Cerebral blood flow and metabolism following subarachnoid haemorrhage: cerebral oxygen uptake and global blood flow during the acute period in patients with SAH

Temporal Dynamics of Cerebral Blood Flow During the Acute Course of Severe Subarachnoid Hemorrhage Studied by Bedside Xenon-Enhanced CT

Background

Compromised cerebral blood flow (CBF) is a crucial factor in delayed cerebral ischemia after subarachnoid hemorrhage (SAH). Repeated measurement of CBF may improve our understanding of the temporal dynamics following SAH. The aim of this study was to assess CBF at different phases of the acute course in poor-grade SAH patients, hypothesizing more pronounced disturbances at day 4–7, and that the initial level of CBF determines the following course of CBF.

Methods

Mechanically ventilated SAH patients were scheduled for bedside measurement of regional and global cortical CBF at day 0–3, 4–7, and 8–12, using xenon-enhanced computed tomography in a mobile setup. Patients were dichotomized depending on high or low initial global cortical CBF and cutoff level 30 ml/100 g/min.

Results

Eighty-one patients were included, and 51 had measurements at day 0–3 and 4–7. In patients with high initial CBF, the level was unchanged at day 4–7; 37.7 (IQR 32.6–46.7) ml/100 g/min versus 36.8 (IQR 29.5–44.8). The low-CBF group showed a slight increase from 23.6 (IQR 21.0–28.1) ml/100 g/min to 28.4 (IQR 22.7–38.3) (P = 0.025), still markedly lower than the high-CBF group (P = 0.016). In the low-CBF group, CBF increased in patients who received hypertension, hypervolemia, and hemodilution (HHH therapy) but remained low in standard treated patients. For the subset of 27 patients examined also at day 8–12, the differences depending on initial CBF level were no longer statistically significant. Among patients with still low CBF at day 4–7, the proportion who had poor short-term outcome was 55% compared to 35% (n.s.) for patients with high CBF.

Conclusions

CBF studied in poor-grade SAH patients at large did not show any statistically significant changes over time. Stratifying patients by high or low initial CBF and whether HHH therapy was given revealed an association between low initial CBF and persistent low CBF at day 4–7. These findings may be of clinical relevance in managing SAH patients with low early CBF.

Hemodynamic Disturbances in the Early Phase After Subarachnoid Hemorrhage: Regional Cerebral Blood Flow Studied by Bedside Xenon-enhanced CT

BACKGROUND

The mechanisms leading to neurological deterioration and the devastating course of delayed cerebral ischemia (DCI) after subarachnoid hemorrhage (SAH) are still not well understood. Bedside xenon-enhanced computerized tomography (XeCT) enables measurements of regional cerebral blood flow (rCBF) during neurosurgical intensive care. In the present study, CBF characteristics in the early phase after severe SAH were explored and related to clinical characteristics and early clinical course outcome.

MATERIALS AND METHODS

Patients diagnosed with SAH and requiring mechanical ventilation were prospectively enrolled in the study. Bedside XeCT was performed within day 0 to 3.

RESULTS

Data from 64 patients were obtained. Median global CBF was 34.9 mL/100 g/min (interquartile range [IQR], 26.7 to 41.6). There was a difference in CBF related to age with higher global CBF in the younger patients (30 to 49 y). CBF was also related to the severity of SAH with lower CBF in Fisher grade 4 compared with grade 3. rCBF disturbances and hypoperfusion were common; in 43 of the 64 patients rCBF<20 mL/100 g/min was detected in more than 10% of the region-of-interest (ROI) area and in 17 patients such low-flow area exceeded 30%. rCBF was not related to the localization of the aneurysm; there was no difference in rCBF of ipsilateral compared with contralateral vascular territories. In patients who initially were in Hunt & Hess grade I to III, median global CBF day 0 to 3 was significantly lower for patients who were in poor neurological state at discharge compared with patients in good neurological state, 25.5 mL/100 g/min (IQR, 21.3 to 28.3) versus 37.8 mL/100 g/min (IQR, 30.5 to 47.6).

CONCLUSIONS

CBF disturbances are common in the early phase after SAH. In many patients, CBF was heterogenic and substantial areas with low rCBF were detected. Age and CT Fisher grade were factors influencing global cortical CBF. Bedside XeCT may be a tool to identify patients at risk of deteriorating so they can receive intensified management, but this needs further exploration.

Non-invasive assessment of vasospasm following aneurysmal SAH using C-arm FDCT parenchymal blood volume measurement in the neuro-interventional suite: Technical feasibility

INTRODUCTION

Cerebral vasospasm is the leading cause of morbidity and mortality in patients with aneurysmal subarachnoid haemorrhage (SAH) surviving the initial ictus. Commonly used techniques for vasospasm assessment are digital subtraction angiography and transcranial Doppler sonography. These techniques can reliably identify only the major vessel spasm and fail to estimate its haemodynamic significance. To overcome these issues and to enable comprehensive non-invasive assessment of vasospasm inside the interventional suite, a novel protocol involving measurement of parenchymal blood volume (PBV) using C-arm flat detector computed tomography (FDCT) was implemented.

MATERIALS AND METHODS

Patients from the neuro-intensive treatment unit (ITU) with suspected vasospasm following aneurysmal SAH were scanned with a biplane C-arm angiography system using an intravenous contrast injection protocol. The PBV maps were generated using prototype software. Contemporaneous clinically indicated MR scan including the diffusion- and perfusion-weighted sequences was performed. C-arm PBV maps were compared against the MR perfusion maps.

RESULTS

Distribution of haemodynamic impairment on C-arm PBV maps closely matched the pattern of abnormality on MR perfusion maps. On visual comparison between the two techniques, the extent of abnormality indicated PBV to be both cerebral blood flow and cerebral blood volume weighted.

CONCLUSION

C-arm FDCT PBV measurements allow an objective assessment of the severity and localisation of cerebral hypoperfusion resulting from vasospasm. The technique has proved feasible and useful in very sick patients after aneurysmal SAH. The promise shown in this early study indicates that it deserves further evaluation both for post-SAH vasospasm and in other relevant clinical settings.

Hypothermia as a neuroprotective strategy in subarachnoid hemorrhage: a pathophysiological review focusing on the acute phase

Aneurysmal subarachnoid hemorrhage (SAH) remains a very prevalent challenge in neurosurgery associated with a high morbidity and mortality due to the lack of specific treatment modalities. The prognosis of SAH patients depends primarily on three factors: (i) the severity of the initial bleed, (ii) the endovascular or neurosurgical procedure to occlude the aneurysm and (iii) the occurrence of late sequelae, namely delayed ischemic neurological deficits due to cerebral vasospasm. While neurosurgeons and interventionalists have put significant efforts in minimizing periprocedural complications and a multitude of investigators have been devoted to the research on chronic vasospasm, the acute phase of SAH has not been studied in comparable detail. In various experimental studies during the past decade, hypothermia has been shown to reduce neuronal damage after ischemia, traumatic brain injury and other cerebrovascular diseases. Clinically, only some of these encouraging results could be reproduced. This review analyses results of studies on the effects of hypothermia on SAH with special respect to the acute phase in an experimental setting. Based on the available data, some considerations for the application of mild to moderate hypothermia in patients with subarachnoid hemorrhage are given.

Current advances in the diagnosis of vasospasm

Symptomatic vasospasm leading to delayed ischemia and neurological deficits is one of the most serious complications after aneurysmal subarachnoid hemorrhage (SAH). Reliable and early detection of symptomatic vasospasm is one of the major goals in the management of patients with SAH. In awake patients, the close clinical neurological examination still remains the most important diagnostic measure. In comatous or sedated patients, cerebral angiography remains the mainstay of the diagnostic workup for vasospasm. However, angiography does not allow assessing the hemodynamic relevance of vasospasm and is not suited for early identification of cerebral hypoperfusion and ischemia. Therefore, a large panel of new monitoring techniques for the assessment of regional cerebral perfusion has been recently introduced into the clinical management of SAH patients. This article briefly reviews the most relevant methods for monitoring cerebral perfusion and discusses their clinical predictive value for the diagnosis of vasospasm. On the basis of the currently available monitoring technologies, an algorithm for the diagnosis of vasospasm is presented.

Neuroprotective effects of anti-tumor necrosis factor-alpha antibody on apoptosis following subarachnoid hemorrhage in a rat model

Recent studies have emphasized the importance of apoptosis in subarachnoid hemorrhage (SAH) and the subsequent early brain injury. However, the apoptotic pathways induced by SAH in different brain regions are not fully understood. We investigated gene expression levels of classical apoptosis-related molecules (caspase-3, bax, and bcl-2) following SAH in the hippocampus of male Wistar rats. Temporally specific changes were found in caspase-3 and bax messenger RNA only. Interestingly, we found increased expression of bax, but not caspase-3, in the prefrontal cortex, which indicates different molecular mechanisms of apoptosis in distinct brain regions. Most important, changes in expression were reversed by functional blockade of tumor necrosis factor-alpha, which has a critical role in brain injury. In addition, we found that apoptosis induced by SAH may be associated with a relative elevation of pro-brain derived neurotrophic factor.

The importance of early brain injury after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (aSAH) is a medical emergency that accounts for 5% of all stroke cases. Individuals affected are typically in the prime of their lives (mean age 50 years). Approximately 12% of patients die before receiving medical attention, 33% within 48 h and 50% within 30 days of aSAH. Of the survivors 50% suffer from permanent disability with an estimated lifetime cost more than double that of an ischemic stroke. Traditionally, spasm that develops in large cerebral arteries 3-7 days after aneurysm rupture is considered the most important determinant of brain injury and outcome after aSAH. However, recent studies show that prevention of delayed vasospasm does not improve outcome in aSAH patients. This finding has finally brought in focus the influence of early brain injury on outcome of aSAH. A substantial amount of evidence indicates that brain injury begins at the aneurysm rupture, evolves with time and plays an important role in patients' outcome. In this manuscript we review early brain injury after aSAH. Due to the early nature, most of the information on this injury comes from animals and few only from autopsy of patients who died within days after aSAH. Consequently, we began with a review of animal models of early brain injury, next we review the mechanisms of brain injury according to the sequence of their temporal appearance and finally we discuss the failure of clinical translation of therapies successful in animal models of aSAH.

Acute perfusion changes after spontaneous SAH: a perfusion CT study

BACKGROUND

Perfusion computed tomography (CT) is a rapid technique that allows the measurement of acute disturbances in local and global cerebral blood flow in patients suffering stroke and spontaneous subarachnoid haemorrhage (SAH). The purpose of this study was to establish the relationship between different measures of brain perfusion made on dynamic-contrast CT reconstructions performed as soon as SAH has been diagnosed and the severity of the bleeding determined by the clinical grade, the extent of the bleeding and the outcome of the patients.

METHODS

After the diagnosis of SAH by conventional CT, a perfusion CT was performed before CT angiography. All imaging studies were performed on a six-slice spiral CT scanner. All images were analysed using perfusion software developed by Philips, which produces perfusion CT quantitative data based on temporal changes in signal intensity during the first pass of a bolus of an iodinated contrast agent. Measurements of mean transient time (MTT), time to peak (TTP), cerebral blood volume (CBV) and cerebral blood flow (CBF) in volumes of interest corresponding to territories perfused by the major cerebral arteries were performed. Different data regarding severity of the bleeding-such as level of consciousness, amount of bleeding in conventional CT-were collected. All poor-grade patients received a ventriculostomy catheter so that ICP recordings were obtained. Also, the occurrence of delayed cerebral ischaemia (DCI) was recorded. Outcome was assessed by the Glasgow Outcome Scale 6 months after the bleeding. For statistical analysis, non-parametric correlations between variables were performed.

FINDINGS

Thirty-nine patients have been included in the study since January 2007. In SAH patients there are increasing perfusion abnormalities as the severity of the bleeding increases. The most affected perfusion parameters are TTP and MTT, as they significantly increase with the clinical severity of the bleeding and the total volume of bleeding (P < 0.01, Spearman's Rho). When average MTT time is increased over 5.9 s there is a 20-fold (95% CI = 2.1-182) risk of poor outcome. All patients presenting this MTT time suffered from DCI. This value has a positive predictive value of 100% for DCI and 90% for a poor outcome.

CONCLUSIONS

SAH causes cerebral blood flow abnormalities even in the acute phase of the illness, consisting mainly of an increase in circulation times (TTP and MTT), which are correlated with the severity of the bleeding.

Hypoperfusion in the acute phase of subarachnoid hemorrhage

PURPOSE

Acute disruption of cerebral perfusion and metabolism is a well-established hallmark of the immediate phase after subarachnoid hemorrhage (SAH). It is thought to contribute significantly to acute brain injury, but despite its prognostic importance, the exact mechanism and time course is largely unknown and remains to be characterized.

METHODS

We investigated changes in cerebral perfusion after SAH in both an experimental and clinical setting. Using an animal model of massive, experimental SAH (n=91), we employed Laser-Doppler flowmetry (LDF), parenchymal microdialysis (MD; n=61), Diffusion-weighted imaging (DWI) and MR spectroscopy (MRS; n=30) to characterize the first hours after SAH in greater detail. The effect of prophylactic treatment with hypothermia (HT; 32°C) and an endothelin-A (ET-A) receptor antagonist (Clazosentan) was also studied. In a group of patients presenting with acute SAH (n=17) we were able to determine cerebral blood flow (CBF) via Xenon-enhanced computed tomography (XeCT) within 12 h after the ictus.

RESULTS

The acute phase after SAH is characterized both experimentally and clinically by profound and prolonged hypoperfusion independent from current intracranial pressure (ICP), indicating acute vasospasm. Experimentally, when treated with hypothermia or a ET-A receptor antagonist prophylactically, acute hypoperfusion improved rapidly. DWI showed a generalized, significant decline of the apparent diffusion coefficient (ADC) after SAH, indicating cytotoxic edema which was not present under hypothermia. SAH causes a highly significant reduction in glucose, as well as accumulation of lactate, glutmate and aspartate (MD and MRS). HT significantly ameliorated these metabolic disturbances.

CONCLUSION

Acute vasospasm, cytotoxic edema and a general metabolic stress response occur immediately after experimental SAH. Prophylactic treatment with hypothermia or ET-A antagonists can correct these disturbances in the experimental setting. Clinically, prolonged and ICP-independent hypoperfusion was also confirmed. As the initial phase is of particular importance regarding the neurological outcome and is amenable to beneficial intervention, the acute stage after SAH demands further investigation and warrants the exploration of measures to improve the immediate management of SAH patients.

PET in Cerebrovascular Disease

Investigation of the interplay between the cerebral circulation and brain cellular function is fundamental to understanding both the pathophysiology and treatment of stroke. Currently, PET is the only technique that provides accurate, quantitative in vivo regional measurements of both cerebral circulation and cellular metabolism in human subjects. We review normal human cerebral blood flow and metabolism and human PET studies of ischemic stroke, carotid artery disease, vascular dementia, intracerebral hemorrhage and aneurysmal subarachnoid hemorrhage and discuss how these studies have added to our understanding of the pathophysiology of human cerebrovascular disease.

Time-course of cerebral perfusion and tissue oxygenation in the first 6 h after experimental subarachnoid hemorrhage in rats

Present knowledge about hemodynamic and metabolic changes after subarachnoid hemorrhage (SAH) originates from neuromonitoring usually starting with aneurysm surgery and animal studies that have been focusing on the first 1 to 3 h after SAH. Most patients, however, are referred to treatment several hours after the insult. We examined the course of hemodynamic parameters, cerebral blood flow, and tissue oxygenation (ptiO2) in the first 6 h after experimental SAH. Sixteen Sprague-Dawley rats were subjected to SAH using the endovascular filament model or served as controls (n=8). Bilateral local cortical blood flow, intracranial pressure, cerebral perfusion pressure, and ptiO2 were followed for 6 h after SAH. After induction of SAH, local cortical blood flow rapidly declined to 22% of baseline and returned to 80% after 6 h. The decline of local cortical blood flow markedly exceeded the decline of cerebral perfusion pressure. ptiO2 declined to 57%, recovered after 2 h, and reached > or =140% of baseline after 6 h. Acute vasoconstriction after SAH is indicated by the marked discrepancy of cerebral perfusion pressure and local cortical blood flow. The excess tissue oxygenation several hours after SAH suggests disturbed oxygen utilization and cerebral metabolic depression. Aside from the sudden increase of intracranial pressure at the time of hemorrhage and delayed cerebral vasospasm, the occurrence of acute vasoconstriction and disturbed oxygen utilization may be additional factors contributing to secondary brain damage after SAH.

Perfusion-weighted MRI to evaluate cerebral autoregulation in aneurysmal subarachnoid haemorrhage

INTRODUCTION

The aim of this study was to evaluate autoregulatory mechanisms in different vascular territories within the first week after aneurysmal subarachnoid haemorrhage (SAH) by perfusion-weighted magnetic resonance imaging (PW-MRI). For this purpose, regional cerebral blood flow and volume (rCVF and rCBV) were measured in relation to different degrees of angiographically visible cerebral vasospasm (CVS).

MATERIALS AND METHODS

In 51 SAH patients, PW-MRI and digital subtraction angiography were performed about 5 days after onset of SAH. Regional CBF and rCBV were analysed in the territories of the anterior cerebral artery (ACA), the middle cerebral artery (MCA) and the basal ganglia of each hemisphere in relationship to the degree of CVS in the particular territory. Correlations between rCBF, rCBV and CVS were analysed.

RESULTS

CVS was found in 22 out of 51 patients in at least one territory. In all territories, rCBV decreased with increasing degree of CVS, correlated with a decrease of rCBF. In the ACA territories, SAH patients with severe CVS had significantly lower rCBF compared to healthy subjects and to SAH patients without CVS. In the basal ganglia, rCBF and rCBV of the control group were significantly higher compared to the patients without and with moderate vasospasms.

CONCLUSION

PW-MRI showed simultaneous decrease of rCBF and rCBV in patients with SAH. The fact that rCBV did not increase in territories with CVS to maintain rCBF reveals dysfunctional vascular autoregulation. Vasospasms in the microvasculature are most evident in the basal ganglia, showing decreased rCBV and rCBF even in SAH patients without CVS.

Enhancement of cerebral blood flow using systemic hypertonic saline therapy improves outcome in patients with poor-grade spontaneous subarachnoid hemorrhage

OBJECT

Systemic administration of 23.5% hypertonic saline enhances cerebral blood flow (CBF) in patients with poor-grade spontaneous subarachnoid hemorrhage (SAH). Whether the increment of change in CBF correlates with changes in autoregulation of CBF or outcome at discharge remains unknown.

METHODS

Thirty-five patients with poor-grade spontaneous SAH received 2 ml/kg 23.5% hypertonic saline intravenously, and they underwent bedside transcranial Doppler (TCD) ultrasonography and intracranial pressure (ICP) monitoring. Seventeen of them underwent Xe-enhanced computed tomography (CT) scanning for measuring CBF. Outcome was assessed using the modified Rankin Scale (mRS) at discharge from the hospital. The data were analyzed using repeated-measurement analysis of variance and Dunnett correction. A comparison was made between patients with favorable and unfavorable outcomes using multivariate logistic regression.

RESULTS

The authors observed a maximum increase in blood pressure by 10.3% (p < 0.05) and cerebral perfusion pressure (CPP) by 21.2% (p < 0.01) at 30 minutes, followed by a maximum decrease in ICP by 93.1% (p < 0.01) at 60 minutes. Changes in ICP and CPP persisted for longer than 180 and 90 minutes, respectively. The results of TCD ultrasonography showed that the baseline autoregulation was impaired on the ipsilateral side of ruptured aneurysm, and increments in flow velocities were higher and lasted longer on the contralateral side (48.75% compared with 31.96% [p = 0.045] and 180 minutes compared with 90 minutes [p < 0.05], respectively). The autoregulation was briefly impaired on the contralateral side during the infusion. A dose-dependent effect of CBF increments on favorable outcome was seen on Xe-CT scans (mRS Score 1-3, odds ratio 1.27 per 1 ml/100 g tissue x min, p = 0.045).

CONCLUSIONS

Bolus systemic hypertonic saline therapy may be used for reversal of cerebral ischemia to normal perfusion in patients with poor-grade SAH.

Vasospasm as the sole cause of cerebral ischemia: how strong is the evidence?

✓ The authors review literature that challenges the view that vasospasm involving large arteries is the exclusive cause of delayed ischemic neurological deficits (DINDs) following subarachnoid hemorrhage. They discuss alternative mechanisms and review the evidence supporting a potential role for thromboembolism. They conclude that vasospasm and thromboembolism play interrelated and additive roles in the development of DINDs, and that this interaction provides opportunities for novel therapeutic approaches.

Molecular mechanisms of early brain injury after subarachnoid hemorrhage

OBJECTIVES

Increasing body of experimental and clinical data indicates that early brain injury after initial bleeding largely contributes to unfavorable outcome after subarachnoid hemorrhage (SAH). This review presents molecular mechanisms underlying brain injury at its early stages after SAH.

METHODS

PubMed was searched using term 'subarachnoid hemorrhage' and key words referring to molecular and cellular pathomechanisms of SAH-induced early brain injury.

RESULTS

The authors reviewed intracranial phenomena and molecular agents that contribute to the early development of pathological sequelae of SAH in cerebral and vascular tissues, including cerebral ischemia and its interactions with injurious blood components, blood-brain barrier disruption, brain edema and apoptosis.

DISCUSSION

It is believed that detailed knowledge of molecular signaling pathways after SAH will serve to improve therapeutic interventions. The most promising approach is the protection of neurovascular unit including anti-apoptosis therapy.

Using CT in the Diagnosis and Management of Patients with Cerebral Vasospasm

Cerebral vasospasm remains a serious complication of aneurysmal subarachnoid hemorrhage. Efforts in improving its clinical outcome have been focused on early diagnosis and applying effective treatment regimens. Standard diagnostic modalities currently used do not fully address this complex disease. The use of CT angiography and CT perfusion are discussed, with emphasis on its potential role in not only detecting vasospasm, but also in guiding management decisions and assessing clinical outcome.

Early transcranial Doppler after subarachnoid hemorrhage: clinical and radiological correlations

BACKGROUND

The initial decrease in the level of consciousness after subarachnoid hemorrhage (SAH) is commonly considered secondary to cerebral hypoperfusion and metabolic depression. Age, intracranial pressure, and the amount of cisternal blood are closely related to the clinical grade on admission after SAH. Transcranial Doppler (TCD) may partially and indirectly estimate cerebral blood flow through analysis of flow velocity in the middle cerebral artery (MCA). Besides, pulsatility index (PI) can also be considered an indirect estimator of cerebrovascular resistance. The objective of this study was to determine the TCD parameters in the early stage after SAH and to analyze their correlation with the main clinical and radiological variables on admission.

METHODS

A series of 52 consecutive patients diagnosed with SAH, with an abnormal computed tomography (CT) scan on admission and a TCD performed in the first 24 hours from the onset of the hemorrhage, were retrospectively reviewed. Age, sex, clinical grade, presence of cisternal blood or hydrocephalus on initial CT scan, and parameters of TCD examination were recorded for every patient. The relationship between sonographic and clinical and radiological variables was evaluated by partial correlation test, Kruskal-Wallis, and Student t test for paired samples.

RESULTS

There were no significant differences in blood flow velocities or PIs between the left and right sides. Lower velocities and higher PIs correlated with a worse clinical condition at admission. Lower velocities also correlated with larger amounts of cisternal blood on the initial CT scan. No significant correlation was observed between PI and the amount of blood in the initial CT scan.

CONCLUSIONS

A global decrease in blood velocity in the MCA along with a rise in PI is present in the first 24 hours after SAH. These changes correlate with the clinical deterioration and partially with the amount of blood in the initial CT scan. These findings support the hypothesis that low cerebral perfusion caused by high intracranial pressure leads to diffuse ischemic changes in the early phase of SAH.

Hypertonic fluid resuscitation from subarachnoid hemorrhage in rats: A comparison between small volume resuscitation and mannitol

OBJECTIVE

Death and severe morbidity after subarachnoid hemorrhage (SAH) are mainly caused by global cerebral ischemia through increased intracranial pressure (ICP) and decreased cerebral blood flow (CBF). We have recently demonstrated neuroprotective effects of small volume resuscitation (7.5% saline in combination with 6% dextran 70) in an animal model of SAH, leading to normalization of increased ICP, reduced morphological damage and improved neurological recovery. In the present study, we compared the concept of small volume resuscitation represented by two clinically licenced hypertonic-hyperoncotic saline solutions with the routinely used hyperosmotic agent-mannitol-and investigated their effects on ICP, CBF, neurological recovery and morphological damage after SAH in rats.

METHODS

60 dextran-resistant Wistar rats were subjected to SAH by an endovascular filament. ICP, MABP (mean arterial blood pressure) and bilateral local CBF were continuously recorded. All animals were randomly assigned to four groups: (I) NaCl 0.9% (4 ml/kg bw), (II) 7.5% NaCl+6% dextran 70 (4 ml/kg bw), (III) 7.2% NaCl+HES 200,000 (4 ml/kg bw) and (IV) 20% mannitol (9.33 ml/kg bw) given 30 min after SAH. Neurological deficits were assessed on days 1, 3 and 7 after SAH. The morphological damage was evaluated on day 7 after SAH.

RESULTS

The induction of SAH resulted in an immediate ICP increase to 46.6+/-3.2 mm Hg (mean+/-S.E.M.) and 29.6+/-1.3 (mean+/-S.E.M.) mm Hg 90 min post-SAH. While a treatment with both hypertonic saline solutions (II, III) decreased ICP as well as the 20% mannitol solution, only the group treated with hypertonic saline and dextran 70 (II) showed an increase of ipsilateral CBF for 20 min after the infusion and significantly more surviving neurons in the motorcortex and caudoputamen. Mortality was reduced from 60% (I) and 73% (III and IV), respectively, to 40% in group II.

CONCLUSION

Of all hypertonic solutions investigated, small volume resuscitation with NaCl 7.5% in combination with 6% dextran 70 evolved to be most effective in terms of reducing the initial harmful sequelae of SAH, leading to lowered ICP and less morphological damage after SAH in the rat.

Cerebral perfusion heterogeneity and complexity in patients with acute subarachnoid haemorrhage

BACKGROUND

The pathophysiological mechanisms of impaired perfusion during acute subarachnoid haemorrhage (SAH) are incompletely understood. Cerebral perfusion at the micro vascular level can be assessed by single photon emission computed tomography (SPECT). We used a SPECT approach with 99mTc-ECD to measure the cerebral perfusion heterogeneity and complexity in patients with acute aneurysmal SAH or perimesencephalic non-aneurysmal SAH (PNSAH).

METHODS

The perfusion SPECT data of 61 patients with aneurysmal SAH, 18 patients with PNSAH, and 20 healthy control subjects were analysed by dividing the brain into 384 regions of interest. The magnitude of spatial perfusion heterogeneity was assessed by calculating the relative dispersion (RD=coefficient of variation). The fractal dimension (FD) was used to describe the overall complexity of global cerebral perfusion.

RESULTS

Patients with aneurysmal SAH (RD=11.30+/-2.17, P<0.001) and PNSAH (10.38+/-2.27, P=0.023) had a higher perfusion heterogeneity than control subjects (8.69+/-0.80). Patients with aneurysmal SAH tended to have a higher perfusion heterogeneity than patients with PNSAH (P=0.061). Also the overall complexity of cerebral perfusion was decreased in aneurysmal SAH (FD=1.11+/-0.06, P<0.001) and PNSAH (1.11+/-0.06, P=0.004) as compared with control subjects (1.17+/-0.06). Acute SAH causes increased regional cerebral perfusion heterogeneity and decreased overall complexity of global cerebral perfusion.

CONCLUSION

Non-invasive assessment of cerebral perfusion characteristics is feasible with SPECT and fractal analysis in patients with acute SAH and may help evaluating micro vascular function in SAH.

Posttraumatic vasospasm: the epidemiology, severity, and time course of an underestimated phenomenon: a prospective study performed in 299 patients

OBJECT

The purpose of this prospective study was to evaluate the cumulative incidence, duration, and time course of cerebral vasospasm after traumatic brain injury (TBI) in a cohort of 299 patients.

METHODS

Transcranial Doppler (TCD) ultrasonography studies of blood flow velocity in the middle cerebral and basilar arteries (VMCA and VBA, respectively) were performed at regular intervals during the first 2 weeks posttrauma in association with 133Xe cerebral blood flow (CBF) measurements. According to current definitions of vasospasm, five different criteria were used to classify the patients: A (VMCA > 120 cm/second); B (VMCA > 120 cm/second and a Lindegaard ratio [LR] > 3); C (spasm index [SI] in the anterior circulation > 3.4); D (VBA > 90 cm/second); and E (SI in the posterior circulation > 2.5). Criteria C and E were considered to represent hemodynamically significant vasospasm. Mixed-effects spline models were used to analyze the data of multiple measurements with an inconsistent sampling rate. Overall 45.2% of the patients demonstrated at least one criterion for vasospasm. The patients in whom vasospasm developed were significantly younger and had lower Glasgow Coma Scale scores on admission. The normalized cumulative incidences were 36.9 and 36.2% for patients with Criteria A and B, respectively. Hemodynamically significant vasospasm in the anterior circulation (Criterion C) was found in 44.6% of the patients, whereas vasospasm in the BA-Criterion D or E-was found in only 19 and 22.5% of the patients, respectively. The most common day of onset for Criteria A, B, D, and E was postinjury Day 2. The highest risk of developing hemodynamically significant vasospasm in the anterior circulation was found on Day 3. The daily prevalence of vasospasm in patients in the intensive care unit was 30% from postinjury Day 2 to Day 13. Vasospasm resolved after a duration of 5 days in 50% of the patients with Criterion A or B and after a period of 3.5 days in 50% of those patients with Criterion D or E. Hemodynamically significant vasospasm in the anterior circulation resolved after 2.5 days in 50% of the patients. The time course of that vasospasm was primarily determined by a decrease in CBF.

CONCLUSIONS

The incidence of vasospasm after TBI is similar to that following aneurysmal subarachnoid hemorrhage. Because vasospasm is a significant event in a high proportion of patients after severe head injury, close TCD and CBF monitoring is recommended for the treatment of such patients.

Jugular bulb oximetry for prediction of vasospasm following subarachnoid hemorrhage

BACKGROUND

Cerebral vasospasm adversely impacts the outcome of those suffering aneurysmal subarachnoid hemorrhage (SAH). Prediction of vasospasm could improve outcomes. We hypothesized that preclinical vasospasm would be heralded by an increase in cerebral oxygen extractions (AVDO2) which could be detected by jugular bulb oximetry. A pilot study was conducted to address this hypothesis.

METHODS

Fourteen consenting patients with aneurysmal SAH, undergoing early surgery, were entered into the study. Four patients were withdrawn from the study secondary to failure of catheters or religious belief. At the time of craniotomy, a jugular bulb catheter was placed. Post-operatively, arterial and jugular bulb blood samples were taken every 12 hours to calculate AVDO2. As this was an observational study, no change in management occurred based on measurements.

RESULTS

Four of 10 patients had clinical vasospasm. These patients had a significant rise in AVDO2 approximately one day prior to the onset of neurologic deficits (P<0.001). Symptoms resolved along with a significant improvement in AVDO2 on instituting hypertensive, hemo-dilutional, and hypervolemic therapy in these patients. The six patients who did not exhibit clinical vasospasm did not demonstrate significant rise in AVDO2.

CONCLUSIONS

Jugular bulb oximetry is simple and cost effective. Increases in AVDO2 using this technique were predictive of clinically evident vasospasm in the subsequent hours to days. This investigation supports a larger study to assess the utility of jugular bulb oximetry in predicting vasospasm in aneurysmal SAH.

Haemodynamic and metabolic disturbances in the acute stage of subarachnoid haemorrhage demonstrated by PET

OBJECTIVE

To investigate the occurrence of early haemodynamic and metabolic changes in the acute stage of subarachnoid haemorrhage (SAH).

MATERIAL AND METHODS

Eleven SAH patients were studied. Regional cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2) and oxygen extraction ratio (OER) were measured with positron emission tomography (PET) 22-53 h after haemorrhage, utilizing 15O-labelled water bolus and the 15O-inhalation technique. Ten volumes of interest (VOIs) representing vascular territories were outlined in each patient according to a standardized procedure. The occurrence of irreversible ischaemia, penumbra, oligaemia, hyperperfusion and normal haemodynamics according to PET criteria was investigated. These pathophysiological categories were related to final tissue outcome as determined by follow-up computed tomography (CT).

RESULTS

All five tissue subtypes were represented in the vascular region VOIs; oligaemia was the predominant pathophysiological pattern. When global changes were analysed, blood flow was reduced in three, oxygen metabolism was reduced in four, and OER was increased in four of seven unsedated patients, respectively. The sedated patients all had markedly reduced CBF and CMRO2 and OER in the high or supranormal range.

CONCLUSION

Haemodynamic and metabolic disturbances proved to be common after SAH. These abnormalities probably reflect the primary brain injury caused by the initial haemorrhage. The impact of secondary insults such as acute hydrocephalus, brain oedema, vasospasm, seizures, hypotension and hypoxaemia are likely to be dependent on the degree of primary injury, which can be assessed by PET.

Cerebral vasospasm and ischaemic infarction in clipped and coiled intracranial aneurysm patients

The influence of the treatment modalities (clipping/coiling) on the incidence of vasospasm and ischaemic infarction in aneurysm patients is still judged controversially. The purpose of this study was to analyse and compare retrospectively cerebral vasospasm and ischaemic infarction, as well as neurological deficits and outcome within a large population of clipped and coiled patients with ruptured and unruptured aneurysms. Within a 2-year period, a total of 144 interventions (53 clipping/91 coiling) entered the study. Daily bilateral transcranial Doppler sonographic monitoring was performed to observe vasospasm development. All cerebral computed tomography (cCT) and magnetic resonance imaging (MRI) scans were reviewed with respect to occurrence and localization of ischaemic infarctions. Focal neurological deficits were recorded and clinical outcome was evaluated using the Glasgow Outcome Scale. Statistical analysis included the use of multivariate logistic regression models to find determinants of vasospasm, ischaemic infarction and neurological deficits. Altogether, vasospasm was detected after 77 (53.5%) interventions, 61.8% in females (P < 0.01). Clipped patients significantly more often exhibited vasospasms (69.8 vs. 44.0%, P < 0.005) and were treated 1 week longer at the intensive care unit (P < 0.005). Seventy-seven patients (53.5%) developed ischaemic infarctions, 62.3% after clipping and 48.4% after coiling (P > 0.05). In the multivariate analysis, aneurysm-rupture was the strongest predictor for vasospasm and vasospasm was the strongest predictor for infarction. Neurological deficits at discharge (46.5%) were independent of treatment modality, the same applied for the mean Glasgow Outcome Scores. There was no significant difference in mortality between surgical and endovascular treatment (9.4 vs. 12.1%). Whilst the vasospasm incidence was significantly higher after surgical treatment, ischaemic infarctions were only slightly more frequent. The incidence of neurological deficits and clinical outcome was similar in both treatment groups.

Subarachnoid hemorrhage induces dynamic changes in regional cerebral metabolism in rats

Following a subarachnoid hemorrhage (SAH), adult rats exhibit dynamic regional changes in cerebral glucose metabolism characterized by an increase in metabolic rates and a subsequent upregulation of cytochrome oxidase (CO). We evaluated both local cerebral metabolic rates for glucose (ICMRglc: (mol/100 g/min) and CO in 23 brain regions of interest (ROI). Sham animals underwent anesthesia and superficial surgery; saline-controls received an injection of 0.9% saline into the cisterna magna; and SAH rats received an injection of autologous blood into the cisterna magna. This blood, measured by albumin labeled with radioactive carbon 14, distributed throughout the brain but predominated ventrally. After experimental animals were sacrificed at day 0 (3 h), 1, 3, and 7 days postinjection, ROI were analyzed using [14C]2-deoxy-D-glucose autoradiography and CO histochemistry. ICMRglc in SAH rats increased in many regions (ranging from 0.7% to 32.2% above sham levels). Cytochrome oxidase also increased from 1% to 9% above sham levels, peaking on day 3. Conversely, saline-controls exhibited prolonged depression of ICMRglc (ranging from 11% to 35% below sham levels) and CO (ranging from 4% to 11% below sham levels) from day 0 through day 7. All saline-control ROI for all time points showed this metabolic depression, and between 91% and 95% of saline-control ROI presented lower CO levels as compared to sham. Overall, ICMRglc and CO levels were greater in SAH than in saline-control ROI. However, when considering the influence of subarachnoid blood on metabolic changes in SAH animals, both CO and 2DG levels did not correlate well with the amount of 14C-albumin binding. While previous studies have measured both metabolic rates of glucose and CO soon after SAH, this is the first to simultaneously conduct these measurements in the same SAH rat model.

Cerebral circulation and metabolism in the acute stage of subarachnoid hemorrhage

OBJECT

The mechanism of reduction of cerebral circulation and metabolism in patients in the acute stage of aneurysmal subarachnoid hemorrhage (SAH) has not yet been fully clarified. The goal of this study was to elucidate this mechanism further.

METHODS

The authors estimated cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), O2 extraction fraction (OEF), and cerebral blood volume (CBV) preoperatively in eight patients with aneurysmal SAH (one man and seven women, mean age 63.5 years) within 40 hours of onset by using positron emission tomography (PET). The patients' CBF, CMRO2, and CBF/CBV were significantly lower than those in normal control volunteers. However, OEF and CBV did not differ significantly from those in control volunteers. The significant decrease in CBF/CBV, which indicates reduced cerebral perfusion pressure, was believed to be caused by impaired cerebral circulation due to elevated intracranial pressure (ICP) after rupture of the aneurysm. In two of the eight patients, uncoupling between CBF and CMRO2 was shown, strongly suggesting the presence of cerebral ischemia.

CONCLUSIONS

The initial reduction in CBF due to elevated ICP, followed by reduction in CMRO, at the time of aneurysm rupture may play a role in the disturbance of CBF and cerebral metabolism in the acute stage of aneurysmal SAH.

The role of transcranial Doppler in the management of patients with subarachnoid haemorrhage--a review

Introduced 15 years ago, transcranial Doppler (TCD) recordings of blood-velocity in patients with recent subarachnoid haemorrhage (SAH) have two objectives: to detect elevated blood velocities suggesting cerebral vasospasm (VSP) and to identify patients at risk for delayed cerebral ischemic deficits (DID). The pathophysiological cascade causing DID is complex. Discrepancies between blood velocities and DID (presuming that there actually is an "ischemic threshold" for blood velocity in absolute terms, which seems most unlikely) have been demonstrated, particularly in patients with elevated intracranial pressure (ICP) levels. Furthermore, the vessel showing the highest blood velocity is not always the one perfusing the area where ischemic symptoms arise, nor does the site of the greatest subarachnoid blood clot always relate to the ischemic brain region. Moreover, it is probable that the complex haemodynamic changes following SAH and the subsequent development of VSP may be underestimated if only considering the crude intracranial artery blood velocities. Cerebral blood flow measurements combined with TCD to assess both flow and velocity have emphasised this point. Despite these findings and ignoring the basic principles of cerebral haemodynamics, cerebral vasospasm is still being assessed from the intracranial velocity measurement alone. The addition of at least a careful measurement from the extracranial internal carotid artery--using the same TCD equipment and taking only a few short minutes to perform--allows a much more accurate assessment of the degree and the effects of vasospasm. This probably explains why the clinical value of TCD is still debated. There is still uncertainty as to the best method to prevent and to treat VSP, and the overall outcome after SAH depends on so many factors besides VSP. Conclusive evidence may therefore be hard to obtain, and it appears sound to conclude that even with advanced investigation technology available, proper selection, pre- peri- and postoperative care and timing of surgery remain cornerstones in the management of these patients,--equal in importance to their treatment in the operating room or in the interventional angiography suite.

Effect of clot removal and surgical manipulation on regional cerebral blood flow and delayed vasospasm in early aneurysm surgery for subarachnoid hemorrhage

BACKGROUND

Effect of clot removal and surgical manipulation on cerebral blood flow (CBF) and delayed vasospasm was studied in early aneurysm surgery for subarachnoid hemorrhage (SAH).

METHODS

Thirty-two patients in this study fulfilled the following criteria: ruptured anterior communicating aneurysms, computed tomography (CT) within 2 days and unilateral pterional approach within 3 days after the ictus, bilaterally symmetrical clots without intracerebral hematoma, no postoperative complication, and CBF studies with single photon emission computed tomography (SPECT) with 123I-IMP.

RESULTS

Postoperative regional hypoperfusion due to brain retraction was frequently recognized on 123I-IMP-SPECT without infarction. The regional CBF (rCBF) showed a continuous fall during the first 4 weeks after the ictus, followed by improvement. The rCBF in the vicinity of the surgical route was significantly lower, especially in the acute stage (Day 3-7). A significant association between decrease of cisternal blood after surgery and the degree of local vasospasm and local CBF values during spasm stage was observed in the interhemispheric cisterns, A2 and medial frontal cortex, but not in the sylvian fissure or insular cisterns, M1 or M2, and frontal watershed and temporal cortex.

CONCLUSIONS

The present study provides evidence for the effectiveness of direct clot removal by early surgery for SAH on local vasospasm and CBF reduction. However, a potential improvement in local CBF with clot removal could be masked by brain retraction, which was demonstrated to affect rCBF adversely. Therefore, it is critical to perform brain retraction as gently as possible.

Oxidative stress in the human brain after subarachnoid hemorrhage

OBJECT

The aim of this study was to verify the patterns of antioxidant enzymatic activity of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in the human brain after subarachnoid hemorrhage (SAH) to verify whether an "oxidative stress situation" characterizes the brain response to subarachnoid bleeding.

METHODS

Forty samples of gyrus rectus or temporal operculum that were obtained during a surgical approach to anterior circulation aneurysms were used for this study. The activity of total SOD, GSH-Px, and the SOD/GSH/Px ratio (which expresses the balance between the production of hydrogen peroxides by dismutation of superoxide radicals and the scavenging potential) were calculated in each case. Twelve samples were obtained from patients who underwent surgery for unruptured aneurysms (control group); 13 samples were obtained during surgical procedures performed within 72 hours of SAH; and 15 samples were obtained during delayed surgical procedures (> 10 days post-SAH). Ten patients presented with clinical deterioration caused by arterial vasospasm. In both SAH groups, the mean total SOD activity was significantly higher than in the control group (p=0.029). The mean activity of GSH-Px did not differ significantly between the SAH and control groups (p=0.731). There was a significant increase in the SOD/GSH-Px ratio in both SAH groups, as compared with controls (p < 0.05). There was a significant correlation between the enzymatic activity and the clinical severity of the hemorrhage, with findings of lower values of SOD and, mainly, of the SOD/GSH-Px ratio in the poor-grade patients. The SOD/GSH-Px ratio was 2.14+/-0.44 in patients who presented with clinical vasospasm and 1.24+/-0.2 in cases without vasospasm.

CONCLUSIONS

The results of this study show an imbalance of the antioxidant enzymatic activities in the human brain after SAH. which is linked to the severity of the initial bleeding and possibly modified by the development of arterial vasospasm.

Jugular saturation (SjvO2) monitoring in subarachnoid hemorrhage (SAH)

Jugular saturation (SjvO2) monitoring was performed in 26 SAH patients to evaluate the incidence of normal (0.56-0.74) and pathological SjvO2 values in this population and to describe its time course in the first 12 days. We also attempt to quantify the influence of systemic and cerebral hemodynamics on SjvO2 and to assess the relationship between cerebral injury volume measured on CT scan and SjvO2. Mean SjvO2 was 0.66 +/- 0.07 (354 samples, median 0.67, range 0.43-0.89). 73% of the observations (259/354) were in the normal range. On serial measurements, we identified only 37/354 (10%) desaturation episodes (D.E.). ICP was significantly higher during low SjvO2 observation (p = 0.008). No statistical differences were noted regarding the influence of MAP, CPP, PaCO2, PaO2 on SjvO2 but during D.E., lower PaCO2 and CPP were more frequently observed. CT scan lesions > 25 ml were associated initially with lower SjvO2 values and with higher values at second CT.

Early detection of vasospasm after acute subarachnoid hemorrhage using continuous EEG ICU monitoring

The neurologic morbidity of delayed ischemic deficits from vasospasm following aneurysmal subarachnoid hemorrhage (SAH) continues to be the most debilitating complication from this devastating illness. Neurologic critical care is focused on recognition and treatment of these secondary insults but often the treatment is withheld until an irreversible deficit becomes manifest. Continuous EEG (cEEG) monitoring provides a unique potential to recognize early secondary insults and offers an opportunity for early intervention. We studied 32 SAH patients using cEEG and trending of the quantitative measure, relative alpha (RA), to determine if reductions in RA variability occurred with documented vasospasm. In 19/19 patients with angiographically documented vasospasm, we found that RA variability was decreased by a mean of two grades and improved with resolution of vasospasm. In 10/19 this reduction in RA variability preceded the diagnosis of vasospasm by a mean of 2.9 days (SD 1.73). The positive predictive and negative predictive values are 76% and 100%, respectively. Non-diagnostic clinical signs at the time of RA variability reduction and vasospasm were present in 12/19 patients. Thus decreased RA variability is able to provide early detection of neurologic complications such as vasospasm in patients before clear clinical symptoms and signs occur.

Morphological changes of intraparenchymal arterioles after experimental subarachnoid hemorrhage in dogs

OBJECTIVE

Morphological and microcirculatory changes in intraparenchymal vessels after subarachnoid hemorrhage (SAH) have not yet been fully clarified. We conducted this experimental study to investigate the serial morphological changes of intraparenchymal arterioles after SAH.

METHODS

SAH was produced by injecting autologous arterial blood into the cisterna magna twice at 48-hour intervals in 30 dogs. The dogs were killed 3, 7, or 14 days after SAH, and then perfusion-fixed specimens of both anterior sylvian giri were obtained by using two methods. Microvascular corrosion casts produced by arterial injection of polyester resin were examined using scanning electron microscopy, and the widths of 40 arterioles of each animal were measured. Sectioned slices from the brain surface to 500 microns deep were examined by light microscopy, and external diameter, internal diameters, and wall thickness of the arterioles at depths of 50, 200, and 500 microns from the brain surface were morphometrically evaluated in 40 arterioles of each animal. In control animals receiving cisternal injections of mock cerebrospinal fluid (n = 10) and in healthy control animals (n = 10), the same examination and evaluation were performed.

RESULTS

Corrosion casts of arterioles showed tapered narrowing with folding after SAH, and the width of the arterioles significantly decreased 3 and 7 days after SAH (P < 0.01). Morphometric examination by light microscopy showed a significant decrease of internal diameter of arterioles associated with a significant increase of wall thickness at any depth from the brain surface 3 and 7 days after SAH (P < 0.05 or P < 0.01). These findings improved 14 days after SAH. Control animals receiving cisternal injections of mock cerebrospinal fluid showed no significant differences compared with healthy control animals.

CONCLUSION

These results suggest that constriction of intraparenchymal arterioles occurs after SAH and may contribute to delayed cerebral ischemia.

[Measurement of arteriovenous oxygen difference in the monitoring of patients with subarachnoid hemorrhage due to cerebral aneurysm]

The arterious venous oxygen difference (AVDO2) due to the close relationship with cerebral metabolic rate of oxygen and cerebral blood flow shows metabolic alterations that occur in some pathological situations in the brain including subarachnoid haemorrhage. The AVDO2 was calculated by the Fick equation and the results evaluated by the Glasgow outcome scale. Measurements of arteriojugular oxygen difference were carried out in 30 patients with subarachnoid haemorrhage due to rupture of intracranial aneurysms, as an attempt to monitor the relationship between changes in AVDO2, clinical picture, and evolution of the patients. The subarachnoid haemorrhage was diagnosed by CT scan in 17 patients and by lumbar punction in 13 and the diagnosis of arterial vasospasm was carried out by clinical evaluation and confirmed by four vessels angiogram in only eight patients. Eighteen patients were admitted with Hunt & Hess (H&H) I/II, seven with H&H III and five with H&H IV/V. Nineteen patients had AVDO2 normal and this group had three deaths; five patients had AVDO2 continuously low with three deaths; and six patients had AVDO2 continuously high with two deaths. The patients with normal AVDO2 had better prognosis and clinical evolution than the patients with abnormal values of AVDO2. In conclusion, AVDO2 measurements could not be correlated with the diagnosis of vasospasm, but was useful in the early identification of metabolic changes that occur after subarachnoid haemorrhage and could be used as an supplementary monitoring in the clinical evaluation of patients with this pathology.

Effects of oxyhemoglobin on local and propagated vasodilatory responses induced by adenosine, adenosine diphosphate, and adenosine triphosphate in rat cerebral arterioles

After subarachnoid hemorrhage (SAH), cerebral arteries display impaired vasomotor control, resulting in decreased regional cerebral blood flow. Recently, propagation of vasomotor responses has been recognized as an important regulatory mechanism in microcirculation. In this study, the authors tested the hypothesis that oxyhemoglobin (OxyHb) inhibits the vasodilatory effect of chemical mediators such as adenosine and adenine nucleotides at a local and/or propagated site. Penetrating intracerebral arterioles were surgically isolated from the middle cerebral arteries of rat brains, cannulated, and observed videomicroscopically in an organ bath under an inverted microscope. The effects of 10(-5) M OxyHb on vasoactive responses to adenosine, adenosine diphosphate (ADP), and adenosine triphosphate (ATP) were examined. The drugs were extraluminally applied either to the bath (10(-10)-10(-3) M) or, using pressure microejection (pipette concentration 10(-2) M), locally. The ATP and ADP initially constricted and then significantly dilated the vessels after both extraluminal application and microapplication. Furthermore, local microstimulation by these drugs produced conducted vasodilation. Adenosine elicited significant vasodilation after both extraluminal and local stimulation. Again, conducted vasodilation was observed. The vasomotor responses that were induced by a maximum local stimulation corresponded in magnitude to those observed at bath concentrations of 10(-5) to 10(-4) M of the same drug. Pretreatment with OxyHb constricted arterioles to an average of 87% of control and blunted extraluminally induced dilation at low concentrations (10(-10)-10(-8)) of ATP and ADP, but did not affect vasodilation induced by 10(-4) M or greater concentrations of ATP, ADP, or adenosine. Although the local response to local microstimulation was unaltered, propagated vasodilation as a response to ATP, ADP, and adenosine was significantly attenuated by OxyHb. These findings indicate that vasodilatory propagation plays an important role in the regulation of brain microcirculation and that its impairment by OxyHb could, in part, explain the cerebral hypoperfusion that is observed after SAH.

Early cerebral blood flow and vascular reactivity to acetazolamide in predicting the outcome after ruptured cerebral aneurysm

The sequential cerebral blood flow (CBF) and CBF response to acetazolamide (AZ; 1 g i.v.) within 4 days after initial subarachnoid hemorrhage (SAH) were monitored in 50 patients by stable xenon-enhanced computed tomography (xenon CT). The mean global CBF of the subjects declined with the neurological grading (Hunt & Kosnik), and it was impossible to predict the occurrence of vasospasm from the value of the plain CBF at the acute phase of SAH. However, the CBF response to AZ at the acute phase of SAH among patients resulting in a poor outcome was significantly diminished compared to that among patients resulting in a good outcome. The usefulness of the CBF response to AZ in the acute phase of SAH is discussed.

Brain energy metabolism in the acute stage of experimental subarachnoid haemorrhage: local changes in cerebral glucose utilization

An experimental model was used to investigate acute alterations of cerebral metabolic activity in rats subjected to subarachnoid haemorrhage (SAH). Haemorrhages were produced in anaesthetized animals by injecting 0.3 ml of autologous, arterial nonheparinized blood into the cisterna magna. Control rats received subarachnoid injections of mock-cerebrospinal fluid to study the effect of sudden raised intracranial pressure, or underwent sham operation. Three hours after SAH rats were given an intravenous injection of [14C]-2-deoxyglucose. Experiments were terminated by decapitation, and the brains were removed and frozen. Regional brain metabolic activity was studied by quantitative autoradiography. In comparison with sham-operated controls, cerebral metabolic activity was diffusely decreased after SAH. Statistically significant decreases in metabolic rate were observed in 23 of 27 brain regions studied. Subarachnoid injections of mock-cerebrospinal fluid also produced depression of cerebral metabolic activity, but quantitatively these changes were not as pronounced and diffuse as in SAH rats. The present study shows that a widespread depression of brain metabolism occurs in the acute stage after experimental SAH and is probably secondary to the subarachnoid presence of blood itself and/or blood products.