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Cognitive Function Monitoring
The hardest thing of all is to find a black cat in the dark room especially if there is no cat. Kung Fu Tzu
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.
Table 10.1
Neurocognitive domains
| 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.
Table 10.2
Differential diagnostics of cognitive impairment
| 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.
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