Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection

Protecting the injured central nervous system: Do anesthesia or hypothermia ameliorate secondary injury?

Traumatic injury to the central nervous system (CNS) and stroke initiate a cascade of processes that expand the area of tissue loss. The current review considers recent studies demonstrating that the induction of an anesthetic state or cooling the affected tissue (hypothermia) soon after injury can have a therapeutic effect. We first provide an overview of the neurobiological processes that fuel tissue loss after traumatic brain injury (TBI), spinal cord injury (SCI) and stroke. We then examine the rehabilitative effectiveness of therapeutic anesthesia across a variety of drug categories through a systematic review of papers in the PubMed database. We also review the therapeutic benefits hypothermia, another treatment that quells neural activity. We conclude by considering factors related to the safety, efficacy and timing of treatment, as well as the mechanisms of action. Clinical implications are also discussed.

Commonly Overlooked Factors in Biocompatibility Studies of Neural Implants

Biocompatibility of cutting-edge neural implants, surgical tools and techniques, and therapeutic technologies is a challenging concept that can be easily misjudged. For example, neural interfaces are routinely gauged on how effectively they determine active neurons near their recording sites. Tissue integration and toxicity of neural interfaces are frequently assessed histologically in animal models to determine tissue morphological and cellular changes in response to surgical implantation and chronic presence. A disconnect between histological and efficacious biocompatibility exists, however, as neuronal numbers frequently observed near electrodes do not match recorded neuronal spiking activity. The downstream effects of the myriad surgical and experimental factors involved in such studies are rarely examined when deciding whether a technology or surgical process is biocompatible. Such surgical factors as anesthesia, temperature excursions, bleed incidence, mechanical forces generated, and metabolic conditions are known to have strong systemic and thus local cellular and extracellular consequences. Many tissue markers are extremely sensitive to the physiological state of cells and tissues, thus significantly impacting histological accuracy. This review aims to shed light on commonly overlooked factors that can have a strong impact on the assessment of neural biocompatibility and to address the mismatch between results stemming from functional and histological methods.

Recent advances in arterial spin labeling perfusion MRI in patients with vascular cognitive impairment

Cognitive impairment (CI) is a major health concern in aging populations. It impairs patients' independent life and may progress to dementia. Vascular cognitive impairment (VCI) encompasses all cerebrovascular pathologies that contribute to cognitive impairment (CI). Moreover, the majority of CI subtypes involve various aspects of vascular dysfunction. Recent research highlights the critical role of reduced cerebral blood flow (CBF) in the progress of VCI, and the detection of altered CBF may help to detect or even predict the onset of VCI. Arterial spin labeling (ASL) is a non-invasive, non-ionizing perfusion MRI technique for assessing CBF qualitatively and quantitatively. Recent methodological advances enabling improved signal-to-noise ratio (SNR) and data acquisition have led to an increase in the use of ASL to assess CBF in VCI patients. Combined with other imaging modalities and biomarkers, ASL has great potential for identifying early VCI and guiding prediction and prevention strategies. This review focuses on recent advances in ASL-based perfusion MRI for identifying patients at high risk of VCI.

Embracing Heterogeneity in The Multicenter Stroke Preclinical Assessment Network (SPAN) Trial

The Stroke Preclinical Assessment Network (SPAN) is a multicenter preclinical trial platform using rodent models of transient focal cerebral ischemia to address translational failure in experimental stroke. In addition to centralized randomization and blinding and large samples, SPAN aimed to introduce heterogeneity to simulate the heterogeneity embodied in clinical trials for robust conclusions. Here, we report the heterogeneity introduced by allowing the 6 SPAN laboratories to vary most of the biological and experimental model variables and the impact of this heterogeneity on middle cerebral artery occlusion (MCAo) performance. We included the modified intention-to-treat population of the control mouse cohort of the first SPAN trial (n=421) and examined the biological and procedural independent variables and their covariance. We then determined their impact on the dependent variables cerebral blood flow drop during MCAo, time to achieve MCAo, and total anesthesia duration using multivariable analyses. We found heterogeneity in biological and procedural independent variables introduced mainly by the site. Consequently, all dependent variables also showed heterogeneity among the sites. Multivariable analyses with the site as a random effect variable revealed filament choice as an independent predictor of cerebral blood flow drop after MCAo. Comorbidity, sex, use of laser Doppler flow to monitor cerebral blood flow, days after trial onset, and maintaining anesthesia throughout the MCAo emerged as independent predictors of time to MCAo. Total anesthesia duration was predicted by most independent variables. We present with high granularity the heterogeneity introduced by the biological and model selections by the testing sites in the first trial of cerebroprotection in rodent transient filament MCAo by SPAN. Rather than trying to homogenize all variables across all sites, we embraced the heterogeneity to better approximate clinical trials. Awareness of the heterogeneity, its sources, and how it impacts the study performance may further improve the study design and statistical modeling for future multicenter preclinical trials.

Neurosurgical Anesthesia: Optimizing Outcomes with Agent Selection

Anesthesia in neurosurgery embodies a vital element in the development of neurosurgical intervention. This undisputed interest has offered surgeons and anesthesiologists an array of anesthetic selections to utilize, though with this allowance comes the equally essential requirement of implementing a maximally appropriate agent. To date, there remains a lack of consensus and official guidance on optimizing anesthetic choice based on operating priorities including hemodynamic parameters (e.g., CPP, ICP, MAP) in addition to the route of procedure and pathology. In this review, the authors detail the development of neuroanesthesia, summarize the advantages and drawbacks of various anesthetic classes and agents, while lastly cohesively organizing the current literature of randomized trials on neuroanesthesia across various procedures.

Vascular and neuronal effects of general anesthesia on the brain: An fMRI study

BACKGROUND AND PURPOSE

A number of functional magnetic resonance imaging (fMRI) studies rely on application of anesthetic agents during scanning that can modulate and complicate interpretation of the measured hemodynamic blood oxygenation level-dependent (BOLD) response. The purpose of the present study was to investigate the effect of general anesthesia on two main components of BOLD signal including neuronal activity and vascular response.

METHODS

Breath-holding (BH) fMRI was conducted in wakefulness and under anesthesia states in 9 patients with drug-resistant epilepsy who needed to get scanned under anesthesia during laser interstitial thermal therapy. BOLD and BOLD cerebrovascular reactivity (BOLD-CVR) maps were compared using t-test between two states to assess the effect of anesthesia on neuronal activity and vascular factors (p < .05).

RESULTS

Overall, our findings revealed an increase in BOLD-CVR and decrease in BOLD response under anesthesia in several brain regions. The results proposed that the modulatory mechanism of anesthetics on neuronal and vascular components of BOLD signal may work in different ways.

CONCLUSION

This experiment for the first human study showed that anesthesia may play an important role in dissociation between neuronal and vascular responses contributed to hemodynamic BOLD signal using BH fMRI imaging that may assist the implication of general anesthesia and interpretation of outcomes in clinical setting.

Comparison of cerebral metabolic rate of oxygen, blood flow, and bispectral index under general anesthesia

Significance

The optical measurement of cerebral oxygen metabolism was evaluated.

Aim

Compare optically derived cerebral signals to the electroencephalographic bispectral index (BIS) sensors to monitor propofol-induced anesthesia during surgery.

Approach

Relative cerebral metabolic rate of oxygen (rCMRO 2 ) and blood flow (rCBF) were measured by time-resolved and diffuse correlation spectroscopies. Changes were tested against the relative BIS (rBIS) ones. The synchronism in the changes was also assessed by the R-Pearson correlation.

Results

In 23 measurements, optically derived signals showed significant changes in agreement with rBIS: during propofol induction, rBIS decreased by 67% [interquartile ranges (IQR) 62% to 71%],rCMRO 2 by 33% (IQR 18% to 46%), and rCBF by 28% (IQR 10% to 37%). During recovery, a significant increase was observed for rBIS (48%, IQR 38% to 55%),rCMRO 2 (29%, IQR 17% to 39%), and rCBF (30%, IQR 10% to 44%). The significance and direction of the changes subject-by-subject were tested: the coupling between the rBIS,rCMRO 2 , and rCBF was witnessed in the majority of the cases (14/18 and 12/18 for rCBF and 19/21 and 13/18 forrCMRO 2 in the initial and final part, respectively). These changes were also correlated in time ( R > 0.69 to R = 1 , p - values < 0.05 ).

Conclusions

Optics can reliably monitorrCMRO 2 in such conditions.

Cot-side imaging of functional connectivity in the developing brain during sleep using wearable high-density diffuse optical tomography

Studies of cortical function in newborn infants in clinical settings are extremely challenging to undertake with traditional neuroimaging approaches. Partly in response to this challenge, functional near-infrared spectroscopy (fNIRS) has become an increasingly common clinical research tool but has significant limitations including a low spatial resolution and poor depth specificity. Moreover, the bulky optical fibres required in traditional fNIRS approaches present significant mechanical challenges, particularly for the study of vulnerable newborn infants. A new generation of wearable, modular, high-density diffuse optical tomography (HD-DOT) technologies has recently emerged that overcomes many of the limitations of traditional, fibre-based and low-density fNIRS measurements. Driven by the development of this new technology, we have undertaken the first cot-side study of newborn infants using wearable HD-DOT in a clinical setting. We use this technology to study functional brain connectivity (FC) in newborn infants during sleep and assess the effect of neonatal sleep states, active sleep (AS) and quiet sleep (QS), on resting state FC. Our results demonstrate that it is now possible to obtain high-quality functional images of the neonatal brain in the clinical setting with few constraints. Our results also suggest that sleep states differentially affect FC in the neonatal brain, consistent with prior reports.

Comparative Assessment of Propofol and Ketamine on Hemodynamic Indices and Cerebral Oximetry of Pediatric Patients Undergoing Cardiac Catheterization

Background

Propofol and ketamine are widely used in the induction and maintenance of anesthesia and sedation with different cardiovascular and respiratory effects. In cardiac anesthesia (including pediatric cardiac catheterization), due to the high risk of neurologic complications, cerebral oximetry can effectively monitor cerebral blood oxygen saturation to prevent neurological and respiratory complications.

Objectives

This study aimed to compare the effect of propofol and ketamine on hemodynamic indices and cerebral oxygenation results in children undergoing cardiac catheterization.

Methods

This clinical trial study was performed on 48 patients who were candidates for cardiac catheterization by easy and continuous sampling. Patients were randomly divided into 2 groups: ketamine and propofol. In the ketamine group, ketamine was injected at a dose of 1 - 2 mg/kg, and in the propofol group, propofol was injected at a dose of 0.5 - 1.5 mg/kg. In both groups, incremental doses were repeated as needed. The hemodynamic indices, including blood pressure, heart rate, and peripheral SpO₂, were recorded. Cerebral regional oxygen saturation (RSO₂) was recorded using infrared spectroscopic sensors. Data were analyzed using chi-square, independent t-test, paired t-test, and 1-way analysis of variance (ANOVA).

Results

The results showed that all demographic characteristics of patients and also the mean duration of catheterization were homogeneous between the 2 groups. Hemodynamic indices (such as systolic, diastolic, and mean arterial blood pressure) did not show a significant difference between the 2 groups; however, in the ketamine group compared to the propofol group, the heart rate was significantly higher, and mean RSO₂ was lower (P = 0.023).

Conclusions

Propofol has fewer complications than ketamine and is a good drug for sedating children undergoing cardiac catheterization.

Effect of early Sanguinate (PEGylated carboxyhemoglobin bovine) infusion on cerebral blood flow to the ischemic core in experimental middle cerebral artery occlusion

BACKGROUND

Sanguinate, a bovine PEGylated carboxyhemoglobin-based oxygen carrier with vasodilatory, oncotic and anti-inflammatory properties designed to release oxygen in hypoxic tissue, was tested to determine if it improves infarct volume, collateral recruitment and blood flow to the ischemic core in hyperacute middle cerebral artery occlusion (MCAO).

METHODS

Under an IACUC approved protocol, 14 mongrel dogs underwent endovascular permanent MCAO. Seven received Sanguinate (8 mL/kg) intravenously over 10 min starting 30 min following MCAO and seven received a similar volume of normal saline. Relative cerebral blood flow (rCBF) was assessed using neutron-activated microspheres prior to MCAO, 30 min following MCAO and 30 min following intervention. Pial collateral recruitment was scored and measured by arterial arrival time (AAT) immediately prior to post-MCAO microsphere injection. Diffusion-weighted 3T MRI was used to assess infarct volume approximately 2 hours after MCAO.

RESULTS

Mean infarct volumes for control and Sanguinate-treated subjects were 4739 mm3 and 2585 mm3 (p=0.0443; r2=0.687), respectively. Following intervention, rCBF values were 0.340 for controls and 0.715 in the Sanguinate group (r2=0.536; p=0.0064). Pial collateral scores improved only in Sanguinate-treated subjects and AAT decreased by a mean of 0.314 s in treated subjects and increased by a mean of 0.438 s in controls (p<0.0276).

CONCLUSION

Preliminary results indicate that topload bolus administration of Sanguinate in hyperacute ischemic stroke significantly improves infarct volume, pial collateral recruitment and CBF in experimental MCAO immediately following its administration.

Influence of pneumoperitoneum and head-down maneuver on the cerebral microvasculature in rabbits

BACKGROUND

With recent advances in robot-assisted techniques, an increasing number of surgeries are being performed with pneumoperitoneum and head-down maneuver (HDM) that may affect the cerebral microcirculation. For the first time, this study investigated the direct influence of pneumoperitoneum and HDM on the cerebral microvasculature in rabbits.

METHODS

Adult male rabbits were randomly allocated to the following groups (n = 7 each): control, pneumoperitoneum alone (P), and pneumoperitoneum with HDM (P + HDM) for 120 min. A closed cranial window was installed above the parietal bone to visualize the pial microvasculature. Pial arteriolar diameter and hemodynamic and blood gas parameters were measured during the 140-min observation period. Brain edema was assessed by evaluation of the brain water content at the end of the experiment.

RESULTS

Rabbits in the P and P + HDM groups exhibited a similar degree of immediate pial arteriolar dilation following the initiation of both P and P + HDM (P: 1.11 ± 0.03, p = 0.0044 and P + HDM: 1.07 ± 0.02, p = 0.0004, relative changes from the baseline value by defining the baseline as one). In the P + HDM group, pial arteriole diameter returned to the baseline level following the discontinuation of pneumoperitoneum and HDM (1.05 ± 0.03, p = 0.0906, vs. baseline). In contrast, the pial arterioles remained dilated as compared to the baseline level in the P group after discontinuation of pneumoperitoneum. There were no changes in pial arteriole diameter in the animals in the control group. Heart rate, blood gas parameters, and brain water content were not significantly different between the groups.

CONCLUSION

The pial arterioles dilated immediately after pneumoperitoneum with or without HDM. The pial arterioles remained dilated 20 min after discontinuation of pneumoperitoneum alone but constricted upon discontinuation of pneumoperitoneum plus HDM. Pneumoperitoneum and HDM for 2 h did not cause brain edema.

Post-cardiac arrest Sedation Promotes Electroencephalographic Slow-wave Activity and Improves Survival in a Mouse Model of Cardiac Arrest

BACKGROUND

Patients resuscitated from cardiac arrest are routinely sedated during targeted temperature management, while the effects of sedation on cerebral physiology and outcomes after cardiac arrest remain to be determined. The authors hypothesized that sedation would improve survival and neurologic outcomes in mice after cardiac arrest.

METHODS

Adult C57BL/6J mice of both sexes were subjected to potassium chloride-induced cardiac arrest and cardiopulmonary resuscitation. Starting at the return of spontaneous circulation or at 60 min after return of spontaneous circulation, mice received intravenous infusion of propofol at 40 mg · kg-1 · h-1, dexmedetomidine at 1 µg · kg-1 · h-1, or normal saline for 2 h. Body temperature was lowered and maintained at 33°C during sedation. Cerebral blood flow was measured for 4 h postresuscitation. Telemetric electroencephalogram (EEG) was recorded in freely moving mice from 3 days before up to 7 days after cardiac arrest.

RESULTS

Sedation with propofol or dexmedetomidine starting at return of spontaneous circulation improved survival in hypothermia-treated mice (propofol [13 of 16, 81%] vs. no sedation [4 of 16, 25%], P = 0.008; dexmedetomidine [14 of 16, 88%] vs. no sedation [4 of 16, 25%], P = 0.002). Mice receiving no sedation exhibited cerebral hyperemia immediately after resuscitation and EEG power remained less than 30% of the baseline in the first 6 h postresuscitation. Administration of propofol or dexmedetomidine starting at return of spontaneous circulation attenuated cerebral hyperemia and increased EEG slow oscillation power during and early after sedation (40 to 80% of the baseline). In contrast, delayed sedation failed to improve outcomes, without attenuating cerebral hyperemia and inducing slow-wave activity.

CONCLUSIONS

Early administration of sedation with propofol or dexmedetomidine improved survival and neurologic outcomes in mice resuscitated from cardiac arrest and treated with hypothermia. The beneficial effects of sedation were accompanied by attenuation of the cerebral hyperemic response and enhancement of electroencephalographic slow-wave activity.

EDITOR’S PERSPECTIVE

Groin Puncture to Recanalization Time May Be a Strong Predictor of mTICI 2c/3 over mTICI 2b in Patients with Large Vessel Occlusions Successfully Recanalized with Mechanical Thrombectomy

Mechanical thrombectomy (MT) is an important therapeutic option in the management of acute ischemic stroke (AIS) caused by large vessel occlusions (LVO). While achieving a modified thrombolysis in cerebral infarction (mTICI), grades of 2b, 2c, and 3 are all considered successful recanalization; recent literature suggests that mTICI grades of 2c/3 are associated with superior outcomes than 2b. The aim of this preliminary study is to determine whether any baseline or procedural parameters can predict whether successfully recanalized patients achieve an mTICI grade of 2c/3 over 2b. Consecutive patients from 9/2019 to 10/2021 who were successfully recanalized following MT for confirmed LVO were included in the study. Baseline and procedural data were collected through manual chart review and analyzed to ascertain whether any variables of interest could predict mTICI 2c/3. A total of 47 patients were included in the preliminary study cohort, with 35 (74.5%) achieving an mTICI score of 2c/3 and 12 (25.5%) achieving an mTICI score of 2b. We found that a lower groin puncture to recanalization time was a strong, independent predictor of TICI 2c/3 (p = 0.015). These findings emphasize the importance of minimizing procedure time in achieving superior reperfusion but must be corroborated in larger scale studies.

General anesthesia versus conscious sedation during endovascular treatment in posterior circulation large vessel occlusion: A systematic review and meta-analysis

Purpose:

The optimal anesthetic approach in the endovascular treatment (EVT) of patients with posterior circulation large vessel occlusion (PC-LVO) strokes is not clear. Little data has been published and no randomized clinical trials have been conducted so far. We aimed to perform an updated meta-analysis to compare clinical and procedural outcomes between conscious sedation (CS) and general anesthesia (GA).

Methods:

We reviewed the literature of the studies reporting CS and GA in patients with endovascularly-treated PC-LVO. The primary outcome was the functional outcome at 3 months measured using the modified Rankin Scale (mRS). A good functional outcome was defined as having a mRS 0–2. Secondary outcomes were mortality at 3 months, final successful recanalization (modified Thrombolysis in Cerebral Infarction (mTICI) scale from 2b to 3) and complete recanalization (mTICI of 3) and times from stroke onset to EVT completion. Random-effects models were completed to pool the outcomes and the I2 value was calculated to assess heterogeneity.

Findings:

Eight studies with a total of 1351 patients were included. The pooled results reveal that CS use was associated with higher rates of good outcome (OR 2.41, 95% CI 1.58–3.64, I2 = 49.67%) and with lower mortality at 3 months (OR 0.48, 95% CI 0.28–0.82, I2 =57.11%). No significant differences were observed in the final reperfusion rates, procedural duration, and time from stroke onset to EVT completion.

Conclusion:

In this meta-analysis, GA was associated with significantly lower rates of functional independence at 3 months in patients with PC-LVO strokes.

Effects of Anesthesia on Cerebral Blood Flow and Functional Connectivity of Nonhuman Primates

Nonhuman primates (NHPs) are the closest living relatives of humans and play a critical and unique role in neuroscience research and pharmaceutical development. General anesthesia is usually required in neuroimaging studies of NHPs to keep the animal from stress and motion. However, the adverse effects of anesthesia on cerebral physiology and neural activity are pronounced and can compromise the data collection and interpretation. Functional connectivity is frequently examined using resting-state functional MRI (rsfMRI) to assess the functional abnormality in the animal brain under anesthesia. The fMRI signal can be dramatically suppressed by most anesthetics in a dose-dependent manner. In addition, rsfMRI studies may be further compromised by inter-subject variations when the sample size is small (as seen in most neuroscience studies of NHPs). Therefore, proper use of anesthesia is strongly demanded to ensure steady and consistent physiology maintained during rsfMRI data collection of each subject. The aim of this review is to summarize typical anesthesia used in rsfMRI scans of NHPs and the effects of anesthetics on cerebral physiology and functional connectivity. Moreover, the protocols with optimal rsfMRI data acquisition and anesthesia procedures for functional connectivity study of macaque monkeys are introduced.

Increased capillary stalling is associated with endothelial glycocalyx loss in subcortical vascular dementia

Proper regulation and patency of cerebral microcirculation are crucial for maintaining a healthy brain. Capillary stalling, i.e., the brief interruption of microcirculation has been observed in the normal brain and several diseases related to microcirculation. We hypothesized that endothelial glycocalyx, which is located on the luminal side of the vascular endothelium and involved in cell-to-cell interaction regulation in peripheral organs, is also related to cerebral capillary stalling. We measured capillary stalling and the cerebral endothelial glycocalyx (cEG) in male mice using in vivo optical coherence tomography angiography (OCT-A) and two-photon microscopy. Our findings revealed that some capillary segments were prone to capillary stalling and had less cEG. In addition, we demonstrated that the enzymatic degradation of the cEG increased the capillary stalling, mainly by leukocyte plugging. Further, we noted decreased cEG along with increased capillary stalling in a mouse model of subcortical vascular dementia (SVaD) with impaired cortical microcirculation. Moreover, gene expression related to cEG production or degradation changed in the SVaD model. These results indicate that cEG mediates capillary stalling and impacts cerebral blood flow and is involved in the pathogenesis of SVaD.

The Quantitative Associations Between Near Infrared Spectroscopic Cerebrovascular Metrics and Cerebral Blood Flow: A Scoping Review of the Human and Animal Literature

Cerebral blood flow (CBF) is an important physiologic parameter that is vital for proper cerebral function and recovery. Current widely accepted methods of measuring CBF are cumbersome, invasive, or have poor spatial or temporal resolution. Near infrared spectroscopy (NIRS) based measures of cerebrovascular physiology may provide a means of non-invasively, topographically, and continuously measuring CBF. We performed a systematically conducted scoping review of the available literature examining the quantitative relationship between NIRS-based cerebrovascular metrics and CBF. We found that continuous-wave NIRS (CW-NIRS) was the most examined modality with dynamic contrast enhanced NIRS (DCE-NIRS) being the next most common. Fewer studies assessed diffuse correlation spectroscopy (DCS) and frequency resolved NIRS (FR-NIRS). We did not find studies examining the relationship between time-resolved NIRS (TR-NIRS) based metrics and CBF. Studies were most frequently conducted in humans and animal studies mostly utilized large animal models. The identified studies almost exclusively used a Pearson correlation analysis. Much of the literature supported a positive linear relationship between changes in CW-NIRS based metrics, particularly regional cerebral oxygen saturation (rSO2), and changes in CBF. Linear relationships were also identified between other NIRS based modalities and CBF, however, further validation is needed.

In Vivo Magnetic Resonance Thermometry for Brain and Body Temperature Variations in Canines under General Anesthesia

The core body temperature tends to decrease under general anesthesia. Consequently, monitoring the core body temperature during procedures involving general anesthesia is essential to ensure patient safety. In veterinary medicine, rectal temperature is used as an indicator of the core body temperature, owing to the accuracy and convenience of this approach. Some previous studies involving craniotomy reported differences between the brain and core temperatures under general anesthesia. However, noninvasive imaging techniques are required to ascertain this because invasive brain temperature measurements can cause unintended temperature changes by inserting the temperature sensors into the brain or by performing the surgical operations. In this study, we employed in vivo magnetic resonance thermometry to observe the brain temperatures of patients under general anesthesia using the proton resonance frequency shift method. The rectal temperature was also recorded using a fiber optic thermometer during the MR thermometry to compare with the brain temperature changes. When the rectal temperature decreased by 1.4 ± 0.5 °C (mean ± standard deviation), the brain temperature (white matter) decreased by 4.8 ± 0.5 °C. Furthermore, a difference in the temperature reduction of the different types of brain tissue was observed; the reduction in the temperature of white matter exceeded that of gray matter mainly due to the distribution of blood vessels in the gray matter. We also analyzed and interpreted the core temperature changes with the body conditioning scores of subjects to see how the body weight affected the temperature changes.

Role of gut microbiota in neuropathy and neuropathic pain states: A systematic preclinical review

Gut microbiota has implications in Central Nervous System (CNS) disorders. Our study systematically identified preclinical studies aimed to investigate the possible gut microbiota contribution in neuropathy and neuropathic pain. The systematic review is reported in accordance with PRISMA checklist and guidelines outlined updated to 2020. We included research articles reporting neuropathy-related behavioral evaluations and/or neurological scores coupled to gut microbiota analysis performed by high-throughput technologies in the last ten years. Two investigators performed a search through 3 electronic bibliographic databases for full-text articles (PubMed, Scopus, and EMBASE) and three registries (Prospero, SyRF, and bioRxiv), cross-references, and linear searches. We assessed the methodological quality via the CAMARADES checklist and appraised the heterogeneous body of evidence by narrative synthesis. In total, there were 19 eligible studies. The most of these reports showed significant changes in gut microbiota setting in neuropathy conditions. The major gut microbiome remodeling was through fecal microbiome transplantation. Mechanistic proof of the gut-CNS communication was achieved by measuring inflammatory mediators, metabolic products, or neurotransmitters. As a limitation, we found considerable heterogeneity across eligible studies. We conclude that the current understanding of preclinical findings suggested an association between neuropathy and/or neuropathic pain and gut microbiota modifications. Our analysis provides the basis for further studies targeting microbiota for managing symptoms of neuropathy or other neuroinflammation-based CNS disorders. The systematic review protocol was registered on the international database Prospero under the registration number (# 257628).

High-resolution relaxometry-based calibrated fMRI in murine brain: Metabolic differences between awake and anesthetized states

Functional magnetic resonance imaging (fMRI) techniques using the blood-oxygen level-dependent (BOLD) signal have shown great potential as clinical biomarkers of disease. Thus, using these techniques in preclinical rodent models is an urgent need. Calibrated fMRI is a promising technique that can provide high-resolution mapping of cerebral oxygen metabolism (CMR_O2). However, calibrated fMRI is difficult to use in rodent models for several reasons: rodents are anesthetized, stimulation-induced changes are small, and gas challenges induce noisy CMR_O2 predictions. We used, in mice, a relaxometry-based calibrated fMRI method which uses cerebral blood flow (CBF) and the BOLD-sensitive magnetic relaxation component, R₂', the same parameter derived in the deoxyhemoglobin-dilution model of calibrated fMRI. This method does not use any gas challenges, which we tested on mice in both awake and anesthetized states. As anesthesia induces a whole-brain change, our protocol allowed us to overcome the former limitations of rodent studies using calibrated fMRI. We revealed 1.5-2 times higher CMR_O2, dependent upon brain region, in the awake state versus the anesthetized state. Our results agree with alternative measurements of whole-brain CMR_O2 in the same mice and previous human anesthesia studies. The use of calibrated fMRI in rodents has much potential for preclinical fMRI.

Cerebral Autoregulation in Unilateral Carotid Agenesis: How Low Can We Go?

Dysgenesis of the internal carotid artery (ICA) is a rare vascular disorder. It has a variety of different grades (agenesis, aplasia, and hypoplasia) and is more common on the right side. Although the ICA is an important vessel, most patients are asymptomatic due to collateral circulation. Recognition of this rare anomaly is important, particularly when considering patients for surgeries that demand permissive hypotension. We present and discuss the perioperative implications of a rare case of congenital absence of left carotid artery proposed for an urgent laryngeal biopsy and tracheostomy. The internal jugular vein was invaded with a tumor and so was removed, affecting venous drainage.

Neonatal Anesthesia and Oxidative Stress

Neonatal anesthesia, while often essential for surgeries or imaging procedures, is accompanied by significant risks to redox balance in the brain due to the relatively weak antioxidant system in children. Oxidative stress is characterized by concentrations of reactive oxygen species (ROS) that are elevated beyond what can be accommodated by the antioxidant defense system. In neonatal anesthesia, this has been proposed to be a contributing factor to some of the negative consequences (e.g., learning deficits and behavioral abnormalities) that are associated with early anesthetic exposure. In order to assess the relationship between neonatal anesthesia and oxidative stress, we first review the mechanisms of action of common anesthetic agents, the key pathways that produce the majority of ROS, and the main antioxidants. We then explore the possible immediate, short-term, and long-term pathways of neonatal-anesthesia-induced oxidative stress. We review a large body of literature describing oxidative stress to be evident during and immediately following neonatal anesthesia. Moreover, our review suggests that the short-term pathway has a temporally limited effect on oxidative stress, while the long-term pathway can manifest years later due to the altered development of neurons and neurovascular interactions.

Cerebral oxygen desaturation events during and functional outcomes after prehospital anaesthesia: A prospective pilot study

Background

During prehospital anaesthesia, oxygen delivery to the brain might be inadequate to match the oxygen consumption, with unknown long‐term functional outcomes. We aimed to evaluate the feasibility of monitoring cerebral oxygenation during prehospital anaesthesia and determining the long‐term outcomes.

Methods

We performed a prospective observational feasibility study in two helicopter emergency medical services units. Frontal lobe regional oxygen saturation (rSO₂) of adult patients undergoing prehospital anaesthesia was monitored with near‐infrared spectroscopy (NIRS) by a Nonin H500 oximeter. The outcome was evaluated with a modified Rankin Scale (mRS) at 30 days and 1 year. Health‐related quality of life (HRQoL) was measured with a 15D instrument at 1 year.

Results

Of 101 patients enrolled, 83 were included. The mean baseline rSO₂ was 79% (73–84). Desaturation for at least 5 min to rSO₂ below 50% or a decrease of 10% from baseline occurred in four (5%, 95% CI 2%–12%) and 19 (23%, 95% CI 15–93) patients. At 1 year, 32 patients (53%, 95% CI 41–65) achieved favourable neurological outcomes. The median 15D score was 0.889 (Q1–Q3, 0.796–0.970).

Conclusion

Monitoring cerebral oxygenation with a hand‐held oximeter during prehospital anaesthesia and collecting data on functional outcomes and HRQoL are feasible. Only half of the patients achieved a favourable functional outcome. The effects of cerebral oxygenation on outcomes during prehospital critical care need to be assessed in future studies.

Effect of Anesthetics on Functional Connectivity of Developing Brain

The potential anesthetic neurotoxicity on the neonate is an important focus of research investigation in the field of pediatric anesthesiology. It is essential to understand how these anesthetics may affect the development and growth of neonatal immature and vulnerable brains. Functional magnetic resonance imaging (fMRI) has suggested that using anesthetics result in reduced functional connectivity may consider as core sequence for the neurotoxicity and neurodegenerative changes in the developed brain. Anesthetics either directly impact the primary structures and functions of the brain or indirectly alter the hemodynamic parameters that contribute to cerebral blood flow (CBF) in neonatal patients. We hypothesis that anesthetic agents may either decrease the brain functional connectivity in neonatal patients or animals, which was observed by fMRI. This review will summarize the effect and mechanism of anesthesia on the rapid growth and development infant and neonate brain with fMRI through functional connectivity. It is possible to provide the new mechanism of neuronal injury induced by anesthetics and objective imaging evidence in animal developing brain.

Critical Angiographic and Sonographic Analysis of Intra Aneurysmal and Downstream Hemodynamic Changes After Flow Diversion

Introduction

Successful treatment of intracranial aneurysms after flow diversion (FD) is dependent on the flow modulating effect of the device. We aimed to investigate the intra-aneurysmal and parent vessel hemodynamic changes, as well as the incidence of silent emboli following treatment with various FD devices.

Methods

We evaluated the appearance of the eclipse sign in nine distinct phases of cerebral angiography before and immediately after FD placement in correlation with aneurysm occlusion. Angiographic and clinical data of consecutive procedures were analyzed retrospectively. Patients who had successful FD procedure without adjunctive coiling, visible eclipse sign on post embolization angiography, and reliable follow-up angiographic data were included in the analysis. Detailed analysis of hemodynamic data from transcranial doppler after FD was performed in selected patients, such as monitoring for silent emboli.

Results

Among all patients (N = 65) who met inclusion criteria, complete aneurysm occlusion at 12 months was achieved in 89% (58/65). Eclipse sign prior to FD was observed in 42% (27/65) with unchanged appearance in 4.6% (3/65) of the treated patients. None of these three patients achieved complete aneurysm occlusion. Among all analyzed variables, such as aneurysm size, device type used, age, and appearance of the eclipse sign pre- and post-FD, the most reliable predictor of permanent aneurysm occlusion at 12 months was earlier, prolonged, and sustained eclipse sign visibility in more than three angiographic phases in comparison to the baseline (p &lt; 0.001). Elevation in flow velocities within the ipsilateral vascular territory was noted in 70% (9/13), and bilaterally in 54% (7/13) of the treated patients. None of the patients had silent emboli.

Conclusions

Intra-aneurysmal and parent vessel hemodynamic changes after FD can be reliably assessed by the cerebral angiography and transcranial doppler with important implications for the prediction of successful treatment.

Optimized mouse model of embolic MCAO: From cerebral blood flow to neurological outcomes

The embolic middle cerebral artery occlusion (eMCAO) model mimics ischemic stroke due to large vessel occlusion in humans and is amenable to thrombolytic therapy with rtPA. However, two major obstacles, the difficulty of the eMCAO surgery and unpredictable occurrence of clot autolysis, had impeded its application in mice. In this study, we modified catheters to produce suitable fibrin-rich embolus and optimized the eMCAO model using cerebral blood flow (CBF) monitored by both laser Doppler flowmetry (LDF) and 2D laser speckle contrast imaging (LSCI) to confirm occlusion of MCA. The results showed that longer embolus resulted in higher mortality. There was a compensatory increase in MCA territory perfusion after eMCAO associated with decreased infarct volume; however, this was only partly dependent on recanalization as clot autolysis was only observed in ∼30% of mice. Cortical CBF monitoring with LSCI showed that the size of peri-core area at 3 h displayed the best correlation with infarct volume that is attributed to compensatory collateral blood flow. The peri-core area best predicted functional outcome after eMCAO. In summary, we developed a reliable eMCAO mouse model that better mimics embolic ischemic stroke in humans, which will increase the potential for successful translation of stroke neuroprotective therapies.

Site-specific different dynamic cerebral autoregulation and cerebrovascular response to carbon dioxide in posterior cerebral circulation during isometric exercise in healthy young men

Different cerebral blood flow (CBF) responses to exercise between the posterior cerebral artery (PCA) and vertebral artery (VA) have been previously observed, though the physiological mechanisms remain unknown. There is regional heterogeneity in sympathetic innervation between the PCA and VA, which may affect CBF regulation, especially during sympathoexcitation. Thus, in the present study, we hypothesized that different CBF regulatory mechanisms between PCA and VA contribute to heterogeneous CBF responses to isometric exercise. To test this hypothesis, in thirteen healthy young men, dynamic cerebral autoregulation (CA) and cerebrovascular CO2 reactivity (CVR), were identified in each artery during a 2-min isometric handgrip (IHG) exercise at 30% of maximum voluntary contraction. Similar to previous data, PCA cerebrovascular conductance (CVC) index was decreased from rest (P < 0.004), but not VA CVC during IHG exercise (P > 0.084). Dynamic CA in both PCA and VA were unaltered during the IHG exercise (P = 0.129). On the other hand, PCA CVR was increased during the IHG exercise (P < 0.001) while VA CVR was unchanged (P = 0.294). In addition, individual exercise-induced changes in end-tidal partial pressure of CO2 was related to the individual change in PCA blood velocity (P < 0.046), but was not observed for VA blood flow (P > 0.420). Therefore, these exercise-induced differences in CVR between PCA and VA may contribute to exercise-induced heterogeneous CBF response in the posterior cerebral circulation. These findings indicate that the site-specific posterior CBF should be considered in further research for assessing posterior cerebral circulation.

Unique spatiotemporal fMRI dynamics in the awake mouse brain

Human imaging studies have shown that spontaneous brain activity exhibits stereotypic spatiotemporal reorganization in awake, conscious conditions with respect to minimally conscious states. However, whether and how this phenomenon can be generalized to lower mammalian species remains unclear. Leveraging a robust protocol for resting-state fMRI (rsfMRI) mapping in non-anesthetized, head-fixed mice, we investigated functional network topography and dynamic structure of spontaneous brain activity in wakeful animals. We found that rsfMRI networks in the awake state, while anatomically comparable to those observed under anesthesia, are topologically configured to maximize interregional communication, departing from the underlying community structure of the mouse axonal connectome. We further report that rsfMRI activity in wakeful animals exhibits unique spatiotemporal dynamics characterized by a state-dependent, dominant occurrence of coactivation patterns encompassing a prominent participation of arousal-related forebrain nuclei and functional anti-coordination between visual-auditory and polymodal cortical areas. We finally show that rsfMRI dynamics in awake mice exhibits a stereotypical temporal structure, in which state-dominant coactivation patterns are configured as network attractors. These findings suggest that spontaneous brain activity in awake mice is critically shaped by state-specific involvement of basal forebrain arousal systems and document that its dynamic structure recapitulates distinctive, evolutionarily relevant principles that are predictive of conscious states in higher mammalian species.

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fMRI networks in awake mice depart from underlying anatomical structure

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fMRI dynamics in wakeful mice is critically shaped by arousal-related nuclei

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Occurrence and topography of rsfMRI coactivation patterns define conscious states

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fMRI coactivation dynamics defines a signature of consciousness in the mouse brain

Transcranial Doppler ultrasonography detects the elevation of cerebral blood flow during ictal-phase of pentetrazol-induced seizures in dogs

OBJECTIVE

To investigate the association between changes in cerebral blood flow and electrographic epileptic seizure in dogs using transcranial Doppler ultrasonography (TCD).

ANIMALS

6 healthy Beagle dogs.

PROCEDURES

Each dog was administered pentetrazol (1.5 mg/kg/min) or saline (0.9% NaCl) solution under general anesthesia with continuous infusion of propofol. Both pentetrazol and saline solution were administered to all 6 dogs, with at least 28 days interval between the experiments. Blood flow waveforms in the middle cerebral artery and the basilar artery were obtained using TCD at baseline, after pentetrazol administration, and after diazepam administration. TCD velocities, including peak systolic velocity, end-diastolic velocity, and mean velocity and resistance variables, were determined from the Doppler waveforms.

RESULTS

During ictal-phase of pentetrazol-induced seizures, the TCD velocities significantly increased in the basilar and middle cerebral arteries while TCD vascular resistance variables did not change in either artery. The TCD velocities significantly decreased after diazepam administration. Systemic parameters, such as the heart rate, mean arterial pressure, systemic vascular resistance, cardiac index, end-tidal carbon dioxide, oxygen saturation, and body temperature, did not change significantly during seizures.

CLINICAL RELEVANCE

This study showed that cerebral blood flow, as obtained from TCD velocities, increased by 130% during ictal-phase of pentetrazol-induced seizures in dogs. The elevated velocities returned to baseline after seizure suppression. Thus, TCD may be used to detect electrographic seizures during the treatment of status epilepticus in dogs, and further clinical studies clarifying the association between changes in cerebral blood flow and non-convulsive seizure cases are needed.

Non-invasive in situ Visualization of the Murine Cranial Vasculature

Understanding physiologic and pathologic central nervous system function depends on our ability to map the entire in situ cranial vasculature and neurovascular interfaces. To accomplish this, we developed a non-invasive workflow to visualize murine cranial vasculature via polymer casting of vessels, iterative sample processing and micro-computed tomography, and automatic deformable image registration, feature extraction, and visualization. This methodology is applicable to any tissue and allows rapid exploration of normal and altered pathologic states.

Effect of Thiopental on Ischemic Stroke in Rat Brain in Spontaneously Hypertensive Rats

Motivation and Problem Statement. Thiopental is an anesthetic drug related to the condition of controlling the area of neurological contexts. This study is related to the analysis of effectiveness for the condition of thiopental application on spontaneously hypertensive rats. Methodology. We have evaluated the thiopental induction as the anesthetic agent. The hypertensive rats were selected to administer thiopental in the form of anesthesia. The selection and application of hypertensive strokes are related to the derivation of an inducible model to assess the efficacy for analyzing the ischemic stroke parameters which relate to the human body. We used middle cerebral artery occlusion (MCAO) models related to spontaneous hypertension with the area of examining the complications in ischemic stroke. Results and Conclusion. The study focused on the experimental analysis based on the selection of spontaneously hypertensive rats associated with the incidence of ischemic stroke. Application of thiopental has reported the weak functionality and mechanism on the relaxation of neuronal activity in the case of rat brain. The considered population of the spontaneously hypertensive rats is evaluated based on the condition of effectiveness as well as the duration of the medication effects within the rat brain. Involvement of thiopental in the case of ischemic stroke has provided the area of risk development for high rate of death incidences after occurrence of acute ischemic stroke. A complication in the area of defining neuroprotective actions provides difficulty in drawing an appropriate conclusion of the study.

Dynamics of isoflurane-induced vasodilation and blood flow of cerebral vasculature revealed by multi-exposure speckle imaging

BACKGROUND

Anesthetized animal models are used extensively during neurophysiological and behavioral studies despite systemic effects from anesthesia that undermine both accurate interpretation and translation to awake human physiology. The majority of work examining the impact of anesthesia on cerebral blood flow (CBF) has been restricted to before and after measurements with limited spatial resolution.

NEW METHOD

We used multi-exposure speckle imaging (MESI), an advanced form of laser speckle contrast imaging (LSCI), to characterize the dynamics of isoflurane anesthesia induction on cerebral vasculature and blood flow in the mouse brain.

RESULTS

The large anatomical changes caused by isoflurane are depicted with wide-field imagery and video highlighting the induction of general anesthesia. Within minutes of exposure, both vessel diameter and blood flow increased drastically compared to the awake state and remained elevated for the duration of imaging. An examination of the dynamics of anesthesia induction reveals that blood flow increased faster in arteries than in veins or parenchyma regions.

COMPARISON WITH EXISTING METHODS

MESI offers robust hemodynamic measurements across large fields-of-view and high temporal resolutions sufficient for continuous visualization of cerebrovascular events featuring major changes in blood flow.

CONCLUSION

The large alterations caused by isoflurane anesthesia to the cortical vasculature and CBF are readily characterized using MESI. These changes are unrepresentative of normal physiology and provide further evidence that neuroscience experiments would benefit from transitioning to un-anesthetized awake animal models.

Putative Roles of Astrocytes in General Anesthesia

General anesthetics are a mainstay of modern medicine, and although much progress has been made towards identifying molecular targets of anesthetics and neural networks contributing to endpoints of general anesthesia, our understanding of how anesthetics work remains unclear. Reducing this knowledge gap is of fundamental importance to prevent unwanted and life-threatening side-effects associated with general anesthesia. General anesthetics are chemically diverse, yet they all have similar behavioral endpoints, and so for decades, research has sought to identify a single underlying mechanism to explain how anesthetics work. However, this effort has given way to the 'multiple target hypothesis' as it has become clear that anesthetics target many cellular proteins, including GABAA receptors, glutamate receptors, voltage-independent K+ channels, and voltagedependent K+, Ca2+ and Na+ channels, to name a few. Yet, despite evidence that astrocytes are capable of modulating multiple aspects of neural function and express many anesthetic target proteins, they have been largely ignored as potential targets of anesthesia. The purpose of this brief review is to highlight the effects of anesthetic on astrocyte processes and identify potential roles of astrocytes in behavioral endpoints of anesthesia (hypnosis, amnesia, analgesia, and immobilization).

Noninvasive and invasive mechanical ventilation for neurologic disorders

Patients with acute neurologic injuries frequently require mechanical ventilation due to diminished airway protective reflexes, cardiopulmonary failure secondary to neurologic insults, or to facilitate gas exchange to precise targets. Mechanical ventilation enables tight control of oxygenation and carbon dioxide levels, enabling clinicians to modulate cerebral hemodynamics and intracranial pressure with the goal of minimizing secondary brain injury. In patients with acute spinal cord injuries, neuromuscular conditions, or diseases of the peripheral nerve, mechanical ventilation enables respiratory support under conditions of impending or established respiratory failure. Noninvasive ventilatory approaches may be carefully considered for certain disease conditions, including myasthenia gravis and amyotrophic lateral sclerosis, but may be inappropriate in patients with Guillain-Barré syndrome or when relevant contra-indications exist. With regard to discontinuing mechanical ventilation, considerable uncertainty persists about the best approach to wean patients, how to identify patients ready for extubation, and when to consider primary tracheostomy. Recent consensus guidelines highlight these and other knowledge gaps that are the focus of active research efforts. This chapter outlines important general principles to consider when initiating, titrating, and discontinuing mechanical ventilation in patients with acute neurologic injuries. Important disease-specific considerations are also reviewed where appropriate.

Assessing rheoencephalography dynamics through analysis of the interactions among brain and cardiac networks during general anesthesia

Cerebral blood flow (CBF) reflects the rate of delivery of arterial blood to the brain. Since no nutrients, oxygen or water can be stored in the cranial cavity due to space and pressure restrictions, a continuous perfusion of the brain is critical for survival. Anesthetic procedures are known to affect cerebral hemodynamics, but CBF is only monitored in critical patients due, among others, to the lack of a continuous and affordable bedside monitor for this purpose. A potential solution through bioelectrical impedance technology, also known as rheoencephalography (REG), is proposed, that could fill the existing gap for a low-cost and effective CBF monitoring tool. The underlying hypothesis is that REG signals carry information on CBF that might be recovered by means of the application of advanced signal processing techniques, allowing to track CBF alterations during anesthetic procedures. The analysis of REG signals was based on geometric features extracted from the time domain in the first place, since this is the standard processing strategy for this type of physiological data. Geometric features were tested to distinguish between different anesthetic depths, and they proved to be capable of tracking cerebral hemodynamic changes during anesthesia. Furthermore, an approach based on Poincaré plot features was proposed, where the reconstructed attractors form REG signals showed significant differences between different anesthetic states. This was a key finding, providing an alternative to standard processing of REG signals and supporting the hypothesis that REG signals do carry CBF information. Furthermore, the analysis of cerebral hemodynamics during anesthetic procedures was performed by means of studying causal relationships between global hemodynamics, cerebral hemodynamics and electroencephalogram (EEG) based-parameters. Interactions were detected during anesthetic drug infusion and patient positioning (Trendelenburg positioning and passive leg raise), providing evidence of the causal coupling between hemodynamics and brain activity. The provided alternative of REG signal processing confirmed the hypothesis that REG signals carry information on CBF. The simplicity of the technology, together with its low cost and easily interpretable outcomes, should provide a new opportunity for REG to reach standard clinical practice. Moreover, causal relationships among the hemodynamic physiological signals and brain activity were assessed, suggesting that the inclusion of REG information in depth of anesthesia monitors could be of valuable use to prevent unwanted CBF alterations during anesthetic procedures.

An atlas of dynamic peripheral blood mononuclear cell landscapes in human perioperative anaesthesia/surgery

BACKGROUND

The number of patients receiving anaesthesia is increasing, but the impact of general anaesthesia on the patient's immune system remains unclear. The aim of the present study is to investigate dynamics of systemic immune cell responses to anaesthesia during perioperative period at a single-cell solution.

METHODS

The peripheral blood mononuclear cells (PBMCs) and clinical phenomes were harvested and recorded 1 day before anaesthesia and operation, just after anaesthesia (0 h), and 24 and 48 h after anaesthesia. Single-cell sequencing of PBMCs was performed with 10× genomics. Subsequently, data analysis was performed with R packages: Seurat, clusterProfiler and CellPhoneDB.

RESULTS

We found that the cluster of CD56+ NK cells changed at 0 h and the cluster of monocytes increased at 24 and 48 h after anaesthesia. The characteristic genes of CD56+ NK cells were mainly enriched in the Jak-STAT signalling pathway and in cell adhesion molecules (24 h) and carbon metabolism (48 h). The communication between CD14+ monocytes and other cells decreased substantially 0 and 48 h after operation. The number of plasma cells enriched in protein export in men was substantially higher than that in women, although the total number in patients decreased 24 h after operation. CD14+ monocytes dominated that cell-cell communications appeared in females, while CD8+ NKT cells dominated that cell-cell communications appeared in male. The number of plasma cells increased substantially in patients with major surgical trauma, with enrichments of pentose phosphate pathway. The communications between plasma cells with other cells varied between surgical severities and anaesthetic forms. The intravenous anaesthesia caused major alterations of cell types, including CD14+ monocytes, plasmas cells and MAIT cells, as compared with inhalation anaesthesia.

CONCLUSION

We initially reported the roles of perioperative anaesthesia/surgery in temporal phenomes of circulating immune cells at a single-cell solution. Thus, the protection against immune cell changes would benefit the recovery from anaesthesia/surgery.

Electroencephalographic Burst-Suppression, Perioperative Neuroprotection, Postoperative Cognitive Function, and Mortality: A Focused Narrative Review of the Literature

Burst-suppression is an electroencephalographic pattern that results from a diverse array of pathophysiological causes and/or metabolic neuronal suppression secondary to the administration of anesthetic medications. The purpose of this review is to provide an overview of the physiological mechanisms that underlie the burst-suppression pattern and to present in a comprehensive way the available evidence both supporting and in opposition to the clinical use of this electroencephalographic pattern as a therapeutic measure in various perioperative settings.

Transient Hypoperfusion to Ischemic/Anoxic Spreading Depolarization is Related to Autoregulatory Failure in the Rat Cerebral Cortex

Background

In ischemic stroke, cerebral autoregulation and neurovascular coupling may become impaired. The cerebral blood flow (CBF) response to spreading depolarization (SD) is governed by neurovascular coupling. SDs recur in the ischemic penumbra and reduce neuronal viability by the insufficiency of the CBF response. Autoregulatory failure and SD may coexist in acute brain injury. Here, we set out to explore the interplay between the impairment of cerebrovascular autoregulation, SD occurrence, and the evolution of the SD-coupled CBF response.

Methods

Incomplete global forebrain ischemia was created by bilateral common carotid artery occlusion in isoflurane-anesthetized rats, which induced ischemic SD (iSD). A subsequent SD was initiated 20–40 min later by transient anoxia SD (aSD), achieved by the withdrawal of oxygen from the anesthetic gas mixture for 4–5 min. SD occurrence was confirmed by the recording of direct current potential together with extracellular K⁺ concentration by intracortical microelectrodes. Changes in local CBF were acquired with laser Doppler flowmetry. Mean arterial blood pressure (MABP) was continuously measured via a catheter inserted into the left femoral artery. CBF and MABP were used to calculate an index of cerebrovascular autoregulation (rCBFx). In a representative imaging experiment, variation in transmembrane potential was visualized with a voltage-sensitive dye in the exposed parietal cortex, and CBF maps were generated with laser speckle contrast analysis.

Results

Ischemia induction and anoxia onset gave rise to iSD and aSD, respectively, albeit aSD occurred at a longer latency, and was superimposed on a gradual elevation of K⁺ concentration. iSD and aSD were accompanied by a transient drop of CBF (down to 11.9 ± 2.9 and 7.4 ± 3.6%, iSD and aSD), but distinctive features set the hypoperfusion transients apart. During iSD, rCBFx indicated intact autoregulation (rCBFx < 0.3). In contrast, aSD was superimposed on autoregulatory failure (rCBFx > 0.3) because CBF followed the decreasing MABP. CBF dropped 15–20 s after iSD, but the onset of hypoperfusion preceded aSD by almost 3 min. Taken together, the CBF response to iSD displayed typical features of spreading ischemia, whereas the transient CBF reduction with aSD appeared to be a passive decrease of CBF following the anoxia-related hypotension, leading to aSD.

Conclusions

We propose that the dysfunction of cerebrovascular autoregulation that occurs simultaneously with hypotension transients poses a substantial risk of SD occurrence and is not a consequence of SD. Under such circumstances, the evolving SD is not accompanied by any recognizable CBF response, which indicates a severely damaged neurovascular coupling.

99mTc-HMPAO SPECT imaging reveals brain hypoperfusion during status epilepticus

Status epilepticus (SE) is a clinical emergency with high mortality. SE can trigger neuronal death or injury and alteration of neuronal networks resulting in long-term cognitive decline or epilepsy. Among the multiple factors contributing to this damage, imbalance between oxygen and glucose requirements and brain perfusion during SE has been proposed. Herein, we aimed to quantify by neuroimaging the spatiotemporal course of brain perfusion during and after lithium-pilocarpine-induced SE in rats. To this purpose, animals underwent ^99mTc-HMPAO SPECT imaging at different time points during and after SE using a small animal SPECT/CT system. ^99mTc-HMPAO regional uptake was normalized to the injected dose. In addition, voxel-based statistical parametric mapping was performed. SPECT imaging showed an increase of cortical perfusion before clinical seizure activity onset followed by regional hypo-perfusion starting with the first convulsive seizure and during SE. Twenty-four hours after SE, brain ^99mTc-HMPAO uptake was widely decreased. Finally, chronic epileptic animals showed regionally decreased perfusion affecting hippocampus and cortical sub-regions. Despite elevated energy and oxygen requirements, brain hypo-perfusion is present during SE. Our results suggest that insufficient compensation of required blood flow might contribute to neuronal damage and neuroinflammation, and ultimately to chronic epilepsy generated by SE.

Periprocedural Management During Stroke Thrombectomy

PURPOSE OF REVIEW

Endovascular therapy (EVT) for acute ischemic stroke caused by large vessel occlusion is a powerful and evidence-based tool to achieve reperfusion and results in improved neurologic outcome. Focus has now shifted toward optimizing the procedure. We reviewed the relevant current literature on periprocedural stroke care such as pretreatment with IV tissue plasminogen activator (tPA), choice of anesthesia, ventilation strategy, and blood pressure management.

RECENT FINDINGS

IV tPA should not be withheld in a patients with stroke eligible for EVT. A meta-analysis of randomized trials on general anesthesia (GA) vs procedural sedation has shown better neurologic outcomes with protocol-based GA in centers with dedicated neuroanesthesia teams. There are no data from randomized trials on blood pressure control, but according to available evidence, systolic blood pressure should probably be held at >140 mm Hg during the procedure and <160 mm Hg after reperfusion. In ventilated patients, extreme deviations from normoxemia and normocapnia should be avoided.

SUMMARY

Periprocedural care influences the outcome after EVT for large vessel ischemic stroke. More evidence from prospective ongoing and future studies is urgently needed to identify its optimization.

Adoption of computerized tomography perfusion imaging in the diagnosis of acute cerebral infarct under optimized deconvolution algorithm

Objectives:

To explore the significance of the hemodynamic parameters of Computerized Tomography Perfusion Imaging (CTPI) under the deconvolution optimization algorithm for the diagnosis and treatment of patients with acute cerebral infarct (ACI).

Methods:

A hundred and ten patients with ACI from December 2018 to September 2019 were selected for research, and CTPI was performed before and after Edaravone injection treatment. Then, the CTPI deconvolution algorithm based on the weighted adaptive (WA) total variation (TV) (WA-TV) optimization was constructed, which was compared with tensor total variation (TTV) and Motion-adaptive sparse parity (MASP). Brain Perfusion 4.0 was applied to obtain the relative time to peak (rTTP), the relative transit time of mean (rMTT), relative cerebral blood volume (rCBV), and relative cerebral blood flow (rCBF) of the core infarction area (CIA) and penumbra ischemic (PI).

Results:

In four parameters of rTTP, rMTT, rCBV, and CBF, the peak signal to noise ratio (PSNR) of the WA-TV algorithm was higher than the MSAP and TTV algorithms, while the Mean Square Error (MSE) and Mean Absolute Error (MAE) were lower than MSAP and TTV algorithms (P<0.05); the parameters of rCBV (71.56±9.87), rCBF (43.17±7.06) of the CIA before treatment were higher than PI (23.66±7.22; 18.37±3.99), rMTT (124.83±9.73) and rTTP (122.57±7.41) were lower than the PI (183.17±10.16); 150.74±9.74) (P<0.05). After treatment, the rCBV and rCBF of PI were higher than before treatment, and rMTT and rTTP were lower than before treatment (P<0.05), and there was no obvious difference in rCBV, rCBF, rMTT, and rTTP before and after treatment in the CIA (P>0.05).

Conclusion:

Compared with TTV and MASP, the WA-TV algorithm performs better in noise reduction and artifact reduction. The CTPI parameters of rCBV, rCBF, rMTT, and rTTP are all important indications for the diagnosis of PI and ACI.

Overview and Diagnostic Accuracy of Near Infrared Spectroscopy in Carotid Endarterectomy: A Systematic Review and Meta-analysis

OBJECTIVE

Carotid endarterectomy is recommended for the prevention of ischaemic stroke due to carotid stenosis. However, the risk of stroke after carotid endarterectomy has been estimated at 2% - 5%. Monitoring intra-operative cerebral oxygenation with near infrared spectroscopy (NIRS) has been assessed as a strategy to reduce intra- and post-operative complications. The aim was to summarise the diagnostic accuracy of NIRS to detect intra-operative ischaemic events, the values associated with ischaemic events, and the relative contribution of external carotid contamination to the NIRS signal in adults undergoing carotid endarterectomy.

DATA SOURCES

EMBASE, MEDLINE, Cochrane Centre Register of Controlled Trials, and reference lists through May 2019 were searched.

REVIEW METHODS

Non-randomised and randomised studies assessing NIRS as an intra-operative monitoring tool in carotid endarterectomy were included. Studies using NIRS as the reference were excluded. Risk of bias was assessed using the Newcastle Ottawa Scale, RoB-2, and QUADAS-2.

RESULTS

Seventy-six studies were included (n = 8 480), under local (n = 1 864) or general (n = 6 582) anaesthesia. Seven studies were eligible for meta-analysis (n = 524). As a tool for identifying intra-operative ischaemia, specificity increased with more stringent NIRS thresholds, while there was unpredictable variation in sensitivity across studies. A Δ20% threshold under local anaesthesia resulted in pooled estimates for sensitivity and specificity of 70.5% (95% confidence interval, CI, 54.1 - 82.9) and 92.4% (95% CI 85.5 - 96.1) compared with awake neurological monitoring. These studies had low or unclear risk of bias. NIRS signal consistently dropped across clamping and recovered to pre-clamp values upon de-clamp in most studies, and larger decreases were observed in patients with ischaemic events. The contribution of extracranial signal to change in signal across clamp varied from 3% to 50%.

CONCLUSION

NIRS has low sensitivity and high specificity to identify intra-operative ischaemia compared with awake monitoring. Extracranial signal contribution was highly variable. Ultimately, data from high quality studies are desperately needed to determine the utility of NIRS.

Correlation of Carotid Doppler Blood Flow With Invasive Cardiac Output Measurements in Cardiac Surgery Patients

OBJECTIVE

Carotid Doppler ultrasound has been a topic of recent interest, as it may be a promising noninvasive hemodynamic monitoring tool. In this study, the relation between carotid artery blood flow and invasive cardiac output (CO) was evaluated.

DESIGN

A prospective, observational study.

SETTING

A single-institution, tertiary referral hospital.

PARTICIPANTS

Eighteen elective cardiac surgery patients.

INTERVENTIONS

CO was measured by calibrated pulse contour analysis. Simultaneously, carotid artery pulsed-wave Doppler measurements were obtained in the operating room in three clinical settings: after induction of anesthesia (T1), after a passive leg raise maneuverer (T2), and at the end of surgery (T3).

MEASUREMENTS AND MAIN RESULTS

Correlation and trending between carotid artery blood flow and invasive CO were evaluated. Furthermore, two Bland-Altman plots were constructed to evaluate the level of agreement between carotid artery-derived CO and invasive CO measurements. Carotid artery blood flow correlated moderately with invasive CO (ρ = 0.67, 95% confidence interval 0.56-0.76, p < 0.05). Concordance between the percentage change of carotid artery blood flow and invasive CO from T1 to T3 was 72%. The level of agreement between carotid artery-derived CO and invasive CO was ±2.29; ±2.57 L/min, with a bias of 0.1; -0.54 L/min, and mean error of 50% and 48%, for the two Bland-Altman analyses, respectively. Intraexamination precision was acceptable.

CONCLUSIONS

In cardiac surgery patients, carotid artery blood flow correlated moderately with invasive CO measurements. However, the trending ability of carotid artery blood flow was poor, and carotid artery-derived CO tended not to be interchangeable with invasive CO.

Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation

Brain function critically depends on a close matching between metabolic demands, appropriate delivery of oxygen and nutrients, and removal of cellular waste. This matching requires continuous regulation of cerebral blood flow (CBF), which can be categorized into four broad topics: 1) autoregulation, which describes the response of the cerebrovasculature to changes in perfusion pressure; 2) vascular reactivity to vasoactive stimuli [including carbon dioxide (CO2)]; 3) neurovascular coupling (NVC), i.e., the CBF response to local changes in neural activity (often standardized cognitive stimuli in humans); and 4) endothelium-dependent responses. This review focuses primarily on autoregulation and its clinical implications. To place autoregulation in a more precise context, and to better understand integrated approaches in the cerebral circulation, we also briefly address reactivity to CO2 and NVC. In addition to our focus on effects of perfusion pressure (or blood pressure), we describe the impact of select stimuli on regulation of CBF (i.e., arterial blood gases, cerebral metabolism, neural mechanisms, and specific vascular cells), the interrelationships between these stimuli, and implications for regulation of CBF at the level of large arteries and the microcirculation. We review clinical implications of autoregulation in aging, hypertension, stroke, mild cognitive impairment, anesthesia, and dementias. Finally, we discuss autoregulation in the context of common daily physiological challenges, including changes in posture (e.g., orthostatic hypotension, syncope) and physical activity.