performed by trained personnel.103
Thus far, the CAM is the only delirium assessment validated for use in the ED. Using lay interviewers to perform the CAM and a geriatrician’s assessment as the reference standard, Monette et al. observed that the CAM was 86% sensitive and 100% specific in ED patients. They also reported that the CAM had excellent interobserver reliability (kappa = 0.91) in this setting.105
However, the CAM takes up to 10 minutes to perform,102
which can be challenging in a highly demanding ED environment. The Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) may be more feasible in the ED because it takes less than two minutes to perform. The CAM-ICU primarily uses the same the same four features as the CAM: 1) acute onset of mental status changes or a fluctuating course, 2) inattention, 3) altered level consciousness, and 4) disorganized thinking. Similar to the CAM, a patient must have both features 1 and 2, and either feature 3 or 4 to meet criteria for delirium. However, there are several notable differences between these two assessments. The CAM-ICU uses brief neuropsychiatric screening assessments to test for inattention and disorganized thinking. These screening assessments help minimize subjectivity and improve its ease of use. The CAM-ICU also slightly modifies the original CAM’s feature 1, requiring either an acute change in mental status or fluctuating course.106
In the latest iteration, the CAM-ICU also reorders features 3 and 4 of the CAM; the CAM-ICU’s feature 3 is altered level of consciousness and feature 4 is disorganized thinking. The rationale for this change is detailed in the next paragraph. Lastly, the CAM-ICU also uses the Richmond Agitation and Sedation Scale to help determine altered level of consciousess.106
Testing all four features of the CAM-ICU typically takes less than two minutes to perform. However, using the algorithm provided in , the CAM-ICU can take less than 1 minute to perform in many cases. This algorithm provides a stepwise approach to performing the CAM-ICU and allows the rater to stop the assessment early, especially if either feature 1 (acute change in mental status or fluctuating course) or feature 2 (inattention) is negative. Disorganized thinking (CAM-ICU’s feature 4) is performed only if features 1 and 2 are both positive, and there is no evidence of any altered level of consciousness (CAM-ICU’s feature 3). Because the majority of CAM-ICU positive patients has altered mental status or a fluctuating course, inattention, and altered level consciousness, disorganized thinking (CAM-ICU’s feature 4) is usually not assessed in the clinical setting. For this reason, the latest version of the CAM-ICU reverses the order of the original CAM’s features 3 and 4 as described in the previous paragraph.
Algorithm for performing the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) in the clinical setting. The shaded hexagons indicate a stopping point for the CAM-ICU.
The CAM-ICU has been validated in mechanically ventilated and non-mechanically ventilated intensive care unit patients. Ely et al. reported that the CAM-ICU was highly sensitive (93% – 100%) and specific (89–100%) with excellent interrater reliability (kappa= 0.84 to 0.96) between nurses and physicians.107, 108
However, the CAM-ICU has not been validated in the ED patients and spectrum bias may exist. A validation study in the ED setting is currently ongoing.
Several other delirium instruments exist in the literature (). Similar to the CAM, these instruments require subjective assessments and many take up to 10 minutes to complete, making them difficult to perform in the ED.109–122
However, the Nursing Delirium Screening Scale (NuDESc) may be potentially useful in the ED because it takes less than two minutes to perform. The NuDESc is a checklist that asks nurses about the presence of disorientation, inappropriate behavior, inappropriate communication, hallucinations, and the presence of psychomotor retardation over an 8-hour shift.113
However, the NuDESc does not assess for an acute change in mental status or fluctuating course and inattention, which are cardinal to the diagnosis of delirium. Despite this, the NuDESc appears to have excellent diagnostic characteristics. Using the CAM as the reference standard, Gaudreau et al. reported the NuDESc to be 86% sensitive and 87% specific.113
Radtke et al. observed that the NuDESc was 95% sensitive and 87% specific compared to a research assistant’s assessment using the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition
The NuDESc’s interrater and interobserver reliability are unknown and will be important to elucidate given its use of subjective observations. Similar to the CAM-ICU, the NuDESc still requires validation in the ED setting.