Isoflurane suppresses cortical spreading depolarizations compared to propofol--implications for sedation of neurocritical care patients

Stroke and Translational Research - Review of Experimental Models with a Focus on Awake Ischaemic Induction and Anaesthesia

Animal models are an indispensable tool in the study of ischaemic stroke with hundreds of drugs emerging from the preclinical pipeline. However, all of these drugs have failed to translate into successful treatments in the clinic. This has brought into focus the need to enhance preclinical studies to improve translation. The confounding effects of anaesthesia on preclinical stroke modelling has been raised as an important consideration. Various volatile and injectable anaesthetics are used in preclinical models during stroke induction and for outcome measurements such as imaging or electrophysiology. However, anaesthetics modulate several pathways essential in the pathophysiology of stroke in a dose and drug dependent manner. Most notably, anaesthesia has significant modulatory effects on cerebral blood flow, metabolism, spreading depolarizations, and neurovascular coupling. To minimise anaesthetic complications and improve translational relevance, awake stroke induction has been attempted in limited models. This review outlines anaesthetic strategies employed in preclinical ischaemic rodent models and their reported cerebral effects. Stroke related complications are also addressed with a focus on infarct volume, neurological deficits, and thrombolysis efficacy. We also summarise routinely used focal ischaemic stroke rodent models and discuss the attempts to induce some of these models in awake rodents.

Isoflurane lowers the cerebral metabolic rate of oxygen and prevents hypoxia during cortical spreading depolarization in vitro: An integrative experimental and modeling study

Cortical spreading depolarization (SD) imposes a massive increase in energy demand and therefore evolves as a target for treatment following acute brain injuries. Anesthetics are empirically used to reduce energy metabolism in critical brain conditions, yet their effect on metabolism during SD remains largely unknown. We investigated oxidative metabolism during SD in brain slices from Wistar rats. Extracellular potassium ([K+]o), local field potential and partial tissue oxygen pressure (ptiO2) were measured simultaneously. The cerebral metabolic rate of oxygen (CMRO2) was calculated using a reaction-diffusion model. By that, we tested the effect of clinically relevant concentrations of isoflurane on CMRO2 during SD and modeled tissue oxygenation for different capillary pO2 values. During SD, CMRO2 increased 2.7-fold, resulting in transient hypoxia in the slice core. Isoflurane decreased CMRO2, reduced peak [K+]o, and prolonged [K+]o clearance, which indicates reduced synaptic transmission and sodium-potassium ATPase inhibition. Modeling tissue oxygenation during SD illustrates the need for increased capillary pO2 levels to prevent hypoxia. In the absence thereof, isoflurane could improve tissue oxygenation by lowering CMRO2. Therefore, isoflurane is a promising candidate for pre-clinical studies on neuronal survival in conditions involving SD.

The neurophysiological effect of mild hypothermia in gyrencephalic brains submitted to ischemic stroke and spreading depolarizations

Objective

Characterize the neurophysiological effects of mild hypothermia on stroke and spreading depolarizations (SDs) in gyrencephalic brains.

Methods

Left middle cerebral arteries (MCAs) of six hypothermic and six normothermic pigs were permanently occluded (MCAo). Hypothermia began 1 h after MCAo and continued throughout the experiment. ECoG signals from both frontoparietal cortices were recorded. Five-minute ECoG epochs were collected 5 min before, at 5 min, 4, 8, 12, and 16 h after MCAo, and before, during, and after SDs. Power spectra were decomposed into fast (alpha, beta, and gamma) and slow (delta and theta) frequency bands.

Results

In the vascular insulted hemisphere under normothermia, electrodes near the ischemic core exhibited power decay across all frequency bands at 5 min and the 4th hour after MCAo. The same pattern was registered in the two furthest electrodes at the 12th and 16th hour. When mild hypothermia was applied in the vascular insulted hemispheres, the power decay was generalized and seen even in electrodes with uncompromised blood flow. During SD analysis, hypothermia maintained increased delta and beta power during the three phases of SDs in the furthest electrode from the ischemic core, followed by the second furthest and third electrode in the beta band during preSD and postSD segments. However, in hypothermic conditions, the third electrode showed lower delta, theta, and alpha power.

Conclusion

Mild hypothermia attenuates all frequency bands in the vascularly compromised hemisphere, irrespective of the cortical location. During SD formation, it preserves power spectra more significantly in electrodes further from the ischemic core.

Cortical spreading depolarization-induced constriction of penetrating arteries can cause watershed ischemia: A potential mechanism for white matter lesions

Periventricular white matter lesions (WMLs) are common MRI findings in migraine with aura (MA). Although hemodynamic disadvantages of vascular supply to this region create vulnerability, the pathophysiological mechanisms causing WMLs are unclear. We hypothesize that prolonged oligemia, a consequence of cortical spreading depolarization (CSD) underlying migraine aura, may lead to ischemia/hypoxia at hemodynamically vulnerable watershed zones fed by long penetrating arteries (PAs). For this, we subjected mice to KCl-triggered single or multiple CSDs. We found that post-CSD oligemia was significantly deeper at medial compared to lateral cortical areas, which induced ischemic/hypoxic changes at watershed areas between the MCA/ACA, PCA/anterior choroidal and at the tip of superficial and deep PAs, as detected by histological and MRI examination of brains 2-4 weeks after CSD. BALB-C mice, in which MCA occlusion causes large infarcts due to deficient collaterals, exhibited more profound CSD-induced oligemia and were more vulnerable compared to Swiss mice such that a single CSD was sufficient to induce ischemic lesions at the tip of PAs. In conclusion, CSD-induced prolonged oligemia has potential to cause ischemic/hypoxic injury at hemodynamically vulnerable brain areas, which may be one of the mechanisms underlying WMLs located at the tip of medullary arteries seen in MA patients.

Balanced volatile sedation with isoflurane in critically ill patients with aneurysmal subarachnoid hemorrhage - a retrospective observational study

Introduction

In patients with severe aneurysmal subarachnoid hemorrhage (SAH) deep sedation is often used early in the course of the disease in order to control brain edema formation and thus intracranial hypertension. However, some patients do not reach an adequate sedation depth despite high doses of common intravenous sedatives. Balanced sedation protocols incorporating low-dose volatile isoflurane administration might improve insufficient sedation depth in these patients.

Methods

We retrospectively analyzed ICU patients with severe aneurysmal SAH who received isoflurane in addition to intravenous anesthetics in order to improve insufficient sedation depth. Routinely recorded data from neuromonitoring, laboratory and hemodynamic parameters were compared before and up to 6 days after initiation of isoflurane.

Results

Sedation depth measured using the bispectral index improved in thirty-six SAH patients (-15.16; p = 0.005) who received additional isoflurane for a mean period of 9.73 ± 7.56 days. Initiation of isoflurane sedation caused a decline in mean arterial pressure (-4.67 mmHg; p = 0.014) and cerebral perfusion pressure (-4.21 mmHg; p = 0.013) which had to be balanced by increased doses of vasopressors. Patients required increased minute ventilation in order to adjust for the increase in PaCO₂ (+2.90 mmHg; p < 0.001). We did not detect significant increases in mean intracranial pressure. However, isoflurane therapy had to be terminated prematurely in 25% of the patients after a median of 30 h due to episodes of intracranial hypertension or refractory hypercapnia.

Discussion

A balanced sedation protocol including isoflurane is feasible for SAH patients experiencing inadequately shallow sedation. However, therapy should be restricted to patients without impaired lung function, hemodynamic instability and impending intracranial hypertension.

Nonpharmacological modulation of cortical spreading depolarization

AIMS

Cortical spreading depolarization (CSD) is a wave of pathologic neuronal dysfunction that spreads through cerebral gray matter, causing neurologic disturbance in migraine and promoting lesion development in acute brain injury. Pharmacologic interventions have been found to be effective in migraine with aura, but their efficacy in acutely injured brains may be limited. This necessitates the assessment of possible adjunctive treatments, such as nonpharmacologic methods. This review aims to summarize currently available nonpharmacological techniques for modulating CSDs, present their mechanisms of action, and provide insight and future directions for CSD treatment.

MAIN METHODS

A systematic literature review was performed, generating 22 articles across 3 decades. Relevant data is broken down according to method of treatment.

KEY FINDINGS

Both pharmacologic and nonpharmacologic interventions can mitigate the pathological impact of CSDs via shared molecular mechanisms, including modulating K⁺/Ca²⁺/Na⁺/Cl^- ion channels and NMDA, GABA_A, serotonin, and CGRP ligand-based receptors and decreasing microglial activation. Preclinical evidence suggests that nonpharmacologic interventions, including neuromodulation, physical exercise, therapeutic hypothermia, and lifestyle changes can also target unique mechanisms, such as increasing adrenergic tone and myelination and modulating membrane fluidity, which may lend broader modulatory effects. Collectively, these mechanisms increase the electrical initiation threshold, increase CSD latency, slow CSD velocity, and decrease CSD amplitude and duration.

SIGNIFICANCE

Given the harmful consequences of CSDs, limitations of current pharmacological interventions to inhibit CSDs in acutely injured brains, and translational potentials of nonpharmacologic interventions to modulate CSDs, further assessment of nonpharmacologic modalities and their mechanisms to mitigate CSD-related neurologic dysfunction is warranted.

Spatial and temporal frequency band changes during infarct induction, infarct progression, and spreading depolarizations in the gyrencephalic brain

Aim

To describe the spatial and temporal electrocorticographic (ECoG) changes after middle cerebral artery occlusion (MCAo), including those caused by spreading depolarization (SD) in the pig brain.

Methods

The left middle cerebral arteries (MCAs) were clipped in six pigs. The clipping procedure lasted between 8 and 12 min, achieving a permanent occlusion (MCAo). Five-contact ECoG stripes were placed bilaterally over the frontoparietal cortices corresponding to the irrigation territory of the MCA and anterior cerebral artery (ACA). ECoG recordings were performed around 24 h: 1 h before and 23 h after the MCAo, and SDs were quantified. Five-minute ECoG signal segments were sampled before, 5 min, and 4, 8, and 12 h after cerebral artery occlusion and before, during, and after the negative direct current shift of the SDs. The power spectrum of the signals was decomposed into delta, theta, alpha, beta, and gamma bands. Descriptive statistics, Wilcoxon matched-pairs signed-rank tests, and Friedman tests were performed.

Results

Electrodes close to the MCAo showed instant decay in all frequency bands and SD onset during the first 5 h. Electrodes far from the MCAo exhibited immediate loss of fast frequencies and progressive decline of slow frequencies with an increased SD incidence between 6 and 14 h. After 8 h, the ACA electrode reported a secondary reduction of all frequency bands except gamma and high SD incidence within 12-17 h. During the SD, all electrodes showed a decline in all frequency bands. After SD passage, frequency band recovery was impaired only in MCA electrodes.

Conclusion

ECoG can identify infarct progression and secondary brain injury. Severe disturbances in all the frequency bands are generated in the cortices where the SDs are passing by.

Cortical spreading depression induces propagating activation of the thalamus ventral posteromedial nucleus in awake mice

Background

As the relay centre for processing sensory information, the thalamus may involve in the abnormal sensory procedure caused by cortical spreading depression (CSD). However, few studies have focused on the transient response of thalamus during CSD. Our study aimed to investigate the neuronal activity of mouse thalamus ventral posteromedial nucleus (VPM) during CSD by in vivo micro-endoscopic fluorescence imaging of the genetic calcium probe GCaMP6s expressed in excitatory glutamatergic neurons.

Methods

Thirty-four transgenic VGluT2-GCaMP6s mice were used in the experiments. An endoscope was inserted into the VPM for image acquisition. CSD was induced by KCl topically applied unilaterally on the cranial dura. Data were acquired in awake (ipsilateral or contralateral VPM, saline instead of KCl, MK-801 treatment) and anaesthetized (isoflurane, pentobarbital) states. Statistical analysis was performed using analysis of variance (ANOVA) by SPSS.

Results

We found that after CSD induced in ipsilateral motor cortex, the neuronal activity increased and propagated from the posterior-lateral to the anterior-medial part of the VPM with an average speed of 3.47 mm/min. When CSD was induced in visual cortex, the response propagated in opposite direction, from the anterior-medial to the posterior-lateral part of the VPM. Aanaesthetics resulted in the suppression of VPM activation induced by CSD. No significant VPM activation was detected when CSD was induced in contralateral cortex or KCl was replaced by saline. When 5 mM MK-801 was applied to the dura, the electrode failed to record the DC shift of CSD, and there was no significant VPM activation after KCl application.

Conclusion

CSD induced propagating activation of the ipsilateral VPM in awake mice. The response might correlate to the cortical location where CSD was induced and might be affected by anaesthetics. No significant VPM activation was detected in saline and mk801 experiment results indicated that this VPM activation is due to CSD rather than mouse motion or direct effect of the KCl applying to the intact dura. This finding suggests the potential involvement of thalamus in the migraine auras.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-021-01370-z.

Brainstem and Cortical Spreading Depolarization in a Closed Head Injury Rat Model

Traumatic brain injury (TBI) is the leading cause of death in young individuals, and is a major health concern that often leads to long-lasting complications. However, the electrophysiological events that occur immediately after traumatic brain injury, and may underlie impact outcomes, have not been fully elucidated. To investigate the electrophysiological events that immediately follow traumatic brain injury, a weight-drop model of traumatic brain injury was used in rats pre-implanted with epidural and intracerebral electrodes. Electrophysiological (near-direct current) recordings and simultaneous alternating current recordings of brain activity were started within seconds following impact. Cortical spreading depolarization (SD) and SD-induced spreading depression occurred in approximately 50% of mild and severe impacts. SD was recorded within three minutes after injury in either one or both brain hemispheres. Electrographic seizures were rare. While both TBI- and electrically induced SDs resulted in elevated oxidative stress, TBI-exposed brains showed a reduced antioxidant defense. In severe TBI, brainstem SD could be recorded in addition to cortical SD, but this did not lead to the death of the animals. Severe impact, however, led to immediate death in 24% of animals, and was electrocorticographically characterized by non-spreading depression (NSD) of activity followed by terminal SD in both cortex and brainstem.

Effects of Volatile Anesthetics on Postoperative Ischemic Stroke Incidence

Background

Preclinical studies suggest that volatile anesthetics decrease infarct volume and improve the outcome of ischemic stroke. This study aims to determine their effect during noncardiac surgery on postoperative ischemic stroke incidence.

Methods and Results

This was a retrospective cohort study of surgical patients undergoing general anesthesia at 2 tertiary care centers in Boston, MA, between October 2005 and September 2017. Exclusion criteria comprised brain death, age <18 years, cardiac surgery, and missing covariate data. The exposure was defined as median age‐adjusted minimum alveolar concentration of all intraoperative measurements of desflurane, sevoflurane, and isoflurane. The primary outcome was postoperative ischemic stroke within 30 days. Among 314 932 patients, 1957 (0.6%) experienced the primary outcome. Higher doses of volatile anesthetics had a protective effect on postoperative ischemic stroke incidence (adjusted odds ratio per 1 minimum alveolar concentration increase 0.49, 95% CI, 0.40–0.59, P<0.001). In Cox proportional hazards regression, the effect was observed for 17 postoperative days (postoperative day 1: hazard ratio (HR), 0.56; 95% CI, 0.48–0.65; versus day 17: HR, 0.85; 95% CI, 0.74–0.99). Volatile anesthetics were also associated with lower stroke severity: Every 1‐unit increase in minimum alveolar concentration was associated with a 0.006‐unit decrease in the National Institutes of Health Stroke Scale (95% CI, −0.01 to −0.002, P=0.002). The effects were robust throughout various sensitivity analyses including adjustment for anesthesia providers as random effect.

Conclusions

Among patients undergoing noncardiac surgery, volatile anesthetics showed a dose‐dependent protective effect on the incidence and severity of early postoperative ischemic stroke.

The role of spreading depolarizations and electrographic seizures in early injury progression of the rat photothrombosis stroke model

Spreading depolarization (SD) and seizures are pathophysiological events associated with cerebral ischemia. Here, we investigated their role for injury progression in the cerebral cortex. Cerebral ischemia was induced in anesthetized male Wistar rats using the photothrombosis (PT) stroke model. SD and spontaneous neuronal activity were recorded in the presence of either urethane or ketamine/xylazine anesthesia. Blood-brain barrier (BBB) permeability, cerebral perfusion, and cellular damage were assessed through a cranial window and repeated intravenous injection of fluorescein sodium salt and propidium iodide until 4 h after PT. Neuronal injury and early lesion volume were quantified by stereological cell counting and manual and automated assessment of ex vivo T2-weighted magnetic resonance imaging. Onset SDs originated at the thrombotic core and invaded neighboring cortex, whereas delayed SDs often showed opposite propagation patterns. Seizure induction by 4-aminopyridine caused no increase in lesion volume or neuronal injury in urethane-anesthetized animals. Ketamine/xylazine anesthesia was associated with a lower number of onset SDs, reduced lesion volume, and neuronal injury despite a longer duration of seizures. BBB permeability increase inversely correlated with the number of SDs at 3 and 4 h after PT. Our results provide further evidence that ketamine may counteract the early progression of ischemic injury.

Real-time in vivo imaging of extracellular ATP in the brain with a hybrid-type fluorescent sensor

Adenosine 5' triphosphate (ATP) is a ubiquitous extracellular signaling messenger. Here, we describe a method for in-vivo imaging of extracellular ATP with high spatiotemporal resolution. We prepared a comprehensive set of cysteine-substitution mutants of ATP-binding protein, Bacillus FoF1-ATP synthase ε subunit, labeled with small-molecule fluorophores at the introduced cysteine residue. Screening revealed that the Cy3-labeled glutamine-105 mutant (Q105C-Cy3; designated ATPOS) shows a large fluorescence change in the presence of ATP, with submicromolar affinity, pH-independence, and high selectivity for ATP over ATP metabolites and other nucleotides. To enable in-vivo validation, we introduced BoNT/C-Hc for binding to neuronal plasma membrane and Alexa Fluor 488 for ratiometric measurement. The resulting ATPOS complex binds to neurons in cerebral cortex of living mice, and clearly visualized a concentrically propagating wave of extracellular ATP release in response to electrical stimulation. ATPOS should be useful to probe the extracellular ATP dynamics of diverse biological processes in vivo.

Therapeutic implications of cortical spreading depression models in migraine

Migraine is among the most common and disabling neurological diseases in the world. Cortical spreading depression (CSD) is a wave of near-complete depolarization of neurons and glial cells that slowly propagates along the cortex creating the perception of aura. Evidence suggests that CSD can trigger migraine headache. Experimental models of CSD have been considered highly translational as they recapitulate migraine-related phenomena and have been validated for screening migraine therapeutics. Here we outline the essential components of validated experimental models of CSD and provide a comprehensive review of potential modulators and targets against CSD. We further focus on novel interventions that have been recently shown to suppress CSD susceptibility that may lead to therapeutic targets in migraine.

Sedatives in neurocritical care: an update on pharmacological agents and modes of sedation

PURPOSE OF REVIEW

In this article, the specific and general indications for sedatives in the neurocritical care unit are discussed, together with an overview on current insights in sedative protocols for these patients. In addition, physiological effects of sedative agents on the central nervous system are reviewed.

RECENT FINDINGS

In the general ICU population, a large body of evidence supports light protocolized sedation over indiscriminate deep sedation. Unfortunately, in patients with severe acute brain injury, the evidence from randomized controlled trials is scarce to nonexistent, and practice is supported by expert opinion, physiological studies and observational or small interventional trials. The different sedatives each have different beneficial effects and side-effects.

SUMMARY

Extrapolating the findings from studies in the general ICU population suggests to reserve deep continuous sedation in the neuro-ICU for specific indications. Although an improved understanding of cerebral physiological changes in patients with brain injury may be helpful to guide individualized sedation, we still lack the evidence base to make broad recommendations for specific patient groups.

Na+/K+-ATPase α isoform deficiency results in distinct spreading depolarization phenotypes

Compromised Na⁺/K⁺-ATPase function is associated with the occurrence of spreading depolarization (SD). Mutations in ATP1A2, the gene encoding the α2 isoform of the Na⁺/K⁺-ATPase, were identified in patients with familial hemiplegic migraine type 2 (FHM2), a Mendelian model disease for SD. This suggests a distinct role for the α2 isoform in modulating SD susceptibility and raises questions about underlying mechanisms including the roles of other Na⁺/K⁺-ATPase α isoforms. Here, we investigated the effects of genetic ablation and pharmacological inhibition of α1, α2, and α3 on SD using heterozygous knock-out mice. We found that only α2 heterozygous mice displayed higher SD susceptibility when challenged with prolonged extracellular high potassium concentration ([K⁺]_o), a pronounced post SD oligemia and higher SD speed in-vivo. By contrast, under physiological [K⁺]_o, α2 heterozygous mice showed similar SD susceptibility compared to wild-type littermates. Deficiency of α3 resulted in increased resistance against electrically induced SD in-vivo, whereas α1 deficiency did not affect SD. The results support important roles of the α2 isoform in SD. Moreover, they suggest that specific experimental conditions can be necessary to reveal an inherent SD phenotype by driving a (meta-) stable system into decompensation, reminiscent of the episodic nature of SDs in various diseases.

Spreading Depolarizations Occur in Mild Traumatic Brain Injuries and Are Associated with Postinjury Behavior

Millions of people suffer mild traumatic brain injuries (mTBIs) every year, and there is growing evidence that repeated injuries can result in long-term pathology. The acute symptoms of these injuries may or may not include the loss of consciousness but do include disorientation, confusion, and/or the inability to concentrate. Most of these acute symptoms spontaneously resolve within a few hours or days. However, the underlying physiological and cellular mechanisms remain unclear. Spreading depolarizations (SDs) are known to occur in rodents and humans following moderate and severe TBIs, and SDs have long been hypothesized to occur in more mild injuries. Using a closed skull impact model, we investigated the presence of SDs immediately following a mTBI. Animals remained motionless for multiple minutes following an impact and once recovered had fewer episodes of movement. We recorded the defining electrophysiological properties of SDs, including the large extracellular field potential shifts and suppression of high-frequency cortical activity. Impact-induced SDs were also associated with a propagating wave of reduced cerebral blood flow (CBF). In the wake of the SD, there was a prolonged period of reduced CBF that recovered in approximately 90 min. Similar to SDs in more severe injuries, the impact-induced SDs could be blocked with ketamine. Interestingly, impacts at a slower velocity did not produce the prolonged immobility and did not initiate SDs. Our data suggest that SDs play a significant role in mTBIs and SDs may contribute to the acute symptoms of mTBIs.

Spreading Depolarization Waves in Neurological Diseases: A Short Review about its Pathophysiology and Clinical Relevance

Lesion growth following acutely injured brain tissue after stroke, subarachnoid hemorrhage and traumatic brain injury is an important issue and a new target area for promising therapeutic interventions. Spreading depolarization or peri-lesion depolarization waves were demonstrated as one of the significant contributors of continued lesion growth. In this short review, we discuss the pathophysiology for SD forming events and try to list findings detected in neurological disorders like migraine, stroke, subarachnoid hemorrhage and traumatic brain injury in both human as well as experimental studies. Pharmacological and non-pharmacological treatment strategies are highlighted and future directions and research limitations are discussed.

The effect of anesthetic agents on cerebral vasospasms after subarachnoid hemorrhage: A retrospective study

Cerebral vasospasm is the most important cause of morbidity after an aneurysm clipping in the early postoperative period. The aim of this retrospective study was to evaluate whether the incidence of vasospasms differs when using propofol or desflurane for an emergent aneurysm clipping.The data from 102 patients (50 in the propofol group, 52 in the desflurane group) were analyzed. The occurrence of vasospasm based on daily transcranial Doppler, angiography, and cerebral infarction during 14 days after surgery were compared by anesthetic agents. Postoperative data including Glasgow Coma Scale (GCS) score on day 14 after surgery, and the Glasgow Outcome Scale (GOS) score at 3 months were documented.Patients that intraoperatively received propofol for anesthesia maintenance, had higher incidence of transcranial Doppler (TCD)-evident vasospasm than those that received desflurane (54% vs 30.8%, P = .027). The occurrence of TCD-evident vasospasm was still higher (odds ratio: 2.84; 95% confidence interval: 1.12-7.20) in the propofol group than in the desflurane group after adjusting for confounding factors. However, the incidence of angiographic vasospasm, cerebral infarction, and interventions to treat cerebral vasospasms were similar between both groups. GCS score on day 14 after surgery and the GOS score at 3 months were similar between groups.No effect of anesthetic agents on angiographic vasospasm, cerebral infarction, or clinical outcome was observed, whereas desflurane anesthesia was associated with a lower incidence of TCD-evident vasospasms compared to propofol anesthesia. Our study provides a basis for further randomized controlled studies in a larger patient population to clarify the effects of anesthetic agents on the occurrence of cerebral vasospasms.

Systematic review of the pharmacological agents that have been tested against spreading depolarizations

Spreading depolarization (SD) occurs alongside brain injuries and it can lead to neuronal damage. Therefore, pharmacological modulation of SD can constitute a therapeutic approach to reduce its detrimental effects and to improve the clinical outcome of patients. The major objective of this article was to produce a systematic review of all the drugs that have been tested against SD. Of the substances that have been examined, most have been shown to modulate certain SD characteristics. Only a few have succeeded in significantly inhibiting SD. We present a variety of strategies that have been proposed to overcome the notorious harmfulness and pharmacoresistance of SD. Information on clinically used anesthetic, sedative, hypnotic agents, anti-migraine drugs, anticonvulsants and various other substances have been compiled and reviewed with respect to the efficacy against SD, in order to answer the question of whether a drug at safe doses could be of therapeutic use against SD in humans.

Spreading depolarization monitoring in neurocritical care of acute brain injury

PURPOSE OF REVIEW

Spreading depolarizations are unique in being discrete pathologic entities that are well characterized experimentally and also occur commonly in patients with substantial acute brain injury. Here, we review essential concepts in depolarization monitoring, highlighting its clinical significance, interpretation, and future potential.

RECENT FINDINGS

Cortical lesion development in diverse animal models is mediated by tissue waves of mass spreading depolarization that cause the toxic loss of ion homeostasis and limit energy substrate supply through associated vasoconstriction. The signatures of such deterioration are observed in electrocorticographic recordings from perilesional cortex of patients with acute stroke or brain trauma. Experimental work suggests that depolarizations are triggered by energy supply-demand mismatch in focal hotspots of the injury penumbra, and depolarizations are usually observed clinically when other monitoring variables are within recommended ranges. These results suggest that depolarizations are a sensitive measure of relative ischemia and ongoing secondary injury, and may serve as a clinical guide for personalized, mechanistically targeted therapy. Both existing and future candidate therapies offer hope to limit depolarization recurrence.

SUMMARY

Electrocorticographic monitoring of spreading depolarizations in patients with acute brain injury provides a sensitive measure of relative energy shortage in focal, vulnerable brains regions and indicates ongoing secondary damage. Depolarization monitoring holds potential for targeted clinical trial design and implementation of precision medicine approaches to acute brain injury therapy.

Absence of Neuropathology With Prolonged Isoflurane Sedation in Healthy Adult Rats

BACKGROUND

The use of isoflurane sedation for prolonged periods in the critical care environment is increasing. However, isoflurane-mediated neurotoxicity has been widely reported. The goal of the present study was to determine whether long-term exposure to low-dose isoflurane in mechanically ventilated rodents is associated with evidence of neurodegeneration or neuroinflammation.

METHODS

Adult female Sprague-Dawley rats were used in this study. Experimental animals (n=11) were induced with 1.5% isoflurane, intubated, and given a neuromuscular blockade with α-cobratoxin. EEG electrodes were surgically implanted, subcutaneous precordial EKG Ag wire electrodes, and bladder, femoral artery, and femoral vein cannulas permanently placed. After these procedures, the isoflurane concentration was reduced to 0.5% and, in conjunction with the neuromuscular blockade, continued for 7 days. Arterial blood gases and chemistry were measured at 3 time points and core body temperature servoregulated and maintenance IV fluids were given during the 7 days. Experimental animals and untreated controls (n=9) were euthanized on day 7.

RESULTS

Immunohistochemical and cytochemical assays did not detect evidence of microgliosis, astrocytosis, neuronal apoptosis or necrosis, amyloidosis, or phosphorylated-tau accumulation. Blood glucose levels were significantly reduced on days 3/4 and 6/7 and partial pressure of oxygen was significantly reduced, but still within the normal range, on day 6/7. All other blood measurements were unchanged.

CONCLUSIONS

No neuropathologic changes consistent with neurotoxicity were detected in the brain after 1 week of continuous exposure to 0.5% isoflurane in healthy rats. These data suggest that even long exposures to low concentrations of isoflurane have no overt consequences on neuropathology.

Comparison of volatile anesthetic-induced preconditioning in cardiac and cerebral system: molecular mechanisms and clinical aspects

Volatile anesthetic-induced preconditioning (APC) has shown to have cardiac and cerebral protective properties in both pre-clinical models and clinical trials. Interestingly, accumulating evidences demonstrate that, except from some specific characters, the underlying molecular mechanisms of APC-induced protective effects in myocytes and neurons are very similar; they share several major intracellular signaling pathways, including mediating mitochondrial function, release of inflammatory cytokines and cell apoptosis. Among all the experimental results, cortical spreading depolarization is a relative newly discovered cellular mechanism of APC, which, however, just exists in central nervous system. Applying volatile anesthetic preconditioning to clinical practice seems to be a promising cardio-and neuroprotective strategy. In this review, we also summarized and discussed the results of recent clinical research of APC. Despite all the positive experimental evidences, large-scale, long-term, more precisely controlled clinical trials focusing on the perioperative use of volatile anesthetics for organ protection are still needed.

Toxicity of inhaled agents after prolonged administration

Inhaled anesthetics have been utilized mostly for general anesthesia in the operating room and oftentimes for sedation and for treatment of refractory status epilepticus and status asthmaticus in the intensive care unit. These contexts in the ICU setting are related to potential for prolonged administration wherein potential organ toxicity is a concern. Over the last decade, several clinical and animal studies of neurotoxicity attributable to inhaled anesthetics have been emerging, particularly in extremes of age. This review overviews potential for and potential mechanisms of neurotoxicity and systemic toxicity of prolonged inhaled anesthesia and clinical scenarios where inhaled anesthesia has been used in order to assess safety of possible prolonged use for sedation. High dose inhaled agents are associated with postoperative cognitive dysfunction (POCD) and other situations. However, thus far no strong indication of problematic neuro or organ toxicity has been demonstrated after prolonged use of low dose volatile anesthesia.

Novel Therapeutic Targets Against Spreading Depression

Migraine is among the most prevalent and disabling neurological diseases in the world. Cortical spreading depression (SD) is an intense wave of neuronal and glial depolarization underlying migraine aura, and a headache trigger, which has been used as an experimental platform for drug screening in migraine. Here, we provide an overview of novel therapeutic targets that show promise to suppress SD, such as acid-sensing ion channels, casein kinase Iδ, P2X7-pannexin 1 complex, and neuromodulation, and outline the experimental models and essential quality measures for rigorous and reproducible efficacy testing.

Altered hypermetabolic response to cortical spreading depolarizations after traumatic brain injury in rats

Spreading depolarizations are waves of near-complete breakdown of neuronal transmembrane ion gradients, free energy starving, and mass depolarization. Spreading depolarizations in electrically inactive tissue are associated with poor outcome in patients with traumatic brain injury. Here, we studied changes in regional cerebral blood flow and brain oxygen (PbtO2), glucose ([Glc]b), and lactate ([Lac]b) concentrations in rats, using minimally invasive real-time sensors. Rats underwent either spreading depolarizations chemically triggered by KCl in naïve cortex in absence of traumatic brain injury or spontaneous spreading depolarizations in the traumatic penumbra after traumatic brain injury, or a cluster of spreading depolarizations triggered chemically by KCl in a remote window from which spreading depolarizations invaded penumbral tissue. Spreading depolarizations in noninjured cortex induced a hypermetabolic response characterized by a decline in [Glc]b and monophasic increases in regional cerebral blood flow, PbtO2, and [Lac]b, indicating transient hyperglycolysis. Following traumatic brain injury, spontaneous spreading depolarizations occurred, causing further decline in [Glc]b and reducing the increase in regional cerebral blood flow and biphasic responses of PbtO2 and [Lac]b, followed by prolonged decline. Recovery of PbtO2 and [Lac]b was significantly delayed in traumatized animals. Prespreading depolarization [Glc]b levels determined the metabolic response to clusters. The results suggest a compromised hypermetabolic response to spreading depolarizations and slower return to physiological conditions following traumatic brain injury-induced spreading depolarizations.

In vivo imaging reveals that pregabalin inhibits cortical spreading depression and propagation to subcortical brain structures

Migraine is characterized by severe headaches that can be preceded by an aura likely caused by cortical spreading depression (SD). The antiepileptic pregabalin (Lyrica) shows clinical promise for migraine therapy, although its efficacy and mechanism of action are unclear. As detected by diffusion-weighted MRI (DW-MRI) in wild-type (WT) mice, the acute systemic administration of pregabalin increased the threshold for SD initiation in vivo. In familial hemiplegic migraine type 1 mutant mice expressing human mutations (R192Q and S218L) in the Ca_V2.1 (P/Q-type) calcium channel subunit, pregabalin slowed the speed of SD propagation in vivo. Acute systemic administration of pregabalin in vivo also selectively prevented the migration of SD into subcortical striatal and hippocampal regions in the R192Q strain that exhibits a milder phenotype and gain of Ca_V2.1 channel function. At the cellular level, pregabalin inhibited glutamatergic synaptic transmission differentially in WT, R192Q, and S218L mice. The study describes a DW-MRI analysis method for tracking the progression of SD and provides support and a mechanism of action for pregabalin as a possible effective therapy in the treatment of migraine.

Sedation of Patients with Acute Aneurysmal Subarachnoid Hemorrhage with Ketamine Is Safe and Might Influence the Occurrence of Cerebral Infarctions Associated with Delayed Cerebral Ischemia

BACKGROUND

Ketamine has neuroprotective characteristics as well as beneficial cardiocirculatory properties and may thus reduce vasopressor consumption. In contrast, sedation with ketamine (like any other sedative drug) has side effects. This study assesses the influence of ketamine on intracranial pressure (ICP), on the consumption of vasopressors in induced hypertension therapy, and on the occurrence of delayed cerebral ischemia (DCI)-associated cerebral infarctions, with particular focus on the complications of sedation in patients with aneurysmal subarachnoid hemorrhage (SAH).

METHODS

This is a retrospective, observational study. Sixty-five patients with SAH who underwent a period of sedation were included. The clinical course variables (Richmond Agitation and Sedation scale score, ICP values, consumption of vasopressors, complications of sedation, outcome, and other clinical parameters) were analyzed. Cranial computed tomography results were analyzed.

RESULTS

Forty-one patients underwent sedation including ketamine (63.1%). Ketamine decreased the ICP in 92.7% of the cases. Vasopressors was reduced in 53.6%. DCI-associated cerebral infarctions occurred significantly less often in the patient cohort being treated with sedation including ketamine (7.3% vs. 25% in the nonketamine group; P = 0.04). The rate of major complications was not higher in the ketamine group. Outcome was not different regarding the groups if they were sedated with or without ketamine.

CONCLUSIONS

Ketamine decreases the ICP and is not associated with a higher rate of complications. The rate of DCI-associated cerebral infarctions was lower in the ketamine group. Ketamine administration led to a reduction of vasopressors used for induced hypertension.

Anesthesia in Experimental Stroke Research

Anesthetics have enabled major advances in development of experimental models of human stroke. Yet, their profound pharmacologic effects on neural function can confound the interpretation of experimental stroke research. Anesthetics have species-, drug-, and dose-specific effects on cerebral blood flow and metabolism, neurovascular coupling, autoregulation, ischemic depolarizations, excitotoxicity, inflammation, neural networks, and numerous molecular pathways relevant for stroke outcome. Both preconditioning and postconditioning properties have been described. Anesthetics also modulate systemic arterial blood pressure, lung ventilation, and thermoregulation, all of which may interact with the ischemic insult as well as the therapeutic interventions. These confounds present a dilemma. Here, we provide an overview of the anesthetic mechanisms of action and molecular and physiologic effects on factors relevant to stroke outcomes that can guide the choice and optimization of the anesthetic regimen in experimental stroke.

Ischemia-induced spreading depolarization in the retina

Cortical spreading depolarization is a metabolically costly phenomenon that affects the brain in both health and disease. Following severe stroke, subarachnoid hemorrhage, or traumatic brain injury, cortical spreading depolarization exacerbates tissue damage and enlarges infarct volumes. It is not known, however, whether spreading depolarization also occurs in the retina in vivo. We report now that spreading depolarization episodes are generated in the in vivo rat retina following retinal vessel occlusion produced by photothrombosis. The properties of retinal spreading depolarization are similar to those of cortical spreading depolarization. Retinal spreading depolarization waves propagate at a velocity of 3.0 ± 0.1 mm/min and are associated with a negative shift in direct current potential, a transient cessation of neuronal spiking, arteriole constriction, and a decrease in tissue O2 tension. The frequency of retinal spreading depolarization generation in vivo is reduced by administration of the NMDA antagonist MK-801 and the 5-HT(1D) agonist sumatriptan. Branch retinal vein occlusion is a leading cause of vision loss from vascular disease. Our results suggest that retinal spreading depolarization could contribute to retinal damage in acute retinal ischemia and demonstrate that pharmacological agents can reduce retinal spreading depolarization frequency after retinal vessel occlusion. Blocking retinal spreading depolarization generation may represent a therapeutic strategy for preserving vision in branch retinal vein occlusion patients.

Propofol in the treatment of refractory migraine headaches

INTRODUCTION

Refractory/intractable migraine headaches are associated with chronic pain that does not respond to standard care of treatment. Propofol(2,6-diisopropylphenol) in sub-anesthetic doses has been reported to be beneficial in such patients. The present article describes the complete drug profile of propofol in the management of these super-refractory migraine headaches.

AREAS COVERED

The article covers different preclinical and clinical studies available in the literature. Expert commentary: Propofol is useful as an off-label drug molecule in an emergency situation of refractory migraines where it has been found to reduce the pain intensity. The molecule with a narrow therapeutic index and high abuse potential is prescribed only when conventional drugs fail to deliver any relief. There are not adequate double-blind crossover studies that substantiate the effectiveness of propofol in the treatment of migraine headaches. Furthermore, long-term outcomes for the use of propofol in migraine headaches requires an extensive investigation.

Peri-infarct depolarizations during focal ischemia in the awake Spontaneously Hypertensive Rat. Minimizing anesthesia confounds in experimental stroke

Anesthesia profoundly impacts peri-infarct depolarizations (PIDs), but only one prior report has described their monitoring during experimental stroke in awake animals. Since temporal patterns of PID occurrence are model specific, the current study examined PID incidence during focal ischemia in the awake Spontaneously Hypertensive Rat (SHR), and documented the impact of both prior and concurrent isoflurane anesthesia. For awake recordings, electrodes were implanted under isoflurane anesthesia 1day to 5weeks prior to occlusion surgery. Rats were then subjected to permanent or transient (2h) tandem occlusion of the middle cerebral and ipsilateral common carotid arteries, followed by PID monitoring for up to 3days. Comparison perfusion imaging studies evaluated PID-associated hyperemic transients during permanent ischemia under anesthesia at varied intervals following prior isoflurane exposure. Prior anesthesia attenuated PID number at intervals up to 1week, establishing 2weeks as a practical recovery duration following surgical preparation to avoid isoflurane preconditioning effects. PIDs in awake SHR were limited to the first 4h after permanent occlusions. Maintaining anesthesia during this interval reduced PID number, and prolonged their occurrence through several hours following anesthesia termination. Although PID number otherwise correlated with infarct size, PID suppression by anesthesia was not protective in the absence of reperfusion. PIDs persisted up to 36h after transient occlusions. These results differ markedly from the one previous report of such monitoring in awake Sprague-Dawley rats, which found an extended biphasic PID time course during 24h after both permanent and transient filament occlusions. PID occurrence closely reflects the time course of infarct progression in the respective models, and may be more useful than absolute PID number as an index of ongoing pathology.

Episodic Aphasia Associated With Cortical Spreading Depression After Subdural Hemorrhage Evacuation

Cortical spreading depression (CSD) has been associated with many pathological entities including migraine, trauma, hemorrhage, and mitochondrial disease. The clinical diagnosis remains challenging without the other concomitant features such as headache because CSD can mimic seizure or acute stroke. Wereport of a 77 year-old right handed man with a left subdural hematoma evacuation that subsequently developed episodic aphasia, slurred speech, right nasolabial fold flattening, and right pronator drift. In this case report, we discuss our multimodal diagnostic approach and treatment in a patient with episodic aphasia and neurological deficits in order to propose the diagnosis of cortical spreading depression. CSD should be considered when focal deficits in brief episodes occur after stroke and seizures have been ruled out. Treatment choices as illustrated by this case report can have an impact on outcome and resolution of episodes.

Sedation/drugs used in intensive care sedation

PURPOSE OF REVIEW

There is recognition that the use of sedative drugs in critically ill patients is potentially harmful, particularly in relation to ICU delirium and clinical outcomes. In that context, there is an increasing interest in maintaining light sedation, the use of non-gamma-aminobutyric acid agonist agents and antipsychotics.

RECENT FINDINGS

The sedative drugs currently available have limitations relating to duration of action, cost or variability in response. Recent reviews and meta-analyses comparing sedatives in ICU patients differ in their findings depending on whether trials in elective cardiac surgical patients are included. Dexmedetomidine does appear to reduce the number of ventilator days in the less sick critically ill patient. There is currently no evidence to support the routine use of antipsychotics in ICU patients to prevent or treat delirium, although they will reduce agitation and they appear to be well tolerated when used in the critically ill patient. Sedation protocols and early mobilization reduce the use of sedative drugs and improve some outcomes but are challenging to implement in practice.

SUMMARY

The bedside clinician needs to balance the need to sedate the patient and maintain life-saving support, while keeping their patient responsive, cooperative and pain free.

Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature

Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases.

Expanding applications, accuracy, and interpretation of laser speckle contrast imaging of cerebral blood flow

Laser speckle contrast imaging (LSCI) provides a rapid characterization of cortical flow dynamics for functional monitoring of the microcirculation. The technique stems from interactions of laser light with moving particles. These interactions encode the encountered Doppler phenomena within a random interference pattern imaged in widefield, known as laser speckle. Studies of neurovascular function and coupling with LSCI have benefited from the real-time characterization of functional dynamics in the laboratory setting through quantification of perfusion dynamics. While the technique has largely been relegated to acute small animal imaging, its scalability is being assessed and characterized for both chronic and clinical neurovascular imaging.

Measurement of distinctive features of cortical spreading depolarizations with different MRI contrasts

Growing clinical evidence suggests critical involvement of spreading depolarizations (SDs) in the pathophysiology of neurological disorders such as migraine and stroke. MRI provides powerful tools to detect and assess co-occurring cerebral hemodynamic and cellular changes during SDs. This study reports the feasibility and advantages of two MRI scans, based on balanced steady-state free precession (b-SSFP) and diffusion-weighted multi-spin-echo (DT2), heretofore unexplored for monitoring SDs. These were compared with gradient-echo MRI. SDs were induced by KCl application in rat brain. Known for high SNR, the T2- and T1-based b-SSFP contrast was hypothesized to provide higher spatiotemporal specificity than T2*-based gradient-echo scanning. DT2 scanning was designed to provide simultaneous T2 and apparent diffusion coefficient (ADC) measurements, thus enabling combined quantitative assessment of hemodynamic and cellular changes during SDs. Procedures were developed to automate identification of SD-induced responses in all the scans. These responses were analyzed to determine detection sensitivity and temporal characteristics of signals from each scanning method. Cluster analysis was performed to elucidate unique temporal patterns for each contrast. All scans allowed detection of SD-induced responses. b-SSFP scans showed significantly larger relative intensity changes, narrower peak widths and greater spatial specificity compared with gradient-echo MRI. SD-induced effects on ADC, calculated from DT2 scans, showed the most pronounced signal changes, displaying about 20% decrease, as against 10-15% signal increases observed with b-SSFP and gradient-echo scanning. Cluster analysis revealed additional temporal sub-patterns, such as an initial dip on gradient-echo scans and temporally shifted T2 and proton density changes in DT2 data. To summarize, b-SSFP and DT2 scanning provide distinct information on SDs compared with gradient-echo MRI. DT2 scanning, with its potential to simultaneously provide cellular and hemodynamic information, can offer unique information on the inter-relationship between these processes in pathologic brain, which may improve monitoring of spreading depolarizations in (pre)clinical settings.

Spreading depolarization-induced adenosine accumulation reflects metabolic status in vitro and in vivo

Spreading depolarization (SD), a pathologic feature of migraine, stroke and traumatic brain injury, is a propagating depolarization of neurons and glia causing profound metabolic demand. Adenosine, the low-energy metabolite of ATP, has been shown to be elevated after SD in brain slices and under conditions likely to trigger SD in vivo. The relationship between metabolic status and adenosine accumulation after SD was tested here, in brain slices and in vivo. In brain slices, metabolic impairment (assessed by nicotinamide adenine dinucleotide (phosphate) autofluorescence and O2 availability) was associated with prolonged extracellular direct current (DC) shifts indicating delayed repolarization, and increased adenosine accumulation. In vivo, adenosine accumulation was observed after SD even in otherwise healthy mice. As in brain slices, in vivo adenosine accumulation correlated with DC shift duration and increased when DC shifts were prolonged by metabolic impairment (i.e., hypoglycemia or middle cerebral artery occlusion). A striking pattern of adenosine dynamics was observed during focal ischemic stroke, with nearly all the observed adenosine signals in the periinfarct region occurring in association with SDs. These findings suggest that adenosine accumulation could serve as a biomarker of SD incidence and severity, in a range of clinical conditions.

Detecting tissue deterioration after brain injury: regional blood flow level versus capacity to raise blood flow

Regional cerebral blood flow (rCBF) is spatially and temporally adjusted to local energy needs. This coupling involves dilation of vessels both at the site of metabolite exchange and upstream of the activated region. Deficits in upstream blood supply limit the 'capacity to raise rCBF' in response to functional activation and therefore compromise brain function. We here demonstrate in rats that the 'capacity to raise rCBF' can be determined from real-time measurements of rCBF using laser speckle imaging during an energy challenge induced by cortical spreading depolarizations (CSDs). Cortical spreading depolarizations (CSDs) occur with high incidence in stroke and various other brain injuries and cause large metabolic changes. Various conditions of cerebral perfusion were induced, either by modifying microvascular tone, or by altering upstream blood supply independently. The increase in rCBF per unit of time in response to CSD was linearly correlated to the upstream blood supply. In an experimental model of stroke, we found that this marker of the capacity to raise rCBF which, in pathologic tissue may be additionally limited by impaired vasoactive signaling, was a better indicator of the functional status of cerebral tissue than local rCBF levels.

Continuous online microdialysis using microfluidic sensors: dynamic neurometabolic changes during spreading depolarization

Microfluidic glucose biosensors and potassium ion selective electrodes were used in an in vivo study to measure the neurochemical effects of spreading depolarizations (SD), which have been shown to be detrimental to the injured human brain. A microdialysis probe implanted in the cortex of rats was connected to a microfluidic PDMS chip containing the sensors. The dialysate was also analyzed using our gold standard, rapid sampling microdialysis (rsMD). The glucose biosensor performance was validated against rsMD with excellent results. The glucose biosensors successfully monitored concentration changes, in response to SD wave induction, in the range of 10-400 μM with a second time-resolution. The data show that during a SD wave, there is a time delay of 62 ± 24.8 s (n = 4) between the onset of the increase in potassium and the decrease in glucose. This delay can be for the first time demonstrated, thanks to the high-temporal resolution of the microfluidic sensors sampling from a single tissue site (the microdialysis probe), and it indicates that the decrease in glucose is due to the high demand of energy required for repolarization.