Beneficial effects of induced hypertension on experimental stroke in awake monkeys

The dosage of thiopental as pharmacological cerebral protection during non-shunt carotid endarterectomy: A retrospective study

Background

Thiopental has been used as a pharmacological cerebral protection strategy during carotid endarterectomy surgeries. However, the optimal dosage required to induce burst suppression on the electroencephalogram (EEG) remains unknown. This retrospective study aimed to determine the optimal dosage of thiopental required to induce burst suppression during non-shunt carotid endarterectomy.

Methods

The Neurological Institute of Thailand Review Board approved the study. Data were collected from 2009 to 2019 for all non-shunt carotid endarterectomy patients who received thiopental for pharmacological cerebral protection and had intraoperative EEG monitoring. Demographic information, carotid stenosis severity, intraoperative EEG parameters, thiopental dosage, carotid clamp time, intraoperative events, and patient outcomes were abstracted.

Results

The study included 57 patients. Among them, 24 patients (42%) achieved EEG burst suppression pattern with a thiopental dosage of 26.3±10.1 mg/kg/hr. There were no significant differences in perioperative events between patients who achieved burst suppression and those who did not. After surgery, 33.3% of patients who achieved burst suppression were extubated and awakened. One patient in the non-burst suppression group experienced mild neurological deficits. No deaths occurred within one month postoperative.

Conclusions

The optimal dosage of thiopental required to achieve burst suppression on intraoperative EEG during non-shunt carotid endarterectomy was 26.3±10.1 mg/kg/hr.

Blood Pressure Management Before, During, and After Endovascular Thrombectomy for Acute Ischemic Stroke

There is an absence of specific evidence or guideline recommendations on blood pressure management for large vessel occlusion stroke patients. Until randomized data are available, the periprocedural blood pressure management of patients undergoing endovascular thrombectomy can be viewed in two phases relative to the achievement of recanalization. In the hyperacute phase, prior to recanalization, hypotension should be avoided to maintain adequate penumbral perfusion. The American Heart Association guidelines should be followed for the upper end of prethrombectomy blood pressure: ≤185/110 mm Hg, unless post-tissue plasminogen activator administration when the goal is <180/105 mm Hg. After successful recanalization (thrombolysis in cerebral infarction [TICI]: 2b-3), we recommend a target of a maximum systolic blood pressure of < 160 mm Hg, while the persistently occluded patients (TICI < 2b) may require more permissive goals up to <180/105 mm Hg. Future research should focus on generating randomized data on optimal blood pressure management both before and after endovascular thrombectomy, to optimize patient outcomes for these divergent clinical scenarios.

Blood Pressure and Penumbral Sustenance in Stroke from Large Vessel Occlusion

The global burden of stroke remains high, and of the various subtypes of stroke, large vessel occlusions (LVOs) account for the largest proportion of stroke-related death and disability. Several randomized controlled trials in 2015 changed the landscape of stroke care worldwide, with endovascular thrombectomy (ET) now the standard of care for all eligible patients. With the proven success of this therapy, there is a renewed focus on penumbral sustenance. In this review, we describe the ischemic penumbra, collateral circulation, autoregulation, and imaging assessment of the penumbra. Blood pressure goals in acute stroke remain controversial, and we review the current data and suggest an approach for induced hypertension in the acute treatment of patients with LVOs. Finally, in addition to reperfusion and enhanced perfusion, efforts focused on developing therapeutic targets that afford neuroprotection and augment neural repair will gain increasing importance. ET has revolutionized stroke care, and future emphasis will be placed on promoting penumbral sustenance, which will increase patient eligibility for this highly effective therapy and reduce overall stroke-related death and disability.

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.

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.

Blood pressure augmentation in acute ischemic stroke

Although control of hypertension is established as an important factor in the primary and secondary prevention of stroke, management of blood pressure in the setting of acute ischemic stroke remains controversial. Given limited data, the general consensus is that there is no proven benefit to lowering blood pressure in the first hours to days after acute ischemic stroke. Instead, there is concern that relative hypotension may lead to worsening of cerebral ischemia. For many years, the use of blood pressure augmentation ("induced hypertension") has been studied in animal models and in humans as a means of maintaining or improving perfusion to ischemic brain tissue. This approach is now widely used in neurocritical care units to treat delayed neurological deficits after subarachnoid hemorrhage, but its use in ischemic stroke patients remains anecdotal. This article reviews the cerebral physiology, animal models and human studies of induced hypertension as a treatment for acute ischemic stroke. Although there has not been a large, randomized clinical trial of this treatment, the available clinical data suggests that induced hypertension can result in at least short-term neurological improvement, with an acceptable degree of safety.

The Management of Blood Pressure After Stroke

BACKGROUND

Control of hypertension is a well-established goal of primary prevention of stroke, but management of blood pressure in patients with a previous stroke or in the setting of acute stroke is complicated by the effect blood pressure changes may have on cerebral perfusion.

REVIEW SUMMARY

For patients with previous transient ischemic attack or chronic stroke, blood pressure reduction appears to be a safe and important facet of the secondary prevention of recurrent stroke. Less information is available concerning blood pressure management in acute stroke. Current protocols require strict blood pressure control in patients who are treated with thrombolytic therapy, to reduce the risk of hemorrhagic complications. In patients presenting with acute intracerebral hemorrhage, blood pressure reduction does not appear to cause significant reduction of cerebral blood flow, but at this time there are no studies to determine if there is a clinical benefit of acute blood pressure reduction in these patients. Finally, blood pressure reduction is not routinely recommended in patients with acute ischemic stroke, as it may precipitate further cerebral ischemia. Preliminary studies suggest, in fact, that there may be a role in the future for blood pressure elevation in the treatment of patients with acute ischemic stroke.

CONCLUSIONS

Current data support the use of blood pressure reduction in the secondary prevention of stroke in patients with cerebrovascular disease. In the setting of acute stroke, however, data are limited and blood pressure management must be tailored to the specific clinical situation.

Pharmacological, surgical, and neurovascular interventions to augment acute aphasia recovery

Aphasia recovery has often been attributed to a combination of "spontaneous recovery" and rehabilitation. However, a variety of new pharmacological, surgical, and interventional neuroradiology procedures have been developed that can complement rehabilitation in the first days to weeks after stroke by restoring blood flow to dysfunctional but salvageable brain tissue. This paper will review the medical and surgical interventions to improve regional cerebral blood flow that recently have been shown to (1) augment aphasia recovery by improving tissue function, and (2) prevent expansion of the stroke that would otherwise impede recovery. Success with such treatments facilitates aphasia rehabilitation by improving the baseline language performance that must be improved further with language therapy.

Advances in stroke neuroprotection: hyperoxia and beyond

Refinements in patient selection, improved methods of drug delivery, use of more clinically relevant animal stroke models, and the use of combination therapies that target the entire neurovascular unit make stroke neuroprotection an achievable goal. This article provides an overview of the major mechanisms of neuronal injury and the status of neuroprotective drug trials and reviews emerging strategies for treatment of acute ischemic stroke. Advances in the fields of stem cell transplantation, stroke recovery, molecular neuroimaging, genomics, and proteomics will provide new therapeutic avenues in the near future. These and other developments over the past decade raise expectations that successful stroke neuroprotection is imminent.

Blood pressure management during acute ischaemic stroke

Control of hypertension is a well-established goal of primary stroke prevention. Management of blood pressure in patients during acute ischaemic stroke, however, is complicated by the need to maintain brain perfusion. Lowering blood pressure in the acute setting may avoid the deleterious effects of high blood pressure but may also lead to cerebral hypoperfusion and worsening of the ischaemic stroke. Little information is available from clinical trials concerning optimal blood pressure management in acute stroke. Current protocols of thrombolytic therapy require strict blood pressure control below certain prescribed limits; however, in most acute stroke patients not treated with thrombolysis, blood pressure reduction is not routinely recommended and guidelines for target blood pressures are difficult to justify. Preliminary studies, in fact, suggest that there may be a role for blood pressure elevation in the treatment of some patients with acute ischaemic stroke.

Desflurane affords greater protection than halothane against focal cerebral ischaemia in the rat

BACKGROUND

We studied the potential neuroprotective effects of halothane and desflurane, compared with the awake state, on infarct size following 2 h of intraluminal middle cerebral artery occlusion (MCAo) and 22 h of reperfusion.

METHODS

Male Sprague-Dawley rats were anaesthetized with desflurane or halothane, intubated, and mechanically ventilated. Mean arterial pressure (MAP), blood gases, and pH were controlled. Body temperature was maintained at 37.5-38 degrees C. Animals were assigned to one of four groups according to the anaesthetic type (halothane or desflurane) and the duration of anaesthesia: "short-duration", during the preparation only; "long-duration", during both preparation and ischaemia. Twenty-four hours after MCAo, infarcts were visualized by staining with 2,3,5-triphenyltetrazolium chloride. Two additional groups of rats were subjected to the same protocol as that of long-duration halothane and long-duration desflurane with additional pericranial temperature measurements made.

RESULTS

Physiological parameters were comparable between the groups but MAP was higher (P<0.0001) in the short-duration groups. In the short-duration groups, cerebral infarct volumes were not significantly different between anaesthetics (short-duration halothane: 288 (61) mm(3), mean (SD); short-duration desflurane: 269 (71) mm(3), P>0.56). Compared with the awake state (short-duration groups), halothane and desflurane significantly reduced infarct volumes (long-duration halothane: 199 (54) mm(3), P<0.0047 vs short-duration halothane; long-duration desflurane: 121 (55) mm(3), P<0.0001 vs short-duration desflurane). The mean infarct volume in the long-duration desflurane group was significantly lower than that in the long-duration halothane group (P<0.0053). Pericranial temperatures were similar in the desflurane and halothane long-duration groups (P>0.17).

CONCLUSIONS

In rats, desflurane-induced neuroprotection against focal cerebral ischaemia was greater than that conferred by halothane.

The relation between cerebral blood flow velocities as measured by TCD and the incidence of delayed ischemic deficits. A prospective study after subarachnoid hemorrhage

Patients (n = 127) with aneurysmal subarachnoid hemorrhage (SAH) were examined by transcranial Doppler ultrasonography (TCD) in a prospective study to follow the time course of the posthemorrhagic blood flow velocity in both the middle cerebral artery (MCA) and in the anterior cerebral artery (ACA). Results were analysed to reveal their relationship and predictive use with respect to the occurrence of delayed ischemic deficits. Mean flow velocities (MFV) higher than 120 cm sec(-1) in MCA and 90 cm sec(-1) in ACA were interpreted as indicative for significant vasospasm. In 20 of our 127 patients (16%) a delayed ischemic deficit (DID) was subsequently diagnosed clinically (DID+ group). Patients in the DID+ group can be characterized as those individuals who presented early during the observation period post-SAH with highest values of MFV, a faster increase and longer persistence of pathologically elevated MFV-values (exceeding 120 cm sec(-1) in MCA and 90 cm sec(-1) in ACA). They also show a greater difference in MFV-values if one compares the operated to the nonoperated side. Differences in MFV-values obtained in MCA or ACA were statistically significant (p < 0.05) for DID+ and DID- patients. The daily maximal increase of MFV was found between days 9 and 11 after SAH. In the DID+ group, the maximal MFV was 181 +/- 26 cm sec(-1) in MCA and 119 +/- 14 cm sec(-1) in ACA. In contrast to this, patients in the DID- group were found to present with MFV of 138 +/- 11 cm sec(-1) in MCA and 100 +/- 7 cm sec(-1) in ACA respectively. Delayed ischemic deficits appeared three times more often in DID+ patients than in patients with MFV < 120 cm sec(-1), if they showed a MFV > 120 cm sec(-1) in MCA. If pathological values were obtained in ACA, this ratio increases to about four times, if DID + patients presented with MFV > 90 cm sec(-1) versus patients with MFV < 90 cm sec(-1). Daily monitoring of vasospasm using TCD examination is thus helpful to identify patients at high risk for delayed ischemic deficits. This should allow us to implement further preventive treatment regimens.

Effects of induced hypertension on intracranial pressure and flow velocities of the middle cerebral arteries in patients with large hemispheric stroke

BACKGROUND AND PURPOSE

Our aim was to prospectively evaluate the effects of induced arterial hypertension in patients with large ischemic stroke.

METHODS

A total of 47 monitoring sessions in 19 patients with acute, complete, or subtotal middle cerebral artery (MCA) territory stroke were performed. Intracranial pressure (ICP) was monitored using a parenchymal catheter. Mean arterial blood pressure (MAP), ICP, and peak mean flow velocity of the middle cerebral arteries (V(m)MCA) were continuously recorded. Patients with acute ICP crises were excluded. After obtaining baseline values, MAP was raised by an infusion of norepinephrine to reach an MAP increase of at least 10 mm Hg. After MAP had reached a peak plateau level, the norepinephrine infusion was stopped.

RESULTS

Baseline MAP was 83.6+/-1.6 mm Hg and rose to 108.9+/-2.0 mm Hg after infusion of norepinephrine. ICP slightly increased from 11.6+/-0.9 mm Hg to 11.8+/-0.9 mm Hg (P<0.05). Cerebral perfusion pressure rose from baseline 72.2+/-2 mm Hg to 97+/-1 mm Hg (P<0.0001). V(m)MCA was already higher on the affected side during baseline measurements. At maximum MAP levels, V(m)MCA rose by 25.5+/-5.5 cm/s on the affected side and by 8.6+/-1.6 cm/s on the contralateral side.

CONCLUSIONS

In patients with large hemispheric stroke without an acute ICP crisis, induced hypertension enhances cerebral perfusion pressure and augments the V(m)MCA(s), more so on the affected side. The ICP slightly increases; however, this is probably not clinically significant.

Ischaemic brain oedema

Ischaemic brain oedema appears to involve two distinct processes, the relative contribution and time course of which depend on the duration and severity of ischaemia, and the presence of reperfusion. The first process involves an increase in tissue Na+ and water content accompanying increased pinocytosis and Na+, K+ ATPase activity across the endothelium. This is apparent during the early phase of infarction and before any structural damage is evident. This phenomenon is augmented by reperfusion. A second process results from a more indiscriminate and delayed BBB breakdown that is associated with infarction of both the parenchyma and the vasculature itself. Although, tissue Na+ level still seems to be the major osmotic force for oedema formation at this second stage, the extravasation of serum proteases is an additional potentially deleterious factor. The relative importance of protease action is not yet clear, however, degradation of the extracellular matrix conceivably leads to further BBB disruption and softening of the tissue, setting the stage for the most pronounced forms of brain swelling. A number of factors mediate or modulate ischaemic oedema formation, however, most current information comes from experimental models, and clinical data on this microcosmic level is lacking. Clinically significant brain oedema develops in a delayed fashion after large hemispheric strokes and is a cause of substantial mortality. Neurological signs appear to be at least as good as direct ICP measurement and neuroimaging in detecting and gauging the secondary damage produced by stroke oedema. The neuroimaging characteristics of the stroke, specifically the early involvement of greater than half of the MCA territory, are, however, highly predictive of the development of severe oedema over the subsequent hours and days. None of the available medical therapies provide substantial relief from the oedema and raised ICP, or at best, they are temporizing in most cases. Hemicraniectomy appears most promising as a method of avoiding death from brain compression, but the optimum timing and manner of patient selection are currently being investigated. All approaches to massive ischaemic brain swelling are clouded by the potential for survival with poor functional outcome. It is possible to manage blood pressure, serum osmolarity by way of selective fluid administration, and a number of other systemic factors that exaggerate brain oedema. Broad guidelines for treatment of stroke oedema can therefore be given at this time.

Carotid endarterectomy; local or general anaesthesia?

OBJECTIVES

to review the evidence for theoretical and clinical benefits of local or general anaesthesia for carotid endarterectomy.

METHODS

literature review.

RESULTS

animal studies suggest cerebral protection by a variety of general anaesthetic agents but clinical evidence is lacking. There is some clinical evidence that normal cerebral protective reflexes are preserved with local anaesthesia. Shunt insertion is the most widely used method of providing cerebral protection with awake testing the most reliable monitoring technique for the identification of ischaemia. There are therefore theoretical arguments for a reduced risk of perioperative stroke when local anaesthesia is used and this is supported by a meta-analysis of non-randomised studies. Intraoperative blood pressure is always higher with local anaesthesia but the incidence of postoperative haemodynamic instability seems to be independent of anaesthetic technique. There is little evidence that myocardial ischaemia is more common with either anaesthetic technique but meta-analysis of non-randomised again suggests fewer cardiac complications with local anaesthesia. Cranial nerve injury and haematoma formation may be less common with local anaesthesia but the evidence is weak. There is no evidence that surgery is more difficult with local anaesthesia or that it is poorly tolerated by the patients.

CONCLUSIONS

there are theoretical arguments and clinical evidence that the outcome from carotid endarterectomy may be better when local anaesthesia is used with no significant disadvantages. An appropriately designed randomised trial is required to confirm this.

Magnetic resonance imaging of cerebral hemorrhagic stroke

Despite a traditional perception of reliance on computed tomography and lack of acceptance of magnetic resonance imaging (MRI) for detecting acute hemorrhage, MRI appears to be used increasingly in hemorrhagic stroke. This review addresses the MRI findings of acute hemorrhagic stroke obtained using relatively new imaging techniques. These new techniques have resulted in more acute stroke patients undergoing MRI examination. New information about the frequency and appearance of hemorrhage is emerging: for example, approximately 15-26% of cases of acute cerebral infarctions appear to be complicated by intracerebral hemorrhage. The MRI appearances of hemorrhagic transformation of ischemic infarction, as well as acute hypertensive intracerebral hemorrhage, are discussed based on clinical, biochemical, and technical aspects.

Intensive care unit management of the stroke patient

Although the majority of patients with acute stroke do not require intensive care, it is important to recognize when admission to an intensive care unit (ICU) is warranted. Patients undergoing thrombolytic therapy, those with brainstem infarcts referable to the basilar artery, those with large space occupying hemispheric infarcts, and those with fluctuating neurological examinations should be admitted to the ICU for monitoring and treatment.

Neuroprotection in acute ischaemic stroke. II: Clinical potential

In the 4 years since our first article, there has been considerable progress in our understanding of the pathophysiology of acute ischaemic stroke, and the results of well-conducted trials have at last begun to change everyday clinical practice. The timing of the various processes of the ischaemic cascade and the potential time windows for different interventions are better understood. Furthermore, the importance of maintaining cerebral perfusion and optimizing systemic physiological and biochemical factors in order to prevent neurological deterioration ('progressing stroke') is increasingly being realized. Numerous antithrombotic and neuroprotective drugs have been evaluated in clinical trials, and while none has shown unequivocal benefits on its own, prospects for successful intervention are still good. This will probably involve different combinations of treatments targeted on different pathophysiological stroke types, so that the management of acute stroke will offer a considerable challenge to the stroke physicians of the future.

Thiopental and desflurane treatment for brain protection

OBJECTIVE

Thiopental produces cerebral metabolic depression and cerebral vasoconstriction. However, the effect of thiopental on brain tissue oxygen pressure (PO2), carbon dioxide pressure, and pH is not known. In a prospective study, we measured brain tissue gases and pH during thiopental or desflurane treatment that was administered for brain protection during brain artery occlusion.

METHODS

After institutional review board approval, 20 patients undergoing craniotomies for cerebrovascular surgery were tested; 10 were randomized to receive thiopental and 10 to receive desflurane. After each craniotomy, a Neurotrend probe (Diametrics Medical, Minneapolis, MN) was inserted to measure tissue PO2, carbon dioxide pressure, and pH in a tissue region at risk to develop ischemia during temporary brain artery occlusion. Thiopental or desflurane was administered to produce burst suppression of electroencephalography, and then temporary artery occlusion was performed during aneurysm or extracerebral-to-intracerebral bypass surgery.

RESULTS

Thiopental produced no change in tissue gases or pH, but temporary artery clipping in thiopental-treated patients decreased PO2 30% (P < 0.05). Desflurane increased PO2 70% (P < 0.05), and tissue oxygenation remained elevated during temporary artery occlusion. Tissue pH did not decrease in either group during temporary brain artery occlusion.

CONCLUSION

Thiopental has a metabolically neutral effect on brain tissue gases and pH, even though it is known to decrease cerebral oxygen consumption. The metabolic depressant and vasodilator effects of desflurane enhance tissue oxygenation and attenuate tissue PO2 reductions produced by artery occlusion. Both thiopental and desflurane inhibit ischemic lactic acidosis and decreases in pH.

Blood pressure and functional recovery in acute ischemic stroke

BACKGROUND AND PURPOSE

The relevance of elevated blood pressure in acute ischemic stroke and its most appropriate management are unresolved. We aimed to evaluate the rate of functional recovery with relation to early blood pressure management in patients with ischemic stroke.

METHODS

Four hundred eighty-one consecutive ischemic stroke patients were admitted to the Neurology Service within 20.9+/-10.5 hours of symptoms onset as part of the Barcelona Downtown Stroke Registry, including 235 patients who received oral antihypertensive agents within <24 hours after stroke onset. Demographic, clinical (Mathew scale), and CT scan findings were collected prospectively. Mean arterial pressure (MAP) was recorded before hospital arrival and at 7 AM on days 1, 2, and 7 of hospitalization. The primary end point was complete functional recovery at day 7 defined as a score of 0 to 1 on the modified Rankin scale.

RESULTS

Two hundred fifty-two patients achieved complete recovery on day 7. Using logistic regression, independent predictors of complete recovery included mild impairment at stroke presentation, lack of history of hypertension, and absence of brain edema on CT scan. Also, a 20% to 30% drop in MAP on day 2 after stroke onset almost tripled the odds of full recovery (odds ratio, 2.9; 95% CI, 1.3 to 6.3). MAP tended to normalize after stroke in all subjects, more rapidly if hypotensive agents were administered. Brain edema was also less frequent in patients with a greater drop in blood pressure. Despite the fact that a drop in MAP >30% from baseline was observed in 49 patients, this preceded worsening stroke in only 4 patients. Conversely, worsening stroke occurred in 51 patients despite stable blood pressure.

CONCLUSIONS

These results suggest that complete recovery in ischemic stroke is facilitated by a moderate blood pressure reduction when brain edema develops, most likely as the result of a more adequate cerebral perfusion pressure. Conversely, stroke worsening due to pharmacological hypoperfusion is exceptional.

Induced hypertension improves regional blood flow and protects against infarction during focal ischemia: time course of changes in blood flow measured by laser Doppler imaging

OBJECTIVE

To characterize changes in regional blood flow (rCBF) during and after a period of arterial occlusion and determine the effect on rCBF and on the extent of infarction when the mean arterial blood pressure is increased during the period of occlusion.

METHODS

rCBF in the middle cerebral artery (MCA) territory of rabbits was monitored using laser Doppler perfusion imaging before, during, and after a 1- or 2-hour period of MCA occlusion, and the size of the infarction was assessed by 2,3,5-triphenyltetrazolamine chloride staining after 2 hours of reperfusion. Test animals, the mean arterial blood pressure of which was increased by 65 mm Hg with intravenous phenylephrine during the ischemia, were compared with control animals that remained normotensive. The laser Doppler perfusion imager (Lisca Developments Co., Linköping, Sweden) scanned a 3-cm2 area of cortex with a resolution of 4 mm2 every 15 minutes.

RESULTS

MCA occlusion reduced rCBF to 71 +/- 2% of the control level (n = 24, P < 0.001). Hypertension (HTN) restored rCBF to 84 +/- 3% of the control level (n = 12, P < 0.01), but the HTN-induced improvement diminished with time, so that after 1 hour, there was no longer a significant difference between hypertensive and normotensive animals. HTN during the MCA occlusion caused a 97% reduction in infarct size (P < 0.05) in the animals subjected to 1 hour of occlusion but caused only a 45% reduction (P approximately 0.1) in the animals subjected to 2 hours of occlusion.

CONCLUSION

This study supports the use of HTN to minimize ischemic injury from short intervals of major intracranial vessel occlusion but fails to demonstrate protection when HTN is maintained during occlusions of more than 1 hour.

Pharmacological elevation of blood pressure in acute stroke. Clinical effects and safety

BACKGROUND AND PURPOSE

Lowering of blood pressure can adversely affect ischemic symptoms in acute stroke. The aim of our study was to determine whether induced hypertension in stroke is safe and to examine its effects on neurological deficits in patients presenting with acute cerebral ischemia.

METHODS

We retrospectively reviewed all patients admitted to our neurological intensive care unit with the diagnosis of ischemic stroke over a 2.5-year period. Thirty-three patients were not given a pressor agent (Ph- group), while 30 were treated with phenylephrine (Ph+ group) in an attempt to improve cerebral perfusion.

RESULTS

Baseline characteristics showed few differences between the Ph+ and Ph- groups. Intracerebral hemorrhage, brain edema, cardiac morbidity, and mortality were not increased in the Ph+ group. In 10 of 30 Ph+ patients, a systolic blood pressure threshold was identified below which ischemic deficits worsened and above which deficits improved. The mean threshold was 156 mm Hg (range, 120 to 190 mm Hg). The mean number of stenotic/occluded cerebral arteries was greater in those Ph+ patients with an identified clinical blood pressure threshold (mean, 2.1 per patient) than in Ph+ patients without a threshold (mean, 1.2 per patient; P < .05).

CONCLUSIONS

The results suggest that careful use of phenylephrine induced hypertension is not associated with an increase in morbidity or mortality in acute stroke. Although based on a retrospective analysis of clinical practice, this report suggests that a subset of patients, particularly those with multiple stenosis of cerebral arteries, may improve neurologically upon elevation of the blood pressure.

Factors affecting changes in blood pressure after acute stroke

BACKGROUND AND PURPOSE

We sought to establish the pattern of blood pressure (BP) change after hospitalization for acute hemispheric stroke.

METHODS

In 292 patients from the Leicester teaching hospitals with acute hemispheric stroke within the previous 24 hours (139 men; median age, 75 years [range, 42 to 98 years]), we prospectively studied BP changes between admission, 24 hours, 1 week, and 4 to 6 weeks. Changes were assessed in relation to the main stroke risk factors, stroke type and severity, and antihypertensive drug treatment. All subjects were followed up for 1 week, with 117 subjects followed up for 4 to 6 weeks. Changes were assessed by repeated-measures ANOVA, and Student's t tests were used to compare group pairs.

RESULTS

Systolic and diastolic BP fell by 12 mm Hg (95% confidence interval [CI], 8 to 15 mm Hg) and 7 mm Hg (95% CI, 5 to 9 mm Hg), respectively, in the first 24 hours and 22 mm Hg (95% CI, 18 to 25 mm Hg) and 12 mm Hg (95% CI, 10 to 14 mm Hg), respectively, during the first week (all changes significant at P < .01) but no further thereafter. In those patients receiving no antihypertensive medication before or after stroke, the pattern of change was similar to that of the whole group. Previously diagnosed hypertensive subjects (n = 106) had higher initial BP values than did normotensive subjects, although by 1 week the levels were not significantly different. Patients with cerebral hemorrhage confirmed by computed tomography (n = 20) had higher systolic BP, but not diastolic BP, throughout the first week than those with cerebral infarction (n = 89). The severity of stroke, age, and previous stroke history did not appear to alter the BP pattern. Stroke patients who were moderate to heavy alcohol consumers had lower convalescent systolic BP levels than lighter drinkers or abstainers.

CONCLUSIONS

We have demonstrated a marked fall in systolic and diastolic BP levels during the first 7 days after acute hemispheric stroke, with little change thereafter. Higher initial systolic BP values were found in patients with cerebral hemorrhage compared with those with cerebral infarct. Moderate to heavy alcohol consumption before stroke was associated with a greater systolic BP decline in the first week after the event compared with stroke patients who were light drinkers or abstainers.

Acute cerebral blood flow response to dopamine-induced hypertension after subarachnoid hemorrhage

The effects of dopamine-induced hypertension on local cerebral blood flow (CBF) were investigated in 13 patients suspected of suffering clinical vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The CBF was measured in multiple vascular territories using xenon-enhanced computerized tomography (CT) with and without dopamine-induced hypertension. A territorial local CBF of 25 ml/100 gm/min or less was used to define ischemia and was identified in nine of the 13 patients. Raising mean arterial blood pressure from 90 +/- 11 mm Hg to 111 +/- 13 mm Hg (p < 0.05) via dopamine administration increased territorial local CBF above the ischemic range in more than 90% of the uninfarcted territories identified on CT while decreasing local CBF in one-third of the nonischemic territories. Overall, the change in local CBF after dopamine-induced hypertension was correlated with resting local CBF at normotension and was unrelated to the change in blood pressure. Of the 13 patients initially suspected of suffering clinical vasospasm, only 54% had identifiable reversible ischemia. The authors conclude that dopamine-induced hypertension is associated with an increase in flow in patients with ischemia after SAH. However, flow changes associated with dopamine-induced hypertension may not be entirely dependent on changes in systemic blood pressure. The direct cerebrovascular effects of dopamine may have important, yet unpredictable, effects on CBF under clinical pathological conditions. Because there is a potential risk of dopamine-induced ischemia, treatment may be best guided by local CBF measurements.

Cerebral protection during aneurysm surgery with isoflurane anesthesia. Technical note

A strategy for intraoperative cerebral protection is described in which intraoperative electroencephalography is used to titrate the level of inspired isoflurane given for anesthesia to obtain isoelectricity prior to temporary vessel occlusion during repair of difficult aneurysms. During temporary vessel occlusion, arterial blood pressure is maintained or increased with an inotropic or vasopressor agent. After clipping of the aneurysm, the concentration of isoflurane is reduced to allow the patient to awaken in the operating room for early postoperative neurological examination. The combination of a high concentration of isoflurane, temporary vessel occlusion, and maintenance of arterial blood pressure may be a useful protective regimen during neurovascular procedures.

Reduction in focal cerebral ischemia by agents acting at imidazole receptors

Treatment with the alpha 2-adrenergic antagonist idazoxan (IDA) can provide protection from global cerebral ischemia. However, IDA also recognizes another class of receptors, termed imidazole (IM) receptors, which differ from alpha 2-adrenergic receptors and are responsible for the hypotensive actions of some centrally acting agents such as the oxazole rilmenidine (RIL). We therefore sought to determine whether RIL, an agent highly selective for IM receptors, offered protection from focal cerebral ischemia elicited in rat by ligation of the middle cerebral artery (MCA). We compared the effects of RIL with the effects of IDA and the selective non-IM alpha 2-antagonist SKF 86466 (SKF). In addition, we examined whether the neuroprotective effects of RIL and IDA could be attributed to changes in local CBF (LCBF). The MCA was occluded and animals either received immediate administration of drug while arterial pressure was maintained for 1 h or had local CBF increased to 200% of control for 1 h by hypercapnia or hypertension. RIL elicited a significant dose-dependent preservation of tissue to 33% of control at optimal dose (0.75 mg/kg). IDA (3 mg/kg) significantly reduced the size of ischemic infarction by 22%. In contrast, SKF (15 mg/kg) as well as doubling of LCBF did not preserve ischemic tissue. We conclude that both RIL and IDA can reduce focal ischemic infarction but that the mechanism does not appear secondary to antagonism of alpha 2-adrenergic receptors or elevation of LCBF. Occupation of IM receptors, either in the ischemic zone or at remote brain sites, may be responsible for neuroprotection of RIL and IDA.

Autoregulation of cerebral blood flow in experimental focal brain ischemia

The relationship between systemic arterial pressure (SAP) and neocortical microcirculatory blood-flow (CBF) in areas of focal cerebral ischemia was studied in 15 spontaneously hypertensive rats (SHRs) anesthetized with halothane (0.5%). Ischemia was induced by ipsilateral middle cerebral artery/common carotid artery occlusion and CBF was monitored continuously in the ischemic territory using laser-Doppler flowmetry during manipulation of SAP with I-norepinephrine (hypertension) or nitroprusside (hypotension). In eight SHRs not subjected to focal ischemia, we demonstrated that 0.5% halothane and the surgical manipulations did not impair autoregulation. Autoregulation was partly preserved in ischemic brain tissue with a CBF of greater than 30% of preocclusion values. In areas where ischemic CBF was less than 30% of preocclusion values, autoregulation was completely lost. Changes in SAP had a greater influence on CBF in tissue areas where CBF ranged from 15 to 30% of baseline (9% change in CBF with each 10% change in SAP) than in areas where CBF was less than 15% of baseline (6% change in CBF with each 10% change in SAP). These findings demonstrate that the relationship between CBF and SAP in areas of focal ischemia is highly dependent on the severity of ischemia. Autoregulation is lost in a gradual manner until CBF falls below 30% of normal. In areas without autoregulation, the slope of the CBF/SAP relationship is inversely related to the degree of ischemia.

Focal brain ischemia in the rat: methods for reproducible neocortical infarction using tandem occlusion of the distal middle cerebral and ipsilateral common carotid arteries

This article describes a 3-year experience with focal neocortical ischemia in three rat strains. Multiple groups of adult Wistar (n = 50), Fisher 344 (n = 31), and spontaneously hypertensive (n = 72) rats were subjected to permanent occlusion of the distal middle cerebral (MCA) and ipsilateral common carotid arteries (CCA). Twenty-four hours later the animals were killed, and frozen brain sections were stained with hematoxylin and eosin to demarcate infarcted tissue. The infarct volume for each section was quantified with an image analyzer, and the total infarct volume was calculated with an iterative program that summed all interval volumes. Neocortical infarct volume was the largest and most reproducible in the spontaneously hypertensive rats (SHR). Statistical power analysis to project the numbers of animals necessary to detect a 25 or 50% change in infarct volume with alpha = 0.05 and beta = 0.2 revealed that only the SHR model was practical in terms of requisite animals: i.e., less than 10 animals per group. Tandem occlusion of the distal MCA and ipsilateral CCA in the SHR strain provides a surgically simple method for causing large neocortical infarcts with reproducible topography and volume. The interanimal variability in infarct volume that occurs even in the SHR strain dictates that randomized, concomitant controls are necessary in each study to ensure the accurate assessment of experimental manipulations or pharmacologic therapies.

Cerebral resuscitation: pathophysiology and therapy

The interest in the possibility of cerebral resuscitation has been growing exponentially during the last decade. It became clear that pharmacotherapeutic interaction can possibly alter the outcome of cerebral hypoxia/ischemia. The present review is an attempt to provide an organizational framework for a systematic integration of studies specifically dealing with pharmacological treatment post-insult.

Can raising cerebral blood flow improve outcome after acute cerebral infarction?

Cerebral blood flow correlates poorly with outcome after stroke, and most therapies aimed at increasing cerebral perfusion have not succeeded in predictably reducing neurological deficit. Newer approaches such as hemodilution and thrombolysis may prove to be more effective but might be most advantageous if combined with efforts to correct postischemic disturbances in cellular metabolism.