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

Remimazolam in neurosurgery

PURPOSE OF REVIEW

Remimazolam represents a novel intravenous anesthetic agent whose use began in 2020. As a new ultrashort-acting benzodiazepine, it has unique pharmacokinetic properties, such as remifentanil, designed to be active and easily transformed into inactive metabolites by tissue esterases. The purpose is to search the literature and evidences to use this new medication in neurosurgery.

RECENT FINDINGS

Currently, it is allowed for procedural sedation and general anesthesia in a few countries. More advantages of this new drug are predictable onset, short duration, rapid recovery profile, low liability for respiratory depression, cardiovascular depression, lack of injection pain, and known reversible agent, flumazenil. A literature search led to the conclusions that remimazolam may maintain better hemodynamic stability and reduce the episodes of hypotension during coil embolization of cerebral aneurysm and that general anesthesia with remimazolam does not alter cerebral metabolism, cerebral blood flow, and cerebral blood volume. Also, because it facilitates safe and quick arousal, it can be a suitable medication for awake craniotomy.

SUMMARY

With more desirable properties such as reduced risk of prolonged sedation and reliable safety margin, it is expected to increase the safety of sedation and general anesthesia in future.

Effects of Midazolam and Dexmedetomidine on Cognitive Dysfunction Following Open-Heart Surgery: A Comprehensive Review

PURPOSE

Patients undergoing open-heart surgery often face significant challenges in postoperative cognitive dysfunction (POCD). There has been growing interest in understanding how anesthesia medications, such as dexmedetomidine (DEX) and midazolam, impact cognitive function in these patients.

METHOD

This comprehensive review aims to detail the effect of DEX and midazolam on cognitive outcomes following open-heart surgery.

FINDINGS

Midazolam, a highly selective and commonly used benzodiazepine for preoperative anxiolytics and sedation has been associated with POCD. However, evidence regarding its impact on cognitive function is vague; some studies suggest a potential link between midazolam administration and cognitive impairment, while others report no effect or even an improvement in cognitive abilities. DEX is a potential neuroprotective agent in cardiac surgery. The effects of DEX on cognitive function, including a reduction in POCD incidence and severity, have been reported in several studies. It modulates the inflammatory responses, attenuates oxidative stress, and preserves cerebral perfusion. Although DEX and midazolam show promising results, their effects on cognitive function following open-heart surgery are yet to be elucidated.

CONCLUSION

Various factors, including patient characteristics, perioperative management, and surgical procedures, may influence these outcomes, highlighting the need for further research to better understand the roles of these agents in cognitive function following open-heart surgery.

The Impact of Sedative Choice in the Management of Aneurysmal Subarachnoid Hemorrhage: A Scoping Review

Aneurysmal subarachnoid hemorrhage (aSAH) is characterized by high mortality and morbidity. This scoping review assesses the current evidence regarding the use of sedatives and analgesics in the acute intensive care unit management of aSAH. We conducted a systematic search of Ovid MEDLINE, Ovid Embase, Ovid EmCare, APA PsycInfo, CINAHL, and the Cochrane Database of Systematic Reviews from inception to June 2023. Studies were included if they enrolled intensive care unit patients aged 18 or older with a significant proportion (> 20%) who had aSAH and evaluated the impact of one or more commonly used analgosedatives on physiological parameters in the management of aSAH. The methodological quality of the studies was assessed using the Methodological Index for Nonrandomized Studies score. Of 2,583 articles, 11 met the inclusion criteria. The median sample size was 47 (interquartile range 10-127), and the median Methodological Index for Nonrandomized Studies score was 9.5 (interquartile range 8-11). The studies' publication years ranged from 1980 to 2023. Dexmedetomidine and ketamine showed potential benefits in reducing the incidence of cortical spreading depolarization and delayed cerebral ischemia. Propofol and opioids appeared safe but lacked robust evidence for efficacy. Benzodiazepines were associated with increased delayed cerebral ischemia-related cerebral infarctions and cortical spreading depolarization events. The evidence available to guide the use of analgosedative medications in aSAH is critically inadequate. Dexmedetomidine and ketamine warrant further exploration in large-scale prospective studies because of their potential benefits. Improved study designs with consistent definitions and a focus on patient-centered outcomes are necessary to inform clinical practice.

Alterations in Regional Brain Microcirculation in Patients with Sepsis: A Prospective Study Using Contrast-Enhanced Brain Ultrasound

BACKGROUND

Alterations in regional brain microcirculation have not been well studied in patients with sepsis. Regional brain microcirculation can be studied using contrast-enhanced brain ultrasound (CEUS) with microbubble administration.

METHODS

CEUS was used to assess alterations in regional brain microcirculation on 3 consecutive days in 58 patients with sepsis and within 24 h of intensive care unit admission in 10 aged-matched nonseptic postoperative patients. Time-intensity perfusion curve variables (time-to-peak and peak intensity) were measured in different regions of interest of the brain parenchyma. The mean arterial pressure, cardiac index (using transthoracic echocardiography), global cerebral blood flow (using echo-color Doppler of the carotid and vertebral arteries), mean flow velocities of the middle cerebral arteries, and brain autoregulation (using transcranial echo-color Doppler) were measured simultaneously. The presence of structural brain injury in patients with sepsis was confirmed on computed tomography imaging, and encephalopathy, including coma and delirium, was evaluated using the Glasgow Coma Scale and the Confusion Assessment Method in the Intensive Care Unit.

RESULTS

Of the 58 patients with sepsis, 42 (72%) developed acute encephalopathy and 11 (19%) had some form of structural brain injury. Brain autoregulation was impaired in 23 (40%) of the patients with sepsis. Brain microcirculation alterations were observed in the left lentiform nucleus and left white matter of the temporoparietal region of the middle cerebral artery in the sepsis nonsurvivors but not in the survivors or postoperative patients. The alterations were characterized by prolonged time-to-peak (p < 0.01) and decreased peak intensity (p < 0.01) on the time-intensity perfusion curve. Prolonged time-to-peak but not decreased peak intensity was independently associated with worse outcome (p = 0.03) but not with the development of encephalopathy (p = 0.77).

CONCLUSIONS

Alterations in regional brain microcirculation are present in critically ill patients with sepsis and are associated with poor outcome. Trial registration Registered retrospectively on December 19, 2019.

Comprehensive characterization of metabolic consumption and production by the human brain

Metabolism is vital for brain function. However, a systematic investigation to understand the metabolic exchange between the human brain and circulatory system has been lacking. Here, we compared metabolomes and lipidomes of blood samples from the cerebral venous sinus and femoral artery to profile the brain's uptake and release of metabolites and lipids (1,365 metabolites and 140 lipids). We observed a high net uptake of glucose, taurine, and hypoxanthine and identified glutamine and pyruvate as significantly released metabolites by the brain. Triacylglycerols are the most prominent class of lipid consumed by the brain. The brain with cerebral venous sinus stenosis (CVSS) consumed more glucose and lactate and released more glucose metabolism byproducts than the brain with cerebral venous sinus thrombosis (CVST). Our data also showed age-related alterations in the uptake and release of metabolites. These results provide a comprehensive view of metabolic consumption and production processes within the human brain.

The impact of ketamine and thiopental anesthesia on ultraweak photon emission and oxidative-nitrosative stress in rat brains

Anesthetics such as ketamine and thiopental, commonly used for inducing unconsciousness, have distinct effects on neuronal activity, metabolism, and cardiovascular and respiratory systems. Ketamine increases heart rate and blood pressure while preserving respiratory function, whereas thiopental decreases both and can cause respiratory depression. This study investigates the impact of ketamine (100 mg/kg) and thiopental (45 mg/kg) on ultraweak photon emission (UPE), oxidative-nitrosative stress, and antioxidant capacity in isolated rat brains. To our knowledge, no previous study has investigated and compared UPE in the presence and absence of anesthesia. Here, we compare the effects of ketamine and thiopental anesthetics with each other and with a non-anesthetized control group. Ketamine increased UPE, lipid peroxidation, and antioxidant enzyme activity while reducing thiol levels. Conversely, thiopental decreased UPE, oxidative markers, and antioxidant enzyme activity, while increasing thiol levels. UPE was negatively correlated with thiol levels and positively correlated with oxidative stress markers. These findings suggest that the contrasting effects of ketamine and thiopental on UPE are linked to their differing impacts on brain oxidative stress and antioxidant capacity. This research suggests a potential method to monitor brain oxidative stress via UPE during anesthesia, and opens up new ways for understanding and managing anesthetic effects.

Hydrogen sulfide-mediated inhibition of ROCK2 exerts a vasoprotective effect on ischemic brain injury

As a gas molecule, hydrogen sulfide (H2S) exerts neuroprotective effects. Despite its recognized importance, there remains a need for a deeper understanding of H2S's impact on vascular smooth muscle cells and its role in ischemic brain injury. This study employs encompassing cultured primary cerebral vascular smooth muscle cells, oxygen-glucose deprivation/reoxygenation model, in vitro vascular tone assessments, in vivo middle cerebral artery occlusion and reperfusion experimentation in male rats, and the utilization of Rho-associated coiled-coil containing protein kinase 2 (ROCK2) knockout, to unravel the intricate relationship between H2S and cerebrovascular diastolic function. Our findings show that RhoA activation induces heightened vascular smooth muscle cell (VSMC) contraction, whereas the introduction of exogenous H2S mitigates the relaxant effect of the middle cerebral artery in rats through the downregulation of both ROCK1 and ROCK2, with ROCK2 exhibiting a more pronounced effect. Correspondingly, the attenuation of ROCK2 expression yields a more substantial reduction in the protective impact of H2S on cerebral blood flow, as well as learning and memory ability in ischemic injury, compared with the decrease in ROCK1 expression. Moreover, we demonstrate that H2S effectively mitigates the damage induced by oxygen-glucose deprivation/reoxygenation in male mouse primary vascular smooth muscle cells. This effect is characterized by enhanced cell proliferation, reduced lactate dehydrogenase leakage, elevated superoxide dismutase activity, and inhibited apoptosis. Notably, this protective effect is markedly diminished in cells derived from ROCK2 knockout mice. Our study reveals that H2S can relax cerebral vascular smooth muscle and ameliorate ischemic stroke injury by inhibiting the ROCK, with a particular emphasis on the role of ROCK2.NEW & NOTEWORTHY This study employs a diverse array of methods; our collective findings indicate that H2S safeguards against ischemic brain injury by inhibiting ROCK activity, thereby promoting relaxation of cerebral smooth muscle and mitigating the impairment of cerebral smooth muscle cell function caused by oxygen-glucose deprivation/reoxygenation. In addition, our data underscore the critical role of ROCK2 in mediating the cerebral protective effects of H2S, surpassing that of ROCK1.

Microvascular structure variability explains variance in fMRI functional connectivity

The influence of regional brain vasculature on resting-state fMRI BOLD signals is well documented. However, the role of brain vasculature is often overlooked in functional connectivity research. In the present report, utilizing publicly available whole-brain vasculature data in the mouse, we investigate the relationship between functional connectivity and brain vasculature. This is done by assessing interregional variations in vasculature through a novel metric termed vascular similarity. First, we identify features to describe the regional vasculature. Then, we employ multiple linear regression models to predict functional connectivity, incorporating vascular similarity alongside metrics from structural connectivity and spatial topology. Our findings reveal a significant correlation between functional connectivity strength and regional vasculature similarity, especially in anesthetized mice. We also show that multiple linear regression models of functional connectivity using standard predictors are improved by including vascular similarity. We perform this analysis at the cerebrum and whole-brain levels using data from both male and female mice. Our findings regarding the relation between functional connectivity and the underlying vascular anatomy may enhance our understanding of functional connectivity based on fMRI and provide insights into its disruption in neurological disorders.

Safety and Efficacy of Neuroprotective Agents as Adjunctive Therapies for Reperfusion in the Treatment of Acute Ischemic Stroke: A Systematic Review and Meta-analysis of Randomized Controlled Trials

There is still no clear evidence of the efficacy of the application of neuroprotective agents (NPAs) for acute ischemic stroke (AIS) patients receiving reperfusion therapies. This meta-analysis aimed to determine the effects of NPAs versus placebo on functional and safety outcomes as an adjunctive treatment to intravenous thrombolysis (IVT) or endovascular therapy (EVT) in AIS patients. The primary outcome was neurological functional independence, as evaluated by the proportion of patients whose modified Rankin Scale scores were 0 to 2 at 90 days after treatment. Thirteen randomized controlled trials with a total of 3736 patients were included. The application of NPAs was associated with greater odds of functional independence (odds ratio [OR]: 1.28; 95% CI: 1.12 to 1.46; P < 0.001; I2 = 0.0%) within 90 days. However, subgroup analysis of reperfusion therapy type (IVT, EVT, or both) revealed that only the EVT subgroup showed a significant association between NPAs or placebo and functional independence at 90 days (EVT group, OR: 1.43; 95% CI: 1.05 to 1.94; P = 0.022; I2 = 0.0%; IVT group, OR: 1.51; 95% CI: 0.93 to 2.46; P = 0.099; I2 = 39.8%; IVT plus EVT group, OR: 1.17; 95% CI: 0.94 to 1.45; P = 0.157; I2 = 16.0%). This meta-analysis revealed that NPAs could increase the possibility of AIS patients undergoing reperfusion therapies achieving functional independence within 90 days of onset; however, with the limited number of studies on each drug, further evidence is still needed to demonstrate the efficacy of each individual agent as an adjunctive therapy for different means of reperfusion.

Vascular amyloidβ load in the meningeal arterial network correlates with loss of cerebral blood flow and pial collateral vessel enlargement in the J20 murine model of Alzheimer's disease

INTRODUCTION

Global reduction in cerebral blood flow (CBF) is an early pathology in Alzheimer's disease, preceding significant plaque accumulation and neurological decline. Chronic reduced CBF and subsequent reduction in tissue oxygenation and glucose may drive neurodegeneration, yet the underlying cause of globally reduced CBF remains unclear.

METHODS

Using premortem delivery of Methoxy-XO4 to label Aβ, and arterial vascular labeling, we assessed Aβ burden on the pial artery/arteriole network and cerebral blood flow in aged male and female WT and J20 AD mice.

RESULTS

The pial artery/arteriole vascular network selectively displayed extensive vascular Aβ burden. Pial collateral arteriole vessels, the by-pass system that reroutes blood flow during occlusion, displayed significant enlargement in J20 mice. Despite this, CBF was decreased by approximately 15% in 12-month J20 mice when compared to WT littermates.

DISCUSSION

Significant Aβ burden on the meningeal arterial network may contribute to the restriction of CBF. Redistribution of CBF through enlarged pial collateral vessels may serve as a compensatory mechanism to alter CBF during disease progression in cases of CAA.

Cerebral blood flow dynamics during cardiac surgery in infants

BACKGROUND

In this pilot study, we investigated continuous cerebral blood flow velocity measurements to explore cerebrovascular hemodynamics in infants with congenital heart disease undergoing cardiac surgery.

METHODS

A non-invasive transfontanellar cerebral Doppler monitor (NeoDoppler) was used to monitor 15 infants (aged eight days to nine months) during cardiac surgery with cardiopulmonary bypass. Numerical and visual analyses were conducted to assess trends and events in Doppler measurements together with standard monitoring equipment. The mean flow index, calculated as the moving Pearson correlation between mean arterial pressure and time averaged velocity, was utilized to evaluate dynamic autoregulation. Two levels of impaired autoregulation were defined (Mean flow index >0.3/0.45), and percentage of time above these limits were calculated.

RESULTS

High quality recordings were achieved during 90.6% of the monitoring period. There was a significant reduction in time averaged velocity in all periods of cardiopulmonary bypass. All patients showed a high percentage of time with impaired dynamic autoregulation, with Mean flow index >0.3 and 0.45: 73.71% ± 9.06% and 65.16% ± 11.27% respectively. Additionally, the system promptly detected hemodynamic events.

CONCLUSION

Continuous transfontanellar cerebral Doppler monitoring could become an additional tool in enhancing cerebral monitoring in infants during cardiac surgery.

IMPACT

This pilot study demonstrates the feasibility of continuous transfontanellar Doppler monitoring of cerebral blood flow velocities during cardiac surgery in infants. It also demonstrates a high proportion of time with impaired cerebral autoregulation during cardiac surgery based on the Mean flow index. Continuous transfontanellar Doppler could become a useful tool to improve cerebral monitoring and provide new pathophysiological insight.

Role of pterygopalatine ganglion in regulating isoflurane-induced cerebral hyper-perfusion

Cerebral perfusion is functionally regulated by neural mechanisms in addition to the systemic hemodynamic variation, vascular reactivity and cerebral metabolism. Although anesthesia is generally esteemed to suppress the overall brain neural activity and metabolism, a few inhalation anesthetics, such as isoflurane, can increase cerebral perfusion, thus heightening the risks of higher intracranial pressure, bleeding, and brain edema during surgery. With the aid of laser speckle contrast imaging, we observed a transient yet limited effect of cerebral perfusion enhancement in mice from awake to anesthetized conditions with different concentration of isoflurane. Retrograde and antegrade tracing revealed a higher proportion of parasympathetic control more than sympathetic innervation for the blood vessels. Surprisingly, isoflurane directly activated pterygopalatine ganglion (PPG) explants and induced FOS expression in the cholinergic neurons. Chemogenetic activation of cholinergic PPG neurons reduced isoflurane-related cerebral perfusion. On the contrary, ablation of the cholinergic PPG neurons resulted in further enhancement of cerebral perfusion induced by isoflurane. While blocking muscarinic cholinergic receptors resulted in the overall reduction upon isoflurane stimulation, the blockage of nicotinic cholinergic receptors enhanced the isoflurane-induced cerebral perfusion only when PPG neurons exist. Collectively, these results suggest that PPG play important roles in regulating cerebral perfusion under isoflurane inhalation.

Cerebral Protection in Pediatric Cardiac Surgery

Cardiac surgery, both adult and pediatric, has developed very rapidly and impressively over the past 7 decades. Pediatric cardiac surgery, in particular, has revolutionized the management of babies born with congenital heart disease such that now most patients reach adult life and lead comfortable lives. However, these patients are at risk of cerebral lesions, which may be due to perioperative factors, such as side effects of cardiopulmonary bypass and/or anesthesia, and non-perioperative factors such as chromosomal anomalies (common in children with congenital heart disease), the timing of surgery, number of days on the intensive care unit, length of hospitalization and other hospitalizations in the first year of life. The risk of cerebral lesions is particularly relevant to pediatric cardiac surgery given that cerebral metabolism is about 30% higher in neonates, infants and young children compared to adults, which renders their brain more susceptible to ischemic/hypoxic injury. This issue has been a major concern throughout the history of cardiac surgery such that many preventive measures have been implemented over the years. These measures, however, have had only a modest impact and cerebral lesions continue to be a major concern. This is the subject of this review article, which aims to outline these protective measures, offer possible explanations of why these have not resolved the issue, and suggest possible actions that ought to be taken now.

Label free, capillary-scale blood flow mapping in vivo reveals that low-intensity focused ultrasound evokes persistent dilation in cortical microvasculature

Non-invasive, low intensity focused ultrasound is an emerging neuromodulation technique that offers the potential for precision, personalized therapy. An increasing body of research has identified mechanosensitive ion channels that can be modulated by FUS and support acute electrical activity in neurons. However, neuromodulatory effects that persist from hours to days have also been reported. The brain's ability to provide blood flow to electrically active regions involves a multitude of non-neuronal cell types and signaling pathways in the cerebral vasculature; an open question is whether persistent effects can be attributed, at least partly, to vascular mechanisms. Using an in vivo optical approach, we found that microvasculature, and not larger vessels, exhibit significant persistent dilation following sonication without the use of microbubbles. This finding reveals a heretofore unseen aspect of the effects of FUS in vivo and indicates that concurrent changes in neurovascular function may partially underly persistent neuromodulatory effects.

Wearable optical coherence tomography angiography probe with extended depth of field

Significance

Optical coherence tomography (OCT) is widely utilized to investigate brain activities and disorders in anesthetized or restrained rodents. However, anesthesia can alter several physiological parameters, leading to findings that might not fully represent the true physiological state. To advance the understanding of brain function in awake and freely moving animals, the development of wearable OCT probes is crucial.

Aim

We aim to address the challenge of insufficient depth of field (DOF) in wearable OCT probes for brain imaging in freely moving mice, ensuring high lateral resolution while capturing brain vasculature across varying heights.

Approach

We integrated diffractive optical elements (DOEs) capable of generating beams with an extended DOF into a wearable OCT probe. This design effectively overcomes the traditional trade-off between lateral resolution and DOF, enabling the capture of detailed angiographic images in a dynamic and uncontrolled environment.

Results

The enhanced wearable OCT probe achieved a lateral resolution superior to 8    μ m within a 450    μ m axial range. This setup allowed for high-resolution optical coherence tomography angiography (OCTA) imaging with extended DOF, making it suitable for studying brain vasculature in freely moving mice.

Conclusions

The incorporation of DOEs into the wearable OCT probe represents a significant advancement in wearable biomedical imaging. This technology facilitates the acquisition of high-resolution angiographic images with an extended DOF, thus enhancing the ability to study brain function in awake and naturally behaving animals.

Impact of anesthetic induction with etomidate, thiopentone, and propofol on regional cerebral oxygenation: An observational study in patients with traumatic brain injury

Background and Aims

Anesthetic induction plays a pivotal role in determining the operative course and the outcome in patients with acute traumatic brain injury (TBI). The present study compared the effect of anesthetic induction with etomidate, thiopentone, and propofol primarily on systemic hemodynamics and regional cerebral oxygenation (rScO2) and secondarily on the serum cortisol levels in TBI patients.

Material and Methods

In this prospective observational study, eligible patients were recruited and divided into three groups as per the induction agent received. Data collected were hemodynamic parameters and rScO2 levels at baseline, following 3 min of preoxygenation, and over 10 min of induction. Serum cortisol levels were measured before and after 24 h of induction. The statistical analysis was done using R software.

Results

A total of 115 patients were included: 32, 33, and 50 in thiopentone, propofol, and etomidate groups, respectively. A significant increase (P < 0.001) in bilateral rScO2 was noted in all three groups following anesthetic induction. Intergroup comparison of the propofol and the etomidate groups revealed significantly lesser increase in contralateral rScO2 (P = 0.019) and a greater fall in mean arterial pressure (P = 0.003) on using propofol as an induction agent. Trend changes in bilateral rScO2 and hemodynamic parameters were comparable between thiopentone and etomidate groups. An insignificant fall in serum cortisol was observed in etomidate (P = 0.332) and thiopentone (P = 0.364) groups, but a significant increase was observed in the propofol group (P = 0.004). The Glasgow coma scale (GCS) score at discharge improved significantly in all the groups (P < 0.001).

Conclusions

In TBI patients, anesthetic induction with etomidate resulted in least hemodynamic changes compared to induction with thiopentone and propofol. The rScO2 increased in all three groups after induction, with the maximal increase observed with etomidate compared to propofol and thiopentone. Insignificant fall in serum cortisol was observed with etomidate and thiopentone, but not with propofol. Outcome at discharge, assessed with GCS, was comparable in all the groups.

Anesthetics in pathological cerebrovascular conditions

The increasing prevalence of pathological cerebrovascular conditions, including stroke, hypertensive encephalopathy, and chronic disorders, underscores the importance of anesthetic considerations for affected patients. Preserving cerebral oxygenation and blood flow during anesthesia is paramount to prevent neurological deterioration. Furthermore, protecting vulnerable neurons from damage is crucial for optimal outcomes. Recent research suggests that anesthetic agents may provide a potentially therapeutic approach for managing pathological cerebrovascular conditions. Anesthetics target neural mechanisms underlying cerebrovascular dysfunction, thereby modulating neuroinflammation, protecting neurons against ischemic injury, and improving cerebral hemodynamics. However, optimal strategies regarding mechanisms, dosage, and indications remain uncertain. This review aims to clarify the physiological effects, mechanisms of action, and reported neuroprotective benefits of anesthetics in patients with various pathological cerebrovascular conditions. Investigating anesthetic effects in cerebrovascular disease holds promise for developing novel therapeutic strategies.

The sedative effect of intravenous butorphanol in dogs with intracranial space occupying lesions or indicators of intracranial hypertension

OBJECTIVE

To determine whether dogs with magnetic resonance imaging (MRI)-determined intracranial space occupying lesions (MRI-iSOLs) or intracranial hypertension (MRI-ICH) had greater sedation scores and quicker onset of recumbency following premedication with intravenous (IV) butorphanol in comparison with dogs which had normal MRI findings.

STUDY DESIGN

Prospective, observational study.

ANIMALS

A total of 53 dogs presenting for brain MRI were included.

METHODS

Each dog was sedated with 0.2 mg kg-1 butorphanol IV, and the quality of sedation and the onset of recumbency were scored before drug administration and every 5 minutes after IV butorphanol administration for 15 minutes using a modified sedation scale. The maximum sedation score was 18, and onset of recumbency was recorded when a dog lay down without the ability to stand. Each MRI was assessed for the presence or absence of MRI-iSOL and MRI-ICH using T2-weighted sequences. Data were analysed using the Wilcoxon rank sum test or the chi-square test.

RESULTS

Dogs with MRI-iSOL had significantly higher median sedation scores than dogs without MRI-iSOL (12 versus 5, respectively) 15 minutes after butorphanol administration (T15, p < 0.01). A greater number of dogs with MRI-ICH achieved recumbency (n = 9/10; 90%) than those without MRI-ICH (n = 20/43; 46.5%; p = 0.01).

CONCLUSIONS AND CLINICAL RELEVANCE

When intracranial disease is suspected, the administration of butorphanol as a premedicant for anaesthesia could be used to predict the presence of MRI-iSOL and MRI-ICH. If a dog becomes recumbent or has a sedation score > 10 within 15 minutes of butorphanol administration, the animal should be treated with an anaesthesia protocol adapted to the presence of ICH.

Longitudinal Awake Imaging of Mouse Deep Brain Microvasculature with Super-resolution Ultrasound Localization Microscopy

Ultrasound localization microscopy (ULM) is an emerging imaging modality that resolves microvasculature in deep tissues with high spatial resolution. However, existing preclinical ULM applications are largely constrained to anesthetized animals, introducing confounding vascular effects such as vasodilation and altered hemodynamics. As such, ULM quantifications (e.g., vessel diameter, density, and flow velocity) may be confounded by the use of anesthesia, undermining the usefulness of ULM in practice. Here we introduce a method to address this limitation and achieve ULM imaging in awake mouse brain. Pupillary monitoring was used to support the presence of the awake state during ULM imaging. Vasodilation induced by isoflurane was observed by ULM. Upon recovery to the awake state, reductions in vessel density and flow velocity were observed across different brain regions. In the cortex, the effects induced by isoflurane are more pronounced on venous flow than on arterial flow. In addition, serial in vivo imaging of the same animal brain at weekly intervals demonstrated the highly robust longitudinal imaging capability of the proposed technique. The consistency was further verified through quantitative analysis on individual vessels, cortical regions of arteries and veins, and subcortical regions. This study demonstrates longitudinal ULM imaging in the awake mouse brain, which is crucial for many ULM brain applications that require awake and behaving animals.

The morphology of internal elastic lamina corrugations in arteries under physiological conditions

BACKGROUND

In elastic and resistance arteries, an elastin-rich membrane, the Internal Elastic Lamina (IEL), separates the tunica intima from the underlying tunica media. The IEL often appears wrinkled or corrugated in histological images. These corrugations are sometimes ascribed to vessel contraction ex vivo, and to fixation artifacts, and therefore regarded as not physiologically relevant. We examine whether the IEL remains corrugated even under physiological conditions.

METHODS

The diameters of carotid arteries of anesthetized pigs were measured by ultrasound. The arteries were then excised, inflated within a conical sleeve, fixed, and imaged by confocal microscopy. The conical sleeve allows fixing each artery across a wide range of diameters, which bracket its ultrasound diameter. Thus the study was designed to quantify how corrugations change with diameter for a single artery, and test whether corrugations exist when the fixed artery matches the ultrasound diameter.

RESULTS

At diameters below the ultrasound diameter (i.e. when the artery was constricted as compared to ultrasound conditions), the IEL corrugations were found to decrease significantly with increasing diameter, but not fully flatten at the ultrasound diameter. The contour length of the IEL was found to be roughly 10% larger than the circumference of the artery measured by ultrasound. Since ultrasound was conducted with the animal under general anesthesia which induces vasodilation, the physiological diameter is likely to be smaller than the ultrasound diameter, and hence the arteries are likely to have a higher level of corrugation under physiological conditions. For arterial cross sections constricted below the ultrasound diameter, the IEL contour length decreased roughly with the square root of the diameter.

CONCLUSION

The primary conclusions of this study are: a) the IEL is corrugated when the artery is constricted and flattens as the artery diameter increases; b) the IEL is corrugated under physiological conditions and has a contour length at least 10% more than the physiological arterial diameter; and c) the IEL despite being relatively stiffer than the surrounding arterial layers, does not behave like an inextensible membrane.

Regional heterogeneity of cerebral blood flow immediately after the onset of ventricular pacing in anesthetized rats

Selective distribution of cerebral blood flow (CBF) to vital brain regions likely occurs during rapid severe hypotension caused by tachyarrhythmia but has not yet been demonstrated. In this study, we aimed to test the hypothesis that CBF is differentially preserved between brain regions depending on the degree of hypotension. In anesthetized rats, CBF was measured in the motor cortex (MC), medial prefrontal cortex, amygdala, thalamus, dorsal hypothalamus, hippocampus, ventral tegmental area, dorsolateral periaqueductal gray (dlPAG), and parabrachial nucleus (PB) by using laser-Doppler flowmetry. Ventricular pacing was performed for 30 s at 550-800 beats/min. The cerebrovascular CO2 response time and reactivity were evaluated during 5% CO2 exposure. During 1-4 s of ventricular pacing, mean arterial pressure (MAP) rapidly decreased, with minor changes in central venous and intracranial pressures. CBF was relatively well maintained in brain regions other than the MC (Ps ≤ 0.012) when moderate hypotension occurred (-34 mmHg ≤ ΔMAP ≤ -15 mmHg), whereas severe hypotension (-54 mmHg ≤ ΔMAP ≤ -35 mmHg) induced selective CBF distribution to regions other than the MC, thalamus, and dlPAG. The cerebrovascular CO2 response time/reactivity was rapid or high in the thalamus, dlPAG, and PB, which almost completely differed from the brain regions in which CBF was relatively maintained during pacing-induced severe hypotension. These results suggest that regional heterogeneity of CBF arises depending on the degree of tachyarrhythmia-induced hypotension. Clarifying the mechanisms and functions of CBF maintenance would be beneficial to syncope and cerebral ischemia management in patients with arrhythmia.NEW & NOTEWORTHY When lethal tachyarrhythmia occurs, survival is prioritized by counterregulating the cardiovascular system, which is driven by vital brain regions. However, whether limited cerebral blood flow is selectively distributed to vital brain regions is unknown. We demonstrated the preferential maintenance of cerebral blood flow in vital brain regions, depending on the degree of hypotension caused by ventricular pacing, in anesthetized rats. Our data may have clinical implications for syncope and cerebral ischemia management in patients with arrhythmia.

Choroid plexus extracellular vesicle transport of blood-borne insulin-like growth factor 1 to the hippocampus of the immature brain

Reduced serum level of insulin-like growth factor 1 (IGF-1), a major regulator of perinatal development, in extremely preterm infants has been shown to be associated with neurodevelopmental impairment. To clarify the mechanism of IGF-1 transport at the blood-cerebrospinal fluid (CSF) barrier of the immature brain, we combined studies of in vivo preterm piglet and rabbit models with an in vitro transwell cell culture model of neonatal primary murine choroid plexus epithelial (ChPE) cells. We identified IGF-1-positive intracellular vesicles in ChPE cells and provided data indicating a directional transport of IGF-1 from the basolateral to the apical media in extracellular vesicles (EVs). Exposure of the ChPE cells to human IGF-1 on the basolateral side increased the secretion of IGF-1-positive EVs in the apical media. Mass spectrometry analysis displayed similarities in protein content between EVs derived from preterm piglet CSF-derived and ChPE cell-derived EVs. Furthermore, exposure of ChPE cells to human IGF-1 caused an enrichment of human IGF-1 and transmembrane p24 trafficking protein 2, proteins important for perinatal development, in apical media-derived EVs. Moreover, intraventricular injections of ChPE cell-derived EVs in preterm rabbit pups resulted in an uptake of EVs in the brain, displaying penetration through the ependymal lining and deep into the hippocampus. Finally, exposure of rat hippocampus neurons to ChPE cell-derived EVs resulted in internalization of the EVs in hippocampal soma and neurites. In summary, we describe a transport pathway for blood-borne IGF-1 in EVs through the blood-CSF barrier to the hippocampus in the immature brain.

Paediatric acute liver failure: a multidisciplinary perspective on when a critically ill child is unsuitable for liver transplantation

Paediatric acute liver failure is a devastating condition with high morbidity and mortality, which is challenging to manage for the hepatologist, intensivist, and associated specialists. Emergency liver transplantation is required for 10-20% of patients, but for 10% of critically ill children, liver transplantation is deemed unsuitable; the child might be too unwell, or the underlying cause might carry a poor prognosis. Other social, logistical, or ethical considerations are often relevant. Liver transplantation when a patient is too unwell creates perioperative risk to the child that could lead to morbidity, mortality, and potential graft wastage, which is detrimental for others on the waiting list. Donor liver scarcity should prompt an evaluation of whether a transplant is justified through a holistic multidisciplinary lens that considers medical, social, logistical, and ethical concerns. In this Review, we explore, from a multidisciplinary perspective, why a critically unwell child with paediatric acute liver failure might be unsuitable for liver transplantation.

Age-dependent cerebral vasodilation induced by volatile anesthetics is mediated by NG2+ vascular mural cells

Anesthesia can influence cerebral blood flow by altering vessel diameter. Using in vivo two-photon imaging, we examined the effects of volatile anesthetics, sevoflurane and isoflurane, on vessel diameter in young and adult mice. Our results show that these anesthetics induce robust dilation of cortical arterioles and arteriole-proximate capillaries in adult mice, with milder effects in juveniles and no dilation in infants. This anesthesia-induced vasodilation correlates with decreased cytosolic Ca2+ levels in NG2+ vascular mural cells. Optogenetic manipulation of these cells bidirectionally regulates vessel diameter, and their ablation abolishes the vasodilatory response to anesthetics. In immature brains, NG2+ mural cells are fewer in number and express lower levels of Kir6.1, a subunit of ATP-sensitive potassium channels. This likely contributes to the age-dependent differences in vasodilation, as Kir6.1 activation promotes, while its inhibition reduces, anesthesia-induced vasodilation. These findings highlight the essential role of NG2+ mural cells in mediating anesthesia-induced cerebral vasodilation.

Assessment of Hyperacute Cerebral Ischemia Using Laser Speckle Contrast Imaging

Background: Accurate diagnosis of cerebral ischemia severity is crucial for clinical decision making. Laser speckle contrast imaging-based cerebral blood flow imaging can help assess the severity of cerebral ischemia by monitoring changes in blood flow. Method: In this study, we simulated hyperacute ischemia in rats, isolating arterial and venous flow-related signals from cortical vasculature. Pearson correlation was used to examine the correlation between damaged vessels. Granger causality analysis was used to investigate causality correlation in ischemic vessels. Results: Resting state analysis revealed a negative Pearson correlation between regional arteries and veins. Following cerebral ischemia induction, a positive artery-vein correlation emerged, which vanished after blood flow reperfusion. Granger causality analysis demonstrating enhanced causality coefficients for middle artery-vein pairs during occlusion, with a stronger left-right arterial effect than that of right-left, which persisted after reperfusion. Conclusions: These processing approaches amplify the understanding of cerebral ischemic images, promising potential future diagnostic advancements.

Consciousness and Energy Processing in Neural Systems

BACKGROUND

Our understanding of the relationship between neural activity and psychological states has advanced greatly in recent decades. But we are still unable to explain conscious experience in terms of physical processes occurring in our brains.

METHODS

This paper introduces a conceptual framework that may contribute to an explanation. All physical processes entail the transfer, transduction, and transformation of energy between portions of matter as work is performed in material systems. If the production of consciousness in nervous systems is a physical process, then it must entail the same. Here the nervous system, and the brain in particular, is considered as a material system that transfers, transduces, and transforms energy as it performs biophysical work.

CONCLUSIONS

Evidence from neuroscience suggests that conscious experience is produced in the organic matter of nervous systems when they perform biophysical work at classical and quantum scales with a certain level of dynamic complexity or organization. An empirically grounded, falsifiable, and testable hypothesis is offered to explain how energy processing in nervous systems may produce conscious experience at a fundamental physical level.

Type 2 diabetes remodels collateral circulation and promotes leukocyte adhesion following ischemic stroke

Type 2 diabetes mellitus (T2DM) is associated with impaired leptomeningeal collateral compensation and poor stroke outcome. Neutrophils tethering and rolling on endothelium after stroke can also independently reduce flow velocity. However, the chronology and topological changes in collateral circulation in T2DM is not yet defined. Here, we describe the spatial and temporal blood flow dynamics and vessel remodeling in pial arteries and veins and leukocyte-endothelial adhesion following middle cerebral artery (MCA) stroke using two-photon microscopy in awake control and T2DM mice. Relative to control mice prior to stroke, T2DM mice already exhibited smaller pial vessels with reduced flow velocity. Following stroke, T2DM mice displayed persistently reduced blood flow in pial arteries and veins, resulting in a poor recovery of downstream penetrating arterial flow and a sustained deficit in microvascular flow. There was also persistent increase of leukocyte adhesion to the endothelium of veins, coincided with elevated neutrophils infiltration into brain parenchyma in T2DM mice compared to control mice after stroke. Our data suggest that T2DM-induced increase in chronic inflammation may contribute to the remodeling of leptomeningeal collateral circulation and the observed hemodynamics deficiency that potentiates poor stroke outcome.

Comparing Vascular Morphology and Hemodynamics in Patients with Vein of Galen Malformations Using Intracranial 4D Flow MRI

BACKGROUND AND PURPOSE

Vein of Galen malformation (VOGM) is the most common congenital cerebrovascular malformation, and many patients have high mortality rates and poor cognitive outcomes. Quantitative diagnostic tools are needed to improve clinical outcomes, and the purpose of this study was to characterize intracranial blood flow in VOGM using quantitative 4D flow MRI.

MATERIALS AND METHODS

A prospective study of children with VOGM was conducted by acquiring 4D flow MRI to quantify total blood inflow to the brain, flow in the pathologic falcine sinus, and flow in the superior sagittal sinus. Linear regression was used to test the relationships between these flows and age, clinical status, and the mediolateral diameter of the outflow tract of the lesion through the falcine or straight sinus diameter, which is a known morphologic prognostic metric.

RESULTS

In all 11 subjects (mean age, 22 [SD,17 ] weeks), total blood flow to the brain always exceeded normal levels (mean, 1063 [SD, 403] mL/minute). Significant correlations were observed between falcine sinus flow and the mediolateral diameter of the straight or falcine sinus, the posterior cerebral artery/MCA flow ratio and age at scanning, and superior sagittal sinus flow proximal to malformation inflow and age at scanning.

CONCLUSIONS

Using 4D flow MRI, we established the hemodynamic underpinnings of the mediolateral diameter of the straight or falcine sinus and investigated metrics representing parenchymal venous drainage that could be used to monitor the normalization of hemodynamics during embolization therapy.

Dynamic neuroreceptor positron emission tomography in non-anesthetized rats using point source based motion correction: A feasibility study with [11C]ABP688

To prevent motion artifacts in small animal positron emission tomography (PET), animals are routinely scanned under anesthesia or physical restraint. Both may potentially alter metabolism and neurochemistry. This study investigates the feasibility of fully awake acquisition and subsequent absolute quantification of dynamic brain PET data via pharmacokinetic modelling in moving rats using the glutamate 5 receptor radioligand [11C]ABP688 and point source based motion correction. Five male rats underwent three dynamic [11C]ABP688 PET scans: two test-retest awake PET scans and one scan under anesthesia for comparison. Specific radioligand binding was determined via the simplified reference tissue model (reference: cerebellum) and outcome parameters BPND and R1 were evaluated in terms of stability and reproducibility. Test-retest measurements in awake animals gave reliable results with high correlations of BPND (y = 1.08 × -0.2, r = 0.99, p < 0.01) and an acceptable variability (mean over all investigated regions 15.7 ± 2.4%). Regional [11C]ABP688 BPNDs under awake and anesthetized conditions were comparable although in awake scans, absolute radioactive peak uptakes were lower and relative blood flow in terms of R1 was higher. Awake small animal PET with absolute quantification of neuroreceptor availability is technically feasible and reproducible thereby providing a suitable alternative whenever effects of anesthesia are undesirable, e.g. in sleep research.

Anesthetic Management and Considerations During Surgical Dissection of a Schwannoma Causing Severe Cervical Spinal Canal Stenosis and Vertebral Artery Compression

Neurosurgical cases require meticulous anesthetic planning and execution by the anesthesiologist. This report aims to illuminate the careful considerations required in several aspects of anesthetic management, including spinal positioning during intubation/throughout the case, neuromonitoring, and anesthetic agent selection to ensure adequate neural tissue perfusion and optimal outcomes in neuroanesthesia cases. We describe the anesthetic case of a large cervical spine schwannoma resection in a 64-year-old woman who experienced various neurological symptoms due to this mass. MRI revealed that the mass was causing severe spinal canal stenosis, jugular vein effacement, and compression of the vertebral artery. This patient, classified as an American Society of Anesthesiologists (ASA) III, was optimized in preoperative clinic visits. She was deemed an appropriate candidate for a posterior cervical spine laminectomy with tumor resection and instrumentation which was recommended by both Otolaryngology and Neurosurgery. Intraoperatively, a video laryngoscopy was performed to limit extreme cervical spine movement during intubation. To allow for continuous neuromonitoring throughout the case, intravenous infusions of propofol and remifentanil were the primary anesthetic along with half a minimum alveolar concentration of sevoflurane to avoid intraoperative awareness. No major neurological changes were noted during the case. Additionally, ASA standard monitoring, an arterial line, and a Bispectral Index (BIS) monitor were utilized. All anesthetic agents were titrated to achieve optimal blood pressure and BIS readings. The surgery was completed successfully and the patient did not require transfusion of any blood products. She was successfully extubated and transferred to the neurocritical care unit with no postoperative complications.

Spatiotemporal relationships between neuronal, metabolic, and hemodynamic signals in the awake and anesthetized mouse brain

Neurovascular coupling (NVC) and neurometabolic coupling (NMC) provide the basis for functional magnetic resonance imaging and positron emission tomography to map brain neurophysiology. While increases in neuronal activity are often accompanied by increases in blood oxygen delivery and oxidative metabolism, these observations are not the rule. This decoupling is important when interpreting brain network organization (e.g., resting-state functional connectivity [RSFC]) because it is unclear whether changes in NMC/NVC affect RSFC measures. We leverage wide-field optical imaging in Thy1-jRGECO1a mice to map cortical calcium activity in pyramidal neurons, flavoprotein autofluorescence (representing oxidative metabolism), and hemodynamic activity during wake and ketamine/xylazine anesthesia. Spontaneous dynamics of all contrasts exhibit patterns consistent with RSFC. NMC/NVC relative to excitatory activity varies over the cortex. Ketamine/xylazine profoundly alters NVC but not NMC. Compared to awake RSFC, ketamine/xylazine affects metabolic-based connectomes moreso than hemodynamic-based measures of RSFC. Anesthesia-related differences in NMC/NVC timing do not appreciably alter RSFC structure.

Label free, capillary-scale blood flow mapping in vivo reveals that low intensity focused ultrasound evokes persistent dilation in cortical microvasculature

Non-invasive, low intensity focused ultrasound (FUS) is an emerging neuromodulation technique that offers the potential for precision, personalized therapy. An increasing body of research has identified mechanosensitive ion channels that can be modulated by FUS and support acute electrical activity in neurons. However, neuromodulatory effects that persist from hours to days have also been reported. The brain's ability to provide targeted blood flow to electrically active regions involve a multitude of non-neuronal cell types and signaling pathways in the cerebral vasculature; an open question is whether persistent effects can be attributed, at least partly, to vascular mechanisms. Using a novel in vivo optical approach, we found that microvascular responses, unlike larger vessels which prior investigations have explored, exhibit persistent dilation following sonication without the use of microbubbles. This finding and approach offers a heretofore unseen aspect of the effects of FUS in vivo and indicate that concurrent changes in neurovascular function may partially underly persistent neuromodulatory effects.

Intracranial pressure-flow relationships in traumatic brain injury patients expose gaps in the tenets of models and pressure-oriented management

Background: The protocols and therapeutic guidance established for treating traumatic brain injury (TBI) in neurointensive care focus on managing cerebral blood flow (CBF) and brain tissue oxygenation based on pressure signals. The decision support process relies on assumed relationships between cerebral perfusion pressure (CPP) and blood flow, pressure-flow relationships (PFRs), and shares this framework of assumptions with mathematical intracranial hemodynamics models. These foundational assumptions are difficult to verify, and their violation can impact clinical decision-making and model validity. Methods: A hypothesis- and model-driven method for verifying and understanding the foundational intracranial hemodynamic PFRs is developed and applied to a novel multi-modality monitoring dataset. Results: Model analysis of joint observations of CPP and CBF validates the standard PFR when autoregulatory processes are impaired as well as unmodelable cases dominated by autoregulation. However, it also identifies a dynamical regime -or behavior pattern-where the PFR assumptions are wrong in a precise, data-inferable way due to negative CPP-CBF coordination over long timescales. This regime is of both clinical and research interest: its dynamics are modelable under modified assumptions while its causal direction and mechanistic pathway remain unclear. Conclusion: Motivated by the understanding of mathematical physiology, the validity of the standard PFR can be assessed a) directly by analyzing pressure reactivity and mean flow indices (PRx and Mx) or b) indirectly through the relationship between CBF and other clinical observables. This approach could potentially help to personalize TBI care by considering intracranial pressure and CPP in relation to other data, particularly CBF. The analysis suggests a threshold using clinical indices of autoregulation jointly generalizes independently set indicators to assess CA functionality. These results support the use of increasingly data-rich environments to develop more robust hybrid physiological-machine learning models.

Anesthesia Blunts Carbon Dioxide Effects on Glymphatic Cerebrospinal Fluid Dynamics in Mechanically Ventilated Rats

BACKGROUND

Impaired glymphatic clearance of cerebral metabolic products and fluids contribute to traumatic and ischemic brain edema and neurodegeneration in preclinical models. Glymphatic perivascular cerebrospinal fluid flow varies between anesthetics possibly due to changes in vasomotor tone and thereby in the dynamics of the periarterial cerebrospinal fluid (CSF)-containing space. To better understand the influence of anesthetics and carbon dioxide levels on CSF dynamics, this study examined the effect of periarterial size modulation on CSF distribution by changing blood carbon dioxide levels and anesthetic regimens with opposing vasomotor influences: vasoconstrictive ketamine-dexmedetomidine (K/DEX) and vasodilatory isoflurane.

METHODS

End-tidal carbon dioxide (ETco2) was modulated with either supplemental inhaled carbon dioxide to reach hypercapnia (Etco2, 80 mmHg) or hyperventilation (Etco2, 20 mmHg) in tracheostomized and anesthetized female rats. Distribution of intracisternally infused radiolabeled CSF tracer 111In-diethylamine pentaacetate was assessed for 86 min in (1) normoventilated (Etco2, 40 mmHg) K/DEX; (2) normoventilated isoflurane; (3) hypercapnic K/DEX; and (4) hyperventilated isoflurane groups using dynamic whole-body single-photon emission tomography. CSF volume changes were assessed with magnetic resonance imaging.

RESULTS

Under normoventilation, cortical CSF tracer perfusion, perivascular space size around middle cerebral arteries, and intracranial CSF volume were higher under K/DEX compared with isoflurane (cortical maximum percentage of injected dose ratio, 2.33 [95% CI, 1.35 to 4.04]; perivascular size ratio 2.20 [95% CI, 1.09 to 4.45]; and intracranial CSF volume ratio, 1.90 [95% CI, 1.33 to 2.71]). Under isoflurane, tracer was directed to systemic circulation. Under K/DEX, the intracranial tracer distribution and CSF volume were uninfluenced by hypercapnia compared with normoventilation. Intracranial CSF tracer distribution was unaffected by hyperventilation under isoflurane despite a 28% increase in CSF volume around middle cerebral arteries.

CONCLUSIONS

K/DEX and isoflurane overrode carbon dioxide as a regulator of CSF flow. K/DEX could be used to preserve CSF space and dynamics in hypercapnia, whereas hyperventilation was insufficient to increase cerebral CSF perfusion under isoflurane.

EDITOR’S PERSPECTIVE

Optimal bispectral index exists in healthy patients undergoing general anesthesia: A validation study

PURPOSE

Continuous cerebrovascular reactivity monitoring in both neurocritical and intra-operative care has gained extensive interest in recent years, as it has documented associations with long-term outcomes (in neurocritical care populations) and cognitive outcomes (in operative cohorts). This has sparked further interest into the exploration and evaluation of methods to achieve an optimal cerebrovascular reactivity measure, where the individual patient is exposed to the lowest insult burden of impaired cerebrovascular reactivity. Recent literature has documented, in neural injury populations, the presence of a potential optimal sedation level in neurocritical care, based on the relationship between cerebrovascular reactivity and quantitative depth of sedation (using bispectral index (BIS)) - termed BISopt. The presence of this measure outside of neural injury patients has yet to be proven.

METHODS

We explore the relationship between BIS and continuous cerebrovascular reactivity in two cohorts: (A) healthy population undergoing elective spinal surgery under general anesthesia, and (B) healthy volunteer cohort of awake controls.

RESULTS

We demonstrate the presence of BISopt in the general anesthesia population (96% of patients), and its absence in awake controls, providing preliminary validation of its existence outside of neural injury populations. Furthermore, we found BIS to be sufficiently separate from overall systemic blood pressure, this indicates that they impact different pathophysiological phenomena to mediate cerebrovascular reactivity.

CONCLUSIONS

Findings here carry implications for the adaptation of the individualized physiologic BISopt concept to non-neural injury populations, both within critical care and the operative theater. However, this work is currently exploratory, and future work is required.

Evaluating the diagnostic performance of non-contrast magnetic resonance angiography sequences in the pre-procedural comprehensive analysis of direct carotid cavernous fistula

PURPOSE

Endovascular treatment of direct carotid cavernous fistula (DCCF) requires invasive diagnostic cerebral angiography for diagnosis and planning; however, a less invasive modality like magnetic resonance angiography (MRA) can be useful, especially in high-risk cases. This single-centre study evaluated a newer MR angiography (MRA) sequence, silent MRA and the traditional time of flight (TOF) MRA for pre-procedural treatment planning of DCCF.

METHODS

All consecutive DCCF patients who underwent TOF, silent MRA and diagnostic cerebral angiography were included in the study. Angiographic features like rent size, location, draining veins and collateral communicating arteries were analysed and compared between the two MRA sequences, with digital subtraction angiography (DSA) as the gold standard.

RESULTS

Fifteen patients were included in the study. TOF MRA exhibited better sensitivity (76.9% vs 69.2%) in identifying the rent location, correctly pinpointing the location in 93.3% compared to 73.3% with silent MRA. Both MRA sequences showed good agreement with DSA for primary sac and rent size. TOF MRA correctly identified 86.2% of 210 total venous structures compared to 96% by silent MRA. Silent MRA demonstrated higher sensitivity (90% vs 76%) and accuracy (87.69 vs 94.36) in visualisation of involved veins compared to TOF MRA.

CONCLUSION

Arterial characteristics of DCCF like rent location and rent size were better assessed by TOF MRA. Although both MRA identified venous features, silent MRA correlated better with DSA irrespective of the size and proximity to the site of the fistula. Combining both sequences can evaluate various angioarchitectural features of DCCF useful for therapeutic planning.

Volatile Anesthetic Sedation for Critically Ill Patients

Volatile anesthetics have multiple properties that make them useful for sedation in the intensive care unit. The team-based approach to volatile anesthetic sedation leverages these properties to provide a safe and effective alternative to intravenous sedatives.

Mesoscopic mapping of hemodynamic responses and neuronal activity during pharmacologically induced interictal spikes in awake and anesthetized mice

Imaging hemodynamic responses to interictal spikes holds promise for presurgical epilepsy evaluations. Understanding the hemodynamic response function is crucial for accurate interpretation. Prior interictal neurovascular coupling data primarily come from anesthetized animals, impacting reliability. We simultaneously monitored calcium fluctuations in excitatory neurons, hemodynamics, and local field potentials (LFP) during bicuculline-induced interictal events in both isoflurane-anesthetized and awake mice. Isoflurane significantly affected LFP amplitude but had little impact on the amplitude and area of the calcium signal. Anesthesia also dramatically blunted the amplitude and latency of the hemodynamic response, although not its area of spread. Cerebral blood volume change provided the best spatial estimation of excitatory neuronal activity in both states. Targeted silencing of the thalamus in awake mice failed to recapitulate the impact of anesthesia on hemodynamic responses suggesting that isoflurane's interruption of the thalamocortical loop did not contribute either to the dissociation between the LFP and the calcium signal nor to the alterations in interictal neurovascular coupling. The blood volume increase associated with interictal spikes represents a promising mapping signal in both the awake and anesthetized states.

[Prehospital postcardiac-arrest-sedation and -care in the Federal Republic of Germany-a web-based survey of emergency physicians]

BACKGROUND

This study evaluates the implementation of postcardiac-arrest-sedation (PCAS) and -care (PRC) by prehospital emergency physicians in Germany.

MATERIALS AND METHODS

Analysis of a web-based survey from October to November 2022. Questions were asked about implementation, medications used, complications, motivation for implementing or not implementing PCAS, and measures and target parameters of PRC.

RESULTS

A total of 500 emergency physicians participated in the survey. In all, 73.4% stated that they regularly performed PCAS (hypnotics: 84.7%; analgesics: 71.1%; relaxants: 29.7%). Indications were pressing against the respirator (88.3%), analgesia (74.1%), synchronization to respirator (59.5%), and change of airway device (52.6%). Reasons for not performing PCAS (26.6%) included unconscious patients (73.7%); concern about hypotension (31.6%), re-arrest (26.3%), and worsening neurological assessment (22.5%). Complications of PCAS were observed by 19.3% of participants (acute hypotension [74.6%]); (re-arrest [32.4%]). In addition to baseline monitoring, PRC included 12-lead-electrocardiogram (96.6%); capnography (91.6%); catecholamine therapy (77.6%); focused echocardiography (20.6%), lung ultrasound (12.0%) and abdominal ultrasound (5.6%); induction of hypothermia (13.6%) and blood gas analysis (7.4%). An etCO2 of 35-45 mm Hg was targeted by 40.6%, while 9.0% of participants targeted an SpO2 of 94-98% and 19.2% of participants targeted a systolic blood pressure of ≥ 100 mm Hg.

CONCLUSIONS

Prehospital PRC in Germany is heterogeneous and deviations from its target parameters are frequent. PCAS is frequent and associated with relevant complications. The development of preclinical care algorithms for PCAS and PRC within preclinical care seems urgently needed.

Multiomic-Based Molecular Landscape of FaDu Xenograft Tumors in Mice after a Combinatorial Treatment with Radiation and an HSP90 Inhibitor Identifies Adaptation-Induced Targets of Resistance and Therapeutic Intervention

Treatments involving radiation and chemotherapy alone or in combination have improved patient survival and quality of life. However, cancers frequently evade these therapies due to adaptation and tumor evolution. Given the complexity of predicting response based solely on the initial genetic profile of a patient, a predetermined treatment course may miss critical adaptation that can cause resistance or induce new targets for drug and immunotherapy. To address the timescale for these evasive mechanisms, using a mouse xenograft tumor model, we investigated the rapidity of gene expression (mRNA), molecular pathway, and phosphoproteome changes after radiation, an HSP90 inhibitor, or combination. Animals received radiation, drug, or combination treatment for 1 or 2 weeks and were then euthanized along with a time-matched untreated group for comparison. Changes in gene expression occur as early as 1 week after treatment initiation. Apoptosis and cell death pathways were activated in irradiated tumor samples. For the HSP90 inhibitor and combination treatment at weeks 1 and 2 compared with Control Day 1, gene-expression changes induced inhibition of pathways including invasion of cells, vasculogenesis, and viral infection among others. The combination group included both drug-alone and radiation-alone changes. Our data demonstrate the rapidity of gene expression and functional pathway changes in the evolving tumor as it responds to treatment. Discovering these phenotypic adaptations may help elucidate the challenges in using sustained treatment regimens and could also define evolving targets for therapeutic efficacy.

Impact of Age-Related Change in Caval Flow Ratio on Hepatic Flow Distribution in the Fontan Circulation

BACKGROUND

The Fontan operation is a palliative technique for patients born with single ventricle heart disease. The superior vena cava (SVC), inferior vena cava (IVC), and hepatic veins are connected to the pulmonary arteries in a total cavopulmonary connection by an extracardiac conduit or a lateral tunnel connection. A balanced hepatic flow distribution (HFD) to both lungs is essential to prevent pulmonary arteriovenous malformations and cyanosis. HFD is highly dependent on the local hemodynamics. The effect of age-related changes in caval inflows on HFD was evaluated using cardiac magnetic resonance data and patient-specific computational fluid dynamics modeling.

METHODS

SVC and IVC flow from 414 patients with Fontan were collected to establish a relationship between SVC:IVC flow ratio and age. Computational fluid dynamics modeling was performed in 60 (30 extracardiac and 30 lateral tunnel) patient models to quantify the HFD that corresponded to patient ages of 3, 8, and 15 years, respectively.

RESULTS

SVC:IVC flow ratio inverted at ≈8 years of age, indicating a clear shift to lower body flow predominance. Our data showed that variation of HFD in response to age-related changes in caval inflows (SVC:IVC, 2, 1, and 0.5 corresponded to ages, 3, 8, and 15+, respectively) was not significant for extracardiac but statistically significant for lateral tunnel cohorts. For all 3 caval inflow ratios, a positive correlation existed between the IVC flow distribution to both the lungs and the HFD. However, as the SVC:IVC ratio changed from 2 to 0.5 (age, 3-15+) years, the correlation's strength decreased from 0.87 to 0.64, due to potential flow perturbation as IVC flow momentum increased.

CONCLUSIONS

Our analysis provided quantitative insights into the impact of the changing caval inflows on Fontan's long-term HFD, highlighting the importance of SVC:IVC variations over time on Fontan's long-term hemodynamics. These findings broaden our understanding of Fontan hemodynamics and patient outcomes.

High spatiotemporal mapping of cortical blood flow velocity with an enhanced accuracy

Cerebral blood flow velocity is one of the most essential parameters related to brain functions and diseases. However, most existing mapping methods suffer from either inaccuracy or lengthy sampling time. In this study, we propose a particle-size-related calibration method to improve the measurement accuracy and a random-access strategy to suppress the sampling time. Based on the proposed methods, we study the long-term progress of cortical vasculopathy and abnormal blood flow caused by glioma, short-term variations of blood flow velocity under different anesthetic depths, and cortex-wide connectivity of the rapid fluctuation of blood flow velocities during seizure onset. The experimental results demonstrate that the proposed calibration method and the random-access strategy can improve both the qualitative and quantitative performance of velocimetry techniques and are also beneficial for understanding brain functions and diseases from the perspective of cerebral blood flow.

MousePZT: A simple, reliable, low-cost device for vital sign monitoring and respiratory gating in mice under anesthesia

Small animal studies in biomedical research often require anesthesia to reduce pain or stress experienced by research animals and to minimize motion artifact during imaging or other measurements. Anesthetized animals must be closely monitored for the safety of the animals and to prevent unintended effects of altered physiology on experimental outcomes. Many currently available monitoring devices are expensive, invasive, or interfere with experimental design. Here, we present MousePZT, a low-cost device based on a simple piezoelectric sensor, with a custom circuit and computer software that allows for measurements of both respiratory rate and heart rate in a non-invasive, minimal contact manner. We find the accuracy of the MousePZT device in measuring respiratory and heart rate matches those of commercial systems. Using the widely-used gas isoflurane and injectable ketamine/xylazine combination, we also demonstrate that changes in respiratory rate are more easily detected and can precede changes in heart rate associated with variations in anesthetic depth. Additional circuitry on the device outputs a respiration-locked trigger signal for respiratory-gating of imaging or other data acquisition and has high sensitivity and specificity for detecting respiratory cycles. We provide detailed instruction documents and all necessary microcontroller and computer software, enabling straightforward construction and utilization of this device.

High-frequency repetitive transcranial magnetic stimulation promotes ipsilesional functional hyperemia and motor recovery in mice with ischemic stroke

Neurovascular decoupling plays a significant role in dysfunction following an ischemic stroke. This study aimed to explore the effect of low- and high-frequency repetitive transcranial magnetic stimulation on neurovascular remodeling after ischemic stroke. To achieve this goal, we compared functional hyperemia, cerebral blood flow regulatory factors, and neurochemical transmitters in the peri-infract cortex 21 days after a photothrombotic stroke. Our findings revealed that low- and high-frequency repetitive transcranial magnetic stimulation increased the real-time cerebral blood flow in healthy mice and improved neurobehavioral outcomes after stroke. Furthermore, high-frequency (5-Hz) repetitive transcranial magnetic stimulation revealed stronger functional hyperemia recovery and increased the levels of post-synaptic density 95, neuronal nitric oxide synthase, phosphorylated-endothelial nitric oxide synthase, and vascular endothelial growth factor in the peri-infract cortex compared with low-frequency (1-Hz) repetitive transcranial magnetic stimulation. The magnetic resonance spectroscopy data showed that low- and high-frequency repetitive transcranial magnetic stimulation reduced neuronal injury and maintained excitation/inhibition balance. However, 5-Hz repetitive transcranial magnetic stimulation showed more significant regulation of excitatory and inhibitory neurotransmitters after stroke than 1-Hz repetitive transcranial magnetic stimulation. These results indicated that high-frequency repetitive transcranial magnetic stimulation could more effectively promote neurovascular remodeling after stroke, and specific repetitive transcranial magnetic stimulation frequencies might be used to selectively regulate the neurovascular unit.

Clinical Outcomes After Traumatic Brain Injury and Exposure to Extracranial Surgery: A TRACK-TBI Study

Importance

Traumatic brain injury (TBI) is associated with persistent functional and cognitive deficits, which may be susceptible to secondary insults. The implications of exposure to surgery and anesthesia after TBI warrant investigation, given that surgery has been associated with neurocognitive disorders.

Objective

To examine whether exposure to extracranial (EC) surgery and anesthesia is related to worse functional and cognitive outcomes after TBI.

Design, Setting, and Participants

This study was a retrospective, secondary analysis of data from the Transforming Research and Clinical Knowledge in Traumatic Brain Injury (TRACK-TBI) study, a prospective cohort study that assessed longitudinal outcomes of participants enrolled at 18 level I US trauma centers between February 1, 2014, and August 31, 2018. Participants were 17 years or older, presented within 24 hours of trauma, were admitted to an inpatient unit from the emergency department, had known Glasgow Coma Scale (GCS) and head computed tomography (CT) status, and did not undergo cranial surgery. This analysis was conducted between January 2, 2020, and August 8, 2023.

Exposure

Participants who underwent EC surgery during the index admission were compared with participants with no surgery in groups with a peripheral orthopedic injury or a TBI and were classified as having uncomplicated mild TBI (GCS score of 13-15 and negative CT results [CT- mTBI]), complicated mild TBI (GCS score of 13-15 and positive CT results [CT+ mTBI]), or moderate to severe TBI (GCS score of 3-12 [m/sTBI]).

Main Outcomes and Measures

The primary outcomes were functional limitations quantified by the Glasgow Outcome Scale-Extended for all injuries (GOSE-ALL) and brain injury (GOSE-TBI) and neurocognitive outcomes at 2 weeks and 6 months after injury.

Results

A total of 1835 participants (mean [SD] age, 42.2 [17.8] years; 1279 [70%] male; 299 Black, 1412 White, and 96 other) were analyzed, including 1349 nonsurgical participants and 486 participants undergoing EC surgery. The participants undergoing EC surgery across all TBI severities had significantly worse GOSE-ALL scores at 2 weeks and 6 months compared with their nonsurgical counterparts. At 6 months after injury, m/sTBI and CT+ mTBI participants who underwent EC surgery had significantly worse GOSE-TBI scores (B = -1.11 [95% CI, -1.53 to -0.68] in participants with m/sTBI and -0.39 [95% CI, -0.77 to -0.01] in participants with CT+ mTBI) and performed worse on the Trail Making Test Part B (B = 30.1 [95% CI, 11.9-48.2] in participants with m/sTBI and 26.3 [95% CI, 11.3-41.2] in participants with CT+ mTBI).

Conclusions and Relevance

This study found that exposure to EC surgery and anesthesia was associated with adverse functional outcomes and impaired executive function after TBI. This unfavorable association warrants further investigation of the potential mechanisms and clinical implications that could inform decisions regarding the timing of surgical interventions in patients after TBI.

Chemotherapy-associated hemorrhagic posterior reversible encephalopathy syndrome (PRES) with considerations for circle of Willis variants on cerebral blood flow and autoregulation: A case report

RATIONALE

Hodgkin lymphoma, a lymphatic system cancer, is treated by chemotherapy, radiation therapy, and hematopoietic stem cell transplantation. Posterior reversible encephalopathy syndrome (PRES) is a rare neurotoxic effect associated with several drugs and systemic conditions. This case study emphasizes the potential risks of intensive chemotherapy regimens and postulates the impact of the circle of Willis variants on the heterogeneity of hemispheric lesions in PRES.

PATIENT CONCERNS

A 42-year-old woman diagnosed with stage IIA nodular sclerosing Hodgkin lymphoma and chronic thrombocytopenia presented after 6 years of initial diagnosis and 4 years post-haploidentical transplant. She underwent planned chemotherapy with ifosfamide, carboplatin, and etoposide.

DIAGNOSES

She developed an alteration in her mental status. A computerized tomography scan and angiogram of the head and neck revealed findings consistent with PRES and a left fetal-type posterior cerebral artery with an aplastic A1 segment of the left anterior cerebral artery. One hour later she was found comatose with clinical sequelae of an uncal herniation.

INTERVENTIONS

Subsequent events led to emergent intubation, and administration of 23.4% hypertonic saline. A repeat computerized tomography scan showed a right intraparenchymal hemorrhage with fluid-fluid levels measuring up to 4.7 cm, bilateral subarachnoid hemorrhage, right uncal herniation, and 15 mm of leftward midline shift. She emergently underwent a right decompressive hemi-craniectomy.

OUTCOMES

An magnetic resonance imaging of the brain demonstrated bilateral cytotoxic edema involving the parieto-occipital lobes. Despite interventions, the patient's neurological condition deteriorated, leading to a declaration of brain death on the 8th day.

LESSONS

This case underscores the importance of recognizing the severe neurological complications, including PRES, associated with chemotherapeutic treatments in Hodgkin lymphoma. PRES may also be exacerbated by coagulopathies such as thrombocytopenia in this case. The circle of Willis variants may influence cerebral blood flow, autoregulation, and other factors of hemodynamics, leading to increased susceptibility to both radiographic lesion burden and the worst clinical outcomes.

Protoporphyrin IX in serum of high-grade glioma patients: A novel target for disease monitoring via liquid biopsy

High-grade gliomas (HGG) carry a dismal prognosis. Diagnosis comprises MRI followed by histopathological evaluation of tissue; no blood biomarker is available. Patients are subjected to serial MRIs and, if unclear, surgery for monitoring of tumor recurrence, which is laborious. MRI provides only limited diagnostic information regarding the differentiation of true tumor progression from therapy-associated side effects. 5-aminolevulinic acid (5-ALA) is routinely used for induction of protoporphyrin IX (PpIX) accumulation in malignant glioma tissue, enabling improved tumor visualization during fluorescence-guided resection (FGR). We investigated whether PpIX can also serve as a serum HGG marker to monitor relapse. Patients (HGG: n = 23 primary, pHGG; n = 5 recurrent, rHGG) undergoing FGR received 5-ALA following standard clinical procedure. The control group of eight healthy volunteers (HCTR) also received 5-ALA. Serum was collected before and repeatedly up to 72 h after drug administration. Significant PpIX accumulation in HGG was observed after 5-ALA administration (ANOVA: p = 0.005, post-hoc: HCTR vs. pHGG p = 0.029, HCTR vs. rHGG p = 0.006). Separation of HCTR from pHGG was possible when maximum serum PpIX levels were reached (CI95% of tMax). ROC analysis of serum PpIX within CI95% of tMax showed successful classification of HCTR and pHGG (AUCROC 0.943, CI95% 0.884-1.000, p < 0.001); the optimal cut-off for diagnosis was 1275 pmol PpIX/ml serum, reaching 87.0% accuracy, 90.5% positive predictive and 84.0% negative predictive value. Baseline PpIX level was similar in patient and control groups. Thus, 5-ALA is required for PpIX induction, which is safe at the standard clinical dosage. PpIX is a new target for liquid biopsy in glioma. More extensive clinical studies are required to characterize its full potential.

Effects of Low-Dose Glucagon on Subcutaneous Insulin Absorption in Pigs

Background

Slow insulin absorption prevents the development of a fully automated artificial pancreas with subcutaneous insulin delivery.

Objective

We have hypothesized that glucagon could be used as a vasodilator to accelerate insulin absorption in a bihormonal subcutaneous artificial pancreas. The present proof-of-concept study is the first study to investigate the pharmacokinetics of insulin after subcutaneous administration of a low dose of glucagon at the site of subcutaneous insulin injection.

Methods

Twelve anesthetized pigs were randomized to receive a subcutaneous injection of 10 IU insulin aspart with either 100 µg glucagon or the equivalent volume of placebo (0.9% saline solution) injected at the same site. Arterial samples were collected for 180 minutes to determine insulin, glucagon, and glucose concentrations.

Results

Glucagon did not influence the insulin concentration Tmax in plasma. The plasma insulin AUC0-∞ was significantly larger after glucagon administration (P < 0.01). The glucagon group had significantly higher glucose concentrations in the first 30 minutes after insulin administration (P < 0.05).

Conclusions

This proof-of-concept study indicates that glucagon may increase the total absorption of a single dose of subcutaneously injected insulin. This is a novel observation. However, we did not observe any reduction in insulin concentration Tmax, as we had hypothesized. Further, glucagon induced a significant, undesirable increase in early blood glucose concentrations.