Issues associated with the identification of cognitive change following coronary artery bypass grafting

What Do Cancer Surgery and orthopedic Surgery Elderly Patients Have in Common? A Long-term Postoperative Cognitive Dysfunction in Orthopedic and Cancer Patients Original Research

Objectives-background

Postoperative cognitive dysfunction (POCD) involves decline in several cognitive domains after surgery and is particularly common after cardiac surgery, while also common among other types of surgery. Given the potential effects of such cognitive dysfunction on the quality of life, it is important to study it in multiple populations in order to limit its occurrence.

Study design

We present the long-term neuropsychological outcome of 200 patients, 100 of whom had orthopedic surgery and 100 oncological surgery.

Methods

We administered a series of neuropsychological tests assessing attention, complex scanning, verbal working memory, executive functioning, short-term and long-term memory, and visuospatial perception before surgery, prior to discharge, at 3-month follow-up and 6 years after surgery. We compared the performance of these patients to normative datasets.

Results

Despite equivalent levels of pre-surgery performance between patients, oncology patients exceeded their preoperative neurocognitive levels, suggesting less postoperative cognitive dysfunction in orthopedic patients overall, in all neuropsychological domains at a 6-year follow-up, except short-term retention. In contrast, orthopedic patients showed no improvement, and, instead, showed some cognitive decline, which remained consistent over time.

Conclusions

Our findings highlight the critical role of the type of surgery utilized in the development of POCD and have implications for clinical management and patients' quality of life in the very long term. Health policy professionals should be aware that patients' low POCD may persist in the long term, and this is useful from a clinician's point of view.

Mirtazapine prevents cell activation, inflammation, and oxidative stress against isoflurane exposure in microglia

Mirtazapine is an antidepressant drug that has been proven to possess a cognitive enhancer efficiency. In this study, we evaluated the potential protective effects of mirtazapine on BV2 microglia in response to isoflurane exposure. Our results show that mirtazapine attenuated isoflurane-induced expression of microglia-specific protein Iba1 in BV2 microglia. Mirtazapine prevented isoflurane-induced production of the pro-inflammatory factors interleukin (IL)-1β and IL-18 by inhibiting the activation of the nod-like receptor family protein 3 (NLRP3) inflammasome in BV2 microglia. The increased reactive oxygen species (ROS) production and elevated expression level of NADPH oxidase 4 (NOX4) in isoflurane-induced BV2 microglia were mitigated by mirtazapine. Isoflurane exposure reduced triggering receptor expressed on myeloid cells 2 (TREM2) expression in BV2 microglia, which was restored by mirtazapine. Moreover, silencing of TREM2 abolished the inhibitory effects of mirtazapine on ionized calcium-binding adapter molecule 1 (Iba1) expression and inflammation in BV2 microglia. From these results, we could infer that mirtazapine exerted a protective effect on BV2 microglia against isoflurane exposure-caused microglia activation, neuroinflammation, and oxidative stress via inducing TREM2 activation. Hence, mirtazapine might be a potential intervention strategy to prevent isoflurane exposure-caused cognitive dysfunction in clinical practice.

Role of Dexmedetomidine in Early POCD in Patients Undergoing Thoracic Surgery

Objective

To evaluate whether a low-dose perioperative infusion of Dex reduces early POCD.

Design

This study was a double-blind, randomized, placebo-controlled trial that randomly assigned patients to Dex or saline placebo infused during surgery and patient-controlled intravenous analgesia (PCIA) infusion. Patients were assessed for postoperative cognitive decline. Interventions. Dex was infused at a loading dose of 0.5 μg/kg intravenously (15 min after entering the operation room) followed by a continuous infusion at a rate of 0.5 μg/kg/h until one-lung ventilation or artificial pneumothorax ended. Patients in the Dex group received regular PCIA pump with additional dose of Dex (200 μg).

Results

In total, 126 patients were randomized, and 102 patients were involved in the result analysis. The incidence of POCD was 36.54% (19/52) in the Dex group and 32.00% (16/50) in the normal saline (NS) group, with no statistic difference. No significant difference was observed between the two groups in terms of Telephone Interview for Cognitive Status-Modified (TICS-m) scores at different times. However, the TICS-m score at 7 days after surgery was significantly lower than that at 30 days in 102 patients (32.93 ± 0.42 vs. 33.92 ± 0.47, P = 0.03). The visual analogue scale scores in the Dex group were significantly lower than those in the NS group 1 day postoperation at rest and activity (2.00 [1.00-3.00] vs. 3.00 [2.00-4.00], P < 0.01; 4.00 [3.00-5.00] vs. 5.00 [4.00-6.00], P < 0.05, respectively). Patients receiving Dex or NS had no statistical difference in activities of daily living (ADLs) scores at 7 and 30 days after surgery, but the ADL score at 30 days after surgery showed a significant reduction compared with that at 7 days (P < 0.01). Patients in the Dex group had a shorter hospital length of stay (15.26 ± 3.77 vs. 17.69 ± 5.09, P = 0.02) and less expenses (52458.71 ± 10649.30 vs. 57269.03 ± 9269.98, P = 0.04) than those in the NS group.

Conclusions

Low-dose Dex in the perioperative period did not reduce the incidence of early POCD in thoracic surgery. However, it relieved postoperative pain, decreased the hospitalization expenses, and shortened the length of stay.

Anesthesiology and cognitive impairment: a narrative review of current clinical literature

Background

The impact of general anesthesia on cognitive impairment is controversial and complex. A large body of evidence supports the association between exposure to surgery under general anesthesia and development of delayed neurocognitive recovery in a subset of patients. Existing literature continues to debate whether these short-term effects on cognition can be attributed to anesthetic agents themselves, or whether other variables are causative of the observed changes in cognition. Furthermore, there is conflicting data on the relationship between anesthesia exposure and the development of long-term neurocognitive disorders, or development of incident dementia in the patient population with normal preoperative cognitive function. Patients with pre-existing cognitive impairment present a unique set of anesthetic considerations, including potential medication interactions, challenges with cooperation during assessment and non-general anesthesia techniques, and the possibility that pre-existing cognitive impairment may impart a susceptibility to further cognitive dysfunction.

Main body

This review highlights landmark and recent studies in the field, and explores potential mechanisms involved in perioperative cognitive disorders (also known as postoperative cognitive dysfunction, POCD). Specifically, we will review clinical and preclinical evidence which implicates alterations to tau protein, inflammation, calcium dysregulation, and mitochondrial dysfunction. As our population ages and the prevalence of Alzheimer’s disease and other forms of dementia continues to increase, we require a greater understanding of potential modifiable factors that impact perioperative cognitive impairment.

Conclusions

Future research should aim to further characterize the associated risk factors and determine whether certain anesthetic approaches or other interventions may lower the potential risk which may be conferred by anesthesia and/or surgery in susceptible individuals.

Cognitive outcomes following coronary artery bypass grafting: A systematic review and meta-analysis of 91,829 patients

Background

Cognitive impairments, including delirium, are common after coronary artery bypass grafting (CABG) surgery, as described in over three decades of research. Our aim was to pool estimates across the literature for the first-time, relative to time (from pre- to post-CABG) and diagnosis (cognitive impairment, delirium and dementia).

Methods

A systematic search of four databases was undertaken. 215 studies incorporating data from 91,829 patients were used to estimate the prevalence of cognitive impairments pre- and post-CABG, including delirium and dementia post-CABG, using random effects meta-analyses.

Results

Pre-surgical cognitive impairment was seen in 19% of patients. Post-operatively, cognitive impairment was seen in around 43% of patients acutely; this resolved to 19% at 4–6 months and then increased to 25% of patients between 6-months to 1-year post-operatively. In the long term, between 1 and 5-years post-operatively, cognitive impairment increased and was seen in nearly 40% of patients. Post-operative delirium was apparent in 18% of CABG patients which increased to 24% when a diagnostic instrument was utilized alongside clinical criteria. Dementia was present in 7% of patients 5–7 years post-surgery.

Conclusion

The results of this meta-analysis demonstrate that cognitive impairment and delirium are major issues in CABG patients which require specific attention. It is imperative that appropriate methods for investigating cognitive impairment, and screening for delirium using a diagnostic instrument, occur in both pre-and post-CABG settings.

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This meta-analysis pooled results of 91,829 patients, including 215 studies.

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Cognitive impairment and delirium are seen in up to 40% of CABG patients.

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Appropriate methods investigating cognitive impairment are crucial post-CABG.

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Appropriate methods of screening for delirium are crucial post-CABG.

Hypothermia-induced platelet aggregation and cognitive decline in coronary artery bypass surgery: a pilot study

Hypothermia-induced platelet aggregation (HIPA) was previously reported in whole blood exposed to synthetic surfaces at 24°-32°C in one-third of normal subjects tested. Cardiopulmonary bypass, conducted with hypothermia, may lead to such aggregation, resulting in microvascular occlusion contributing to cognitive impairment. This pilot study was conducted to explore the relationship between HIPA and cognitive outcome at hospital discharge in patients undergoing coronary artery bypass graft (CABG) surgery as a first step toward a longer-term study.

Patients (n=45) undergoing mild to moderate hypothermia (32°-28°8C) during CABG surgery underwent cognitive testing preoperatively and prior to hospital discharge. Tests included: visual and verbal memory, mental processing speed, executive function, language, and intellectual function. HIPA was identified using an in vitro assay in which blood flowing in polyvinychloride tubing was subjected to hypothermia, and platelet aggregates were detected using microscopy and passing the exiting blood through a 20-μm pore filter.

Forty-four percent of patients exhibited HIPA. The entire cohort exhibited significant postoperative cognitive decline in verbal memory, mental processing speed and executive function. There was greater cognitive decline in the group with HIPA compared with the group not exhibiting this phenomenon. The patients with HIPA showed significant decline in four of five cognitive measures whereas patients not exhibiting this phenomenon declined in only two of five cognitive measures.

HIPA appears to be associated with an added risk of cognitive decline immediately following CABG surgery employing mild to moderate hypothermia. The findings of our study suggest the long-term cognitive effects of hypothermia-induced platelet aggregation need to be explored.

Dementia and depression with ischemic heart disease: a population-based longitudinal study comparing interventional approaches to medical management

BACKGROUND

We compared the proportion of ischemic heart disease (IHD) patients newly diagnosed with dementia and depression across three treatment groups: percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) and medical management alone (IHD-medical).

METHODS AND FINDINGS

De-identified, individual-level administrative records of health service use for the population of Manitoba, Canada (approximately 1.1 million) were examined. From April 1, 1993 to March 31, 1998, patients were identified with a diagnosis of IHD (ICD-9-CM codes). Index events of CABG or PCI were identified from April 1, 1998 to March 31, 2003. Outcomes were depression or dementia after the index event. Patients were followed forward to March 31, 2006 or until censored. Proportional hazards regression analysis was undertaken. Independent variables examined were age, sex, diabetes, hypertension and income quintile, medical management alone for IHD, or intervention by PCI or CABG. Age, sex, diabetes, and presence of hypertension were all strongly associated with the diagnosis of depression and dementia. There was no association with income quintile. Dementia was less frequent with PCI compared to medical management; (HR = 0.65; p = 0.017). CABG did not provide the same protective effect compared to medical management (HR = 0.90; p = 0.372). New diagnosis depression was more frequent with interventional approaches: PCI (n = 626; hazard ratio = 1.25; p = 0.028) and CABG (n = 1124, HR = 1.32; p = 0.0001) than non-interventional patients (n = 34,508). Subsequent CABG was nearly 16-fold higher (p<0.0001) and subsequent PCI was 22-fold higher (p<0.0001) for PCI-managed than CABG-managed patients.

CONCLUSIONS

Patients managed with PCI had the lowest likelihood of dementia-only 65% of the risk for medical management alone. Both interventional approaches were associated with a higher risk of new diagnosed depression compared to medical management. Long-term myocardial revascularization was superior with CABG. These findings suggest that PCI may confer a long-term protective effect from dementia. The mechanism(s) of dementia protection requires elucidation.

Neuropsychological outcomes after coronary artery bypass grafting

Short- and long-term cognitive declines after cardiac surgery with cardiopulmonary bypass have been reported, but the frequency, severity, nature, and etiology of postoperative cognitive changes have been difficult to quantify. Current studies have corrected the principal methodological shortcoming of earlier studies by including control groups, and have shown that while early postoperative cognitive decline does occur in some patients, it is generally mild and reversible by 3 months after surgery. Late cognitive changes do occur, but comparison with patients undergoing off-pump surgery or those being treated medically suggests that these changes are not specific to CABG or more specifically to the use of cardiopulmonary bypass.

Evaluation of Cognitive Function Associated With Chemotherapy: A Review of Published Studies and Recommendations for Future Research

Purpose

There is evidence that some cancer survivors suffer cognitive impairment after chemotherapy. Determining if a patient has cognitive impairment is challenging, especially because impairment is usually subtle.

Patients and Methods

We assessed the design of studies evaluating cognitive function during or after chemotherapy in adult patients with solid tumors. We also reviewed methods used to evaluate cognitive function in subjects with other diseases and make recommendations for future studies.

Results

We identified 22 studies that met our criteria: 82% included women with breast cancer. Eight studies were longitudinal, 12 were cross-sectional, and two were follow-ups of cross-sectional studies. Sixteen studies used a battery of neuropsychological (NP) tests to assess subjects, and 13 included a control group. Ten studies (45%) had no explicit definition of cognitive impairment; most others used z scores or T scores and defined impairment based on standard deviations below the mean, but there was no consistency in for the cutoff point used or the number of tests required.

Conclusion

There is no consistency in defining cognitive impairment, in the NP batteries used, or in statistical methods in studies of cognitive function of cancer patients. We suggest guidelines to define criteria for cognitive impairment. Use of summary scores and control groups is recommended. Practice effect should be adjusted for in longitudinal studies. A balance is needed between comprehensive batteries and briefer tests, which still need to be sensitive to mild impairment.

Detection of Postoperative Cognitive Decline After Coronary Artery Bypass Graft Surgery is Affected by the Number of Neuropsychological Tests in the Assessment Battery

BACKGROUND

The assessment of postoperative cognitive dysfunction after coronary artery bypass graft surgery is made with the repeated administration of cognitive tests. This classification is vulnerable to error, and it has been suggested that increasing the number of tests in a battery while maintaining constant inclusion criteria for postoperative cognitive dysfunction increases the rate of false positive classification of deterioration. The current study tested this by applying a constant rule for cognitive dysfunction using combinations of two to seven cognitive tests.

METHODS

Two hundred and four coronary artery bypass graft patients (surgical) and 90 healthy nonsurgical controls aged 55 years or older completed a battery of cognitive tests at baseline (preoperative) and 1 week later (postoperative). In both groups, postoperative cognitive dysfunction was classified using all unique combinations of two to seven cognitive tests when performance deteriorated on two or more tests by at least the value of the baseline standard deviation.

RESULTS

The average incidence of cognitive dysfunction progressively increased in both groups as the number of cognitive tests increased from two (surgical: 13.3%; control: 3.1%) to seven tests (surgical: 49.4%; control: 41.1%).

CONCLUSIONS

Increasing the number of tests used to classify postoperative cognitive dysfunction appears to increase the sensitivity to change in the coronary artery bypass graft group. However, accompanying false positive classifications suggest that this improved sensitivity reflected increased error. Future rules for postoperative cognitive dysfunction need to account for this error and include a control group.

Assessing cognitive function in cancer patients

GOALS OF WORK

Some patients with cancer suffer cognitive impairment after chemotherapy. A brief, sensitive instrument is required to screen patients for cognitive impairment. In this study, we compare three possible screening instruments.

MATERIALS AND METHODS

Cancer patients (n=31) who had received adjuvant chemotherapy within 2 years underwent cognitive evaluation on three occasions. Fluent English speakers (n=20) completed the High Sensitivity Cognitive Screen (HSCS), the computer-based Headminder and CogHealth, and the Functional Assessment of Cancer Therapy-cognitive function (FACT-COG) questionnaire. Patients not fluent in English (NESB) (n=11) performed CogHealth and Headminder.

RESULTS

The patients were aged 31-65 years, and 94% were women with breast cancer. At baseline, 6 of 20 (30%) had moderate-severe cognitive impairment on HSCS, 17 of 31 (55%) had scores greater than one standard deviation (SD) below the mean for normative data in one to two of three domains on Headminder, and on CogHealth, 8 of 31 (26%) were greater than one SD below the mean in at least two of six domains. A large practice effect was seen for the HSCS, with moderate-severe cognitive impairment decreasing from 30 to 5% between the first and second assessment. On FACT-COG, 9 of 19 patients (47%) rated their cognition as greater than one SD below that of a pre-chemotherapy breast cancer control group, with impact on quality of life greater than one SD below for 10 of 19 (53%) patients. No correlation was seen between objective cognitive testing and the FACT-COG.

CONCLUSIONS

CogHealth and Headminder were suitable for NESB patients. The HSCS is not recommended for longitudinal studies with short intervals between testing due to practice effect. There is poor correlation between the patients' perception of their cognitive impairment and the objective tests.

Chronic neurocognitive effects of critical illness

PURPOSE OF REVIEW

Until relatively recently critical care practitioners have focused on survival of their patients and not long-term outcomes. An increasing body of research has examined patient outcomes beyond discharge from the intensive care unit and hospital. One area of focus is neurobehavioral outcomes including neurocognitive sequelae and neuropsychiatric disorders such as depression and anxiety. Cognitive functions are brain-based or mental activities that involve acquiring, storing, retrieving, and using information and include domains such as memory, attention, executive function, mental processing speed, spatial abilities, and general intelligence. It is known from other medical specialties that impaired cognitive function can have a broad, substantial, and long-lasting impact on a patient's life. This paper examines the current evidence for neurocognitive impairments in survivors of critical illness.

RECENT FINDINGS

Recent studies support the hypothesis that critical illness can lead to significant impairments in neurocognitive function. Current work indicates that the neurocognitive impairments can last for months or years after a patient arrives home and may have important consequences for quality of individual and family life and for ability to return to work as well as substantial economic costs. The mechanisms of neurocognitive impairments are not fully understood, but in acute respiratory distress syndrome hypoxemic burden appears important.

SUMMARY

Among the potential consequences of critical illness are now included neurocognitive impairments. Future research should include the search for strategies for the early identification of neurocognitive impairments, mechanisms of brain injury, and therapeutic modalities designed to prevent or decrease neurocognitive morbidity.

The sensitivity and specificity of three common statistical rules for the classification of post-operative cognitive dysfunction following coronary artery bypass graft surgery

BACKGROUND

The application of statistical rules to determine post-operative cognitive dysfunction (POCD) has varied, and partially explains the wide range of reported incidences of POCD in the literature. The current study assessed the sensitivity and specificity of three commonly used statistical rules in a sample of coronary artery bypass graft (CABG) patients and healthy non-surgical controls.

METHODS

Two hundred and four CABG patients [mean age, 68.8 years; standard deviation (SD), 7.0 years] completed neuropsychological assessment pre-operatively (baseline) and 1 week and 3 months post-operatively. Ninety age- and gender-matched non-surgical controls (mean age, 67.8 years; SD, 7.9 years) completed the same tasks at the same time points. POCD was determined in each group using three rules: the 1SD decline on two or more tasks; the 20% decline on 20% of tasks rule; and a modified reliable change index.

RESULTS

The modified reliable change index demonstrated the greatest combination of sensitivity and specificity. The 20% decline on 20% of tasks rule detected the largest incidence of impairment in the CABG group, but showed large incidences of false positive classifications in the control group. The 1SD rule detected the lowest incidence of POCD in the CABG group, but detected a larger incidence of impairment in the control group.

CONCLUSIONS

The use of the modified reliable change index is recommended, given the sensitivity to change it displayed and the low rates of false positive classification in the control sample. The use of control groups in future research is also recommended.

Examination of the Use of Cognitive Domains in Postoperative Cognitive Dysfunction After Coronary Artery Bypass Graft Surgery

BACKGROUND

Cognitive domain summary scores have been used to examine postoperative cognitive dysfunction in a number of influential studies. To successfully examine cognitive dysfunction in this way, the domains need to be consistent during the assessment time points or the results are distorted. The current study examines two methods of determining cognitive domains and examines their temporal stability during serial cognitive assessments after coronary artery bypass graft surgery.

METHODS

Two hundred and four coronary artery bypass graft patients and 80 matched healthy control subjects 55 years or older completed a battery of neuropsychological assessments at baseline and at 7 days and 3 months. Domains were determined in two ways. The first was based on precedence, and neuropsychological tests were allocated to commonly attributed cognitive domains. The second method was to conduct principal components analysis to statistically determine the domains at each time. The stability of these factors was then assessed over time by conducting repeated analysis.

RESULTS

There were discrepancies between the two methods used to determine decline, and among the factors in the control and surgical groups. Stability with time was not evident as the factors varied within the groups.

CONCLUSIONS

The assessment of postoperative cognitive dysfunction would be best served by the use of individual test results with efforts made to minimize false-positive classification as the extracted cognitive domains do not appear to be temporally consistent, and were sample specific.

Neurologic Injury Associated with CABG Surgery: Outcomes, Mechanisms, and Opportunities for Improvement

Neurologic injuries, whether subtle or overt, are a major source of morbidity secondary to coronary artery bypass graft (CABG) surgery. A comprehensive review of research in the area of neurologic injury is provided. We conclude this article by providing insight regarding areas requiring further investigation in order to reduce sustainably the risk of these iatrogenic events among patient undergoing CABG surgery.

Clinical identification of cognitive impairment in ICU survivors: insights for intensivists

BACKGROUND

A growing body of research has demonstrated the presence of ongoing cognitive impairment in large numbers of ICU survivors.

OBJECTIVE

This review offers a practical framework for practicing intensivists and those following patients after their ICU stay for the identification of cognitive impairment in ICU survivors.

CONCLUSIONS

Early detection of cognitive impairment in critically ill patients is an important and achievable goal, but overt cognitive impairment remains unrecognized in most cases. However, it can be identified by objective (test scores) or subjective evidence (clinical judgment, patient observation, family interaction).

Statistical and conceptual issues in defining post-operative cognitive dysfunction

The occurrence of post-operative cognitive dysfunction is a distressing complication following surgery. In an effort to gain a more complete understanding of patients' cognitive recovery following surgical procedures common neuropsychological assessment tools have been adopted in a repeated measures design. It is widely regarded that this represents the most comprehensive method of determining cognitive status in this population but it has resulted in a number of statistical and conceptual difficulties in attempting to infer significant change. The current paper outlines these core difficulties and provides some potential methods to overcome these.

Research issues in the evaluation of cognitive impairment in intensive care unit survivors

Neuropsychological assessment has been utilized extensively in the research of cognitive outcomes associated with medical illnesses, such as HIV, and post-surgical procedures, such as coronary artery bypass graft. However, few investigations of intensive care unit (ICU) survivors have examined cognitive function as a clinical outcome. Significant clinical questions exist regarding the impact of critical illness on long-term cognitive function. Many of these questions can be systematically evaluated through the use of standardized neuropsychological assessment instruments within the context of well designed, prospective research trials. This review will provide information for clinical researchers interested in the study of neuropsychological outcomes in intensive care unit survivors ( a comparison article in this issue will address clinical issues related to cognitive functioning).

Detection of cognitive decline after coronary surgery: a comparison of computerized and conventional tests

BACKGROUND

Postoperative cognitive decline is a common complication after coronary artery bypass graft (CABG) surgery. Postoperative cognitive decline is defined on the basis of change in cognitive function detected with repeated assessments using neuropsychological tests. Therefore improvement in neuropsychological testing instruments may increase our understanding of postoperative cognitive decline.

METHODS

Fifty patients undergoing CABG surgery completed both a conventional and a computerized battery of tests before and 6 days after CABG surgery. Fifty age- and education-matched controls completed the same test batteries 6 days apart. The reliability and the sensitivity to postoperative cognitive decline were computed for each battery.

RESULTS

Both test batteries detected postoperative cognitive decline 6 days after CABG surgery. For the computerized battery, the reliability of the reaction times (intraclass correlation 0.89-0.92) was greater than for any test from the conventional battery (intraclass correlation 0.56-0.71), although accuracy measures were less reliable (intraclass correlation 0.61-0.89). The computerized battery detected all the cases of POCD identified by the conventional test battery and also five cases that were classified as normal by the conventional tests.

CONCLUSION

Computerized tests are suitable for measuring cognitive change after CABG surgery and may detect change in a greater proportion of patients 6 days after CABG surgery than conventional neuropsychological tests.