The aging brain and anesthesia

Activating ryanodine receptor improves isoflurane-induced cognitive dysfunction

BACKGROUND

Postoperative cognitive dysfunction (POCD) is characterized by impaired learning and memory. 6 h duration isoflurane anesthesia is an important factor to induce POCD, and the dysfunction of ryanodine receptor (RyR) in the hippocampus may be involved in this process. We investigated the expression of RyR3 in the hippocampus of mice after 6-h duration isoflurane anesthesia, as well as the improvement of RyR receptor agonist caffeine on POCD mice, while attempting to identify the underlying molecular mechanism.

MATERIALS

We constructed a POCD model using 8-week-old male C57BL/6J mice that were exposed to 6-h duration isoflurane. Prior to the three-day cognitive behavioral experiment, RyR agonist caffeine were injected. Fear conditioning and location memory tests were used in behavioral studies. We also exposed the mouse neuroblastoma cell line Neuro-2a (N2A) to 6-h duration isoflurane exposure to simulate the conditions of in vivo cognitive dysfunction. We administered ryanodine receptor agonist (caffeine) and inhibitor (ryanodine) to N2a cells. Following that, we performed a series of bioinformatics analysis to discover proteins that are involved in the development of cognitive dysfunction. Rt-PCR and Western blot were used to assess mRNA level and protein expression.

RESULTS

6-h duration isoflurane anesthesia induced cognitive dysfunction and increased RyR3 mRNA levels in hippocampus. The mRNA levels of RyR3 in cultured N2a cells after anesthesia were comparable to those in vivo, and the RyR agonist caffeine corrected the expression of some cognitive-related phenotypic proteins that were disturbed after anesthesia. Intraperitoneal injection of RyR agonist caffeine can improve cognitive function after isoflurane anesthesia in mice, and bioinformatics analyses suggest that CaMKⅣ may be involved in the molecular mechanism.

CONCLUSION

Ryanodine receptor agonist caffeine may improve cognitive dysfunction in mice after isoflurane anesthesia.

Intra-operative electroencephalogram frontal alpha-band spectral analysis and postoperative delirium in cardiac surgery: A prospective cohort study

BACKGROUND

Postoperative delirium (POD) remains a frequent complication after cardiac surgery, with pre-operative cognitive status being one of the main predisposing factors. However, performing complete pre-operative neuropsychological testing is challenging. The magnitude of frontal electroencephalographic (EEG) α oscillations during general anaesthesia has been related to pre-operative cognition and could constitute a functional marker for brain vulnerability.

OBJECTIVE

We hypothesised that features of intra-operative α-band activity could predict the occurrence of POD.

DESIGN

Single-centre prospective observational study.

SETTING

University hospital, from 15 May 2019 to 15 December 2021.

PATIENTS

Adult patients undergoing elective cardiac surgery.

MAIN OUTCOME MEASURES

Pre-operative cognitive status was assessed by neuropsychological tests and scored as a global z score. A 5-min EEG recording was obtained 30 min after induction of anaesthesia. Anaesthesia was maintained with sevoflurane. Power and peak frequency in the α-band were extracted from the frequency spectra. POD was assessed using the Confusion Assessment Method for Intensive Care Unit, the Confusion Assessment Method and a chart review.

RESULTS

Sixty-five (29.5%) of 220 patients developed POD. Delirious patients were significantly older with median [IQR] ages of 74 [64 to 79] years vs. 67 [59 to 74] years; P  < 0.001) and had lower pre-operative cognitive z scores (-0.52 ± 1.14 vs. 0.21 ± 0.84; P  < 0.001). Mean α power (-14.03 ± 4.61 dB vs. -11.59 ± 3.37 dB; P  < 0.001) and maximum α power (-11.36 ± 5.28 dB vs. -8.85 ± 3.90 dB; P  < 0.001) were significantly lower in delirious patients. Intra-operative mean α power was significantly associated with the probability of developing POD (adjusted odds ratio, 0.88; 95% confidence interval (CI), 0.81 to 0.96; P  = 0.007), independently of age and only whenever cognitive status was not considered.

CONCLUSION

A lower intra-operative frontal α-band power is associated with a higher incidence of POD after cardiac surgery. Intra-operative measures of α power could constitute a means of identifying patients at risk of this complication.

TRIAL REGISTRATION

NCT03706989.

Assessment of long-term cognitive dysfunction in older patients who undergo heart surgery

INTRODUCTION

Older patients are more likely to have cognitive dysfunction, and a great proportion of patients undergone surgical procedures are older adults. Postoperative cognitive dysfunction (POCD) has been shown as a consistent complication after major surgical procedures such as heart surgery.

AIM

To determine the presence of long-term POCD in ≥65-year-old patients undergoing coronary artery bypass grafting and aortic valve replacement, and to establish related risk factors.

METHODS

We prospectively and sequentially included 44 patients with coronary disease and aortic stenosis scheduled for heart surgery. Follow-up of all patients was standardized and a neurocognitive evaluation were performed preoperatively and at 1, 6 and 12 months after surgery.

RESULTS

Patients experienced a significantly postoperative cognitive dysfunction (33.5%, 63.4% and 38.9% at 1, 6 and 12 months, respectively) from baseline (20.5%). Patient-associated aspects such as age (p<0.01), history of smoking (p<0.01), arterial hypertension (p=0.022), diabetes mellitus (p=0.024), heart failure (p=0.036) and preoperative cognitive dysfunction (p<0.01), and surgery-associated aspects such as EuroSCORE (p<0.01) and operation time (p<0.01) were identified as related risk factors.

CONCLUSIONS

Older patients who underwent heart surgery had long-term POCD. Both patient- and surgery-related risk factors were established as related risk factors. These findings suggest that the prevalence of cognitive dysfunction after cardiac surgery in older patients could be related to a possible progression to dementia. In addition, many of the risk factors identified may be modifiable but in practice, these patients are not attended to for their possible cognitive impairment.

Comparison of bispectral index and patient state index as measures of sedation depth during surgeries using remimazolam tosilate

BACKGROUND

The Bispectral Index (BIS) and the Patient State Index (PSI) are commonly used measures to assess intraoperative sedation depth. However, model differences lead to different results, which in turn interferes with clinicians' judgment on the depth of anesthesia. Remimazolam tosilate (RT) for injection is a new benzodiazepine used in sedation. In its clinical application, there are few effective indicators for sedation depth monitoring. To close this gap, this study aims to compare BIS and PSI in measuring the sensitivity and specificity of intraoperative RT and to explore the safety of RT for intraspinal anesthesia in elderly patients.

METHODS

This study included 40 patients undergoing elective electro-prostatectomy with intraspinal anesthesia, who were monitored by BIS and PSI simultaneously during operation. Remimazolam tosylate 0.1 mg/kg was intravenously administered after the intraspinal anesthesia when patients were in a completely painless status. Then BIS, PSI, the Modified Observer's Assessment of Alertness and Sedation (MOAA/S) scores and vital signs were observed and recorded per minute for 10 min. Pearson's correlation analysis and linear regression model were used to compare BIS and PSI sedation scores, and to test their associations with the MOAA/S score, respectively. ROC curves were drawn to compare the sensitivity and specificity of BIS and PSI. Changes of vital signs were presented as mean ± standard deviation. Perioperative liver and kidney function indicators were analyzed using a paired t-test to evaluate the safety of RT for intraspinal anesthesia in the elderly patients.

RESULTS

According to Pearson's correlation analysis, a significant (P < 0.01) correlation between BIS and PSI was found when used to monitor intraoperative sedation of RT (r = 0.796). Significant associations between BIS and MOAA/S (r = 0.568, P < 0.01), and between PSI and MOAA/S (r = 0.390, P < 0.01) were also found. The areas under the ROC curves of BIS and PSI were 0.801 ± 0.022 and 0.734 ± 0.026, respectively, suggesting that both measures may predict patients' state of consciousness and BIS was more accurate than PSI. Vital signs remained stable throughout the study. No abnormal changes of clinical significance were found based on laboratory test results of liver and kidney function.

CONCLUSION

BIS and PSI are strongly associated for monitoring the sedation of RT intraoperatively. Both methods can accurately reflect sedation depth. According to correlation analyses with MOAA/S scale and ROC curves, BIS is more accurate than PSI during such intraoperative monitoring. In addition, RT can be safely used in elderly patients under intraspinal anesthesia for supportive sedation, with stable vital signs and sound kidney and liver safety profiles.

TRIAL REGISTRATION

http://www.chictr.org.cn (ChiCTR2100051912).

Oscillatory and aperiodic neuronal activity in working memory following anesthesia

OBJECTIVE

Anesthesia and surgery are associated with cognitive impairment, particularly memory deficits. So far, electroencephalography markers of perioperative memory function remain scarce.

METHODS

We included male patients >60 years scheduled for prostatectomy under general anesthesia. We obtained neuropsychological assessments and a visual match-to-sample working memory task with simultaneous 62-channel scalp electroencephalography 1 day before and 2 to 3 days after surgery.

RESULTS

Twenty-six patients completed both pre- and postoperative sessions. Compared with preoperative performance, verbal learning deteriorated after anesthesia (California Verbal Learning Test total recall; t₂₅ = -3.25, p = 0.015, d = -0.902), while visual working memory performance showed a dissociation between match and mismatch accuracy (match*session F_1,25 = 3.866, p = 0.060). Better verbal learning was associated with an increase of aperiodic brain activity (total recall r = 0.66, p = 0.029, learning slope r = 0.66, p = 0.015), whereas visual working memory accuracy was tracked by oscillatory theta/alpha (7 - 9 Hz), low beta (14 - 18 Hz) and high beta/gamma (34 - 38 Hz) activity (matches: p < 0.001, mismatches: p = 0.022).

CONCLUSIONS

Oscillatory and aperiodic brain activity in scalp electroencephalography track distinct features of perioperative memory function.

SIGNIFICANCE

Aperiodic activity provides a potential electroencephalographic biomarker to identify patients at risk for postoperative cognitive impairments.

Microstate analyses as an indicator of anesthesia-induced unconsciousness

OBJECTIVE

The objective of this study was to identify differences in electroencephalographic microstate topographies across three perioperative phases: anesthetic pre-induction, surgical anesthesia, and post-anesthesia care unit (PACU) admission.

METHODS

Whole-scalp 16-channel electroencephalographic recordings were taken throughout the perioperative period on n = 22 adult, non-cardiac surgical patients.

RESULTS

Several differences between perioperative periods were identified. Most notably, during surgical anesthesia, patients demonstrated increased mean duration and, consequently, a reduction in the occurrence of microstates when compared to both preoperative baseline and PACU admission. We also observed the presence of microstate F with propofol anesthesia during surgery, which had been previously identified with propofol infusion in laboratory settings using human volunteers. Finally, we observed inverse age effects with mean occurrence and duration of microstates, particularly during PACU recovery.

CONCLUSIONS

Microstate duration is significantly increased during surgery compared to both pre-induction and PACU recovery. These data suggest that microstate topographies may be useful in monitoring anesthetic depth.

SIGNIFICANCE

This work highlights the potential for microstate analysis in the perioperative setting. We identified distinct topographical signatures across perioperative periods and with increasing age, which is predictive of post-operative delirium.

EEG responses to standardised noxious stimulation during clinical anaesthesia: a pilot study

Background

During clinical anaesthesia, the administration of analgesics mostly relies on empirical knowledge and observation of the patient's reactions to noxious stimuli. Previous studies in healthy volunteers under controlled conditions revealed EEG activity in response to standardised nociceptive stimuli even at high doses of remifentanil and propofol. This pilot study aims to investigate the feasibility of using these standardised nociceptive stimuli in routine clinical practice.

Methods

We studied 17 patients undergoing orthopaedic trauma surgery under general anaesthesia. We evaluated if the EEG could track standardised noxious phase-locked electrical stimulation and tetanic stimulation, a time-locked surrogate for incisional pain, before, during, and after the induction of general anaesthesia. Subsequently, we analysed the effect of tetanic stimulation on the surgical pleth index as a peripheral, vegetative, nociceptive marker.

Results

We found that the phase-locked evoked potentials after noxious electrical stimulation vanished after the administration of propofol, but not at low concentrations of remifentanil. After noxious tetanic stimulation under general anaesthesia, there were no consistent spectral changes in the EEG, but the vegetative response in the surgical pleth index was statistically significant (Hedges' g effect size 0.32 [95% confidence interval 0.12-0.77], P=0.035).

Conclusion

Our standardised nociceptive stimuli are not optimised for obtaining consistent EEG responses in patients during clinical anaesthesia. To validate and sufficiently reproduce EEG-based standardised stimulation as a marker for nociception in clinical anaesthesia, other pain models or stimulation settings might be required to transfer preclinical studies into clinical practice.

Clinical trial registration

DRKS00017829.

Population pharmacokinetic and pharmacodynamic model of propofol externally validated in Korean elderly subjects

The Eleveld propofol pharmacokinetic (PK) model, which was developed based on a broad range of populations, showed greater bias (- 27%) in elderly subjects in a previous validation study conducted by Vellinga and colleagues. We aimed to develop and externally validate a new PK-pharmacodynamic (PK-PD) model of propofol for elderly subjects. A population PK-PD model was constructed using propofol plasma concentrations and bispectral index (BIS) values that were obtained from 31 subjects aged 65 years older in previously published phase I studies. The predictive performance of the newly-developed PK-PD model (Choi model) was assessed in a separate Korean elderly population and compared with that of the Eleveld model. A three-compartment mammillary model using an allometric expression and a sigmoid E_max model well-described the time courses of propofol concentrations and BIS values. The V₁, V₂, V₃, Cl, Q₁, Q₂, E₀, E_max, Ce₅₀, γ, and k_e0 of a 60-kg subject were 8.36, 58.0, 650 L, 1.26, 0.917, 0.669 L/min, 92.1, 18.7, 2.21 μg/mL, 2.89, and 0.138 /min, respectively. In the Choi model and Eleveld model, pooled biases (95% CI) of the propofol concentration were 7.78 ( 3.09-12.49) and 16.70 (9.46-23.93) and pooled inaccuracies were 22.84 (18.87-26.81) and 24.85 (18.07-31.63), respectively. The Choi PK model was less biased than the Eleveld PK model in Korean elderly subjects (age range: 65.0-79.0 yr; weight range: 45.0-75.3 kg). Our results suggest that the Choi PK model, particularly, is applicable to target-controlled infusion in non-obese Korean elderly subjects.

Age-dependent Electroencephalogram Characteristics During Different Levels of Anesthetic Depth

Objective The monitoring of anesthetic depth based on electroencephalogram derivation is not currently adjusted for age. Here we analyze the influence of age factors on electroencephalogram characteristics. Methods Frontal electroencephalogram recordings were obtained from 80 adults during routine clinical anesthesia. The characteristics of electroencephalogram with age and anesthesia were observed during four kinds of anesthesia. Results The slow wave power, δ power, Bispectral Index (BIS) and approximate entropy can be used to distinguish different states of anesthesia (P < 0.05). In the deep and very deep anesthesia states, δ power decreased with age (P < 0.0001). In the very deep anesthesia state, θ power decreased with age (P < 0.05). In the deep and very deep anesthesia states, α power decreased with age (P = 0.0002). In the light and deep anesthesia states, β power decreased with age (P = 0.003). In the deep anesthesia state, γ power decreased with age (P = 0.002). In the very deep anesthesia state, permutation entropy increased significantly with age (P = 0.0001). In the very deep anesthesia state, BIS value increased with age (P = 0.006). The slow wave power, approximate entropy, and sample entropy did not show age-dependent changes. Conclusions The influence of age should be considered when using BIS and δ power to monitor the depth of anesthesia, while the influence of age should not be considered when using slow wave power and approximate entropy to monitor the depth of anesthesia.

Moderate sedation with single-dose remimazolam tosilate in elderly male patients undergoing transurethral resection of the prostate with spinal anesthesia: a prospective, single-arm, single-centre clinical trial

Background

Remimazolam tosilate (RT) is a newly listed benzodiazepine for sedation and anesthesia featuring quick onset of effects, short maintenance and recovery times, which is currently under research. This trial was conducted to determine the median effective dose (ED₅₀) and the 95% effective dose (ED₉₅) of single-dose remimazolam for moderate sedation in elderly patients undergoing transurethral resection of the prostate (TURP) under spinal anesthesia, and to evaluate its efficacy and safety.

Methods

Thirty male patients aged 65–80 years old were recruited for selective TURP. Remimazolam was administered intravenously to pain-free patients (VAS score < 1) within 1 min of successful spinal anesthesia by the same anesthesiologist. We used modified Dixon’s up-and-down sequential allocation method to determine the ED₅₀ and ED₉₅ of the agent with an initial dosage of 0.1 mg/kg. Successful sedation was defined as an MOAA/S score ≤ 3 and above 1. A score of > 3 was deemed as failed sedation. Recruitment continued until ten independent pairs (from successful sedation to failed sedation) would give a reliable estimation of the ED₅₀ and ED₉₅ of RT and their 95% confidence intervals.

Results

The ED₅₀ of remimazolam was 0.063 (95% C.I. 0.045–0.073) mg/kg. Its ED₉₅ was 0.079 (95% C.I. 0.07–0.137) mg/kg. Remimazolam was safe in its application.

Conclusions

A single-dose of RT proves to be safe for assisted sedation during TURP in elderly male patients under spinal anesthesia with a lower incidence of adverse events. Its ED₅₀ and ED₉₅ were 0.063 mg/kg and 0.079 mg/kg, respectively.

Trial registration

http://www.chictr.org.cn (ChiCTR2100051912).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01788-1.

Quantitative Analysis of Visually Reviewed Normal Scalp EEG Predicts Seizure Freedom Following Anterior Temporal Lobectomy

Objective

Anterior temporal lobectomy (ATL) is a widely performed and successful intervention for drug‐resistant temporal lobe epilepsy (TLE). However, up to one third of patients experience seizure recurrence within 1 year after ATL. Despite the extensive literature on presurgical electroencephalography (EEG) and magnetic resonance imaging (MRI) abnormalities to prognosticate seizure freedom following ATL, the value of quantitative analysis of visually reviewed normal interictal EEG in such prognostication remains unclear. In this retrospective multicenter study, we investigate whether machine learning analysis of normal interictal scalp EEG studies can inform the prediction of postoperative seizure freedom outcomes in patients who have undergone ATL.

Methods

We analyzed normal presurgical scalp EEG recordings from 41 Mayo Clinic (MC) and 23 Cleveland Clinic (CC) patients. We used an unbiased automated algorithm to extract eyes closed awake epochs from scalp EEG studies that were free of any epileptiform activity and then extracted spectral EEG features representing (a) spectral power and (b) interhemispheric spectral coherence in frequencies between 1 and 25 Hz across several brain regions. We analyzed the differences between the seizure‐free and non–seizure‐free patients and employed a Naïve Bayes classifier using multiple spectral features to predict surgery outcomes. We trained the classifier using a leave‐one‐patient‐out cross‐validation scheme within the MC data set and then tested using the out‐of‐sample CC data set. Finally, we compared the predictive performance of normal scalp EEG‐derived features against MRI abnormalities.

Results

We found that several spectral power and coherence features showed significant differences correlated with surgical outcomes and that they were most pronounced in the 10–25 Hz range. The Naïve Bayes classification based on those features predicted 1‐year seizure freedom following ATL with area under the curve (AUC) values of 0.78 and 0.76 for the MC and CC data sets, respectively. Subsequent analyses revealed that (a) interhemispheric spectral coherence features in the 10–25 Hz range provided better predictability than other combinations and (b) normal scalp EEG‐derived features provided superior and potentially distinct predictive value when compared with MRI abnormalities (>10% higher F1 score).

Significance

These results support that quantitative analysis of even a normal presurgical scalp EEG may help prognosticate seizure freedom following ATL in patients with drug‐resistant TLE. Although the mechanism for this result is not known, the scalp EEG spectral and coherence properties predicting seizure freedom may represent activity arising from the neocortex or the networks responsible for temporal lobe seizure generation within vs outside the margins of an ATL.

The TLR4/NF-κB/MAGI-2 signaling pathway mediates postoperative delirium

Purpose: To evaluate the TLR4/NF-κB/MAGI-2 signaling pathway in postoperative delirium.

Methods: Elderly patients aged 65-80 years who received unilateral hip arthroplasty under subarachnoid anesthesia were included. Pre-anesthesia cerebrospinal fluid and perioperative blood samples were collected. After follow-up, patients were divided into two groups according to the occurrence of postoperative delirium (POD) after surgery. The potential differentially expressed proteins in the two groups were determined by proteomics assay and subsequent western blot validation. A POD model of aged mice was established, and the TLR4/NF-κB/MAGI-2 signaling pathway was determined.

Main findings: The IL-1β and TNF-α levels in pre-anesthesia cerebrospinal fluid and postoperative blood were higher in patients who developed POD than in those patients who did not. Compared with non-POD patients, MAGI-2 was highly expressed in POD patients, as validated by proteomics assays and western blotting. Higher p-NF-κB-p65, TLR4 and MAGI-2 in POD patients were detected by western blot. The POD model in aged mice was successfully established and verified by three behavioral tests. Postoperative inflammatory cytokines and the TLR4/NF-κB/MAGI-2 signaling pathway were increased in mice with POD. Inhibiting TLR4/NF-κB/MAGI-2 signaling pathway could reduce postoperative delirium.

Conclusions: The TLR4/NF-κB/MAGI-2 signaling pathway mediates POD.

Hypercholesterolemia aggravates sevoflurane-induced cognitive impairment in aged rats by inducing neurological inflammation and apoptosis

We aimed to explore the effects of hypercholesterolemia on sevoflurane-induced cognitive impairment in aged rats and the underlying mechanism(s). Aged rats were administrated with high-fat diet, sevoflurane, or both. Thereafter, the plasma levels of total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) were evaluated. The Morris water maze task was performed to evaluate the spatial learning and memory ability of rats. Moreover, Nissl and Evans blue staining were conducted to test nerve damage and detect the blood-brain barrier permeability, respectively. The percentage of apoptotic cells was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The messenger RNA expression of inflammatory factors and protein expression of microglial activation markers and apoptosis-related proteins were tested by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, or western blot analysis, respectively. High-fat diet induced high levels of TC, TG, and LDL but decreased levels of HDL. However, sevoflurane had no effects on these levels. In contrast, sevoflurane significantly induced the impairment of learning and memory, nerve damage, neuroinflammatory damage, and neuronal apoptosis. Hypercholesterolemia exacerbated the sevoflurane-induced impairment in aged rats. These results suggested that hypercholesterolemia aggravates sevoflurane-induced cognitive impairment in aged rats, possibly by inducing neurological inflammation and apoptosis.

Electroacupuncture for the Prevention of Postoperative Cognitive Dysfunction Among Older Adults Undergoing Hip and Knee Arthroplasty: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background: Postoperative cognitive dysfunction (POCD) is a common surgical complication in elderly patients undergoing hip and knee replacement. Electroacupuncture (EA) may have a protective effect on postoperative cognitive function, but relevant evidence remains uncertain. Objective: To systematically evaluate the evidence of EA for the prevention of POCD after total joint arthroplasty. Methods: PubMed, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), China National Knowledge Infrastructure (CNKI), Wanfang Data, VIP, and Chinese Biomedical Literature Database (CBM) databases were searched until May 1, 2021. Randomized controlled trials (RCTs) in which patients undergoing hip and knee replacement pretreated with EA for preventing POCD were included. The risk of bias was assessed by the Cochrane Collaboration tool. Meta-analysis was performed using Review Manager version 5.4. Results: A total of 11 RCTs with 949 patients were identified. Meta-analysis showed that compared with controls, EA pretreatment significantly reduced the incidence of POCD at 1, 3, and 7 days and 3 and 6 months after the operation. EA was also superior in improving the Mini-Mental State Examination (MMSE) scores on the third postoperative day, but not on the first postoperative day. Neuron-specific enolase (NSE) and interleukin-1β (IL-1β) in the EA group were significantly lower than that in the control group. There was no difference in S100β between the EA group and the control group. Compared to the control group, tumor necrosis factor-α (TNF-α) levels were not significantly lower in the EA group at postoperative hour 0, while significantly decreased at postoperative hours 24 and 48. Conclusion: Our results suggest that EA pretreatment is an effective adjunctive therapy for reducing the incidence of POCD for patients receiving total joint replacement surgery. Its effect was embodied in improving the MMSE scores and NSE, IL-1β, and TNF-α levels, whereas it had no significant effect on S100β levels. Meanwhile, the benefits of EA for improving POCD need further strengthening and support from more large-scale, high-quality, and good-homogeneity RCTs. Systematic Review Registration: https://osf.io/xb3e8.

Emergence and fragmentation of the alpha-band driven by neuronal network dynamics

Rhythmic neuronal network activity underlies brain oscillations. To investigate how connected neuronal networks contribute to the emergence of the α-band and to the regulation of Up and Down states, we study a model based on synaptic short-term depression-facilitation with afterhyperpolarization (AHP). We found that the α-band is generated by the network behavior near the attractor of the Up-state. Coupling inhibitory and excitatory networks by reciprocal connections leads to the emergence of a stable α-band during the Up states, as reflected in the spectrogram. To better characterize the emergence and stability of thalamocortical oscillations containing α and δ rhythms during anesthesia, we model the interaction of two excitatory networks with one inhibitory network, showing that this minimal topology underlies the generation of a persistent α-band in the neuronal voltage characterized by dominant Up over Down states. Finally, we show that the emergence of the α-band appears when external inputs are suppressed, while fragmentation occurs at small synaptic noise or with increasing inhibitory inputs. To conclude, α-oscillations could result from the synaptic dynamics of interacting excitatory neuronal networks with and without AHP, a principle that could apply to other rhythms.

Brain oscillations, recorded from electroencephalograms characterize behaviors such as sleep, wakefulness, brain evoked responses, coma or anesthesia. The underlying rhythms for these oscillations are associated at a neuronal population level to fluctuations of the membrane potential between Up (depolarized) and Down (hyperpolarized) states. During anesthesia with propofol, a dominant α-band (8–12Hz) can emerge or disappear, but the underlying mechanism remains unclear. Using modeling, we report that the α-band appears during Up states in neuronal populations driven by short-term synaptic plasticity and synaptic noise. Moreover, we show that three connected neuronal networks representing the thalamocortical loop reproduce the dynamics of the α-band, which emerges following the arrest of excitatory stimulations, but that can disappear by increasing inhibitory inputs. To conclude, short-term plasticity in well connected neuronal networks can explain the emergence and fragmentation of the α-band.

Depression and anxiety symptoms are related to pain and frailty but not cognition or delirium in older surgical patients

OBJECTIVE

In community dwelling older adults, depression and anxiety symptoms can be associated with early cognitive decline. Symptoms of depression and anxiety are common in older adults prior to surgery. However, their significance is unknown. Our objective was to determine whether preoperative depression and anxiety symptoms are associated with postoperative cognitive decline (POCD) and in-hospital delirium, in older surgical patients.

METHODS

We conducted a secondary data analysis of postoperative cognitive dysfunction in a cohort study of patients 65 and older undergoing elective noncardiac surgery. We used the Hospital Anxiety and Depression Scale (HADS) to screen for depression and anxiety symptoms at a home visit prior to surgery and 3 months after surgery. Patients with a history of psychiatric (major depressive disorder, bipolar disorder, and schizophrenia) or neurologic disorder (Parkinson's disease and stroke) were excluded from the parent study.

RESULTS

Out of the 167 patients, 9.6% (n = 16) reported significant depressive symptoms and 21.6% (n = 36) reported significant anxiety symptoms on preoperative screening. There was no association between preoperative or new-onset postoperative depression and anxiety symptoms and the incidence of delirium or POCD three months after surgery. Patients with preoperative depressive symptoms had higher preoperative pain (scores 69 vs. 35.7, p = .002) and frailty (56 vs. 14.6, p <.001).

CONCLUSION

In our cohort, we did not detect an association between preoperative depression and anxiety symptoms and neurocognitive disorders. Preoperative depression and anxiety symptoms were related to physical pain and frailty. Taken together, these suggest that in patients without a formal psychiatric diagnosis, preoperative depression and anxiety symptoms are related to physical state rather than a harbinger of early cognitive decline. Future studies are needed to understand the nature of the relationship between depression and anxiety symptoms and physical state in surgical patients.

Characterizing the electrophysiological abnormalities in visually reviewed normal EEGs of drug-resistant focal epilepsy patients

Routine scalp EEG is essential in the clinical diagnosis and management of epilepsy. However, a normal scalp EEG (based on expert visual review) recorded from a patient with epilepsy can cause delays in diagnosis and clinical care delivery. Here, we investigated whether normal EEGs might contain subtle electrophysiological clues of epilepsy. Specifically, we investigated (i) whether there are indicators of abnormal brain electrophysiology in normal EEGs of epilepsy patients, and (ii) whether such abnormalities are modulated by the side of the brain generating seizures in focal epilepsy. We analysed awake scalp EEG recordings of age-matched groups of 144 healthy individuals and 48 individuals with drug-resistant focal epilepsy who had normal scalp EEGs. After preprocessing, using a bipolar montage of eight channels, we extracted the fraction of spectral power in the alpha band (8-13 Hz) relative to a wide band of 0.5-40 Hz within 10-s windows. We analysed the extracted features for (i) the extent to which people with drug-resistant focal epilepsy differed from healthy subjects, and (ii) whether differences within the drug-resistant focal epilepsy patients were related to the hemisphere generating seizures. We then used those differences to classify whether an EEG is likely to have been recorded from a person with drug-resistant focal epilepsy, and if so, the epileptogenic hemisphere. Furthermore, we tested the significance of these differences while controlling for confounders, such as acquisition system, age and medications. We found that the fraction of alpha power is generally reduced (i) in drug-resistant focal epilepsy compared to healthy controls, and (ii) in right-handed drug-resistant focal epilepsy subjects with left hemispheric seizures compared to those with right hemispheric seizures, and that the differences are most prominent in the frontal and temporal regions. The fraction of alpha power yielded area under curve values of 0.83 in distinguishing drug-resistant focal epilepsy from healthy and 0.77 in identifying the epileptic hemisphere in drug-resistant focal epilepsy patients. Furthermore, our results suggest that the differences in alpha power are greater when compared with differences attributable to acquisition system differences, age and medications. Our findings support that EEG-based measures of normal brain function, such as the normalized spectral power of alpha activity, may help identify patients with epilepsy even when an EEG does not contain any epileptiform activity, recorded seizures or other abnormalities. Although alpha abnormalities are unlikely to be disease-specific, we propose that such abnormalities may provide a higher pre-test probability for epilepsy when an individual being screened for epilepsy has a normal EEG on visual assessment.

Assessment of long-term cognitive dysfunction in older patients who undergo heart surgery

INTRODUCTION

Older patients are more likely to have cognitive dysfunction, and a great proportion of patients undergone surgical procedures are older adults. Postoperative cognitive dysfunction (POCD) has been shown as a consistent complication after major surgical procedures such as heart surgery.

AIM

To determine the presence of long-term POCD in ≥65-year-old patients undergoing coronary artery bypass grafting and aortic valve replacement, and to establish related risk factors.

METHODS

We prospectively and sequentially included 44 patients with coronary disease and aortic stenosis scheduled for heart surgery. Follow-up of all patients was standardized and a neurocognitive evaluation were performed preoperatively and at 1, 6 and 12 months after surgery.

RESULTS

Patients experienced a significantly postoperative cognitive dysfunction (33.5%, 63.4% and 38.9% at 1, 6 and 12 months, respectively) from baseline (20.5%). Patient-associated aspects such as age (p<0.01), history of smoking (p<0.01), arterial hypertension (p=0.022), diabetes mellitus (p=0.024), heart failure (p=0.036) and preoperative cognitive dysfunction (p<0.01), and surgery-associated aspects such as EuroSCORE (p<0.01) and operation time (p<0.01) were identified as related risk factors.

CONCLUSIONS

Older patients who underwent heart surgery had long-term POCD. Both patient- and surgery-related risk factors were established as related risk factors. These findings suggest that the prevalence of cognitive dysfunction after cardiac surgery in older patients could be related to a possible progression to dementia. In addition, many of the risk factors identified may be modifiable but in practice, these patients are not attended to for their possible cognitive impairment.

Molecular Diversity of Anesthetic Actions Is Evident in Electroencephalogram Effects in Humans and Animals

Anesthetic agents cause unique electroencephalogram (EEG) activity resulting from actions on their diverse molecular targets. Typically to produce balanced anesthesia in the clinical setting, several anesthetic and adjuvant agents are combined. This creates challenges for the clinical use of intraoperative EEG monitoring, because computational approaches are mostly limited to spectral analyses and different agents and combinations produce different EEG responses. Thus, testing of many combinations of agents is needed to generate accurate, protocol independent analyses. Additionally, most studies to develop new computational approaches take place in young, healthy adults and electrophysiological responses to anesthetics vary widely at the extremes of age, due to physiological brain differences. Below, we discuss the challenges associated with EEG biomarker identification for anesthetic depth based on the diversity of molecular targets. We suggest that by focusing on the generalized effects of anesthetic agents on network activity, we can create paths for improved universal analyses.

Effect of perioperative intravenous lidocaine on the incidence of short-term cognitive function after noncardiac surgery: A meta-analysis based on randomized controlled trials

OBJECTIVES

Postoperative cognitive dysfunction is a debilitating postoperative complication. The perioperative neuroprotective effect of lidocaine has conflicting results.

METHODS

In this qualitative review of randomized controlled clinical trials on the perioperative use of lidocaine, we report the effects of intravenous lidocaine on brain function after noncardiac surgery. Studies were identified from PubMed, MEDLINE, and Cochrane Central Register.

RESULTS

Of the 453 retrieved studies, 4 randomized trials were included. No significant association between the use of lidocaine postoperative cognitive states was found (risk ratio 0.67; 95% CI -0.02 to 1.36; I² 89%; p = .06).

CONCLUSIONS

Current evidence cannot suggest that perioperative intravenous use of lidocaine has pharmacological brain neuroprotection after noncardiac surgery. All the included studies were small-scale research, and the total number of participants was small; the results should be interpreted with caution.

Preoperative neutrophil-lymphocyte ratio, an independent risk factor for postoperative cognitive dysfunction in elderly patients with gastric cancer

AIM

This study aimed to investigate the potential risk factors for postoperative cognitive dysfunction (POCD) in elderly patients with gastric cancer (GC) after radical gastrectomy.

METHODS

In total, 221 elderly patients with GC who were scheduled to undergo selective radical gastrectomy in our hospital were enrolled in this study. To define early POCD, the neuropsychological assessment was carried out 1 day before surgery and 7 days after surgery. Receiver operating characteristic curve analysis was carried out to evaluate the predicative and cut-off values of risk factors, including neutrophil-lymphocyte ratio (NLR) for early POCD. The univariate and multivariate logistic regression analyses were performed to investigate risk factors for early POCD.

RESULTS

Of the 221 enrolled elderly patients with GC, 42 were identified as early POCD with an incidence of 19.0% (42 of 221). Receiver operating characteristic curve analysis indicated that NLR was a significant predictor for POCD with a cut-off value of 2.50 and an area under the curve of 0.711 (95% confidence interval: 0.624-0.798, P < 0.001). Preoperative NLR (≥2.50) was the only independent risk factor associated with POCD (odds ratio: 2.44, 95% confidence interval: 1.52-3.68, P = 0.013) by the multivariate logistic regression analysis.

CONCLUSIONS

Preoperative NLR level was an independent risk factor for POCD in elderly patients with GC undergoing curative resection. Geriatr Gerontol Int 2020; 20: 927-931.

Electrophysiological Correlates of Brain Health Help Diagnose Epilepsy and Lateralize Seizure Focus

The absence of epileptiform activity in a scalp electroencephalogram (EEG) recorded from a potential epilepsy patient can cause delays in clinical care delivery. Here we present a machine-learning-based approach to find evidence for epilepsy in scalp EEGs that do not contain any epileptiform activity, according to expert visual review (i.e., "normal" EEGs). We found that deviations in the EEG features representing brain health, such as the alpha rhythm, can indicate the potential for epilepsy and help lateralize seizure focus, even when commonly recognized epileptiform features are absent. Hence, we developed a machine-learning-based approach that utilizes alpha-rhythm-related features to classify 1) whether an EEG was recorded from an epilepsy patient, and 2) if so, the seizure-generating side of the patient's brain. We evaluated our approach using "normal" scalp EEGs of 48 patients with drug-resistant focal epilepsy and 144 healthy individuals, and a naive Bayes classifier achieved area under ROC curve (AUC) values of 0.81 and 0.72 for the two classification tasks, respectively. These findings suggest that our methodology is useful in the absence of interictal epileptiform activity and can enhance the probability of diagnosing epilepsy at the earliest possible time.

Anesthesia and surgery induce cognitive dysfunction in elderly male mice: the role of gut microbiota

It is well known that the incidence of postoperative cognitive dysfunction (POCD) is high in elderly patients. The pathogenesis and therapeutic mechanisms of POCD, however, have not yet been completely elucidated. The effects of gut microbiota, particularly in terms of regulating brain function, have gradually attracted increasing attention. In this study, we investigated the potential role of gut microbiota in POCD in aged male mice and attempted to determine whether alterations in gut microbiota would be helpful in the diagnosis of POCD. POCD and non-POCD mice were classified by hierarchical cluster analysis of behavioral results. Additionally, α- and β-diversity of gut microbiota showed a differential profile between the groups. In total, 24 gut bacteria were significantly altered in POCD mice compared with those in non-POCD mice, in which 13 gut bacteria were significantly correlated with escape latency in the Morris water maze test (MWMT). Remarkably, receiver operating characteristic curves revealed that the Dehalobacteriaceae family and Dehalobacterium genus are potentially important bacteria for the diagnosis of POCD. These findings indicate that alterations in the composition of gut microbiota are probably involved in the pathogenesis of POCD in aged mice. Novel therapeutic strategies regulating specific gut bacteria may be helpful for the prevention and treatment of POCD.

The influence of anesthetic techniques on postoperative cognitive function in elderly patients undergoing hip fracture surgery: General vs spinal anesthesia

BACKGROUND

Hip fracture is common and morbid in elderly patients. Postoperative cognitive dysfunction (POCD) is also very common in these subjects undergoing surgery with an incidence which exceeds 40% in some reports. To date, the evidence is ambiguous as to whether anesthetic technique may affect the patients' outcome as far as postoperative cognitive function is concerned.

OBJECTIVE

The aim of this study was to compare the effect of general and subarachnoid (spinal) anesthesia on the development of POCD up to 30 days after surgery in elderly patients undergoing hip fracture surgery. Methods Subjects over 65 years with hip fracture undergoing surgery were recruited for this study. They were enrolled and randomized to receive either general anesthesia (GA group) or subarachnoid (spinal) anesthesia (S group). Cognitive function was assessed using a battery of neuropsychological tests undertaken preoperatively and at 30 days postoperatively. The incidence of delirium was examined during the same period and their functional status, in terms of activities of daily living was also recorded.

RESULTS

A total of seventy patients, 33 men and 37 females, mean age of 76 years were analyzed. Thirty-three patients received general anesthesia (GA group) and 37 subarachnoid (spinal) anesthesia (S group). The two groups of patients were similar with respect to baseline characteristics, comorbidities and perioperative data. The results of neuropsychological testing showed that there were no significant differences between the groups in eight out of ten neurocognitive tests at baseline and 30 days after surgery. There was a statistically significant decline of the Instrumental Activities of Daily Living Scale score in S group compared with group GA on the 30th postoperative day (p = 0.043). A significant decline was also present in Color-Word Task test in S group compared with group GA at baseline (p = 0.014) and 30 days postoperatively (p = 0.003). Postoperative delirium was present in four patients (12%) for the GA group, and in 10 patients (27%) for the group receiving subarachnoid anesthesia.

CONCLUSION

We concluded that the choice of anesthesia modality does not appear to influence the emergence of postoperative cognitive dysfunction in elderly patients undergoing hip fracture surgery.

Postoperative cognitive dysfunction - current preventive strategies

Improving trends in global health care have resulted in a steady increase in the geriatric population. However, as the population ages, surgery is being performed more frequently in progressively older patients and those with higher prevalence of comorbidities. A significant percentage of elderly patients experience transient postoperative delirium following surgery or long-term postoperative cognitive dysfunction (POCD). Increasing age, educational level, pre-existing mental health, and comorbidities are contributory factors. Comprehensive geriatric assessment provides an objective evaluation on overall medical, social, mental, and functional well-being with scope for preoperative optimization. Preventive strategies for POCD target the surgical and patient-related factors as well as the utilization of the concept of stress-free anesthesia and surgery, that is, Enhanced Recovery After Surgery. This includes care bundles and protocols for the perioperative period which improves outcomes in the elderly. Research on biomarkers of neural injury in POCD is gaining momentum. Pharmacologic agents such as acetylcholine esterase inhibitors promise to have a vital role in the management of POCD but exhibit undesired side effects. Interventions to reduce oxidative stress and neuroinflammation could prove beneficial. Preventive strategies, early recognition, and management of perioperative risk factors seems to be, by far, the best modality to deal with POCD till further progress in therapeutic interventions evolve.

Screening of Potential Genes and Transcription Factors of Postoperative Cognitive Dysfunction via Bioinformatics Methods

Background

The aim of this study was to explore the potential genes and transcription factors involved in postoperative cognitive dysfunction (POCD) via bioinformatics analysis.

Material/Methods

GSE95070 miRNA expression profiles were downloaded from Gene Expression Omnibus database, which included five hippocampal tissues from POCD mice and controls. Moreover, the differentially expressed miRNAs (DEMs) between the two groups were identified. In addition, the target genes of DEMs were predicted using Targetscan 7.1, followed by protein-protein interaction (PPI) network construction, functional enrichment analysis, pathway analysis, and prediction of transcription factors (TFs) targeting the potential targets.

Results

A total of eight DEMs were obtained, and 823 target genes were predicted, including 170 POCD-associated genes. Furthermore, potential key genes in the network were remarkably enriched in focal adhesion, protein digestion and absorption, ECM-receptor interaction, and Wnt and MAPK signaling pathways.

Conclusions

Most potential target genes were involved in the regulation of TFs, including LEF1, SP1, and AP4, which may exert strong impact on the development of POCD.

The Effect of Propofol vs. Isoflurane Anesthesia on Postoperative Changes in Cerebrospinal Fluid Cytokine Levels: Results from a Randomized Trial

Introduction

Aside from direct effects on neurotransmission, inhaled and intravenous anesthetics have immunomodulatory properties. In vitro and mouse model studies suggest that propofol inhibits, while isoflurane increases, neuroinflammation. If these findings translate to humans, they could be clinically important since neuroinflammation has detrimental effects on neurocognitive function in numerous disease states.

Materials and methods

To examine whether propofol and isoflurane differentially modulate neuroinflammation in humans, cytokines were measured in a secondary analysis of cerebrospinal fluid (CSF) samples from patients prospectively randomized to receive anesthetic maintenance with propofol vs. isoflurane (registered with http://www.clinicaltrials.gov, identifier NCT01640275). We measured CSF levels of EGF, eotaxin, G-CSF, GM-CSF, IFN-α2, IL-1RA, IL-6, IL-7, IL-8, IL-10, IP-10, MCP-1, MIP-1α, MIP-1β, and TNF-α before and 24 h after intracranial surgery in these study patients.

Results

After Bonferroni correction for multiple comparisons, we found significant increases from before to 24 h after surgery in G-CSF, IL-10, IL-1RA, IL-6, IL-8, IP-10, MCP-1, MIP-1α, MIP-1β, and TNF-α. However, we found no difference in cytokine levels at baseline or 24 h after surgery between propofol- (n = 19) and isoflurane-treated (n = 21) patients (p > 0.05 for all comparisons). Increases in CSF IL-6, IL-8, IP-10, and MCP-1 levels directly correlated with each other and with postoperative CSF elevations in tau, a neural injury biomarker. We observed CSF cytokine increases up to 10-fold higher after intracranial surgery than previously reported after other types of surgery.

Discussion

These data clarify the magnitude of neuroinflammation after intracranial surgery, and raise the possibility that a coordinated neuroinflammatory response may play a role in neural injury after surgery.

Pharmacologic Considerations of Anesthetic Agents in Geriatric Patients

Aging is a natural process of declining organ function and reserve. Census data show that the geriatric population is expected to grow to nearly 30%. More than half of geriatric patients have 1 or more surgical procedures in their lifetimes. Moreover, this is the population at greatest risk of morbidity and mortality with any given complication. There is remarkable variability in health across the age spectrum, from fit to frail and compromised. This variability requires a unique approach to anesthetic delivery and drug dosing on an individual basis to avoid complications such as postoperative cognitive dysfunction and delirium.

Sensitivity to isoflurane anesthesia increases in autism spectrum disorder Shank3+/∆c mutant mouse model

Autism is a heterogeneous developmental disorder characterized by impaired social interaction, impaired communication skills, and restricted and repetitive behavior. The abnormal behaviors of these patients can make their anesthetic and perioperative management difficult. Evidence in the literature suggests that some patients with autism or specific autism spectrum disorders (ASD) exhibit altered responses to pain and to anesthesia or sedation. A genetic mouse model of one particular ASD, Phelan McDermid Syndrome, has been developed that has a Shank3 haplotype truncation (Shank3^+/Δc). These mice exhibit important characteristics of autism that mimic human autistic behavior. Our study demonstrates that a Shank3^+/ΔC mutation in mice is associated with a reduction in both the MAC and RREC50 of isoflurane and down regulation of NR1 in vestibular nuclei and PSD95 in spinal cord. Decreased expression of NR1 and PSD95 in the central nervous system of Shank3^+/ΔC mice could help reduce the MAC and RREC50 of isoflurane, which would warrant confirmation in a clinical study. If Shank3 mutations are found to affect anesthetic sensitivity in patients with ASD, better communication and stricter monitoring of anesthetic depth may be necessary.

Assessment of different anesthesia depth under total intravenous anesthesia on postoperative cognitive function in laparoscopic patients

Background:

This study aimed to compare the effects of different depths of sedation during total intravenous anesthesia (TIVA) with remifentanil and propofol given by target-controlled infusion (TCI) on postoperative cognitive function in young and middle-aged patients undergoing gynecological laparoscopic surgery.

Materials and Methods:

A total of 150 American Society of Anesthesiologists physical Status I/II patients scheduled for gynecological laparoscopic operation were randomly divided into three groups. Anesthesia was maintained with intravenous infusion of TCI propofol and remifentanil, intermittent injected intravenously with rocuronium. The infusion concentration of propofol and remifentanil was adjusted to maintain bispectral index (BIS) at 30 < BIS ≤ 40 in the first group, 40 < BIS ≤ 50 in the second group, and 50 < BIS ≤ 60 in the third group. Mini–mental state examination (MMSE) and trail-making test (TMT) were used to assess the cognitive function one day preoperatively and one day postoperatively.

Results:

MMSE scores were > 24 sores on the day before anesthesia and the day after surgery in all three groups. However, the first group had the significantly higher MMSE scores than the other two groups after surgery (P < 0.05). Compared with that before anesthesia, TMT completion time was shorter on the day after surgery in the first group, while prolonged in the third group (P < 0.05). The first group had the significantly lower TMT completion time than the other two groups (P < 0.05).

Conclusion:

The depth of sedation, 30 < BIS value ≤ 40, under TIVA with remifentanil and propofol given by TCI had the minimal influence on postoperative cognitive function.

The Ageing Brain: Age-dependent changes in the electroencephalogram during propofol and sevoflurane general anaesthesia

BACKGROUND

Anaesthetic drugs act at sites within the brain that undergo profound changes during typical ageing. We postulated that anaesthesia-induced brain dynamics observed in the EEG change with age.

METHODS

We analysed the EEG in 155 patients aged 18-90 yr who received propofol (n=60) or sevoflurane (n=95) as the primary anaesthetic. The EEG spectrum and coherence were estimated throughout a 2 min period of stable anaesthetic maintenance. Age-related effects were characterized by analysing power and coherence as a function of age using linear regression and by comparing the power spectrum and coherence in young (18- to 38-yr-old) and elderly (70- to 90-yr-old) patients.

RESULTS

Power across all frequency bands decreased significantly with age for both propofol and sevoflurane; elderly patients showed EEG oscillations ∼2- to 3-fold smaller in amplitude than younger adults. The qualitative form of the EEG appeared similar regardless of age, showing prominent alpha (8-12 Hz) and slow (0.1-1 Hz) oscillations. However, alpha band dynamics showed specific age-related changes. In elderly compared with young patients, alpha power decreased more than slow power, and alpha coherence and peak frequency were significantly lower. Older patients were more likely to experience burst suppression.

CONCLUSIONS

These profound age-related changes in the EEG are consistent with known neurobiological and neuroanatomical changes that occur during typical ageing. Commercial EEG-based depth-of-anaesthesia indices do not account for age and are therefore likely to be inaccurate in elderly patients. In contrast, monitoring the unprocessed EEG and its spectrogram can account for age and individual patient characteristics.

Ageing delays emergence from general anaesthesia in rats by increasing anaesthetic sensitivity in the brain

BACKGROUND

Little is known about ageing-related changes in the brain that affect emergence from general anaesthesia. We used young adult and aged Fischer 344 rats to test the hypothesis that ageing delays emergence from general anaesthesia by increasing anaesthetic sensitivity in the brain.

METHODS

Time to emergence was determined for isoflurane (1.5 vol% for 45 min) and propofol (8 mg kg(-1) i.v.). The dose of isoflurane required to maintain loss of righting (LOR) was established in young adult and aged rats. The efficacy of methylphenidate to reverse LOR from general anaesthesia was tested. Separate young adult and aged rats with implanted electroencephalogram (EEG) electrodes were used to test whether ageing increases sensitivity to anaesthetic-induced burst suppression.

RESULTS

Mean time to emergence from isoflurane anaesthesia was 47 s [95% CI 33, 60; young adult) compared with 243 s (95% CI 185, 308; aged). For propofol, mean time to emergence was 13.1 min (95% CI 11.9, 14.0; young adult) compared with 23.1 min (95% CI 18.8, 27.9; aged). These differences were statistically significant. When methylphenidate was administered after propofol, the mean time to emergence decreased to 6.6 min (95% CI 5.9, 7.1; young adult) and 10.2 min (95% CI 7.9, 12.3; aged). These reductions were statistically significant. Methylphenidate restored righting in all rats during continuous isoflurane anaesthesia. Aged rats had lower EEG power and were more sensitive to anaesthetic-induced burst suppression.

CONCLUSIONS

Ageing delays emergence from general anaesthesia. This is due, at least in part, to increased anaesthetic sensitivity in the brain. Further studies are warranted to establish the underlying causes.

Physiology Considerations in Geriatric Patients

Physiology changes at the structural, functional, and molecular levels as people age, and every major organ system experiences physiologic change with time. The changes to the nervous system result mostly in cognitive impairments, the cardiovascular system develops higher blood pressures with lower cardiac output, the respiratory system undergoes a reduction of arterial oxyhemoglobin levels, the gastrointestinal system experiences delayed gastric emptying and reduction of hepatic metabolism, and the renal system experiences a diminished glomerular filtration rate. Combined, these changes create a complex physiologic condition. This unique physiology must be taken into consideration for geriatric patients undergoing general anesthesia.

Sevoflurane and Isoflurane induce structural changes in brain vascular endothelial cells and increase blood-brain barrier permeability: Possible link to postoperative delirium and cognitive decline

A large percentage of patients subjected to general anesthesia at 65 years and older exhibit postoperative delirium (POD). Here, we test the hypothesis that inhaled anesthetics (IAs), such as Sevoflurane and Isoflurane, act directly on brain vascular endothelial cells (BVECs) to increase blood-brain barrier (BBB) permeability, thereby contributing to POD. Rats of young (3-5 months), middle (10-12 months) and old (17-19 months) ages were anesthetized with Sevoflurane or Isoflurane for 3h. After exposure, some were euthanized immediately; others were allowed to recover for 24h before sacrifice. Immunohistochemistry was employed to monitor the extent of BBB breach, and scanning electron microscopy (SEM) was used to examine changes in the luminal surfaces of BVECs. Quantitative immunohistochemistry revealed increased BBB permeability in older animals treated with Sevoflurane, but not Isoflurane. Extravasated immunoglobulin G showed selective affinity for pyramidal neurons. SEM demonstrated marked flattening of the luminal surfaces of BVECs in anesthetic-treated rats. Results suggest an aging-linked BBB compromise resulting from exposure to Sevoflurane. Changes in the luminal surface topology of BVECs indicate a direct effect on the plasma membrane, which may weaken or disrupt their BBB-associated tight junctions. Disruption of brain homeostasis due to plasma influx into the brain parenchyma and binding of plasma components (e.g., immunoglobulins) to neurons may contribute to POD. We propose that, in the elderly, exposure to some IAs can cause BBB compromise that disrupts brain homeostasis, perturbs neuronal function and thereby contributes to POD. If unresolved, this may progress to postoperative cognitive decline and later dementia.

Neuroanesthesiology update

We review topics pertinent to the perioperative care of patients with neurological disorders. Our review addresses topics not only in the anesthesiology literature, but also in basic neurosciences, critical care medicine, neurology, neurosurgery, radiology, and internal medicine literature. We include literature published or available online up through December 8, 2013. As our review is not able to include all manuscripts, we focus on recurring themes and unique and pivotal investigations. We address the broad topics of general neuroanesthesia, stroke, traumatic brain injury, anesthetic neurotoxicity, neuroprotection, pharmacology, physiology, and nervous system monitoring.

Postoperative cognitive dysfunction: current developments in mechanism and prevention

Postoperative cognitive dysfunction (POCD) is a subtle disorder of thought processes, which may influence isolated domains of cognition and has a significant impact on patient health. The reported incidence of POCD varies enormously due to lack of formal criteria for the assessment and diagnosis of POCD. The significant risk factors of developing POCD mainly include larger and more invasive operations, duration of anesthesia, advanced age, history of alcohol abuse, use of anticholinergic medications, and other factors. The release of cytokines due to the systemic stress response caused by anesthesia and surgical procedures might induce the changes of brain function and be involved in the development of postoperative cognitive dysfunction. The strategies for management of POCD should be a multimodal approach involving close cooperation between the anesthesiologist, surgeon, geriatricians, and family members to promote early rehabilitation and avoid loss of independence in these patients.

Brain areas that influence general anesthesia

This document reviews the literature on local brain manipulation of general anesthesia in animals, focusing on behavioral and electrographic effects related to hypnosis or loss of consciousness. Local inactivation or lesion of wake-active areas, such as locus coeruleus, dorsal raphe, pedunculopontine tegmental nucleus, perifornical area, tuberomammillary nucleus, ventral tegmental area and basal forebrain, enhanced general anesthesia. Anesthesia enhancement was shown as a delayed emergence (recovery of righting reflex) from anesthesia or a decrease in the minimal alveolar concentration that induced loss of righting. Local activation of various wake-active areas, including pontis oralis and centromedial thalamus, promoted behavioral or electrographic arousal during maintained anesthesia and facilitated emergence. Lesion of the sleep-active ventrolateral preoptic area resulted in increased wakefulness and decreased isoflurane sensitivity, but only for 6 days after lesion. Inactivation of any structure within limbic circuits involving the medial septum, hippocampus, nucleus accumbens, ventral pallidum, and ventral tegmental area, amygdala, entorhinal and piriform cortex delayed emergence from anesthesia, and often reduced anesthetic-induced behavioral excitation. In summary, the concept that anesthesia works on the sleep-wake system has received strong support from studies that inactivated/lesioned or activated wake-active areas, and weak support from studies that lesioned sleep-active areas. In addition to the conventional wake-sleep areas, limbic structures such as the medial septum, hippocampus and prefrontal cortex are also involved in the behavioral response to general anesthesia. We suggest that hypnosis during general anesthesia may result from disrupting the wake-active neuronal activities in multiple areas and suppressing an atropine-resistant cortical activation associated with movements.