Preoperative electroencephalographic alpha-power changes with eyes opening are associated with postoperative attention impairment and inattention-related delirium severity

BACKGROUND

In the eyes-closed, awake condition, EEG oscillatory power in the alpha band (7-13 Hz) dominates human spectral activity. With eyes open, however, EEG alpha power substantially decreases. Less alpha attenuation with eyes opening has been associated with inattention; thus, we analysed whether reduced preoperative alpha attenuation with eyes opening is associated with postoperative inattention, a delirium-defining feature.

METHODS

Preoperative awake 32-channel EEG was recorded with eyes open and eyes closed in 71 non-neurological, noncardiac surgery patients aged ≥ 60 years. Inattention and other delirium features were assessed before surgery and twice daily after surgery until discharge. Eyes-opening EEG alpha-attenuation magnitude was analysed for associations with postoperative inattention, primarily, and with delirium severity, secondarily, using multivariate age- and Mini-Mental Status Examination (MMSE)-adjusted logistic and proportional-odds regression analyses.

RESULTS

Preoperative alpha attenuation with eyes opening was inversely associated with postoperative inattention (odds ratio [OR] 0.73, 95% confidence interval [CI]: 0.57, 0.94; P=0.038). Sensitivity analyses showed an inverse relationship between alpha-attenuation magnitude and inattention chronicity, defined as 'never', 'newly', or 'chronically' inattentive (OR 0.76, 95% CI: 0.62, 0.93; P=0.019). In addition, preoperative alpha-attenuation magnitude was inversely associated with postoperative delirium severity (OR 0.79, 95% CI: 0.65, 0.95; P=0.040), predominantly as a result of the inattention feature.

CONCLUSIONS

Preoperative awake, resting, EEG alpha attenuation with eyes opening might represent a neural biomarker for risk of postoperative attentional impairment. Further, eyes-opening alpha attenuation could provide insight into the neural mechanisms underlying postoperative inattention risk.

EEG pre-burst suppression: characterization and inverse association with preoperative cognitive function in older adults

The most common complication in older surgical patients is postoperative delirium (POD). POD is associated with preoperative cognitive impairment and longer durations of intraoperative burst suppression (BSup) - electroencephalography (EEG) with repeated periods of suppression (very low-voltage brain activity). However, BSup has modest sensitivity for predicting POD. We hypothesized that a brain state of lowered EEG power immediately precedes BSup, which we have termed "pre-burst suppression" (preBSup). Further, we hypothesized that even patients without BSup experience these preBSup transient reductions in EEG power, and that preBSup (like BSup) would be associated with preoperative cognitive function and delirium risk. Data included 83 32-channel intraoperative EEG recordings of the first hour of surgery from 2 prospective cohort studies of patients ≥age 60 scheduled for ≥2-h non-cardiac, non-neurologic surgery under general anesthesia (maintained with a potent inhaled anesthetic or a propofol infusion). Among patients with BSup, we defined preBSup as the difference in 3-35 Hz power (dB) during the 1-s preceding BSup relative to the average 3-35 Hz power of their intraoperative EEG recording. We then recorded the percentage of time that each patient spent in preBSup, including those without BSup. Next, we characterized the association between percentage of time in preBSup and (1) percentage of time in BSup, (2) preoperative cognitive function, and (3) POD incidence. The percentage of time in preBSup and BSup were correlated (Spearman's ρ [95% CI]: 0.52 [0.34, 0.66], p < 0.001). The percentage of time in BSup, preBSup, or their combination were each inversely associated with preoperative cognitive function (β [95% CI]: -0.10 [-0.19, -0.01], p = 0.024; -0.04 [-0.06, -0.01], p = 0.009; -0.04 [-0.06, -0.01], p = 0.003, respectively). Consistent with prior literature, BSup was significantly associated with POD (odds ratio [95% CI]: 1.34 [1.01, 1.78], p = 0.043), though this association did not hold for preBSup (odds ratio [95% CI]: 1.04 [0.95, 1.14], p = 0.421). While all patients had ≥1 preBSup instance, only 20.5% of patients had ≥1 BSup instance. These exploratory findings suggest that future studies are warranted to further study the extent to which preBSup, even in the absence of BSup, can identify patients with impaired preoperative cognition and/or POD risk.

Perioperative changes in neurocognitive and Alzheimer's disease-related cerebrospinal fluid biomarker in older patients randomised to isoflurane or propofol for anaesthetic maintenance

BACKGROUND

Animal studies have shown that isoflurane and propofol have differential effects on Alzheimer's disease (AD) pathology and memory, although it is unclear whether this occurs in humans.

METHODS

This was a nested randomised controlled trial within a prospective cohort study; patients age ≥60 yr undergoing noncardiac/non-neurological surgery were randomised to isoflurane or propofol for anaesthetic maintenance. Cerebrospinal fluid (CSF) was collected via lumbar puncture before, 24 h, and 6 weeks after surgery. Cognitive testing was performed before and 6 weeks after surgery. Nonparametric methods and linear regression were used to evaluate CSF biomarkers and cognitive function, respectively.

RESULTS

There were 107 subjects (54 randomised to isoflurane and 53 to propofol) who completed the 6-week follow-up and were included in the analysis. There was no significant effect of anaesthetic treatment group, time, or group-by-time interaction for CSF amyloid-beta (Aβ), tau, or phospho-tau_181p levels, or on the tau/Aβ or p-tau_181p/Aβ ratios (all P>0.05 after Bonferroni correction). In multivariable-adjusted intention-to-treat analyses, there were no significant differences between the isoflurane and propofol groups in 6-week postoperative change in overall cognition (mean difference [95% confidence interval]: 0.01 [-0.12 to 0.13]; P=0.89) or individual cognitive domains (P>0.05 for each). Results remained consistent across as-treated and per-protocol analyses.

CONCLUSIONS

Intraoperative anaesthetic maintenance with isoflurane vs propofol had no significant effect on postoperative cognition or CSF Alzheimer's disease-related biomarkers within 6 weeks after noncardiac, non-neurological surgery in older adults.

CLINICAL TRIAL REGISTRATION

NCT01993836.

Preclinical and translational models for delirium: Recommendations for future research from the NIDUS delirium network

Delirium is a common, morbid, and costly syndrome that is closely linked to Alzheimer's disease (AD) and AD-related dementias (ADRD) as a risk factor and outcome. Human studies of delirium have advanced our knowledge of delirium incidence and prevalence, risk factors, biomarkers, outcomes, prevention, and management. However, understanding of delirium neurobiology remains limited. Preclinical and translational models for delirium, while challenging to develop, could advance our knowledge of delirium neurobiology and inform the development of new prevention and treatment approaches. We discuss the use of preclinical and translational animal models in delirium, focusing on (1) a review of current animal models, (2) challenges and strategies for replicating elements of human delirium in animals, and (3) the utility of biofluid, neurophysiology, and neuroimaging translational markers in animals. We conclude with recommendations for the development and validation of preclinical and translational models for delirium, with the goal of advancing awareness in this important field.

Conserved YKL-40 changes in mice and humans after postoperative delirium

Delirium is a common postoperative neurologic complication among older adults. Despite its prevalence (14%-50%) and likely association with inflammation, the exact mechanisms that underpin postoperative delirium are unclear. This project aimed to characterize systemic and central nervous system (CNS) inflammatory changes following surgery in mice and humans. Matched plasma and cerebrospinal fluid (CSF) samples from the "Investigating Neuroinflammation Underlying Postoperative Brain Connectivity Changes, Postoperative Cognitive Dysfunction, Delirium in Older Adults" (INTUIT; NCT03273335) study were compared to murine endpoints. Delirium-like behavior was evaluated in aged mice using the 5-Choice Serial Reaction Time Test (5-CSRTT). Using a well established orthopedic surgical model in the FosTRAP reporter mouse we detected neuronal changes in the prefrontal cortex, an area implicated in attention, but notably not in the hippocampus. In aged mice, plasma interleukin-6 (IL-6), chitinase-3-like protein 1 (YKL-40), and neurofilament light chain (NfL) levels increased after orthopedic surgery, but hippocampal YKL-40 expression was decreased. Given the growing evidence for a YKL-40 role in delirium and other neurodegenerative conditions, we assayed human plasma and CSF samples. Plasma YKL-40 levels were similarly increased after surgery, with a trend toward a greater postoperative plasma YKL-40 increase in patients with delirium. However, YKL-40 levels in CSF decreased following surgery, which paralleled the findings in the mouse brain. Finally, we confirmed changes in the blood-brain barrier (BBB) as early as 9 h after surgery in mice, which warrants more detailed and acute evaluations of BBB integrity following surgery in humans. Together, these results provide a nuanced understanding of neuroimmune interactions underlying postoperative delirium in mice and humans, and highlight translational biomarkers to test potential cellular targets and mechanisms.

Postoperative changes in cognition and cerebrospinal fluid neurodegenerative disease biomarkers

OBJECTIVE

Numerous investigators have theorized that postoperative changes in Alzheimer's disease neuropathology may underlie postoperative neurocognitive disorders. Thus, we determined the relationship between postoperative changes in cognition and cerebrospinal (CSF) tau, p-tau-181p, or Aβ levels after non-cardiac, non-neurologic surgery in older adults.

METHODS

Participants underwent cognitive testing before and 6 weeks after surgery, and lumbar punctures before, 24 h after, and 6 weeks after surgery. Cognitive scores were combined via factor analysis into an overall cognitive index. In total, 110 patients returned for 6-week postoperative testing and were included in the analysis.

RESULTS

There was no significant change from before to 24 h or 6 weeks following surgery in CSF tau (median [median absolute deviation] change before to 24 h: 0.00 [4.36] pg/mL, p = 0.853; change before to 6 weeks: -1.21 [3.98] pg/mL, p = 0.827). There were also no significant changes in CSF p-tau-181p or Aβ over this period. There was no change in cognitive index (mean [95% CI] 0.040 [-0.018, 0.098], p = 0.175) from before to 6 weeks after surgery, although there were postoperative declines in verbal memory (-0.346 [-0.523, -0.170], p = 0.003) and improvements in executive function (0.394, [0.310, 0.479], p < 0.001). There were no significant correlations between preoperative to 6-week postoperative changes in cognition and CSF tau, p-tau-181p, or Aβ42 changes over this interval (p > 0.05 for each).

INTERPRETATION

Neurocognitive changes after non-cardiac, non-neurologic surgery in the majority of cognitively healthy, community-dwelling older adults are unlikely to be related to postoperative changes in AD neuropathology (as assessed by CSF Aβ, tau or p-tau-181p levels or the p-tau-181p/Aβ or tau/Aβ ratios).

TRIAL REGISTRATION

clinicaltrials.gov (NCT01993836).

Electroencephalogram-Based Complexity Measures as Predictors of Post-operative Neurocognitive Dysfunction

Physiologic signals such as the electroencephalogram (EEG) demonstrate irregular behaviors due to the interaction of multiple control processes operating over different time scales. The complexity of this behavior can be quantified using multi-scale entropy (MSE). High physiologic complexity denotes health, and a loss of complexity can predict adverse outcomes. Since postoperative delirium is particularly hard to predict, we investigated whether the complexity of preoperative and intraoperative frontal EEG signals could predict postoperative delirium and its endophenotype, inattention. To calculate MSE, the sample entropy of EEG recordings was computed at different time scales, then plotted against scale; complexity is the total area under the curve. MSE of frontal EEG recordings was computed in 50 patients ≥ age 60 before and during surgery. Average MSE was higher intra-operatively than pre-operatively (p = 0.0003). However, intraoperative EEG MSE was lower than preoperative MSE at smaller scales, but higher at larger scales (interaction p < 0.001), creating a crossover point where, by definition, preoperative, and intraoperative MSE curves met. Overall, EEG complexity was not associated with delirium or attention. In 42/50 patients with single crossover points, the scale at which the intraoperative and preoperative entropy curves crossed showed an inverse relationship with delirium-severity score change (Spearman ρ = -0.31, p = 0.054). Thus, average EEG complexity increases intra-operatively in older adults, but is scale dependent. The scale at which preoperative and intraoperative complexity is equal (i.e., the crossover point) may predict delirium. Future studies should assess whether the crossover point represents changes in neural control mechanisms that predispose patients to postoperative delirium.

Cerebrospinal Fluid Proteome Changes in Older Non-Cardiac Surgical Patients with Postoperative Cognitive Dysfunction

Background:

Postoperative cognitive dysfunction (POCD), a syndrome of cognitive deficits occurring 1–12 months after surgery primarily in older patients, is associated with poor postoperative outcomes. POCD is hypothesized to result from neuroinflammation; however, the pathways involved remain unclear. Unbiased proteomic analyses have been used to identify neuroinflammatory pathways in multiple neurologic diseases and syndromes but have not yet been applied to POCD.

Objective:

To utilize unbiased mass spectrometry-based proteomics to identify potential neuroinflammatory pathways underlying POCD.

Methods:

Unbiased LC-MS/MS proteomics was performed on immunodepleted cerebrospinal fluid (CSF) samples obtained before, 24 hours after, and 6 weeks after major non-cardiac surgery in older adults who did (n = 8) or did not develop POCD (n = 6). Linear mixed models were used to select peptides and proteins with intensity differences for pathway analysis.

Results:

Mass spectrometry quantified 8,258 peptides from 1,222 proteins in > 50%of patient samples at all three time points. Twelve peptides from 11 proteins showed differences in expression over time between patients with versus without

POCD (q < 0.05), including proteins previously implicated in neurodegenerative disease pathophysiology. Additionally, 283 peptides from 182 proteins were identified with trend-level differences (q < 0.25) in expression over time between these groups. Among these, pathway analysis revealed that 50 were from 17 proteins mapping to complement and coagulation pathways (q = 2.44^*10^–13).

Conclusion:

These data demonstrate the feasibility of performing unbiased mass spectrometry on perioperative CSF samples to identify pathways associated with POCD. Additionally, they provide hypothesis-generating evidence for CSF complement and coagulation pathway changes in patients with POCD.

Perioperative Management of Flecainide: A Problem-Based Learning Discussion

Flecainide is a first-line antiarrhythmic drug used to treat atrial arrhythmias and/or supraventricular tachycardia in those without coronary artery disease or structural heart disease. Even though it is an older antiarrhythmic, flecainide accounted for 1.6 million prescriptions in the United States in 2016, and its utilization is generally increasing. Despite its popularity, flecainide may predispose patients to rapid atrial flutter with resultant hemodynamic compromise, particularly in the physiologically stressful perioperative period. This article reviews the pharmacology of flecainide, describes problematic arrhythmias that may arise specifically during flecainide use, and offers recommendations for perioperative flecainide management.

An Open Resource for Non-human Primate Optogenetics

Optogenetics has revolutionized neuroscience in small laboratory animals, but its effect on animal models more closely related to humans, such as non-human primates (NHPs), has been mixed. To make evidence-based decisions in primate optogenetics, the scientific community would benefit from a centralized database listing all attempts, successful and unsuccessful, of using optogenetics in the primate brain. We contacted members of the community to ask for their contributions to an open science initiative. As of this writing, 45 laboratories around the world contributed more than 1,000 injection experiments, including precise details regarding their methods and outcomes. Of those entries, more than half had not been published. The resource is free for everyone to consult and contribute to on the Open Science Framework website. Here we review some of the insights from this initial release of the database and discuss methodological considerations to improve the success of optogenetic experiments in NHPs.

Nonhuman Primate Optogenetics: Recent Advances and Future Directions

Optogenetics is the use of genetically coded, light-gated ion channels or pumps (opsins) for millisecond resolution control of neural activity. By targeting opsin expression to specific cell types and neuronal pathways, optogenetics can expand our understanding of the neural basis of normal and pathological behavior. To maximize the potential of optogenetics to study human cognition and behavior, optogenetics should be applied to the study of nonhuman primates (NHPs). The homology between NHPs and humans makes these animals the best experimental model for understanding human brain function and dysfunction. Moreover, for genetic tools to have translational promise, their use must be demonstrated effectively in large, wild-type animals such as Rhesus macaques. Here, we review recent advances in primate optogenetics. We highlight the technical hurdles that have been cleared, challenges that remain, and summarize how optogenetic experiments are expanding our understanding of primate brain function.

Determinants of disease in the simian immunodeficiency virus-infected rhesus macaque: characterizing animals with low antibody responses and rapid progression

Clinical and laboratory markers of simian immunodeficiency virus (SIV) infection were studied during the first 3 months after intravenous inoculation of rhesus macaques. Virus-binding serum antibody titres were correlated strongly with disease progression (P < 0.005) and were predictive of disease outcome by 7 weeks after inoculation. Low virus-binding serum antibody responses to SIV occurred in animals that also showed acute depletion of circulating CD20+ B cells. Acute damage to the CD4+ T cell and CD20+ B cell populations rendered some animals incapable of mounting virus-specific antibody responses and these macaques became the rapidly progressing cases comprising approximately 20-30% of infected animal cohorts.

[The contamination of human milk with chlororganic pesticides (author's transl)]

A survey on the situation concerning the residues on pesticides in human milk in West Germany is given, based on own investigations. Nearly the whole pattern of chlororganic pesticides - DDT with its metabolites DDE and DDD, hexachlorobenzene (HCB), the different isomeres (alpha-, beta-, gamma-) of benzenehexachloride (BHC) as well as dieldrin and heptachloroepoxid - together with polychlorinated biphenyls (PCB) coming from the environment - were found in all samples of human milk, though in different concentrations. PCB, HCB and beta-BHC had been discovered in human milk only about ten years ago. The residues have decreased in the past years. The concentrations are still so high that the amounts consumed by the suckling exceed the ADI values for the contaminants in question. But in the opinion of the experts the advantages connected with the alimentation with human milk weigh more than the eventual risk by the contamination.

[Capillary gas chromatographic separation of residues of chlorohydrocarbons in foods and identification of Mirex in human fat tissue]

The residue analysis of organochloroinsecticides could be substantially improved by using glass capillary columns. The special advantages of the capillary gas chromatography (separation of complex mixtures, simultaneous determination of by-components, improved reliability at the identification, increased sensitivity) can be used with right handling to directly separate the whole mixture of chlorohydrocarbons that are to be met in foods (insecticides, HCB and PCB). The identification is possible even of microgram amounts per kg substance by a direct coupling of GC and MS working without carrier gas separator. In this way the occurrence of Mirex in samples of human fat tissues could be demonstrated.

[Influence of water activity on the enzymatic changes in freeze-dehydrated muscle III. The breakdown of muscle lipids (author's transl)]

During storage of freeze-dehydrated bovine muscle triglycerides and cholesterolesters are slowly hydrolyzed even at 25% relative humidity (r.h.). The extent of lipid hydrolysis in the tissue increases with rising water activity, the final degree of hydrolysis being dependent on water activity. It has been demonstrated that these changes are due to the effect of muscle enzymes. Phospholipids are not hydrolyzed even at 65% r.h. This might be due to an association of the phospholipids with membranes or to a lack of phospholipase activity in the freeze-dehydrated tissue. The fact that lipids in muscle tissue are hydrolyzed at water activities at which water soluble substrates are not split by hydrolyses agrees well with general ideas about the influence of water activity on the enzymatic breakdown of lipids. Freeze-dehydrated beef should not contain more than 3% moisture in order to prevent undesirable flavour changes caused by lipid changes during storage.

[Influence of water activity on the enzymatic changes in freeze-dehydrated muscle. IV. Change in the activity of glycolytic enzymes during storage (author's transl)]

The influence of water activity (25-65% r.h.) on the changes in activity of glycolytic enzymes during storage (up to 120 days) of freeze-dehydrated bovine muscle was investigated. For this purpose, at different times of storage the decrease of glycogen and the increase in lactate in the rehydrated samples were determined. At 25% r.h. no loss in activity was observed. However, during storage at 40% r.h. and higher the glycolytic activity decreased; this effect increased with rising water activity. The denaturation of the enzyme proteins might be due to Maillard reactions, particularly to the reaction of proteins with the highly reactive glycolytic metabolites glyceraldehyde phosphate and dihydroxyacetone phosphate.

[Influence of water activity on the enzymatic changes in freeze-dehydrated muscle. II. Reactions of carbohydrates (author's transl)]

During storage of prerigor freeze-dried beef, glycogen is not broken down even at 97.5% r.h. (moisture content of the meat about 30%). However, the metabolites of glycogen -- glucose, fructose, and their phosphoric acid esters -- are changed during storage at r.h. greater than 25%, mainly by the effect of glycolytic enzymes. Also nonenzymic reactions of the Maillard type seem to occur. An accelerated breakdown of these carbohydrates with increasing water activity was found. Even though the sugar monophosphates are broken down, no increase in C3 metabolites was found. The reason for this could be that the energy-rich compounds glyceraldehyde phosphate and dihydroxyacetone phosphate form complexes with some proteins. It is suggested that also pyruvate reacts with free amino groups of proteins. The breakdown of carbohydrates increases in uncooked freeze-dried samples above 60% r.h. whereas nonenzymatic reactions of the Maillard type reach a maximum rate at nonenzymatic reactions of the Maillard type reach a maximum rate at 60% r.h. This also shows that the disappearance of carbohydrates during storage of freeze-dried prerigor beef is mainly due to enzymatic processes.

[Phospholipase D - a review (author's transl)]

Phospholipase D (phosphatidylcholine-phosphatidohydrolase, EC 3.1.4.4) hydrolyses lecithin into phosphatidic acid and choline. A review is given on the properties of phospholipase D described in the literature; it deals with the occurrence and distribution of phospholipase D in higher plants, with it's pH and temperature, substrate specifity, activators, inhibitors and with occurrence and properties of bacterial phospholipase D.

[Contamination of milk and milk products with chlorinated hydrocarbons in the Westphalian area. II. Results and discussion]

During the time of August 1972 til end of January 1974 samples of butter from 20 dairies from the westfalian area were investigated with regard to their content of chlorinated hydrocarbons. In all samples of milk and butter could be proved: HCB, alpha-, beta-, and gamma-BHC, Heptachlorepoxid (HE), DDT, DDE, DDD, Dieldrin and PCB's, not however, Aldrin, Heptachlor and o,p'-DDT. With HCB, alpha- and gamma-BHC a dependance on the season was observed with maximum values during the winter months. With DDT, DDE and HE the variations were less. With PCB's dependencies on the season or influences of the location were not be recognised. The structure of farming seems to have a significant influence on the contents of HCB. In the course of butter processing the content on chlorinated hydrocarbons related to milk fat is not changed, metabolization does not play a role, either. With the start of lactation the concentration of chlorinated hydrocarbons especially of PCB's are increased as could be shown with single samples.

[On the contamination of milk and milk products with chlorinated hydrocarbons. I. Methods]

A method of gaschromatographic determination of chlorinated insecticides in milk and butter in the presence of PCB's is described. The fatty components were extracted from milk after adding sodium oxalate and ethanol with diethyl ether and petrol ether. The clean up of the extracts was carried out according to a modification of the method of Hadorn and Zürcher with propylene carbonate as a selective solvent.

[Phospholipase D of cereals (author's transl)]

Phospholipase D containing water insoluble fraction was isolated from mature barley; the enzym preparation only had weak phospholipase B activity. The phospholipase D of barley was activated by Ca2+, diethyl ether and sodium dodecyl sulphate (SDS); EDTA inhibited the enzyme to an extent of 10% of the original activity. Diethyl ether and SDS showed and additive effect. Phospholipase D activated by CaC12, diethyl ether and SDS exhibited a sharp optimum at pH 6.6. Lysophosphatidylcholine was hydrolysed much slower than phosphatidylcholine. Diethyl ether and SDS also increased the breakdown of the lysophosphatidylcholine.