Abstract
Since the increase of lifespan and the growth of the aged population among surgical patients, the topic of cognitive function and better outcome in the postoperative period became an area of great interest to researchers and concern to patients. The most frequent neurological complications occurring postoperatively are postoperative delirium and postoperative cognitive dysfunction. These complications lead to increased hospital mortality, long-term morbidity, and adverse socioeconomic outcomes. To provide top-quality healthcare and reduce neurological complications, we need to detect high-risk patients and target them to minimize risk factors that influence the development of cognitive dysfunction. This includes promoting nonpharmacologic delirium prevention strategies and implementing regular and frequent monitoring of cognitive function including preoperative evaluation of cognitive baseline.
Keywords
Cognitive baseline evaluation, Cognitive monitoring, Confusion assessment method, Postoperative cognitive dysfunction, Postoperative delirium
Contents
Timing, or When to Start? 282
Diagnostic Tools 285
Tools to Assess in the Early Postoperative Period 285
Riker Agitation–Sedation Scale 286
Perioperative Neuropsychological Testing 291
Conclusion 294
References 294
Further Reading 298
The hardest thing of all is to find a black cat in the dark room especially if there is no cat.
Cognitive function is an intellectual process by which one becomes aware of, perceives, or comprehends ideas. It involves all aspects of perception, thinking, reasoning, and remembering. The word origin comes from Latin verb “cognosco,” literally meaning being able “to conceptualize” or “to recognize.” Problems occurring in any of the main cognitive domains result in different types of cognitive dysfunction ( Table 10.1 ). Some of the common cognitive disorders are delirium, dementia, mild cognitive dysfunction, and postoperative cognitive dysfunction (POCD). The problem of cognitive evaluation has always been a topic of discussion, particularly in patients undergoing neurosurgical treatment, elderly patients, or orthopaedic patients, as their mental status may be already impaired and very fragile. The routine preoperative evaluation of the patient does not include assessment of their mental function, although it would be beneficial for the patient to prevent the development of neurological complications as well as risk evaluation and postoperative recovery.
| Brain structures | Cognitive domains | Function descriptions |
|---|---|---|
| Anterior temporal lobe Dorsolateral prefrontal cortex Hippocampal–diencephalic system | Memory and learning | Recognition memory, long-term memory, implicit learning, recall |
| Frontal lobe Temporal lobe | Language | Object naming, word finding, fluency, grammar and syntax, receptive language |
| Parietal lobe | Social cognition | Recognition of emotions, theory of mind |
| Temporal lobe | Attention | Sustained attention, divided attention, selective attention |
| Frontal lobe | Executive functioning | Planning, decision-making, flexibility, working memory, inhibition, abstract reasoning |
| Parietal lobe–visual cortex Temporal lobe–visual cortex Left parietal lobe Cerebellum | Perception-motor function | Visual perception, visual-constructional reasoning, coordination |
To monitor cognitive function, there are two principals to keep in mind. We need to know the patient’s mental status at baseline and have some useful tools to diagnose any changes. In this chapter, we will discuss both of these aspects.
Timing, or When to Start?
Evaluation of cognitive status of a patient should be performed initially during the hospital admission or preoperatively in the population to identify baseline cognitive status of an individual. This is particularly important with respect to elderly patients, as it is the only way to effectively identify any changes occurring postoperatively, during either the hospital stay or postdischarge.
The next step would be checking the mental status postoperatively to detect any signs of developing postoperative delirium (PD) ( Table 10.2 ). Ideally, this would involve the use of a validated delirium tool, such as the confusion assessment method (CAM). In particular the 3D-CAM provides online training and is validated for use by nonspecialists. Delirium can occur as early as within a couple of hours after arousal and last up to 7 days postoperatively or even post discharge. Therefore, constant and precise evaluation of cognitive status is highly recommended during the entire hospital stay for all high-risk patients.
| Types of cognitive impairments | Definition | Sequence of development | Forms | Cognition | Attention/perception | Outcome |
|---|---|---|---|---|---|---|
| Emergence agitation (delirium) | Is a condition associated with postanesthetic recovery characterized in psychomotor agitation or hypoactive alteration in mental status (somnolence), often meet in pediatric practice | Onset: minutes/hours Course: transitory | Hyperactive Hypoactive | Altered | Altered | Resolves completely after anesthetic agents have been metabolized |
| Postoperative delirium | A disturbance of consciousness with a reduced ability to focus, sustain or shift attention, a change in cognition or the development of a perceptual disturbance | Onset: hours/days Course: transitory, fluctuating | Hypoactive Hyperactive Mixed type | Altered | Altered | Resolves completely within days/weeks |
| Postoperative cognitive dysfunction | Mild neurocognitive impairment disorder, characterized by a functional decline in two or more cognitive domains | Onset: weeks/months Course; Transitory/permanent | Early within 6 months after surgery Late, 6 months postoperatively | Altered | Normal/altered | If persists for more than 3 months after surgery may result in increased 5-year postsurgical mortality and morbidity |
| Dementia | Is a family of major neurocognitive disorders characterized by memory impairment and/or deficit in other cognitive domains The impairment must be acquired and represent a significant decline from a previous level of functioning and interfere with independence in everyday activities | Onset: insidious Months/years Course: progressive | Vascular (multiinfarct) dementia (VaD) Alzheimer disease (AD) Parkinson disease with dementia (PDD) Dementia with Lewy body (DLB) Frontotemporal dementia (FTD) | Altered | Normal | Considered as nonreversible illness |
| Mild cognitive impairment | Is a mild neurocognitive disorder associated with memory problems in the absence of dementia or impairment in activities of daily living | Onset: months/years Course: progressive | Single memory mild cognitive impairment (amnestic) Multiple domains mild cognitive impairment Single nonmemory mild cognitive impairment | Altered | Normal | MCI predicts progression to dementia, with an annual conversion rate reported as high as 25% |
When the vulnerable stage of the early postoperative period has passed, we need to follow up with patients who are high risk (i.e., aged patients) to assess for development of POCD at 3 and 6 months postoperatively, and ideally even longer.
Diagnostic Tools
To obtain the best results, cognitive function should be monitored with special and dedicated tests, which evaluate memory, cognitive flexibility, motor performance, sensorimotor speed, and executive function. Some neuropsychological tests can be administered by nonspecialized caretakers (i.e., anesthesiologist, nurses), although appropriate training would be preferable. It is essential to refer for neuropsychologist consultation if a patient is suspected to have cognitive impairment as it provides a complete and comprehensive assessment, including other psychological aspects such as mood and emotional status, behavior, and personality changes.
Tools to Assess in the Early Postoperative Period
During arousal from general anesthesia, some patients can experience a condition called emergence agitation; this complication is more often seen in pediatric populations, although up to 3% of adults can develop it in postanesthesia care unit. Individuals may become agitated or hyperexcited or have disinhibition, crying, restlessness, or mental confusion. Emergence delirium usually resolves by itself as anesthetic drugs are metabolized; patients restore a clear mental state after about 15–20 min. The Riker agitation–sedation scale and the Richmond sedation–agitation scale are useful, reliable scales that have been designed to diagnose patients’ agitation rather than sedation. Both have a great advantage such as quick and easy to use in an emergency situation.
Riker Agitation–Sedation Scale
| 7 | Dangerous agitation | Pulling at ET tube, trying to remove catheters, climbing over bed rail, striking at staff, thrashing side to side |
| 6 | Very agitated | Does not calm, despite frequent verbal reminding of limits; requires physical restraints, biting ET tube |
| 5 | Agitated | Anxious or mildly agitated, attempting to sit up, calms down to verbal instructions |
| Non-agitated | ||
| 4 | Calm and cooperative | Calm, awakens easily, follows commands |
| 3 | Sedated | Difficult to arouse, awakens to verbal stimuli or gentle shaking but drifts off again, follows simple commands |
| 2 | Very sedated | Arouses to physical stimuli but does not communicate or follow commands, may move spontaneously |
| 1 | Unarousable | Minimal or no response to noxious stimuli, does not communicate or follow commands |
The next complication that may develop in the early postoperative period is PD. It has been defined by the American Psychiatric Association’s Diagnostic and Statistical Manual, fifth edition (DSM-V), which lists five key features that characterize it: a disturbance of consciousness with a reduced ability to focus, sustain or shift attention, a change in cognition or the development of a perceptual disturbance that is not better accounted for by a preexisting, established, or evolving dementia. The disturbance must develop over a short period of time (hours to days) and tends to fluctuate during the course of the day; and there must be evidence from the history, physical examination, or laboratory findings that the disturbance is not caused by the direct physiological consequences of a general medical condition.
Patients diagnosed with PD require rapid active action toward reducing the symptoms and treatment of the underlying cause of this severe complication. There are a number of tests available to detect PD such as CAM ( Table 10.3 ), CAM short version (CAM-ICU), 3-min confusion assessment method (3D-CAM), and Nursing Delirium Screening Scale (NU-DES), which are quick tools based on DSM-V criteria.
| Feature 1 | Acute onset and fluctuating course | Is there evidence of an acute change in mental status from the patient’s baseline? |
|
| Feature 2 | Inattention | Does the patient have difficulty focusing attention? |
|
| Feature 3 | Disorganized Thinking | Was the patient’s thinking disorganized or incoherent? |
|
| Feature 4 | Altered level of Consciousness | Overall, how would you rate this patient’s level of consciousness? |
|
CAM is considered to be the gold standard tool; it is a simple, fast, clinical test designed for medical practitioners as well as nonphysicians. It has a sensitivity of 94%–100% and a specificity of 90%–95% with appropriate training. It has been widely used in different clinical environments such as the ICU and aged care departments, so the scale has been adapted to suit these specific needs. CAM has also been translated into different languages and has been used internationally in several studies. The more recent validation of the 3D-CAM with online training increases sensitivity and specificity when used by nonspecialists. This tool includes a structured interview, so interpretation of features by nonspecialists is less critical to the diagnosis.
CAM-ICU : This scale was specifically developed for use in nonverbal (i.e., mechanically ventilated) patients. When administered by a trained health care professional, the CAM-ICU takes only 1–2 min. This shortened version has a proven reliability also in non-ICU wards, with a high sensitivity (94%) and a high specificity (89%). The CAM-ICU allows the diagnosis of POD in four steps. In the first step, variations from baseline mental status in the preceding 24 h are evaluated, using the Richmond agitation/sedation scale (RASS). The RASS score for an alert and calm patient is 0. Negative scores indicate hypoactivity (−1: drowsy; −2: light sedation; −3: moderate sedation; −4: deep sedation; −5: unarousable); positive scores (+1: restless; +2: agitated; +3: very agitated; +4: combative) indicate a hyperactive patient. The second step is to detect inattention. Patients are either asked to squeeze the operator’s hand when they hear the letter “A” among a list of letters, or to recognize previously seen images among a series of both seen and distracting images. The third step is the assessment of patient’s actual state of consciousness with the RASS, which should be different from zero (either negative or positive) for the symptom to be positive. The fourth step is the evaluation of disorganized thinking. Patients should answer four yes/no questions. Examples are “Is there the sun during the night?”, “Are you in the hospital?”, “Is ice cold?”, and “Is fire hot?” Also, the examiner shows two fingers to the patient, who is asked to hold up the same number of fingers and then, without the demonstration of the examiner, should hold up the same number of fingers on the other hand. The diagnosis of POD comes with at least three positive symptoms among the four described, in particular, with the first, the second, and the third symptoms positive, or as an alternative, the first, the second, and the fourth.
Nursing Delirium Screening Scale (Nu-DESC) is another sensitive and quick test for screening a PD in the surgical ward. It has a sensitivity between 32% and 95% and reported specificity around 87%. The Nu-DESC is an observational five-item scale that diagnoses symptoms such as (1) disorientation, (2) inappropriate behavior, (3) inappropriate communication, (4) hallucinations, and (5) psychomotor retardation. Each item is rated from 0 to 2 based on the severity of symptoms, and the total score varies from 0 to 10. The cutoff for delirium is reported to be 2.
Several other scores can be used as a second choice: Bedside Confusion Scale, Clinical Assessment of Confusion, Cognitive Test for Delirium, Confusion Rating Scale, Delirium-O-Meter, Delirium Observation Screening, Delirium Symptom Interview, NEECHAM Delirium Rating Scale, or the Memorial Delirium Assessment Scale ( Table 10.4 ). These are useful tools to evaluate PD but due to the long structure are demanding on time.
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