Induced hypertension for the treatment of acute MCA occlusion beyond the thrombolysis window: case report

Anesthetic Management of Emergency Endovascular Thrombectomy for Acute Ischemic Stroke, Part 1: Patient Characteristics, Determinants of Effectiveness, and Effect of Blood Pressure on Outcome

In the United States, stroke ranks fifth among all causes of death and is the leading cause of serious long-term disability. The 2018 American Heart Association stroke care guidelines consider endovascular thrombectomy to be the standard of care for patients who have acute ischemic stroke in the anterior circulation when arterial puncture can be made within 6 hours of symptom onset or within 6-24 hours of symptom onset when specific eligibility criteria are satisfied. The aim of this 2-part review is to provide practical perspective on the clinical literature regarding anesthesia care of patients treated with endovascular thrombectomy. Part 1 (this article) reviews the development of endovascular thrombectomy and the determinants of endovascular thrombectomy effectiveness irrespective of method of anesthesia. The first aim of part 1 is to explain why rapid workflow and maintenance of blood pressure are necessary to help support the ischemic brain until, as a result of endovascular thrombectomy, reperfusion is accomplished. The second aim of part 1, understanding the nonanesthesia factors determining endovascular thrombectomy effectiveness, is necessary to identify numerous biases present in observational reports regarding anesthesia for endovascular thrombectomy. With this background, in part 2 (the companion to this article), the observational literature is briefly summarized, largely to identify its weaknesses, but also to develop hypotheses derived from it that have been recently tested in 3 randomized clinical trials of sedation versus general anesthesia for endovascular thrombectomy. In part 2, these 3 trials are reviewed both from a functional outcomes perspective (meta-analysis) and a methodological perspective, providing specifics regarding anesthesia and hemodynamic management. Part 2 concludes with a pragmatic approach to anesthesia decision making (sedation versus general anesthesia) and acute phase anesthesia management of patients treated with endovascular thrombectomy.

Blood-brain barrier breakdown and neovascularization processes after stroke and traumatic brain injury

PURPOSE OF REVIEW

Angiogenesis or vascular reorganization plays a role in recovery after stroke and traumatic brain injury (TBI). In this review, we have focused on two major events that occur during stroke and TBI from a vascular perspective - what is the process and time course of blood-brain barrier (BBB) breakdown? and how does the surrounding vasculature recover and facilitate repair?

RECENT FINDINGS

Despite differences in the primary injury, the BBB changes overlap between stroke and TBI. Disruption of BBB involves a series of events: formation of caveolae, trans and paracellular disruption, tight junction breakdown and vascular disruption. Confounding factors that need careful assessment and standardization are the severity, duration and extent of the stroke and TBI that influences BBB disruption. Vascular repair proceeds through long-term neovascularization processes: angiogenesis, arteriogenesis and vasculogenesis. Enhancing each of these processes may impart beneficial effects in endogenous recovery.

SUMMARY

Our understanding of BBB breakdown acutely after the cerebrovascular injury has come a long way; however, we lack a clear understanding of the course of BBB disruption and BBB recovery and the evolution of individual cellular events associated with BBB change. Neovascularization responses have been widely studied in stroke for their role in functional recovery but the role of vascular reorganization after TBI in recovery is much less defined.

Effects of Acute Systemic Hypoxia and Hypercapnia on Brain Damage in a Rat Model of Hypoxia-Ischemia

Therapeutic hypercapnia has the potential for neuroprotection after global cerebral ischemia. Here we further investigated the effects of different degrees of acute systemic hypoxia in combination with hypercapnia on brain damage in a rat model of hypoxia and ischemia. Adult wistar rats underwent unilateral common carotid artery (CCA) ligation for 60 min followed by ventilation with normoxic or systemic hypoxic gas containing 11%O2,13%O2,15%O2 and 18%O2 (targeted to PaO2 30-39 mmHg, 40-49 mmHg, 50-59 mmHg, and 60-69 mmHg, respectively) or systemic hypoxic gas containing 8% carbon dioxide (targeted to PaCO2 60-80 mmHg) for 180 min. The mean artery pressure (MAP), blood gas, and cerebral blood flow (CBF) were evaluated. The cortical vascular permeability and brain edema were examined. The ipsilateral cortex damage and the percentage of hippocampal apoptotic neurons were evaluated by Nissl staining and terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling (TUNEL) assay as well as flow cytometry, respectively. Immunofluorescence and western blotting were performed to determine aquaporin-4 (AQP4) expression. In rats treated with severe hypoxia (PaO2 < 50 mmHg), hypercapnia augmented the decline of MAP with cortical CBF and damaged blood-brain barrier permeability (p < 0.05). In contrast, in rats treated with mild to moderate hypoxia (PaO2 > 50 mmHg), hypercapnia protected against these pathophysiological changes. Moreover, hypercapnia treatment significantly reduced brain damage in the ischemic ipsilateral cortex and decreased the percentage of apoptotic neurons in the hippocampus after the CCA ligated rats were exposed to mild or moderate hypoxemia (PaO2 > 50 mmHg); especially under mild hypoxemia (PaO2 > 60 mmHg), hypercapnia significantly attenuated the expression of AQP4 protein with brain edema (p < 0.05). Hypercapnia exerts beneficial effects under mild to moderate hypoxemia and augments detrimental effects under severe hypoxemia on brain damage in a rat model of hypoxia-ischemia.

Cerebral collaterals and collateral therapeutics for acute ischemic stroke

Cerebral collaterals are vascular redundancies in the cerebral circulation that can partially maintain blood flow to ischemic tissue when primary conduits are blocked. After occlusion of a cerebral artery, anastomoses connecting the distal segments of the MCA with distal branches of the ACA and PCA (known as leptomeningeal or pial collaterals) allow for partially maintained blood flow in the ischemic penumbra and delay or prevent cell death. However, collateral circulation varies dramatically between individuals, and collateral extent is significant predictor of stroke severity and recanalization rate. Collateral therapeutics attempt to harness these vascular redundancies by enhancing blood flow through pial collaterals to reduce ischemia and brain damage after cerebral arterial occlusion. While therapies to enhance collateral flow remain relatively nascent neuroprotective strategies, experimental therapies including inhaled NO, transient suprarenal aortic occlusion, and electrical stimulation of the parasympathetic sphenopalatine ganglion show promise as collateral therapeutics with the potential to improve treatment of acute ischemic stroke.

Augmenting collateral blood flow during ischemic stroke via transient aortic occlusion

Collateral circulation provides an alternative route for blood flow to reach ischemic tissue during a stroke. Blood flow through the cerebral collaterals is a critical predictor of clinical prognosis after stroke and response to recanalization, but data on collateral dynamics and collateral therapeutics are lacking. Here, we investigate the efficacy of a novel approach to collateral blood flow augmentation to increase collateral circulation by optically recording blood flow in leptomeningeal collaterals in a clinically relevant model of ischemic stroke. Using high-resolution laser speckle contrast imaging (LSCI) during thromboembolic middle cerebral artery occlusion (MCAo), we demonstrate that transiently diverting blood flow from peripheral circulation towards the brain via intra-aortic catheter and balloon induces persistent increases in blood flow through anastomoses between the anterior and middle cerebral arteries. Increased collateral flow restores blood flow in the distal middle cerebral artery segments to baseline levels during aortic occlusion and persists for over 1 hour after removal of the aortic balloon. Given the importance of collateral circulation in predicting stroke outcome and response to treatment, and the potential of collateral flow augmentation as an adjuvant or stand-alone therapy for acute ischemic stroke, this data provide support for further development and translation of collateral therapeutics including transient aortic occlusion.

Vascular remodeling after ischemic stroke: mechanisms and therapeutic potentials

The brain vasculature has been increasingly recognized as a key player that directs brain development, regulates homeostasis, and contributes to pathological processes. Following ischemic stroke, the reduction of blood flow elicits a cascade of changes and leads to vascular remodeling. However, the temporal profile of vascular changes after stroke is not well understood. Growing evidence suggests that the early phase of cerebral blood volume (CBV) increase is likely due to the improvement in collateral flow, also known as arteriogenesis, whereas the late phase of CBV increase is attributed to the surge of angiogenesis. Arteriogenesis is triggered by shear fluid stress followed by activation of endothelium and inflammatory processes, while angiogenesis induces a number of pro-angiogenic factors and circulating endothelial progenitor cells (EPCs). The status of collaterals in acute stroke has been shown to have several prognostic implications, while the causal relationship between angiogenesis and improved functional recovery has yet to be established in patients. A number of interventions aimed at enhancing cerebral blood flow including increasing collateral recruitment are under clinical investigation. Transplantation of EPCs to improve angiogenesis is also underway. Knowledge in the underlying physiological mechanisms for improved arteriogenesis and angiogenesis shall lead to more effective therapies for ischemic stroke.

Case of “Slow” Stroke from Carotid Artery Occlusion Treated by Delayed but Cautious Endovascular Intervention

In a challenging case of carotid occlusion with slowly evolving stroke, we used brain imaging to facilitate endovascular revascularization resulting in the relief of the patient's symptoms. Patients with carotid occlusion and continued neurological worsening or fluctuations present enormous treatment challenges. These patients may present “slow” strokes with subacute infarcts that present significant challenges and risks during attempts at revascularization of the occluded artery. We present such a case in which we used multimodal imaging techniques, including MR-perfusion, to facilitate endovascular revascularization. Our approach of delayed but cautious intra-arterial thrombolytic therapy, guided by brain imaging, and followed by stent placement across the residual stenosis, enabled revascularization of the occluded artery without overt in-hospital complications.

Hyperacute ischemic stroke management: reperfusion and evolving therapies

Management of acute ischemic stroke patients is organized around several priorities aimed at ensuring optimal patient outcomes, the first of which is reperfusion therapy, followed by determination of pathogenic mechanism by provision of a comprehensive workup to determine probable cause of the ischemic stroke or transient ischemic attack, for the purpose of providing appropriate prophylaxis for subsequent events. Provision of secondary prevention measures along with therapies that prevent complications associated with neurologic disability, and evaluation for the most appropriate level of rehabilitation services are the final priorities during acute hospitalization. This article provides an overview of reperfusion therapies and emerging hemodynamic treatments for hyperacute ischemic strokes. Gaps in the scientific evidence that are driving current blood flow augmentation research are identified.

Role of vasopressor administration in patients with acute neurologic injury

INTRODUCTION

Pharmacologic blood pressure elevation is often utilized to prevent or treat ischemia in patients with acute neurologic injury, and routinely requires administration of vasopressor agents. Depending on the indication, vasopressor agents may be administered to treat hypotension or to induce hypertension.

METHODS

Although numerous guideline statements exist regarding the management of blood pressure in these patients, most recommendations are based largely on Class III evidence. Further, there are few randomized controlled trials comparing vasopressor agents in these patients and selection is often guided by expert consensus.

RESULTS

We discuss the clinical evidence regarding vasopressor administration for blood pressure management in patients with acute neurologic injury. The effect of various vasopressors on cerebral hemodynamics is also discussed.

CONCLUSION

Although high-quality clinical data are scarce, the available evidence suggests that norepinephrine should be considered as the vasopressor of choice when blood pressure elevation is indicated in patients with acute neurologic injury.

Theoretic basis and technical implementations of CT perfusion in acute ischemic stroke, part 1: Theoretic basis

CT perfusion (CTP) is a functional imaging technique that provides important information about capillary-level hemodynamics of the brain parenchyma and is a natural complement to the strengths of unenhanced CT and CT angiography in the evaluation of acute stroke, vasospasm, and other neurovascular disorders. CTP is critical in determining the extent of irreversibly infarcted brain tissue (infarct "core") and the severely ischemic but potentially salvageable tissue ("penumbra"). This is achieved by generating parametric maps of cerebral blood flow, cerebral blood volume, and mean transit time.

Intraprocedural plaque protrusion resulting in cerebral embolism during carotid angioplasty with stenting

An 82-year-old man with an asymptomatic left high-grade carotid stenosis was treated with carotid artery stenting (CAS) under distal protection. The procedure consisted with predilation with a 5 x 40 mm percutaneous transluminal angioplasty (PTA) balloon, deployment of a 10 x 20 mm self-expandable stent, post-dilation with a 7 x 20 mm PTA balloon, and aspiration of debris with 60 ml of blood. The cervical carotid angiogram immediately after deflation of the distal blocking balloon demonstrated a small in-stent filling defect of the contrast medium that protruded from the anterior wall of the carotid artery. The following cranial carotid angiogram showed abrupt occlusion of the left middle cerebral artery (MCA). Because the in-stent lesion had vanished in the repeat study after recognition of this embolic event, it was suggested that an embolus had been liberated from the in-stent lesion, reaching the left MCA and obliterating it. In this case, the embolus was speculated to originate in the ruptured plaque, which protruded into the stent through the cells of the device and became liberated into the bloodstream. Attention should be paid so as not to overlook any plaque protrusion, which may be seen subsequently as a cerebral embolism on the angiogram obtained immediately after CAS.

Mild induced hypertension improves blood flow and oxygen metabolism in transient focal cerebral ischemia

BACKGROUND AND PURPOSE

In focal ischemic cortex, cerebral blood flow autoregulation is impaired, and perfusion passively follows blood pressure variations. Although it is generally agreed that profound hypotension is harmful in acute stroke, the hemodynamic and metabolic impact of increased blood pressure on the ischemic core and penumbra are less well understood. We, therefore, tested whether pharmacologically induced hypertension improves cerebral blood flow and metabolism and tissue outcome in acute stroke using optical imaging with high spatiotemporal resolution.

METHODS

Cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen were measured noninvasively using simultaneous multispectral reflectance imaging and laser speckle flowmetry during distal middle cerebral artery occlusion in mice. Hypertension was induced by phenylephrine infusion starting 10 or 60 minutes after ischemia to raise blood pressure by 30% for the duration of ischemia; control groups received saline infusion.

RESULTS

Mild induced hypertension rapidly increased cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen in both the core and penumbra and prevented the expansion of cerebral blood flow deficit during 1 hour distal middle cerebral artery occlusion. Induced hypertension also diminished the deleterious effects of periinfarct depolarizations on cerebral blood flow, oxyhemoglobin, and cerebral metabolic rate of oxygen without altering their frequency. Consistent with this, mild induced hypertension reduced infarct volume by 48% without exacerbating tissue swelling when measured 2 days after 1 hour transient distal middle cerebral artery occlusion.

CONCLUSIONS

Our data suggest that mild induced hypertension increases collateral cerebral blood flow and oxygenation and improves cerebral metabolic rate of oxygen in the core and penumbra, supporting its use as bridging therapy in acute ischemic stroke until arterial recanalization is achieved.