Hesam Aldin VarpaeipersName, Kousha FarhadipersName, Mostafa MohammadipersName, Alireza Khafaee pour khamsehpersName, Tahereh MokhtaripersName (2024date). “Postoperative cognitive dysfunction: a concept analysis.” Aging Clinical and Experimental Researchtitle·j.
Object of study — post-operative cognitive dysfunctionterm·dom as a clinical concept
Research question — what the best definition of POCDterm·dom is, and what its attributes, related terms, antecedents and consequences are
Contribution — a unified definition of POCDterm·dom that separates it from commonly confused surrogate terms
phenomenon · claim-type · cross-domain-transfer · mechanism · claim-relation · replication-status · limitation — grounded in the full text| phenomenon | the lack of conceptual clarity about post-operative cognitive dysfunction — “Conceptual clarity for POCD is lacking in the currently body literature.” | |
| claim-type | existence — “POCD is a subtle-to-extensive cognitive change that affects single or multiple cognitive domains.” | |
| method — evidence | — “Our concept analysis follows Rodgers’ evolutionary method [ 25 ], recommended for analyzing concepts that change over time with increasing research and those that vary across contextual circumstances.” | |
| object of study — evidence | — “Post-operative cognitive dysfunction (POCD) is a concern for clinicians that often presents post-surgery where generalized anesthesia has been used.” | |
| research question — evidence | — “Our two-fold purpose of this concept analysis was to (1) critically appraise the various definitions, while also providing the best definition, of POCD and (2) narratively synthesize the attributes, surrogate or related terms, antecedents (risk factors), and consequences of the concept.” | |
| contribution — evidence | — “While previous studies fell short of providing an in-depth definition of POCD, incorporating its characteristics, risk factors, outcomes, and most importantly differentiating POCD from surrogate terms commonly mistaken for, the current study provides a unified definition of POCD that can be adopted in future studies.” | |
| mechanism | lack of theoretical guidance Studies run without a guiding theory diverge in timing, diagnosis and definition, which may explain the divergent incidence rates. — “This lack of theoretical guidance has led to three potential discrepancies or issues, which, in turn, may explain the divergent incidence rates of POCD that have been reported.” | mechanisms[0] |
| mechanism | compensatory mechanism Cognitive vitality compensates for the cognitive decline of aging. — “CV serves as a compensatory mechanism to adapt against the cognitive decline of aging.” | mechanisms[1] |
| builds-on | Monk et al. [6] — “This idea is supported by Monk et al. [ 6 ], who categorized the development of POCD as early (at hospital discharge) and late (three months after surgery).” | claim_relations[0] |
| sense | POCD - portrayed as reversible MCI by some, as a mild neurocognitive disorder by others — “Liu et al. [ 13 ] portrayed POCD as a reversible form of MCI, while Needham et al. [ 12 ] described POCD as a mild neurocognitive disorder developing between 7 days and 1 year from surgery.” | senses[0] |
| relation | Post-operative cognitive dysfunction —same-as→ POCD — Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities. — “Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities.” | concept_edges[0] |
| weight | Post-operative cognitive dysfunction —same-as→ POCD — 0.9 — “Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities.” | concept_edges[0] |
| relation | Post-operative cognitive dysfunction —is-a→ cognitive impairment — Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities. — “Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities.” | concept_edges[1] |
| weight | Post-operative cognitive dysfunction —is-a→ cognitive impairment — 0.85 — “Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities.” | concept_edges[1] |
| relation | Sustained attention —contrasted-with→ selective attention — Sustained attention is the ability to maintain sensitivity to stimuli, while selective attention is the ability to process a certain part of sensory input while omitting others. — “Sustained attention is the ability to maintain sensitivity to stimuli, while selective attention is the ability to process a certain part of sensory input while omitting others.” | concept_edges[2] |
| weight | Sustained attention —contrasted-with→ selective attention — 0.75 — “Sustained attention is the ability to maintain sensitivity to stimuli, while selective attention is the ability to process a certain part of sensory input while omitting others.” | concept_edges[2] |
| replication | not-applicable | |
| no type for this | mild cognitive impairment → mild NCD — mild NCD is the newer name for what was formerly known as mild cognitive impairment — “Formerly known as mild cognitive impairment, mild NCD refers to the period between age-related normal cognition changes and the onset of dementia symptoms [ 108 ].” | unhoused_relations[0] |
| limitation | The search covered only English studies published after 1998. — “First, the literature search was limited to studies published after ISPOCD1 (1998) and written in English, so some important studies may have been missed.” | limitations[0] |
| limitation | Only three databases were searched and grey literature was excluded. — “Second, the literature search was limited to three online databases, and gray literature was not considered in this study.” | limitations[1] |
finding · quantity · variable · definition · key-term — grounded in the full text| finding | In 686 non-cardiac surgery patients, POCD was largely reversible over time. — “However, a study conducted by Steinmetz et al. [ 31 ] on 686 patients undergoing non-cardiac surgery indicated that POCD is largely reversible over time [ 12 , 13 , 24 , 31 , 32 ].” | content_tags.findings[0] |
| quantity | 36.6% to 42.4% — — “POCD is a serious public health concern, with prevalence rates ranging from 36.6% in young adults to 42.4% in the elderly [ 6 ].” | content_tags.quantities[0] |
| quantity | 5 to 40% — — “The incidence of POD was reported to range from 5 to 40% [ 22 , 103 , 104 ].” | content_tags.quantities[1] |
| quantity | 86 — — “The review process yielded a final set of 86 eligible articles.” | content_tags.quantities[2] |
| key-terms | POCD, post-operative delirium, cognitive dysfunction, neurocognitive disorder, dementia, anesthesia, concept analysis, neuropsychological tests, practice effect, cognitive vitality |
| concept | Post-operative cognitive dysfunction — a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities — “Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities.” | concepts[0] |
| concept | POCD — Post-operative cognitive dysfunction — “Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities.” | concepts[1] |
| concept | cognitive impairment — not defined in this paper's own words; a lasting loss of cognitive ability — “Post-operative cognitive dysfunction (POCD) is a specific cognitive impairment that involves functional impairment of the nervous system’s activities, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial, and visuomotor abilities.” | concepts[2] |
| concept | cognitive dysfunction — difficulties with selective and sustained attention, learning and memory problems, deficits in visual and auditory processing, and processing speed — “The term “cognitive dysfunction” refers to difficulties with selective and sustained attention, learning and memory problems, deficits in visual and auditory processing, and processing speed [ 2 ].” | concepts[3] |
| concept | Sustained attention — the ability to maintain sensitivity to stimuli — “Sustained attention is the ability to maintain sensitivity to stimuli, while selective attention is the ability to process a certain part of sensory input while omitting others.” | concepts[4] |
| concept | selective attention — the ability to process a certain part of sensory input while omitting others — “Sustained attention is the ability to maintain sensitivity to stimuli, while selective attention is the ability to process a certain part of sensory input while omitting others.” | concepts[5] |
| concept | Executive function — the capacity to complete complicated tasks such as planning, reasoning, problem solving, and adaptation to complex situations — “Executive function refers to the capacity to complete complicated tasks such as planning, reasoning, problem solving, and adaptation to complex situations.” | concepts[6] |
| concept | POD — an acute state of fluctuating and altered consciousness due to underlying internal and external factors such as anesthetics, pain, and cerebral hypoperfusion — “POD is an acute state of fluctuating and altered consciousness due to underlying internal and external factors such as anesthetics, pain, and cerebral hypoperfusion [ 102 ].” | concepts[7] |
| concept | CV — Cognitive vitality — “CV refers to an individual’s capacity to adjust to cognitive changes and maintain an optimal level of cognitive functioning, life satisfaction, and independent living by effectively balancing their energy and personal resources.” | concepts[8] |
| concept | practice effect — observing pseudo-improvement in patients’ cognitive function due to repeated exposure to the same questions — “When using the same tools (especially tests like the MMSE) repeatedly within a short period, a potential risk of “practice effect” (PE) arises. PE involves observing pseudo-improvement in patients’ cognitive function due to repeated exposure to the same questions [ 13 ].” | concepts[9] |
| concept | POCI — significant improvement in cognitive function postoperatively that is not affected by a practice effect or natural variability — “POCI refers to significant improvement in cognitive function postoperatively that is not affected by a practice effect or natural variability [ 131 ].” | concepts[10] |
| concept | mild NCD — the period between age-related normal cognition changes and the onset of dementia symptoms — “Formerly known as mild cognitive impairment, mild NCD refers to the period between age-related normal cognition changes and the onset of dementia symptoms [ 108 ].” | concepts[11] |
| concept | mild cognitive impairment — not defined in this paper's own words; the earlier name the paper gives for mild NCD — “Formerly known as mild cognitive impairment, mild NCD refers to the period between age-related normal cognition changes and the onset of dementia symptoms [ 108 ].” | concepts[12] |
Full text — tagged
Postoperative cognitive dysfunctionterm·dom: a concept analysisterm·key Abstract Post-operative cognitive dysfunctionterm·dom (POCDterm·dom) is a concern for clinicians that often presents post-surgery where generalized anesthesiaterm·key has been used. Its prevalence ranges from 36.6% in young adults to 42.4% in older individuals. Conceptual clarity for POCDterm·dom is lacking in the currently body literature. Our two-fold purpose of this concept analysisterm·key was to (1) critically appraise the various definitions, while also providing the best definition, of POCDterm·dom and (2) narratively synthesize the attributes, surrogate or related terms, antecedents (risk factors), and consequences of the concept.
The reporting of our review was guided by the PRISMA statement and the 6-step evolutionary approach to concept analysisterm·key developed by Rodgers. Three databases, including Medline, CINAHL, and Web of Science, were searched to retrieve relevant literature on the concept of POCDterm·dom. Two independent reviewers conducted abstract and full-text screening, data extraction, and appraisal. The review process yielded a final set of 86 eligible articles.
POCDterm·dom was defined with varying severities ranging from subtle-to-extensive cognitive changes (1) affecting single or multiple cognitive domains that manifest following major surgery (2), is transient and reversible, and (3) may last for several weeks to years. The consequences of POCDterm·dom may include impaired quality of life, resulting from withdrawal from the labor force, increased patients’ dependencies, cognitive decline, an elevated risk of dementiaterm·key, rising healthcare costs, and eventual mortality.
This review resulted in a refined definition and comprehensive analysis of POCDterm·dom that can be useful to both researchers and clinicians. Future research is needed to refine the operational definitions of POCDterm·dom so that they better represent the defining attributes of the concept.
The online version contains supplementary material available at 10.1007/s40520-024-02779-7.
Keywords: Post-operative cognitive dysfunctionterm·dom, Delirium, Anesthesiaterm·key, Neurocognitive disordersterm·key Background Cognitive functioning is an evolving process encompassing human life and is a continuous endeavor of learning, maintaining short-and long-term memory, and electing to facilitate executive functioning [ 1 ]. The term “cognitive dysfunctionterm·dom” refers to difficulties with selective and sustained attentionterm·dom, learning and memory problems, deficits in visual and auditory processing, and processing speed [ 2 ]. Cognitive dysfunctionterm·dom can be caused by a direct neurological phenomenon, such as a brain injury, or by a non-direct phenomenon, such as surgery [ 3 ].
Post-operative cognitive dysfunctionterm·dom (POCDterm·dom) is a specific cognitive impairmentterm·dom that involves functional impairment of the nervous system’s activities, such as selective attentionterm·dom, vigilance, perception, learning, memory, executive functionterm·dom, verbal and language abilities, emotion, visuospatial, and visuomotor abilities. POCDterm·dom occurs in the absence of head trauma or other brain-related injuries [ 4 , 5 ]. POCDterm·dom is a serious public health concern, with prevalence rates ranging from 36.6% in young adults to 42.4% in the elderly [ 6 ]. It can occur following major invasive procedures such as cardiac [ 7 ], non-cardiac [ 6 , 8 ], and carotid surgery that are lengthy and intensive [ 9 ]. POCDterm·dom is diagnosed using standardized neuropsychological assessment tools that are available to assess cognitive function both pre- and post-operatively. The most clinically used screening tests for evaluating the overall cognitive functioning of patients are the Mini-Mental State Examination (MMSE; [ 10 ]) and the Montreal Cognitive Assessment (MoCA; [ 11 ]). The most commonly used clinically for assessing specific domains of cognition function rather than the overall assessment of cognitive function, are neuropsychological testterm·key batteries. These include the Trail-Making Test A (assessing visual attention, processing speed, and executive functionterm·dom), Trail-Making Test B (assessing cognitive flexibility, set-shifting, and executive functionsterm·dom), Digit Span Forward (assessing short-term auditory memory and attention), Digit Span Backward tests (assessing working memory and cognitive flexibility), Wechsler Memory Scale (assessing short-term memory, episodic memory and visuo-spatial working memory), and the Wechsler Adult Intelligence Scale (assessing vocabulary, comprehension, arithmetic and reasoning skills) [ 12 – 14 ]. While this information is valuable, due to POCDterm·dom’s nature consisting of subjective and objective aspects, the assessment and diagnosis of POCDterm·dom require approaches that extend beyond sole reliance on standardized test results, such as incorporating patients’ subjective reports alongside the outcomes of neuropsychological teststerm·key for a comprehensive evaluation.
Previous studies [ 6 , 7 , 15 – 17 ] have focused on the variations in the timing of symptom manifestation and their influence on the assessment and diagnosis of POCDterm·dom. As a result, POCDterm·dom has been categorized into early (acute) and late-onset POCDterm·dom. These timing distinctions become essential as it recognized that several health-related outcomes are associated with POCDterm·dom, such as delayed recovery, dependency on financial assistance [ 18 ], decreased quality of life [ 19 ], and an increased risk of death [ 20 ].
Despite the possibility of adverse long-term effects of POCDterm·dom, the phenomenon has yet to be assigned a Diagnostic and Statistical Manual of mental disorders (DSM 5-TR) category [ 21 , 22 ] even in the latest fifth edition; and conceptual clarity of POCDterm·dom needs to be improved. For example, different terms have been used interchangeably to describe POCDterm·dom, such as post-operative cognitive decline and post-operative cognitive impairmentterm·dom. Even the 1st, 2nd and 3rd International Study Group of Post-Operative Cognitive Dysfunctionterm·dom (ISPOCD), the major scientific and scholarly association focusing on this phenomenon, has not provided a clear definition of POCDterm·dom [ 5 , 23 , 24 ]. To address the notable gaps in research while advancing the state of the science, our two-fold purpose of this study was to: (1) critically appraise, discuss, and challenge the various meanings of POCDterm·dom thus providing a befitting definition for both clinical and research purposes; and (2) narratively synthesize the attributes, surrogate or related terms, antecedents including risk factors, and consequences of the concept. Such analysis can potentially lead to the development of a conceptual framework that is testable, and to research that can promote improved patient care and enhanced clinical outcomes.
Methods Design and data sources Our concept analysisterm·key follows Rodgers’ evolutionary method [ 25 ], recommended for analyzing concepts that change over time with increasing research and those that vary across contextual circumstances. The chosen concept for analysis is POCDterm·dom, for which surrogate terms were identified. The method comprises six steps: (1) identifying the concept of interest (2), selecting the appropriate context and sample (3), identifying antecedents, attributes, and consequences (4), evaluating data about the concept’s characteristics (5), providing an illustrative example, and (6) recognizing implications for its ongoing development. Studies were retrieved through searches in PubMed, Cumulative Index of Nursing and Allied Health Literature (CINAHL), and Web of Science databases, assisted by a master’s-prepared university-affiliated librarian. The keywords used for finding relevant articles were: “post-operative cognitive dysfunctionterm·dom,” “post-operative cognitive decline,” “POCDterm·dom,” and “post-operative cognitive impairmentterm·dom.” Database searches were limited to publications after 1998, which was the year of the first ISPOCD convention.
Inclusion criteria encompassed English-language quantitative original and review articles focusing on human subjects that used standard cognitive function assessment for POCDterm·dom (using MoCA, MMSE, battery of tests, etc.), and provided definitions, assessed risk factors, or evaluated consequences (short and long terms) of POCDterm·dom. Also, Webster’s dictionary, lezak’s neuropsychological assessment textbook, and DSM 5-TR were used to provide more accurate definitions of POCDterm·dom and its attributes. Exclusion criteria encompassed conference abstracts, dissertations, letters to editors, opinions, commentary papers, and study protocols. Additionally, animal, in vivo and in vitro laboratory studies were excluded. The initial search yielded a total of 5.662 titles and abstracts from three sources of Web of Science, CINAHL, and PubMed. After exclusion for various reasons detailed in Figs. 1 and 86 studies were eligible for inclusion in the concept analysisterm·key (Fig. 1 ).
– PRISMA flow diagram Two independent reviewers (HV and TM) screened all titles, abstracts, and full-text articles. In the case of any discrepancies, the two reviewers discussed the different views on certain points and came to an agreement. The goal was to include an article that defined POCDterm·dom (attributes) and/or identified risk factors (antecedents) and/or consequences. Lastly, a conceptual and operational definition was formulated. HV and AKPK entered all relevant information related to each area into an Excel 2020 database and discussed the findings with each other. HV and AKPK discussed all findings to ensure consistency and clarity. Four related (surrogate) terms were found in the literature, and they searched separately to find the definition and distinction by the first author.
Results Of the 84 articles included in this concept analysisterm·key (see appendix 1), 33.3% were from the USA ( n = 28), 19% from China ( n = 16), 8.3% from Denmark ( n = 7), 7.1% from Germany ( n = 6), and 4.7% from the UK ( n = 4). The remaining 27.6% represented various countries ( n = 23). In terms of study designs, 52.4% were reviews ( n = 44), 38% were cohort studies ( n = 32), 7.1% were randomized controlled trials (RCT; n = 6), and 2.5% used other designs ( n = 2).
Cognitive function and dysfunction The DSM 5-TR identifies complex attention, executive functionterm·dom, learning and memory, language, perceptual-motor control, and social cognition as the six essential domains of cognitive function [ 22 ].
Attention is the most fundamental element of effective cognitive function [ 22 , 26 ], and may be categorized into sustained, selective, and sustained selective types. Sustained attentionterm·dom is the ability to maintain sensitivity to stimuli, while selective attentionterm·dom is the ability to process a certain part of sensory input while omitting others. Sustained selective attentionterm·dom is the ability to process certain stimuli at the expense of others in a span of time, which some believe is a framework for executive functionterm·dom development [ 27 ]. Executive functionterm·dom refers to the capacity to complete complicated tasks such as planning, reasoning, problem solving, and adaptation to complex situations. It also includes working memory, inhibitory control, and cognitive flexibility. Executive functionterm·dom also controls other cognitive domains such as attention and memory [ 28 ]. Memory and learning are mutually interdependent and can be categorized by recent (short-term), rapid, recall, recognition, and long-term memory. Language or semantic memory is reflective of verbal fluency, grammar use, and syntax. Other important aspects of cognition include perceptual-motor control, which refers to the ability to understand visual perceptions. Finally, social cognition reflects emotion recognition and the ability to discern other’s mental status and feeling states. Cognitive processing is viewed in the cognitive psychology field as a series of sequential phases during which sensory data are converted, reduced or simplified, elaborated, stored, retrieved, and used for effective function and survival [ 29 , 30 ]. According to DSM 5-TR, Neuropsychological testing typically shows cognitive deficits in areas such as executive functionterm·dom, verbal memory, and speed of processing.
In the current literature, three words are primarily used to describe cognitive changes: dysfunction, decline, and impairment. In Webster’s dictionary [ 30 ], dysfunction is defined as damaged (or impaired) unhealthy functioning (abnormal) that can be seen in interpersonal interactions or group interactions. Because POCDterm·dom is often referred to with other deficit terms, such as decline and impairment, these terms are viewed as being related. Per Webster’s dictionary, the word decline (noun) refers to a “gradual physical or mental sinking and wasting away, or the period during which something is deteriorating or approaching its end (downward slope)”. Further, the word impairment is defined as “diminishment or loss of function or ability” [ 30 ]. Thus, the words “dysfunction” and “impairment” are considered approximate, except for some minor differences. Cognitive dysfunctionterm·dom typically describes temporary or reversible alterations in cognitive function, often stemming from factors like fatigue, medication side effects, or acute illnesses, and generally improves when the underlying cause is addressed. Cognitive impairmentterm·dom, on the other hand, suggests more enduring and noticeable deficits in cognitive abilities, often linked to conditions such as mild neurocognitive disorderterm·key (NCD), where cognitive issues exceed normal age-related changes but do not meet the criteria for dementiaterm·key. In contrast, cognitive decline signifies a gradual and progressive deterioration in cognitive function over time, often associated with age-related changes but also seen in conditions like Alzheimer’s disease and various dementiasterm·key. Cognitive decline tends to be an ongoing process and can ultimately become pervasive. These distinctions help clarify the nature and potential reversibility of cognitive changes.
In addressing the subject at hand, numerous studies have reviewed POCDterm·dom definitions. Newman et al., in their review, defined POCDterm·dom as a’significant’ change in postoperative cognition compared to the preoperative period, a definition more consistent than PODterm·dom [ 4 ]. Liu et al. [ 13 ] portrayed POCDterm·dom as a reversible form of MCI, while Needham et al. [ 12 ] described POCDterm·dom as a mild neurocognitive disorderterm·key developing between 7 days and 1 year from surgery. Other studies have suggested that POCDterm·dom can last up to 5 years, and even 7.5 years postoperatively. However, a study conducted by Steinmetz et al. [ 31 ] on 686 patients undergoing non-cardiac surgery indicated that POCDterm·dom is largely reversible over time [ 12 , 13 , 24 , 31 , 32 ].
This uncertainty in the definition of POCDterm·dom is manifested in the methods used by researchers to evaluate the incidence of POCDterm·dom. For instance, Steinmetz et al. utilized the Visual Verbal Learning Test, the Concept Shifting Test, the Stroop Color Word Interference Test, and the Letter Digit Coding Test and calculated the change from the preoperative baseline while also comparing the normative results from healthy individuals to count for the learning effect [ 33 ]. Although Evered et al. [ 32 ] also benefited from the use of results obtained from healthy individuals, their neurocognitive battery measurement consisted of the Consortium to Establish a Registry for Alzheimer’s Disease-Auditory Verbal Learning Test, the Digit-Symbol Substitution Test, Trail Making Tests A and B, the Controlled Oral Word Association Test, the Semantic Fluency Test, the Grooved Pegboard Test, and the National Adult Reading Test, which is different from the Steinmetz study [ 31 ]. Newman et al. used a battery of five tests, comprising the Short Story module of the Randt memory test, the Digit Span and Digit Symbol subtests of the Wechsler Adult Intelligence Scale-Revised test, the Benton Revised Visual Retention test, and the Trail-Making test B [ 34 ].
Defining attributes As noted in Table 1 , the defining attributes (consistent conceptual characteristics) of POCDterm·dom in patients post-surgery are as follows: (1) manifestation following after the acute phase (4–6 weeks), surpassing the usual time needed for recovery from the effects of surgery, which differs from surgery to surgery [ 35 , 36 ] of the post-operative period [ 12 ]; (2) subtle- [ 37 – 39 ] to-extensive cognitive change (continuum of negative impact); (3) affects single or multiple cognitive domains [ 4 , 31 , 33 , 37 ]; (4) reversible nature [ 12 , 38 , 31 , 41 ]; and (5) may last for several days to years [ 5 , 23 , 32 , 34 , 37 , 41 ] Implicitly, POCDterm·dom should be assessed and detected by neuropsychological teststerm·key [ 5 , 12 – 14 ], such as MoCA, MMSE, Digit Span test [ 34 ], trail making test [ 32 ], and other standardized neuropsychological battery of tests.
– Defining attributes (characteristics) of POCDterm·dom Related concepts/surrogate terms Post-operative deliriumterm·key (PODterm·dom) PODterm·dom is an acute state of fluctuating and altered consciousness due to underlying internal and external factors such as anesthetics, pain, and cerebral hypoperfusion [ 102 ]. A critical element in managing PODterm·dom involves appropriately identifying and addressing the condition’s underlying cause(s). Delirium is defined as “a disruption in attention (i.e., diminished capacity to direct, concentrate, sustain, and change in focus of attention) and awareness (reduced orientation to the environment)” or “additional disturbances in cognition,” as noted in the DSM 5-TR [ 22 ] manual. The incidence of PODterm·dom was reported to range from 5 to 40% [ 22 , 103 , 104 ].
Major neurocognitive disorderterm·key (dementiaterm·key) Formerly known as dementiaterm·key, major NCD is any progressive and irreversible cognitive disorder characterized by a cognitive deterioration that interrupts a person’s ability to perform various occupational, home, or social tasks. Dementiaterm·key is seen as pathological changes in the brain with several potential causes, as opposed to a distinct illness or syndrome [ 105 , 106 ]. Dementiaterm·key occurs as part of a spectrum of diseases that include Alzheimer’s, vascular (occurs with stroke and diabetes) dementiaterm·key, dementiaterm·key with Lewy bodies (DWLB), Parkinson’s, and mixed varieties [ 107 ].
Mild neurocognitive disorderterm·key Formerly known as mild cognitive impairmentterm·dom, mild NCDterm·dom refers to the period between age-related normal cognition changes and the onset of dementiaterm·key symptoms [ 108 ]. Mild NCDterm·dom is a cognitive impairmentterm·dom with little interference in everyday instrumental tasks, thus different from dementiaterm·key [ 109 , 110 ]. Mild NCDterm·dom can be treated or prevented from progressing to a more severe stage [ 111 ], which can be considered a reversible condition. Mild NCDterm·dom is not associated with surgery per se but can occur as a result of aging (degenerative diseases) and changes in the environment (such as moving to a nursing home) [ 112 ].
Diagnosing mild neurocognitive disorderterm·key (NCD) is applicable when composite scores in multiple domains deviate 1–2 standard deviation from normal, and major NCD is when the score is 2 or more standard deviation from the mean [ 22 ].
Cognitive vitalityterm·key (CVterm·dom) CVterm·dom refers to an individual’s capacity to adjust to cognitive changes and maintain an optimal level of cognitive functioning, life satisfaction, and independent living by effectively balancing their energy and personal resources. CVterm·dom serves as a compensatory mechanism to adapt against the cognitive decline of aging. Although CVterm·dom isn’t measured in a singular manner, its scope can be outlined by five essential domains: (1) physiological and metabolic health; (2) physical capability; (3) cognitive function; (4) psychological well-being; and (5) social well-being [ 113 , 102 ]. CVterm·dom is closely related to resilience and may reflect an individual’s capacity to recover from assaults such as surgery; it can increase the quality of life and result in healthy longevity [ 114 , 115 ].
Antecedents (risk factors) The risk factors of POCDterm·dom, as mentioned in Table 1 , can be separated in 3 groups. First, lower educational level [ 45 , 46 ], illiteracy [ 46 , 47 ], and older age [ 20 , 42 – 44 ] that are in relation to lower cognitive reserve ; Second is operation-related risk factors such as, surgical types and techniques (like cardiopulmonary bypass) [ 43 , 44 , 46 , 53 , 54 – 63 ], intraoperative management of homeostasis parameters (cerebral oxygenation, body temperature, blood glucose, and blood pressure) [ 64 – 67 , 76 , 77 , 79 ] and type of anesthesiaterm·key [ 48 , 65 – 79 , 105 ]. The third group consists of other perioperative risk factors such as alcohol use disorder [ 48 , 49 ], genetic factors [ 46 , 47 , 50 ], preexisting cognitive impairmentterm·dom [ 51 , 116 ], comorbidities [ 80 , 81 , 83 – 87 , 117 ], and PODterm·dom [ 41 , 88 – 90 ].
Consequences (outcomes) Outcomes of POCDterm·dom may include impaired quality of life [ 8 , 24 , 34 , 91 – 93 ], which may result from withdrawal from the labor force with increased patients’ dependencies [ 6 , 18 ]; cognitive decline [ 32 , 34 , 93 – 97 ]; increased risk of dementiaterm·key [ 31 , 97 ]; increasing healthcare costs [ 98 , 99 ]; and eventual mortality [ 6 , 18 , 96 , 98 – 101 ].
Conceptual definition of POCDterm·dom Figure 2 provides a comprehensive definition of POCDterm·dom, encompassing modifiable factors (those that can be manipulated by healthcare providers, i.e., surgeon, anesthesiologist, or nurse practitioner, to reduce the risk of incidence) and nonmodifiable factors (those that can’t be changed prior to or during surgery). The definition includes risk factors, defining attributes, and outcomes established based on previously discussed research, offering a thorough insight into POCDterm·dom.
– POCDterm·dom risk factors, defining attributes and outcomes diagram POCDterm·dom manifests following the acute phase (4–6 weeks), surpassing the usual time needed for recovery from the effects of surgery, which differs from surgery to surgery. The post-operative period involves a subtle-to-extensive cognitive change (continuum of negative impact) that affects single or multiple cognitive domains, is reversible, and may last for several days to years. Post-Operative Deliriumterm·key (PODterm·dom), distinct from POCDterm·dom, involves acute confusion and disorientation following surgery, requiring immediate medical attention. Since PODterm·dom primarily entails dysfunction in attention and awareness, while POCDterm·dom involves dysfunction in memory and executive functionterm·dom with or without other cognitive function domains, it is suggested to separate PODterm·dom and POCDterm·dom. Mild neurocognitive disorderterm·key, previously known as mild cognitive impairmentterm·dom, signifies cognitive difficulties that exceed normal age-related changes but fall short of dementiaterm·key, typically involving memory problems. In contrast, major neurocognitive disorderterm·key, commonly referred to as dementiaterm·key, is a severe and often irreversible condition characterized by significant cognitive decline that impedes daily functioning. This decline can stem from various underlying causes like Alzheimer’s disease and vascular dementiaterm·key. These terms collectively reflect the diverse aspects of cognitive health, ranging from temporary postsurgical changes to chronic cognitive impairmentsterm·dom and the promotion of lifelong cognitive well-being. For a precise diagnosis and management of cognitive issues, consultation with healthcare professionals is essential. Cognitive vitalityterm·key represents a holistic approach to maintaining and enhancing cognitive well-being through lifestyle choices such as mental stimulation, a balanced diet, exercise, and social engagement.
According to our findings, we provided four case examples (See Fig. 3 ): ( A ) a patient with a normal cognitive function who is undergoing major surgery (total knee replacement) and will have no PODterm·dom and, after hospital discharge, have normal cognitive function similar to before surgery (no POCDterm·dom). ( B ) a patient with a normal cognitive function who is undergoing major surgery (cardiac surgery) and will have mild PODterm·dom, and after a hospital discharge, it takes 6 weeks to go back to normal cognitive function similar to before surgery (presence of reversible POCDterm·dom). ( C ) a patient with normal cognitive function who is undergoing major surgery (cardiac surgery) and will have severe PODterm·dom, and after a hospital discharge, it takes 10 weeks to go back to normal cognitive function similar to before surgery (presence of reversible POCDterm·dom). ( D ) a patient with a major neurocognitive disorderterm·key who undegoing major surgery (hip replacement) and will have severe PODterm·dom, and after hospital discharge, it takes 10 weeks to go back to cognitive function but is not similar to before surgery (presence of persistent POCDterm·dom/ cognitive decline).
Case Examples of Trajectories of Cognitive Function Before and After Surgery Discussion In this study, an evolutionary approach was used to analyze the concept of POCDterm·dom. Various studies address POCDterm·dom, focusing mainly on a specific patient group and the concept’s risk factors. A recent review also noted that the heterogeneity of previous studies may make drawing solid conclusions from the literature difficult [ 118 ]. While previous studies fell short of providing an in-depth definition of POCDterm·dom, incorporating its characteristics, risk factors, outcomes, and most importantly differentiating POCDterm·dom from surrogate terms commonly mistaken for, the current study provides a unified definition of POCDterm·dom that can be adopted in future studies.
A few studies conducted in 1998 and afterward did adequately defined POCDterm·dom [ 5 , 12 – 14 , 23 , 36 – 40 ] most of these studies identified the reported risk factors [ 20 , 42 – 48 , 51 , 53 – 63 , 65 , 66 ] and outcomes [ 8 , 31 , 32 , 34 , 91 , 92 , 94 – 101 , 119 ] previously reported in our concept analysisterm·key. The problem is that most of these earlier studies were conducted without a clear theoretical framework guiding the research. Consequently, there are significant variations in the foundational principles underlying these studies. As a result, disparities have emerged concerning the precise timing, diagnosis, and even the definition of POCDterm·dom. This lack of theoretical guidance has led to three potential discrepancies or issues, which, in turn, may explain the divergent incidence rates of POCDterm·dom that have been reported. First , the three [ 5 , 23 , 24 ] international societies of POCDterm·dom (ISPOCD) have not provided a transparent, evidence-based, well-established, and consistent definition of POCDterm·dom. As a result, some studies [ 17 , 108 – 110 , 120 – 122 ] assessed POCDterm·dom over a short duration postoperatively, while others [ 111 , 123 – 125 ] examined POCDterm·dom over a long period. To standardize the timing of assessment across studies, it is better to distinguish between POCDterm·dom (occur after acute phase) and PODterm·dom (occur in acute phase), as they have different pathologies and diagnostic criteria. This idea is supported by Monk et al. [ 6 ], who categorized the development of POCDterm·dom as early (at hospital discharge) and late (three months after surgery). Although Monk and colleagues reported the rate of delirium and showed that the incidence of PODterm·dom was higher in patients with POCDterm·dom, they did not explain how they distinguished between PODterm·dom and POCDterm·dom. Also, PODterm·dom detection-related scales such as the Richmond Agitation and Sedation Scale (RASS) or Confusion Assessment Method (CAM)-ICU were not reported. It is suggested that future studies focus on PODterm·dom and report its related variables.
Second , because no universal agreement exists regarding tools to assess POCDterm·dom [ 37 ], previous studies used different measures or scales. MMSE [ 16 , 17 , 34 , 125 , 126 ] and MoCA [ 17 , 122 ] are the tests used most frequently in studies. Also, different neuropsychological teststerm·key (battery) are employed, such as Trail-Making Test A and B Digit Span Forward and Backward, Wechsler Memory Scale, and the Wechsler Adult Intelligence Scale [ 122 , 124 , 126 , 127 ]. When using the same tools (especially tests like the MMSE) repeatedly within a short period, a potential risk of “practice effectterm·dom” (PE) arises. PE involves observing pseudo-improvement in patients’ cognitive function due to repeated exposure to the same questions [ 13 ]. Various tools and scales employed in earlier research make it challenging to pinpoint the specific cognitive domains that surgery is more likely to impact. This occurrence makes the studies too heterogeneous and complex to compare. Future studies should assess at least attention, learning, and memory, which are the fundamentals of cognition and are usually lacking in PODterm·dom patients [ 115 , 128 ].
Third , functional status (including quality of life), an important aspect of differentiating mild and major NCD, and symptoms (such as pain and sleep disruption) that may be associated with POCDterm·dom were usually not evaluated in previous studies [ 129 ]. This information is essential to determine if patients’ symptoms or functional status are mediators or moderators in the development of POCDterm·dom or even if patients’ symptoms lie completely under NCDs. In addition, because POCDterm·dom can impair quality of life [ 24 , 33 , 34 , 91 – 93 ], knowing a patient’s quality of life before surgery and how it could change in the future is also important.
Other than the three previously mentioned discrepancies found in the literature, some minor methodological considerations [ 130 ] differed across the studies. Some studies [ 34 , 42 , 85 , 97 ] did not include a control (non-surgical) group. A control group is critical because it helps in understanding the magnitude of the intervention’s (surgery’s) effect and adjusting for cognitive change caused by normal aging. Furthermore, it is suggested that patients with preexisting mild NCDterm·dom be included in future studies [ 129 ] and that more advanced statistical analysis (multivariate analysis, structural equation modeling) be performed to better correlate between pre- and postoperative cognitive dysfunctionterm·dom with POCDterm·dom.
Over the last two decades, a new term, “post-operative cognitive improvement” (POCIterm·dom) emerged. POCIterm·dom refers to significant improvement in cognitive function postoperatively that is not affected by a practice effectterm·dom or natural variability [ 131 ]. However, which domains of cognitive function should be assessed before and after surgery is not well understood. POCIterm·dom is usually reported in carotid endarterectomy (CEA) surgery [ 127 , 15 ] and coronary artery bypass graft (CABG) surgery [ 15 , 132 , 133 ]. As discussed earlier, these studies did not include non-surgical control groups, so their findings might not be generalizable. Also, it is unclear that POCIterm·dom is unaffected by practice and/or learning effects. One assumption that may be helpful for future studies is that the majority of POCIterm·dom reported in patients may have been caused by symptoms such as pain, memory problems, and dyspnea; therefore, after surgery, when certain symptoms are relieved, and patients are no longer suffering, they may be able to focus (pay attention) on answering neurocognitive assessment tests. This justification was also supported by the finding of Kougias et al. [ 127 ], who showed that cognitive improvement after surgery can be seen in attention, executive functionterm·dom, learning, and memory. Finally, although blood biomarkers and radiological imaging [ 134 , 135 ] were considered in different studies along with neurocognitive tests to detect POCDterm·dom, it is unclear which findings should be considered to support this diagnosis.
Implications for practice Regarding the aforementioned risk factors, its advisable that strategies be developed for nurses and healthcare workers to prevent POCDterm·dom: (1) screening all patients before surgery by conducting a cognitive assessment; (2) optimizing chronic conditions preoperatively appropriately; (3) applying best practices in anesthesiaterm·key management (by a certified registered nurse anesthetist or anesthesiologist); (4) early screening for PODterm·dom (and treating it if applicable); (5) and follow-up with patients about cognitive functioning (short- and long-term) are highly recommended.
Limitations Although this study has many notable strengths, two main limitations are noted. First, the literature search was limited to studies published after ISPOCD1 (1998) and written in English, so some important studies may have been missed. Second, the literature search was limited to three online databases, and gray literature was not considered in this study.
Conclusion POCDterm·dom is a subtle-to-extensive cognitive change that affects single or multiple cognitive domains. It manifests following the acute phase of surgery, is reversible, and may last for several weeks to years. Implicitly, POCDterm·dom should be assessed and detected by neuropsychological teststerm·key. PODterm·dom is an acute change in cognition and should be differentiated from POCDterm·dom. In certain types of surgery, patients may experience POCIterm·dom after periods of POCDterm·dom. However, more studies are needed to support this contention and the findings of this concept analysisterm·key.
Electronic supplementary material Below is the link to the electronic supplementary material.
Supplementary Material 1 Acknowledgements We hereby acknowledge Jessica Sender, the university librarian, for her help with selecting key terms for a comprehensive literature search. Additionally, special thank to Drs Lorraine Robbins, Rebecca Lehto, Jiying Ling, Pallav Deka, and Fabrice Mowbray who helped us to improve the quality of this manuscript and critical appraisal.
Author contributions Conceptualization: H.A.V., M.M.,Literature review and data extraction: H.A.V., A.K.P.K., T.M.,Draft of manuscript: H.A.V., A.K.P.K., T.M.,Final manuscript revising: H.A.V., M.M., K.F.,Tables & figures: H.A.V., K.F.,Cases: H.A.V., K.F.
Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Data availability Not applicable.
Declarations Ethics approval and consent to participate Not applicable.
Consent for publication Authors declared their consent for publication.
Competing interests The authors declare no competing interests.
Footnotes References Associated Data Supplementary Materials Supplementary Material 1 Data Availability Statement Not applicable.