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

Augmentation of perfusion with simultaneous vasodilator and inotropic agents in experimental acute middle cerebral artery occlusion: a pilot study

BACKGROUND

This study tests the hypothesis that simultaneous cerebral blood pressure elevation and potent vasodilation augments perfusion to ischemic tissue in acute ischemic stroke and it varies by degree of pial collateral recruitment.

METHODS

Fifteen mongrel canines were included. Subjects underwent permanent middle cerebral artery occlusion; pial collateral recruitment was scored before treatment. Seven treatment subjects received a continuous infusion of norepinephrine (0.1-1.52 µg/kg/min; titrated 25-45 mmHg above baseline mean arterial pressure while keeping systolic blood pressure below 180 mmHg) and hydralazine (20 mg) starting 30 min post-occlusion. Perfusion (cerebral blood flow-CBF) was evaluated with quantitative dynamic susceptibility contrast MRI 2.5 hours post-occlusion to produce images in mL/100 g/min, and relative CBF measured as ratios. Mean region of interest (ROI) values were reported, and compared and subject to regression analysis to elucidate trends.

RESULTS

Differences in quantitative CBF (qCBF) between treatment and control group varied by degree of pial collateral recruitment, based on Wilcoxon rank sum scores and regression model fit. For poorly collateralized subjects, ipsilateral anatomic, core infarct, and penumbra regions showed treatment with higher qCBF, raised above the ischemic threshold, compared with the control, while well collateralized subjects showed a paradoxical decrease maintained above the ischemic threshold for neuronal death. qCBF on the contralateral side increased regardless of collateralization.

CONCLUSION

Results suggest that perfusion can be augmented in ischemic stroke with norepinephrine and hydralazine. Perfusion augmentation depends on degree of collateralization and territory in question, with some evidence of vascular steal.

Therapeutic Induction of Collateral Flow

Therapeutic induction of collateral flow as a means to salvage tissue and improve outcome from acute ischemic stroke is a promising approach in the era in which endovascular therapy is no longer time-dependent but collateral-dependent. The importance of collateral flow enhancement as a therapeutic for acute ischemic stroke extends beyond those patients with large amounts of salvageable tissue. It also has the potential to extend the time window for reperfusion therapies in patients who are ineligible for endovascular thrombectomy. In addition, collateral enhancement may be an important adjuvant to neuroprotective agents by providing a more robust vascular route for which treatments can gain access to at risk tissue. However, our understanding of collateral hemodynamics, including under comorbid conditions that are highly prevalent in the stroke population, has hindered the efficacy of collateral flow augmentation for improving stroke outcome in the clinical setting. This review will discuss our current understanding of pial collateral function and hemodynamics, including vasoactivity that is critical for enhancing penumbral perfusion. In addition, mechanisms by which collateral flow can be increased during acute ischemic stroke to limit ischemic injury, that may be different depending on the state of the brain and vasculature prior to stroke, will also be reviewed.

Enhance Safety in Aneurysm Surgery: Strategies for Prevention of Intraoperative Vascular Complications

Complications during surgery for intracranial aneurysms can be devastating. Notorious pitfalls include premature rupture, parent vessel occlusion, local cerebral injury and brain contusion, and incomplete neck obliteration. These unfavorable intraoperative events can result in major neurological deficits with permanent morbidity and even mortality. Herein, the author highlights the relevant surgical strategies used in his daily practice of aneurysm surgery (e.g., aneurysm clipping with adenosine-induced temporary cardiac arrest), application of which may help prevent vascular complications and enhance surgical safety through reduction of the associated risks, thus allowing improvement of postoperative outcomes. Overall, all described methods and techniques should be considered as small pieces in the complex puzzle of prevention of vascular complications during aneurysm surgery.

Thomas Willis Lecture: Targeting Brain Arterioles for Acute Stroke Treatment

[Figure: see text].

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.

Influence of simultaneous pressor and vasodilatory agents on the evolution of infarct growth in experimental acute middle cerebral artery occlusion

BACKGROUND

This study sought to test the hypothesis that simultaneous central blood pressure elevation and potent vasodilation can mitigate pial collateral-dependent infarct growth in acute ischemic stroke.

METHODS

Twenty mongrel canines (20-30 kg) underwent permanent middle cerebral artery occlusion (MCAO). Eight subjects received continuous infusion of norepinephrine (0.1-1.5200 µg/kg/min; titrated to a median of 34 mmHg above baseline mean arterial pressure) and hydralazine (20 mg) starting 30 min following MCAO. Pial collateral recruitment was scored prior to treatment and used to predict infarct volume based on a previously reported parameterization. Serial diffusion magnetic resonance imaging (MRI) acquisitions tracked infarct volumes over a 4-hour time frame. Infarct volumes and infarct volume growth between treatment and control groups were compared with each other and to predicted values. Fluid-attenuated inversion recovery (FLAIR) MRI, susceptibility weighted imaging (SWI), and necropsy findings were included in the evaluation.

RESULTS

Differences between treatment and control group varied by pial collateral recruitment based on indicator-variable regression effects analysis with interaction confirmed by regression model fit. Benefit in treatment group was only in subjects with poor collaterals which had 35.7% less infarct volume growth (P=0.0008; ANOVA) relative to controls. Measured infarct growth was significantly lower than predicted by the model (linear regression partial F-test, slope P<0.001, intercept=0.003). There was no evidence for cerebral hemorrhage or posterior reversible encephalopathy syndrome.

CONCLUSION

Our results indicate that a combination of norepinephrine and hydralazine administered in the acute phase of ischemic stroke mitigates infarct evolution in subjects with poor but not good collateral recruitment.

Large animal models of stroke and traumatic brain injury as translational tools

Acute central nervous system injury, encompassing traumatic brain injury (TBI) and stroke, accounts for a significant burden of morbidity and mortality worldwide. Studies in animal models have greatly enhanced our understanding of the complex pathophysiology that underlies TBI and stroke and enabled the preclinical screening of over 1,000 novel therapeutic agents. Despite this, the translation of novel therapeutics from experimental models to clinical therapies has been extremely poor. One potential explanation for this poor clinical translation is the choice of experimental model, given that the majority of preclinical TBI and ischemic stroke studies have been conducted in small animals, such as rodents, which have small lissencephalic brains. However, the use of large animal species such as nonhuman primates, sheep, and pigs, which have large gyrencephalic human-like brains, may provide an avenue to improve clinical translation due to similarities in neuroanatomical structure when compared with widely adopted rodent models. This purpose of this review is to provide an overview of large animal models of TBI and ischemic stroke, including the surgical considerations, key benefits, and limitations of each approach.

Improving Cerebral Blood Flow after Arterial Recanalization: A Novel Therapeutic Strategy in Stroke

Ischemic stroke is caused by a disruption in blood supply to a region of the brain. It induces dysfunction of brain cells and networks, resulting in sudden neurological deficits. The cause of stroke is vascular, but the consequences are neurological. Decades of research have focused on finding new strategies to reduce the neural damage after cerebral ischemia. However, despite the incredibly huge investment, all strategies targeting neuroprotection have failed to demonstrate clinical efficacy. Today, treatment for stroke consists of dealing with the cause, attempting to remove the occluding blood clot and recanalize the vessel. However, clinical evidence suggests that the beneficial effect of post-stroke recanalization may be hampered by the occurrence of microvascular reperfusion failure. In short: recanalization is not synonymous with reperfusion. Today, clinicians are confronted with several challenges in acute stroke therapy, even after successful recanalization: (1) induce reperfusion, (2) avoid hemorrhagic transformation (HT), and (3) avoid early or late vascular reocclusion. All these parameters impact the restoration of cerebral blood flow after stroke. Recent advances in understanding the molecular consequences of recanalization and reperfusion may lead to innovative therapeutic strategies for improving reperfusion after stroke. In this review, we will highlight the importance of restoring normal cerebral blood flow after stroke and outline molecular mechanisms involved in blood flow regulation.

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.

Monitoring Pressure Augmentation in Patients With Ischemic Penumbra Using Continuous Electroencephalogram: Three Cases and a Review of the Literature

BACKGROUND

Continuous electroencephalography (CEEG) is a sensitive, noninvasive surrogate monitor of cerebral blood flow (CBF). Changes in CBF can be seen as changes in the frequencies on the CEEG. This case series suggests that increase in CEEG frequencies may be used to detect improved CBF following pressure augmentation such as with treatment of vasospasm from subarachnoid hemorrhage (SAH) or acute thrombosis from ischemic stroke. The application of this observation to clinical decision-making has not been clearly defined and requires further study.

METHODS

Case series and imaging.

RESULTS

We present 3 patients with ischemic penumbras either from vasospasm from SAH or thrombosis from acute ischemic stroke. All patients were monitored on CEEG and found to have lateralized slowing. During pressure augmentation, the lateralized slowing improved in frequency, which corresponded with improvement in the patients' neurological examinations.

CONCLUSION

Continuous electroencephalography may be used as a noninvasive monitor to allow for individualization of pressure augmentation in cases of vasospasm from SAH or in cases of acute ischemic strokes. This customized approach may allow for less morbidity associated with pressure augmentation in patients who otherwise may have dysfunction of their intracerebral autoregulation.

The effect of induced hypertension on neurological outcome in forebrain ischaemia model in rats

INTRODUCTION

The present study investigated the effects of induced hypertension on hippocampal cell death after forebrain ischaemia in rats.

MATERIALS AND METHODS

In this study, forebrain ischaemia was induced in 20 Sprague-Dawley rats by clamping the bilateral common carotid arteries to induce systemic hypotension for 8min. All rats then underwent reperfusion during which the induced hypertension group (n=10) received intermittent intravenous injections of phenylephrine (5μg) to maintain their mean arterial blood pressure at 20mmHg above baseline for 10min and the control group (n=10) did not receive any treatment. In both groups, the numbers of viable and apoptotic neuronal cells in the cornu ammonis 1 (CA1) area of the hippocampus were evaluated 7 days after the induction of ischaemia.

RESULTS

The mean percentage of viable neuronal cells was higher in the induced hypertension group than in the control group (35% vs. 26%, respectively; p=0.004), but there was no significant difference in the proportion of apoptotic neuronal cells between the groups (57% vs. 43%, respectively; p=0.165).

CONCLUSIONS

Induced hypertension significantly attenuated necrotic cell death in the hippocampal CA1 area, but apoptotic cell death was not affected.

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.

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.

Phenylephrine-induced hypertension during transient middle cerebral artery occlusion alleviates ischemic brain injury in spontaneously hypertensive rats

Arterial hypertension is a major risk factor for ischemic stroke. However, the management of preexisting hypertension is still controversial in the treatment of acute stroke in hypertensive patients. The present study evaluates the influence of preserving hypertension during focal cerebral ischemia on stroke outcome in a rat model of chronic hypertension, the spontaneously hypertensive rats (SHR). Focal cerebral ischemia was induced by transient (1h) occlusion of the middle cerebral artery, during which mean arterial blood pressure was maintained at normotension (110-120mm Hg, group 1, n=6) or hypertension (160-170mm Hg, group 2, n=6) using phenylephrine. T2-, diffusion- and perfusion-weighted MRI were performed serially at five different time points: before and during ischemia, and at 1, 4 and 7 days after ischemia. Lesion volume and brain edema were estimated from apparent diffusion coefficient maps and T2-weighted images. Regional cerebral blood flow (rCBF) was measured within and outside the perfusion deficient lesion and in the corresponding regions of the contralesional hemisphere. Neurological deficits were evaluated after reperfusion. Infarct volume, edema, and neurological deficits were significantly reduced in group 2 vs. group 1. In addition, higher values and rapid restoration of rCBF were observed in group 2, while rCBF in both hemispheres was significantly decreased in group 1. Maintaining preexisting hypertension alleviates ischemic brain injury in SHR by increasing collateral circulation to the ischemic region and allowing rapid restoration of rCBF. The data suggest that maintaining preexisting hypertension is a valuable approach to managing hypertensive patients suffering from acute ischemic stroke.

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.

Automated registration of laser Doppler perfusion images by an adaptive correlation approach: application to focal cerebral ischemia in the rat

Hemodynamic changes are extremely important in analyzing responses from a brain subjected to a stimulus or treatment. The Laser Doppler technique has emerged as an important tool in neuroscience research. This non-invasive method scans a low-power laser beam in a raster pattern over a tissue surface to generate the time course of images in unit of relative flux changes. Laser Doppler imager (LDI) records cerebral perfusion not only in the temporal but also in the spatial domain. The traditional analysis of LD images has been focused on the region-of-interest (ROI) approach, in which the analytical accuracy in an experiment that necessitates a relative repositioning between the LDI and the scanned tissue area will be weakened due to the operator's subjective decision in data collecting. This report describes a robust image registration method designed to obviate this problem, which is based on the adaptive correlation approach. The assumption in mapping corresponding pixels in two images is to correlate the regions in which these pixels are centered. Based on this assumption, correlation coefficients are calculated between two regions by a method in which one region is moved around over the other in all possible combinations. To avoid ambiguity in distinguishing maximum correlation coefficients, an adaptive algorithm is adopted. Correspondences are then used to estimate the transformation by linear regression. We used a pair of phantom LD images to test this algorithm. A reliability test was also performed on each of the 15 sequential LD images derived from an actual experiment by imposing rotation and translation. The result shows that the calculated transformation parameters (rotation: theta =7.7+/-0.5 degrees; translation: Delta x =2.8+/-0.3, Deltaŷ=4.7+/-0.4) are very close to the prior-set parameters (rotation: theta=8 degrees; translation: Delta x=3, Delta y=5). This result indicates that this approach is a valuable adjunct to LD perfusion monitoring. An original sequence of LD images that recorded cerebral perfusion through a cranial window before, during and after middle cerebral artery occlusion (MCAo) is presented, together with the registered image sequence. Cerebral perfusion data acquired in a pixel-based manner from different anatomic locations of the registered LD image sequence are also presented over the whole time-course of the experiment.

Early dramatic recovery during intravenous tissue plasminogen activator infusion: clinical pattern and outcome in acute middle cerebral artery stroke

BACKGROUND AND PURPOSE

Acute-stroke patients receiving standard intravenous tissue plasminogen activator (tPA) have been noted to experience early dramatic recoveries. The prevalence, clinical characteristics, and outcome of patients experiencing dramatic recovery is not well described.

METHODS

We prospectively studied all patients presenting with acute middle cerebral artery (MCA) stroke syndromes and transcranial Doppler (TCD) evidence of an MCA obstruction. All patients received intravenous tPA per the National Institute of Neurological and Communicative Disorders and Stroke protocol, with serial National Institutes of Health Stroke Scale (NIHSS) scores and continuous TCD monitoring. Dramatic recovery was defined as an improvement of > or =10 NIHSS points or a decrease to an NIHSS score of < or =3 by the end of infusion. Outcome at the end of infusion, at 24 hours, and at long-term follow-up were obtained. The timing and pattern of deficit recovery during dramatic recovery was also studied.

RESULTS

Dramatic recovery occurred in 22% of all patients. Compared with patients who did not experience dramatic recovery, those patients who did had significantly lower end-infusion NIHSS (median 2 and range 0 to 16 for dramatic-recovery patients versus median 17 and range 6 to 35 for non-dramatic-recovery patients, P<0.01) and 24-hour NIHSS (median 2 and range 0 to 16 for dramatic-recovery patients versus median 13 and range 2 to 35 for non-dramatic-recovery patients, P<0.01). A long-term modified Rankin Score benefit was noted (median 1 and range 0 to 6 for dramatic-recovery patients versus median 4 and range 0 to 6 for non-dramatic-recovery patients, P<0.01). Baseline clinical characteristics were similar. The only difference was improved TCD-determined flow values at the end of infusion (normal restoration of flow was 58% in dramatic-recovery patients versus 14% in non-dramatic-recovery patients, P<0.01). A characteristic pattern of recovery of deficit was noted.

CONCLUSIONS

Early dramatic recovery in acute MCA stroke patients treated with intravenous tPA is relatively frequent. The benefit of dramatic recovery is maintained at 24 hours and over the long term. TCD monitoring suggests that dramatic recovery is a result of early restoration of MCA flow during the tPA infusion. The consistent pattern of early clinical recovery may help explain the mechanisms by which thrombolysis improves outcome and could suggest targets for enhancing the therapeutic effect of intravenous tPA.

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.

Anesthetic methods in rats determine outcome after experimental focal cerebral ischemia: mechanical ventilation is required to obtain controlled experimental conditions

OBJECTIVE

Anesthetic agents, pH, blood gases and blood pressure have all been found to influence the pathophysiology of experimental stroke. In experimental research, rats are predominantly used to investigate the effects of focal cerebral ischemia. Chloral hydrate, applied intraperitoneally (i.p.), and halothane, applied via face-mask in spontaneously breathing animals or via endotracheal tube in mechanically ventilated animals are popular methods of anesthesia. We investigated the potential of these anesthetic methods to maintain physiologic conditions during focal cerebral ischemia and their influence on postischemic mortality and histological outcome.

METHODS

Thirty male Sprague-Dawley rats were subjected to 90 min of middle cerebral artery occlusion by insertion of an intraluminal thread and assigned to one of three groups (n=10 each): (A) chloral hydrate i.p./spontaneously breathing; (B) halothane in 70:30 (%) N2O/O2 via face-mask/spontaneously breathing; and (C) halothane in 70:30 (%) N2O/O2 via endotracheal tube/mechanically ventilated. Physiologic parameters were measured before, during, and after ischemia. Infarct volume was histologically assessed after 7 days.

RESULTS

All anesthetic techniques except mechanical ventilation via an endotracheal tube resulted in considerably fluctuating blood gases levels, hypercapnia, acidosis and low blood pressure. All spontaneously breathing animals (groups A and B) exhibited a higher postischemic mortality and significantly larger infarct volumes than group C with intubated and ventilated animals.

CONCLUSIONS

Intra- and postischemic physiologic parameters such as blood pressure, pH, and blood gases critically determine outcome after focal cerebral ischemia. Although anesthesia by halothane via face-mask allowed better control of depth of anesthesia than chloral hydrate, we have found this method to be unsatisfactory due to insufficient control of ventilation and waste of anesthetic gases. Experiments with rats requiring normal physiologic parameters should be performed under conditions of controlled mechanical ventilation and sufficient analgesia.

Effect of isoflurane versus nicardipine on blood flow of lumbar paraspinal muscles during controlled hypotension for spinal surgery

STUDY DESIGN

This study compared the effects of isoflurane and nicardipine on regional blood flow of the lumbar paraspinal muscles.

OBJECTIVES

The purpose of this study was to determine whether treatment with hypotensive agents result in ischemia of the lumbar paraspinal muscles, thereby facilitating surgical procedures.

SUMMARY OF BACKGROUND DATA

Despite the general acceptance of controlled hypotension as effective in reducing blood loss during spinal surgery, the changes of blood flow that occur at the lumbar paraspinal muscles when this technique is applied remain unclear. The use of laser Doppler flowmetry allows changes of muscle blood flow to be easily detected in real time with minimal invasion, thereby allowing differences among distinct pharmacological approaches for induction and maintenance of controlled hypotension to be evaluated.

METHODS

The prehypotensive and hypotensive (reduction of mean arterial pressure by 20 mm Hg) blood flow of the lumbar paraspinal muscles were assessed with a laser Doppler flowmeter in 40 patients undergoing lumbar spinal surgery. The first half of the patients (n = 20) received isoflurane, whereas the second half received nicardipine to achieve arterial hypotension.

RESULTS

Compared with the prehypotensive state, during the hypotensive state, patients in the isoflurane group exhibited a 17% to 46% (mean, 33.7%) decrease in lumbar paraspinal muscle blood flow, whereas patients in the nicardipine group exhibited a 24% to 177% (mean, 82.5%) increase in lumbar paraspinal muscle blood flow. Statistical analysis showed a significant difference in the changes of flux after induced hypotension between the isoflurane and nicardipine group (P < 0.001).

CONCLUSIONS

Depending on the pharmacological treatment used to achieve arterial hypotension in spine surgery, there will be either a reduction in paraspinal muscle blood flow (ischemia) or an enhancement of this blood flow (hyperemia).