Hemodilution for cerebral ischemia

Neurosurgery at the University of Miami

The Department of Neurological Surgery at the University of Miami/Jackson Memorial Hospital's legacy of patient care, teaching, and research in the neurosciences extends over a period of 50 years. The department's founder was Dr. David Reynolds. The subsequent chairman, Dr. Hubert Rosomoff, formed a solid foundation that helped put the department on the map. Drs. Barth Green and Roberto Heros, the immediate past chair and co-chairman, garnered both national and international attention for the department. Dr. Green focused his career on complex spine and spinal cord disorders, and was pivotal in creating the world's largest research center for spinal cord injuries. Dr. Heros is a master educator and pioneer neurovascular surgeon, as well as a former president of several neurosurgical national and international organizations. In aggregate, the department has made major contributions to the foundations of neurosurgery.

Cerebral collateral circulation in experimental ischemic stroke

Cerebral collateral circulation is a subsidiary vascular network, which is dynamically recruited after arterial occlusion, and represents a powerful determinant of ischemic stroke outcome. Although several methods may be used for assessing cerebral collaterals in the acute phase of ischemic stroke in humans and rodents, they are generally underutilized. Experimental stroke models may play a unique role in understanding the adaptive response of cerebral collaterals during ischemia and their potential for therapeutic modulation. The systematic assessment of collateral perfusion in experimental stroke models may be used as a “stratification factor” in multiple regression analysis of neuroprotection studies, in order to control the within-group variability. Exploring the modulatory mechanisms of cerebral collaterals in stroke models may promote the translational development of therapeutic strategies for increasing collateral flow and directly compare them in term of efficacy, safety and feasibility. Collateral therapeutics may have a role in the hyperacute (even pre-hospital) phase of ischemic stroke, prior to recanalization therapies.

Parenteral fluid regimens for improving functional outcome in people with acute stroke

BACKGROUND

Parenteral fluids are commonly used in people with acute stroke with poor oral fluid intake. However, the balance between benefit and harm for different fluid regimens is unclear.

OBJECTIVES

To assess whether different parenteral fluid regimens lead to differences in death, or death or dependence, after stroke based on fluid type, fluid volume, duration of fluid administration, and mode of delivery.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (May 2015), the Cochrane Central Register of Controlled Trials (CENTRAL), the Cochrane Database of Systematic Reviews (CDSR) and the Database of Abstracts of Reviews of Effects (DARE) (Cochrane Library 2015, Issue 5), MEDLINE (2008 to May 2015), EMBASE (2008 to May 2015), and CINAHL (1982 to May 2015). We also searched ongoing trials registers (May 2015) and reference lists, performed cited reference searches, and contacted authors.

SELECTION CRITERIA

Randomised trials of parenteral fluid regimens in adults with ischaemic or haemorrhagic stroke within seven days of stroke onset that reported death or dependence.

DATA COLLECTION AND ANALYSIS

One review author screened titles and abstracts. We obtained the full-text articles of relevant studies, and two review authors independently selected trials for inclusion and extracted data. We used Cochrane's tool for bias assessment.

MAIN RESULTS

We included 12 studies (2351 participants: range 27 to 841).Characteristics: The 12 included studies compared hypertonic (colloids) with isotonic fluids (crystalloids); of these, five studies (1420 participants) also compared 0.9% saline with another fluid. No data were available to make other comparisons. Delay from stroke to recruitment varied from less than 24 hours to 72 hours. Duration of fluid delivery was between two hours and 10 days.Bias assessment: Investigators and participants in eight of the 12 included studies were blind to treatment allocation, seven of the 12 included studies gave details of randomisation, and eight of the 12 included studies reported all outcomes measured.

RESULTS

There were no relevant completed trials that addressed the effect of volume, duration, or mode of fluid delivery on death or dependence in people with stroke.The odds of death or dependence were similar in participants allocated to colloids or crystalloid fluid regimens (odds ratio (OR) 0.97, 95% confidence interval (CI) 0.79 to 1.21, five studies, I² = 58%, low-quality evidence), and between 0.9% saline or other fluid regimens (OR 1.04, 95% CI 0.82 to 1.32, three studies, I² = 71%, low-quality evidence). There was substantial heterogeneity in these estimates.The odds of death were similar between colloids and crystalloids (OR 1.02, 95% CI 0.82 to 1.27, 12 studies, I² = 24%, moderate-quality evidence), and 0.9% saline and other fluids (OR 0.87, 95% CI 0.67 to 1.12, five studies, I² = 53%, low-quality evidence). The odds of pulmonary oedema were higher in participants allocated to colloids (OR 2.34, 95% CI 1.28 to 4.29, I² = 0%). Although the studies observed a higher risk of cerebral oedema (OR 0.20, 95% CI 0.02 to 1.74) and pneumonia (OR 0.58, 95% CI 0.17 to 2.01) with crystalloids, we could not exclude clinically important benefits or harms.

AUTHORS' CONCLUSIONS

We found no evidence that colloids were associated with lower odds of death or dependence in the medium term after stroke compared with crystalloids, though colloids were associated with greater odds of pulmonary oedema. We found no evidence to guide the best volume, duration, or mode of parenteral fluid delivery for people with acute stroke.

Swallowing, Nutrition, and Hydration During Acute Stroke Care

Dysphagia occurs in up to half of patients after an acute stroke and may cause dehydration, undernutrition, and aspiration pneumonia. Current evidence suggests that a systematic program of diagnosis and treatment of dysphagia in an acute stroke management plan may yield dramatic reductions in aspiration pneumonia rates. There is also some evidence that nutritional supplementation and proper hydration may reduce morbidity and mortality in acute stroke patients. This article focuses on the recent advances in the evaluation and management of dysphagia, undernutrition, and dehydration related to acute stroke. A summary of pertinent studies in the area of stroke dysphagia and nutrition is also included.

Effects of hemodilution after traumatic brain injury in juvenile rats

BACKGROUND

Normovolemic hemodilution (HD) in adult animal studies has shown exacerbation of traumatic brain injury (TBI) lesion volumes. Similar studies in juvenile rats have not been reported and outcomes are likely to be different. This study investigated the effects of normovolemic hemodilution (21% hematocrit) in a juvenile TBI (jTBI) model.

METHODS

Twenty 17-day-old rats underwent moderate cortical contusion impact injury (CCI) and were divided into four groups: CCI/hemodilution (HD) (group HD), CCI/no HD (group C), Sham/HD (group SHD), and Sham/no HD (group S). Regional laser Doppler flowmetry (LDF), edema formation (MRI-T2WI), water mobility assessed using diffusion weighted imaging (MRI-DWI), open field activity tests, and histological analyses were evaluated for lesion characteristics.

RESULTS

Hemodilution significantly increased blood flow in the HD compared to the C group after TBI. T2WI revealed a significantly increased extravascular blood volume in HD at 1, 7, and 14 days post-CCI. Edematous tissue and total contusional lesion volume were higher in HD-treated animals at 1 and 14 days. DWI revealed that HD, SHD, and C groups had elevated water mobility compared to S groups in the ipsilateral cortex and striatum. Histology showed a larger cortical lesion in the C than HD group. Open field activity was increased in HD, C, and SHD groups compared to the S group.

CONCLUSIONS

Hemodilution results in significant brain hyperemia with increased edema formation, extravascular blood volume, and water mobility after jTBI. Hemodilution results in less cortical damage but did not alter behavior. Hemodilution is likely not to be clinically beneficial following jTBI.

Stroke unit care in clinical practice: an observational study in the Florence center of the European Registers of Stroke (EROS) Project

BACKGROUND

Randomized trials and meta-analyses indicate positive effects of stroke unit (SU) care on survival and dependency of patients with stroke. However, data on the advantages of SU in 'real-world' settings are limited. We prospectively assessed, in a large University Hospital, the effect of SU versus other conventional wards (OCW) care on all-cause mortality, death or dependency, death or institutionalization.

METHODS

In a prospective observational study in the European Registers of Stroke Project, patients hospitalized for first-in-a-lifetime stroke were evaluated for demographics, risk factors, clinical presentation, resource use, 3-month and 1-year survival, and functional outcome.

RESULTS

Overall, 355 patients (54.1% men, mean age 73.4 ± 14.5 years) were registered, 140 (39.4%) admitted to the SU, and 215 (60.6%) to OCW. OCW patients were older, whilst SU patients had more severe strokes according to NIHSS (P for trend = 0.025). SU patients were significantly more often treated by specialists in stroke medicine, stroke nurses, physiotherapists and speech therapists (all P < 0.001), psychologists (P = 0.025), dietitians (P < 0.001), and social workers (P = 0.003). MRI, carotid, and transcranial Doppler were significantly more often performed in SU patients (all P < 0.001). Intravenous fluids (P = 0.003) and intravenous anticoagulation (P < 0.001) were more often prescribed in SU. Controlling for case-mix, SU significantly reduced 1-year mortality (P = 0.020), death or dependency at 3 months (P = 0.006) and 1 year (P = 0.043), and death or institutionalization at 3 months (P = 0.001) and 1 year (P = 0.009).

CONCLUSIONS

We confirmed the benefits of SU care in a clinical setting. Further analyses should define the contribution of individual components of care to stroke outcome.

CONTROVERSIES IN THE SURGICAL TREATMENT OF RUPTURED INTRACRANIAL ANEURYSMS

THE MANAGEMENT OF aneurysmal subarachnoid hemorrhage has evolved over time, including the use of the microscope for aneurysm clip application, improved imaging modalities, endovascular methods for aneurysm treatment, dedicated neurointensive care units, and more aggressive therapy for cerebral vasospasm. Although these advancements have reduced the morbidity and mortality associated with aneurysmal subarachnoid hemorrhage, outcomes for this patient population continue to leave much room for improvement. This work highlights controversial adjuvant techniques, maneuvers, and therapies surrounding the surgical treatment of ruptured cerebral aneurysms that currently lack a consensus opinion. These treatments include centralized care in high-volume centers, as well as the use of antifibrinolytic therapy, routine cerebrospinal fluid diversion, intraoperative hypothermia, temporary clip application, neuroprotective drugs, intraoperative angiography, and decompressive hemicraniectomy. Although definitive answers will only be possible through future multicenter collaboration, we review the controversy surrounding these adjuncts and report the consensus opinion from a highly experienced audience.

Albumin reduces blood-brain barrier permeability but does not alter infarct size in a rat model of neonatal stroke

Human serum albumin therapy confers neurobehavioral and histopathologic neuroprotection in adult stroke models. We investigated whether albumin might also be neuroprotective in ischemic brain injury using a transient filament middle cerebral artery occlusion (tfMCAO) model in 10-d-old rat pups treated with 0.25% albumin or saline 1 h after reperfusion. We performed serial neurobehavioral and magnetic resonance imaging (MRI) assessments immediately after tfMCAO (day 0) and on 1, 3, 7, 14, and 28 d. IgG staining to assess blood-brain barrier (BBB) integrity and standard histology was obtained on 1, 3, and 28 d. Hemispheric infarct volumes from MRI were similar in saline and albumin groups (0 h: 39% and 44%; d 1: 46% and 55%; and d 28:10% and 24%) as were neurobehavioral assessments. IgG staining at 3 d post-ischemia showed loss of BBB integrity that was significantly reduced after albumin. Elevated T2 values suggesting vasogenic edema was seen in albumin compared with saline-treated animals, as was increased water mobility (i.e. increased apparent diffusion coefficient (ADC) reflecting cytotoxic edema. The reasons why albumin was not neuroprotective in neonatal stroke compared with adults remain uncertain. Effective strategies in adult models need to be reassessed in the neonate.

Cerebral vasospasm in subarachnoid hemorrhage

The treatment of vasospasm after subarachnoid hemorrhage remains a formidable challenge. The prompt recognition of this complication is essential to prevent ischemic damage. Initial orders should include adequate fluid and sodium supplementation to avoid volume depletion. Prophylactic hypervolemia is not effective in reducing the incidence of vasospasm and may be deleterious. Oral nimodipine (60 mg every 4 hours for 21 days) should be started on admission because it protects against delayed ischemic damage. Increasing blood flow velocities on serial transcranial Doppler studies are reliable indicators of early development of vasospasm. When symptomatic vasospasm occurs, hemodynamic augmentation therapy should be instituted. Crystalloids and colloids may be used to promote hypervolemia. Colloids may provide additional benefit by producing hemodilution. However, the rheological benefits of hemodilution may be offset by reduced oxygen carrying capacity when hematocrit drops below 28%. Hypertension may be induced by administering inotropic drugs and, in certain cases, cardiac output optimization using dobutamine also is necessary. When aggressive medical therapy fails to reverse ischemic deficits, prompt endovascular intervention is indicated. Focal vasospasm of larger vessels may be effectively treated with angioplasty and the benefits of this procedure are durable. Diffuse vasospasm involving smaller arterial branches may be treated with intra-arterial infusion of vasodilators, such as papaverine, verapamil, or nicardipine. Unfortunately, these dilatory effects tend to be short-lasting. In refractory cases, hypothermia may be considered, although value of this strategy remains largely unexplored.

Physiologic aspects of anemia

The most important adaptive responses from a physiological stance involved the cardiovascular system, consisting in particular of elevation of the cardiac output and its redistribution to favor the coronary and cerebral circulations, at the expense of the splanchnic vascular beds. The evidence regarding these physiological responses, especially in experimental studies that permit the control of many variables, is particularly powerful and convincing. On the other hand, there is a remarkable lack, in quality and quantity, of clinical studies addressing how normal physiological adaptive responses may be affected by a variety of diseases and conditions that often accompany and may complicate anemia, and interactions with other such compounding variables as age and different patient populations. For these reasons, it is not possible to offer guidelines on how to increase, maintain, or even to determine optimal DO2 in high-risk patients and how best transfusion strategies might be used under these conditions. From the brief review of physiological principles and the strong consensus in the literature, it is evident that cardiac function must be a central consideration in decisions regarding transfusion in anemia, because of the critical role it plays in assuring adequate oxygen supply of all vital tissues. Particular attention should be paid to the possible presence of CAD or incipient or cardiac failure, as these conditions may require careful transfusions to improve DO2 at levels that may not necessitate such interventions when cardiac disease is absent. Although the cerebral circulation also serves an obligate aerobic organ unable to tolerate significant hypoxia, there is little convincing evidence to support the notion that cerebral ischemia is aggravated by anemia and that this can be prevented by improved DO2 through rapid correction of anemia. Consequently, the arguments favoring transfusions in the presence of ischemic heart disease do not appear to apply to occlusive cerebrovascular disease. Because firm evidence is lacking on the interactions of concurrent diseases and anemia in various patient populations, understanding of the physiological consequences of anemia, and of the diseases concerned, is useful but not fully sufficient to provide firm and rational guidance to transfusion practice in specific complex clinical instances. A good deal of clinical and experimental investigation is required to support fully rational and comprehensive guidelines. In the meantime, prudent and conservative management, based on awareness of risks and sound understanding of the normal and pathological physiology, must remain the guiding principle.

Advances in understanding protection from cerebral ischemia

PURPOSE OF REVIEW

Cerebral ischemia and protection is a large field, so for the purposes of this review, which focuses on results published in the last 9 months, we have chosen to discuss a few aspects of ischemia in which our understanding has advanced significantly in this period of time. Recent progress in the clinical use of hypothermia for neurological protection as well as laboratory progress on the role of stress proteins, estrogen and a few other potential adjuncts will be discussed.

RECENT FINDINGS

Two papers have now been published documenting improved neurological outcome in patients treated with hypothermia following cardiac arrest, both using randomized clinical trial designs. These reports and several laboratory studies identifying mechanisms of hypothermic brain protection are reviewed. In understanding the mechanisms underlying protection by estrogens, new results on both direct vascular effects and a demonstration that estrogens can reduce apoptosis are presented. The third area to be described is current progress in identifying mechanisms of stress protein protection from ischemia, in which new mechanisms have been identified with the demonstration of inhibition of several points in the cell death cascade. The remaining areas considered touch on the effects of approaches that reduce inflammation by blocking adhesion molecules, those that reduce free radical production and those that improve blood rheology.

SUMMARY

An important common theme in brain protection is reduction of cell death by blocking apoptosis or programmed cell death. While the use of hypothermia should now enter clinical practice, many areas of brain injury require further studies both to define injury mechanisms and to translate these understandings into clinically useful treatments to reduce ischemic brain injury.

The effect of high-dose albumin therapy on local cerebral perfusion after transient focal cerebral ischemia in rats

We have shown that high-concentration albumin therapy is markedly neuroprotective in focal cerebral ischemia. The present study was conducted to ascertain the degree to which hemodynamic alterations are responsible for this therapeutic effect. Normothermic, physiologically regulated male Sprague-Dawley rats received a 2-h period of middle cerebral artery occlusion (MCAo) by insertion of an intraluminal suture coated with poly-L-lysine. Albumin (25% human serum albumin solution) or vehicle (0.9% sodium chloride) was administered intravenously at a dose of 1% of body weight immediately after suture withdrawal following 2-h MCAo. Local cerebral blood flow (LCBF) was measured autoradiographically with 14C-iodoantipyrine after 1 h of recirculation. Novel image-processing methods were used to compare average LCBF data sets against previously obtained infarction-frequency data on a pixel-by-pixel basis. Albumin therapy reduced mean hematocrit by 42% but produced no other systemic alterations. Pixel-based histopathological analysis revealed large, consistent cortical and subcortical infarcts in saline-treated rats with MCAo; albumin therapy reduced mean cortical infarct volume by 85%. Within regions showing albumin-associated neuroprotection, numbers of pixels having LCBF in the upper ischemic-core flow range (0.12-0.24 ml g-1 min-1) were reduced by 8.6-fold by albumin therapy when compared to saline-treated rats; and numbers of pixels with LCBF in the lower penumbral flow range (0.24-0.36 ml g-1 min-1) were reduced by 3. 1-fold in albumin-treated rats (p=0.04 by repeated-measures analysis of variance). Analysis of the [albumin-saline] 3-dimensional difference-image data set revealed a circumferential zone of statistically significant albumin-associated LCBF increase within the posterior portion of the ischemic hemisphere, surrounding the core-region of prior ischemia. Thus, high-concentration albumin therapy improves local perfusion to regions of critical LCBF reduction. The spatial extent of this LCBF effect, however, appears too small to account fully for the marked neuroprotective efficacy of this therapy. We suggest that other, non-hemodynamic mechanisms may also be contributory.

Reducing the risk of rebleeding before early aneurysm surgery: a possible role for antifibrinolytic therapy

Previous studies on the initial nonoperative management of aneurysmal subarachnoid hemorrhage (SAH) demonstrated that antifibrinolytic therapy reduced the risk of rebleeding by approximately 50%; however, prolonged antifibrinolytic treatment was associated with an increase in the incidence of hydrocephalus and delayed ischemic deficit. When early surgical intervention became routine for ruptured aneurysms, the use of antifibrinolytic therapy diminished. However, early surgery is generally performed in the first several days after SAH and the risk of rebleeding remains until the aneurysm is obliterated. Based on a review of the literature, the authors formed two hypotheses: 1) the high-dose intravenous administration of epsilon-aminocaproic acid (EACA), an antifibrinolytic agent, might reduce the risk of recurrent hemorrhage in the interval between SAH and early surgical intervention, and 2) a short course of EACA might not produce the increase in complications previously associated with its prolonged administration. The use of preoperative high-dose EACA therapy was evaluated in 307 patients to determine its safety and efficacy in reducing the incidence of rebleeding before early aneurysm surgery. All patients were admitted within 3 days of their SAH and were classified as Hunt and Hess Grades I to III. Only four patients (1.3%) suffered a recurrent hemorrhage. This compares favorably to the rebleeding rate of 5.7% reported for the early surgery group in the International Cooperative Study on the Timing of Aneurysm Surgery. The incidence of hydrocephalus or symptomatic vasospasm was not unduly elevated in patients receiving preoperative EACA. Thirty-five patients (11.4%) needed temporary cerebrospinal fluid drainage during their hospitalization and, overall, 8.8% required a ventriculoperitoneal shunt. The mean age of the patients who required a shunt was nearly 10 years older than the general study population. Seventy-one patients (23%) developed symptomatic vasospasm and 8.1% suffered a stroke. This study indicates that a brief course of high-dose EACA is safe and may be beneficial in diminishing the risk of rebleeding in good-grade patients prior to early surgical intervention. Further investigation is planned based on these promising results.

Acute stroke

Disruption of cerebral blood flow may influence brain energy metabolism to produce reversible or irreversible neurologic deficits. The emergency physician is in a unique position to provide timely treatment during the first few hours of an acute stroke. He or she must be facile with unique pharmacologic and non-pharmacologic treatment designed for the stroke patient concerning ventilation, blood pressure, and circulation.

Why do all drugs work in animals but none in stroke patients? 1. Drugs promoting cerebral blood flow

Medical treatments which presumably alter cerebral blood flow (CBF) have been quite unimpressive in their effect on stroke outcome. In considering experimental and clinical data from the use of haemodilution and of the antiplatelet agent prostacyclin in focal cerebral ischaemia, and the current work with fibrinolytic agents in acute stroke, several lessons are apparent. Often agents hypothesized to affect CBF receive an underserved reputation based on sparse experimental evidence. Significant even unsuspected differences between species limit application to the clinical setting. Limitations of CBF measurements in experimental models and in humans raise questions about apparent responses to those agents. The failure to confirm a relationship between CBF enhancement and reduction in infarct development experimentally has plagued these approaches. The need for early application of agents which may modulate CBF during cerebral ischaemia is critical. Attention to these general issues and careful application of appropriate models are necessary so that a potentially useful therapeutic intervention is not overlooked.

Evidence for hypoxia-induced, programmed cell death of cultured neurons

Apoptosis, a form of cell death ("programmed" cell death) in which the nucleus and cytoplasm shrink and often fragment, serves to eliminate excessive or unwanted cells during remodeling of embryonic tissues, during organ involution, and in tumor regression. In acute pathological states, such as ischemia, the cells tend to swell and lyse--a process called necrosis. We hypothesize that the delayed neural death clinically associated with hypoxia may, in part, represent apoptosis. A tissue culture model of 24 hours of hypoxia was employed using sympathetic neurons. Pretreatment with an endonuclease inhibitor (aurintricarboxylic acid) decreased cell death by 53%, depolarizing conditions (55 mM potassium chloride) decreased cell death by 33%, and an RNA synthesis inhibitor (actinomycin D) by 26% (all have been shown to prevent apoptosis). Pretreatment with antisense c-myc had no effect. Fluorescent staining with propidium iodide (a DNA marker) demonstrated chromatin condensation and agarose gel electrophoresis demonstrated a DNA "ladder." These data suggest that apoptosis may play a role in hypoxic cell death and that in this paradigm, expression of c-myc is unnecessary. This would suggest a new approach to our understanding of hypoxia and open new strategies to lessen neuronal damage secondary to this process.

The effect of Nicorandil on chronic cerebral vasospasm

The present study is aimed at examining the therapeutic effect of Nicorandil on chronic vasospasm using beagle dogs subjected to a "two-haemorrhage" insult, as well as its dilatory effect on the PDA [phorbol-12,13 diacetate]-induced contraction of the canine basilar artery. 1. A total of 12 animals of either sex, weighing 7 to 12 kg, were assigned into saline control and Nicorandil-treated groups. Immediately after the second induction of subarachnoid haemorrhage (SAH), animals started to receive the agent via the venous route at the constant rate of 10 micrograms/kg/minute for six hours (day 3). On days 4, 5, and 6, the drug was given twice at the same rate for three hours. After the final angiograms, animals were sacrificed by exsanguination. 2. Using ring specimen of the canine basilar artery at a resting tension of 3 g, isometric tension was monitored to examine the effect of Nicorandil on PDA induced contraction. Nicorandil significantly ameliorated chronic vasospasm and inhibited PDA-induced contraction in a dose-dependent fashion. The present data indicate that Nicorandil provides a useful way of treating chronic vasospasm after SAH.

Optimum degree of hemodilution for brain protection in a canine model of focal cerebral ischemia

The ability of hemodilution to lower blood viscosity and increase cerebral blood flow has been proven experimentally; however, the optimum hematocrit for maximum oxygen delivery to ischemic brain tissue is not known, and a study was designed to determine this. Fifty dogs were selected for inclusion in the study using criteria based on changes in somatosensory evoked potentials at the time of arterial occlusion, which were found in a previous study to predict the development of a moderate infarction of relatively constant size. Infarctions were induced by permanent occlusion of the left middle cerebral artery and the azygous anterior cerebral artery. The animals selected for inclusion were divided into five groups of 10 dogs each: 1) a control group; 2) a group with 25% hematocrit; 3) a group with 30% hematocrit; 4) a group with 35% hematocrit; and 5) a group with 40% hematocrit. Isovolemic hemodilution was accomplished 1 hour after occlusion of vessels using dextran infusion and blood withdrawal. The animals were sacrificed after 6 days and infarction volume was determined from fluorescein-stained sections. Statistical analysis was performed using Student's t-test and one-way analysis of variance. Mean infarction volume for each group, expressed as a percentage of total hemispheric volume +/- 1 standard error of the mean, was 28.3% +/- 2.8% for the control group, 33.6% +/- 3.4% for the 25% hematocrit group, 17.1% +/- 2.2% for the 30% hematocrit group, 29.2% +/- 4.3% for the 35% hematocrit group, and 29.9% +/- 2.1% for the 40% hematocrit group. The 30% hematocrit group showed the smallest average infarction size and this size differed significantly (p = 0.02) from the average infarction size in the control animals. These results show that, in this model of focal ischemia, a hematocrit of approximately 30% is optimum for protecting the brain.

Hemodilution reduces early reperfusion injury in an ex vivo rabbit lung preservation model

We sought to reduce early ischemia-reperfusion injury after lung preservation by an initial brief period of hemodilute reperfusion. Left lungs of New Zealand White rabbits were ventilated with room air and reperfused in an ex vivo ventilation-perfusion apparatus after 18 hours of storage at 10 degrees C. Lungs were randomly assigned to one of three groups (n = 6) according to the composition of initial reperfusate. In group 1 (control), preserved lungs were reperfused with whole blood for 20 minutes (hematocrit, 38%). In the experimental groups, blood was diluted to a hematocrit of 10% with Ringer's lactate (group 2) or low-potassium-dextran solution (group 3) for the first 10 minutes of reperfusion, followed immediately by whole blood for 10 minutes. Oxygen tension of left ventricular effluent at the end of the 20-minute assessment period was significantly higher in both hemodiluted groups (mean +/- standard error of the mean: group 2, 81.3 +/- 6.6 mmHg; group 3, 77.0 +/- 9.5 mmHg, versus Group 1, 46.3 +/- 7.4 mmHg; p < 0.006). Similarly, mean tracheal airway pressure was reduced in the hemodiluted groups, suggesting improved compliance (group 2; 3.1 +/- 0.3 mmHg; group 3, 2.8 +/- 0.6 mmHg; versus group 1, 6.5 +/- 1.4 mm Hg; p < 0.05). An initial 10-minute period of hemodilute reperfusion appears to reduce early pulmonary ischemia-reperfusion injury in this 18-hour ex vivo rabbit lung preservation model.

Diaspirin crosslinked hemoglobin (DCLHb): effect of hemodilution during focal cerebral ischemia in rats

The efficacy of hemodilution therapy, to ameliorate cerebral ischemia, is limited by an accompanying decrease in oxygen content. We assessed the effect of hemodilution, with diaspirin cross-linked hemoglobin (DCLHb), on cerebral blood flow (CBF) and infarct after middle cerebral artery occlusion (MCAo). Rats (n = 36) were alloted to a control group in which hematocrit (Hct) was not manipulated, or reduced with DCLHb to 30% (30/DCLHb), 16% (16/DCLHb), or 9% (9/DCLHb). After MCAo, the brain area with a CBF of 0-10 ml.100g-1.min-1 was determined. This area was decreased in the 30/DCLHb and 16/DCLHb groups vs the Control group; and was less in the 9/DCLHb group vs the other groups. Different rats (n = 49) were hemodiluted with DCLHb or Albumin (Alb): Control, 30/Alb, 30/DCLHb, 16/DCLHb, or 9/DCLHb. After 3-hr of MCAo and 2-hr of reperfusion, infarct area was determined. Brain infarct was less in the 30/DCLHb and 16/DCLHb groups vs the Control and 30/Alb groups; and was less in the 9/DCLHb group vs the other groups. The results of this study support the hypothesis that hemodilution with DCLHb decreases cerebral ischemia in a dose-dependent manner, and in terms of brain ischemia is a more proficient hemodiluting fluid than albumin.

The perfluorocarbon fluoromethyloadamantane offers cerebral protection in a model of isovolemic hemodilution in rabbits

BACKGROUND AND PURPOSE

Perfluorocarbons (PFCs) are considered promising cerebral protection agents because they could combine the beneficial effects of decreased blood viscosity with enhanced oxygen-carrying capacity and oxygen tissue delivery, but trials of PFCs as hemodilutants have been very limited. We evaluated fluoromethyloadamantane (FMA), a new perfluorocarbon compound, as an isovolemic hemodilutant and compared it with low-molecular-weight dextran 40 (D40) and a control group.

METHODS

Through a transorbital craniectomy, the internal carotid, anterior, and middle cerebral arteries were coagulated to create a cerebral infarction in anesthetized, mechanically ventilated rabbits. No other experimental procedure was performed in control animals. In the two other groups, hemodilution was commenced 30 minutes after the arterial occlusion with either D40 or FMA. Hemodynamic parameters and brain and systemic temperature were monitored throughout the experiments. All animals were killed 6 hours after the arterial occlusion.

RESULTS

Hemodynamic and metabolic parameters and blood oxygen content were not affected by the infusion of either FMA or D40. Brain and systemic temperature remained constant. The ratio of infarct volume to the hemispheric volume was 19.6 +/- 3.7% in the FMA group (n = 17), 19.9 +/- 4.6% in the D40 group (n = 16), and 40.3 +/- 5.7% in the control group (n = 17). The difference in infarct volume of both FMA and D40 animals compared with controls was statistically significant (P < .01) when tested with Student's t test. There was no significant difference between FMA and D40 groups.

CONCLUSIONS

These results suggest that FMA has cerebral protective properties and should be purified, optimized, and further tested experimentally to develop a stable, efficient, and safe oxygen carrier, potentially suitable for clinical trials.

[Oncotic pressure and hemodilution]

The appropriate fluid therapy in neurosurgical patients remains an area of disagreement between neurosurgeons and anaesthesiologists. Fluid restriction has long been practiced in patients with brain pathology, in order to reduce or prevent the formation of cerebral oedema. This grows from a fear that rapid administration of fluids, particularly noncolloidal fluids, can enhance cerebral oedema, although there is a lack of experimental evidence to substantiate this belief. On the other hand, fluid restriction can lead to relative hypovolaemia, causing haemodynamic instability during anaesthesia and influence defavourably cerebral perfusion. The appropriate fluid management of patients with brain pathology requires a careful review of the Starling's law and a clear understanding of osmolality, oncotic pressure (OP) and the nature of the blood-brain barrier (BBB). The Starling equation of ultrafiltration states that the net movement of fluid between the intra- and extravascular compartments is the result of the summated influences of the pressure gradients (hydrostatic pressure, OP, and osmotic pressure) between those compartments and the properties of the barriers (capillary endothelium) that separate them. In most peripheral tissues this barrier is freely permeable to small molecules and ions and net fluid movement depends on intravascular hydrostatic pressure and OP. Under normal circumstances, intraluminal hydrostatic pressure is higher than interstitial pressure, favouring water egress. By contrast, intraluminal OP is higher than interstitial OP, favouring water retention. These forces do not balance exactly, and fluid accumulation is prevented by the lymphatics. If this net movement exceeds the capacity of the lymphatic clearance mechanisms, fluid accumulates, which is the definition of oedema.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodilution improves cerebral hemodynamics in internal carotid artery occlusion

BACKGROUND AND PURPOSE

Hemodilution may be a useful form of therapy for patients with carotid occlusive disease and hemodynamic ischemia. Accordingly, we evaluated the effects of hemodilution on cerebral hemodynamics and oxygen metabolism in patients with carotid artery occlusion.

METHODS

Using positron emission tomography, we analyzed regional cerebral blood flow, oxygen extraction fraction, oxygen metabolic rate, and blood volume before and after isovolemic hemodilution in five patients with unilateral internal carotid artery occlusion and minor stroke. Hemodilution was accomplished by phlebotomy of 400 mL and infusion of 400 mL of hydroxyethyl starch.

RESULTS

Before hemodilution, the patients had a significant decrease in blood flow and oxygen transport along with significantly elevated oxygen extraction fraction in the cerebral hemisphere with carotid artery occlusion compared with six control subjects. After hemodilution, the hematocrit and arterial oxygen content decreased from 41.2% and 18.6 mL/dL to 36.3% and 16.5 mL/dL, respectively. Both cerebral blood flow and oxygen transport were increased and oxygen extraction fraction was decreased without any change in oxygen consumption. The degree of increase in blood flow and oxygen transport was positively correlated with the ratio of oxygen extraction fraction to blood volume before hemodilution.

CONCLUSIONS

These findings indicate that hemodilution improves oxygen transport as well as blood flow in patients with internal carotid occlusion and decreased perfusion and that this improvement may be more prominent in patients with a severely compromised hemodynamic state. Thus, hemodilution may be useful in patients with hemodynamic ischemia.

Role of hypervolemic hemodilution in focal cerebral ischemia of rats

This study was designed to better define a protocol for hypervolemic hemodilution in acute cerebral ischemia and investigate the mechanism of action of this therapy. Anesthetized rats (n = 40) were subjected to 6 h of middle cerebral artery (MCA) occlusion. At 45 min after MCA occlusion, each rat received one of the following treatment modalities: (1) control, (2) isovolemic hemodilution, (3) hypervolemic nonhemodilution (whole blood), (4) hypervolemic hemodilution (normal saline), and (5) hypervolemic hemodilution (hetastarch). Local cerebral blood flow (CBF) was determined with hydrogen clearance technique, and cardiac output was assessed by measuring the descending aorta blood flow (DAF). Infarction volume was estimated by 2,3,5-triphenyltetrazolium chloride staining method. Hetastarch infusion increased both DAF and local CBF more than the other treatments, by 98% and by 89%, respectively. Hetastarch also reduced infarction volume the most to 71 +/- 19 mm3 (p < 0.01 versus control 117 +/- 32 mm3). A significant correlation between percent (%) changes in local CBF and % changes in DAF existed in ischemic brain regions, and the hetastarch infusion improved local CBF more prominently in profoundly ischemic regions in contrast to isovolemic hemodilution. These data demonstrated the superiority of hypervolemic hemodilution with hetastarch as compared to other similar treatment modalities for acute cerebral ischemia, and indicate that cardiac output augmentation may be more responsible than decreased blood viscosity for the beneficial effect of hypervolemic hemodilution on local CBF in profoundly ischemic regions, as such ischemic brain tissue can severely lose its regulatory control of CBF to alterations in cardiac output.

Beneficial effect of prolonged administration of albumin on ischemic cerebral edema and infarction after occlusion of middle cerebral artery in rats

This study compared the therapeutical effect of the prolonged administration of albumin, 2 g/kg body weight per day, with that of saline or dextran, 0.8 g/kg body weight per day, on cerebral ischemia, using an occlusion of the middle cerebral artery in the rat. Brain water, sodium, and potassium contents were measured 72 hours after middle cerebral artery occlusion. The volume of infarction was represented as volume index, which is a total of the infarction area measured in the five brain slices at 168 hours after middle cerebral artery occlusion. The postischemic administration of albumin at the dose tested elucidated an antiedema effect and reduced the infarction size after regional ischemia in rats. These results strongly support the idea that hemodilution therapy with colloids such as albumin has wide usage as a treatment of patients with ischemic cerebral stroke.

Focal cerebral ischemia in rats: effect of hemodilution with alpha-alpha cross-linked hemoglobin on brain injury and edema

The effect of hemodilution, with alpha-alpha cross-linked hemoglobin (DCLHb), on brain injury and edema was assessed after temporary middle cerebral artery occlusion in rats. Injury was analyzed with 2,3,5-triphenyltetrazolium chloride (TTC) stain and edema by microgravimety. Part A: DCLHb was given to maintain one of the following hematocrits (Hct) and normotension: 1) 45/Hct, 2) 30/Hct, 3) 16/Hct, or 4) 9/Hct. Brain injury (% of ischemic hemisphere, mean +/- SD) was less in the 30/Hct group (31 +/- 4) versus the 45/Hct group (42 +/- 5); and in the 16/Hct (20 +/- 3) and 9/Hct (19 +/- 4) groups versus the 45/Hct and 30/Hct groups. Edema was less in the hemodiluted groups versus the 45/Hct group. Part B: DCLHb was given to maintain one of the following hematocrits and hyper (HTN)-or normotension (Norm): 1) 45/Norm, 2) 30/Norm, 3) 30/HTN, 4) 16/Norm, or 5) 16/HTN. In hematocrit matched groups hypertension decreased brain injury (30/HTN-24 +/- 2 < 30/Norm-34 +/- 4; and 16/HTN-17 +/- 3 < 16/Norm-24 +/- 4). Edema was not effected by hypertension. These results suggest that hemodilution with DCLHb decreases focal ischemic injury, and is most effective when given in a manner that induces hypertension.

The hemodynamic effects of prolonged albumin administration in beagle dogs exposed to experimental subarachnoid hemorrhage

The hemodynamic effects of hyperdynamic hemodilution induced by prolonged (for 1 week) intravenous albumin or low-molecular-weight dextran administration were studied in the beagle two-hemorrhage model. Drug infusion was started immediately after the induction of a subarachnoid hemorrhage and continued for 7 days thereafter, according to the following treatment schedule: Group 1 (physiological saline); Group 2 (10% low-molecular-weight dextran, 0.8 g/kg per day); Groups 3, 4, and 5 (25% albumin, 1, 2, and 3 g/kg per day, respectively). On Day 0 (before subarachnoid hemorrhage) and Day 7, the cardiopulmonary parameters and the blood flow of the vertebral artery (VAF) were measured by the use of the Swan-Ganz catheter and an electromagnetic flowmeter, respectively. Cerebral angiography was carried out on Days 0 and 7. Only the albumin-treated groups showed a significant increase in plasma osmotic pressure, cardiac output, and VAF, as well as a decrease in the hematocrit on Day 7. The increase in cardiac output and VAF was maximal in Group 4. In Group 5, signs of pulmonary edema in the chest roentgenogram were noted in two of the four animals. The angiographic spasm of the basilar artery on Day 7 was not significantly ameliorated by either albumin or dextran. In the albumin-treated groups, the VAF was shown to increase in parallel with the increase of the cardiac output, within the range between 50 and 150%. Thus, this study indicates that the hemodynamic changes induced by prolonged albumin administration improve the cerebral circulation hindered by chronic vasospasm, whereas the increase in cardiac output is considered to be the most reliable indicator regarding the determination of the optimal dosage of albumin.

Therapeutic interventions in acute stroke

1. Potential therapies for ischaemic stroke include agents to reduce oedema, to improve cerebral perfusion, to reduce excitotoxic damage, to minimise free-radical induced injury and to reduce complications such as deep venous thrombosis. 2. Of the anti-oedema drugs, steroids are ineffective and possibly dangerous; intravenous glycerol is unproven. 3. Haemodilution to reduce whole blood viscosity and improve perfusion is ineffective. Thrombolytic drugs have not been adequately tested but several randomised multicentre trials are now commencing. Early treatment and CT scanning are essential. 4. Anticoagulants and antiplatelet drugs may have wide applicability but have not been tested in the acute phase of stroke. A multi-centre trial will address this issue. 5. Neuronal cytoprotection offers exciting prospects for acute stroke treatment. Antagonists of glutamate at the NMDA receptor, calcium and sodium channel blocking agents and free radical scavenging drugs have potent effects experimentally. Several agents are now reaching clinical trials. The calcium antagonist nimodipine has been disappointing in large scale trials but some studies were flawed by late treatment. 6. Successful treatment of acute stroke is likely to combine several approaches. 7. Therapeutic trials in stroke must include CT scanning, early treatment and a multicentre approach to achieve large numbers of patients.

Hydroxyethyl starch 200/0.5 reduces infarct volume after embolic stroke in rats

BACKGROUND AND PURPOSE

We evaluated isovolumic hemodilution with hydroxyethyl starch 200/0.5 in a rat model of focal cerebral ischemia. This compound avoids the unfavorable viscosity and erythrocyte aggregation abnormalities of low molecular weight dextran during administration over a period of several days.

METHODS

Sprague-Dawley rats, anesthetized with 0.5-1% halothane and 70% N2O, were subjected to silicon cylinder (treated and control groups) or sham (sham group) embolization of the cerebral circulation. Thirty minutes after embolization, the treated group (n = 5) was infused with 11 ml/kg of 10% hydroxyethyl starch 200/0.5, and the control (n = 5) and sham (n = 4) groups were infused with saline for 1 hour. In the treated group, 7.1 ml/kg of blood was withdrawn. After 24 hours, the animals were reanesthetized, and cerebral blood flow was determined with [14C]iodoantipyrine. Alternative brain slices were either incubated with 2,3,5-triphenyltetrazolium chloride for infarct volume determination or frozen for ischemic volume and cerebral blood flow determination using autoradiography.

RESULTS

The hematocrit in the treated group was reduced from (mean +/- SEM) 46 +/- 1% to 35 +/- 2% at 1.5 hours (p < 0.01). Cortical blood flow was within the normal range of 115-185 ml/min/100 g, except for the ischemic cortex in the embolized groups, treated and control. The ischemic and infarct volume of the treated group was reduced by 74% (p < 0.05) and 89% (p < 0.05), respectively, from the control group. The treated and sham ischemic and infarct volumes were not statistically different.

CONCLUSIONS

These data suggest that hydroxyethyl starch 200/0.5 could be an effective treatment for ischemic stroke when administered early, because it reduces infarct and ischemic volumes from control values to levels indistinguishable from those of the sham group.

Focal cerebral ischemia in rats: effect of hemodilution with alpha-alpha cross-linked hemoglobin on CBF

Hemodilution has had limited success as a treatment of cerebral ischemia. When using a nonoxygen binding fluid, the therapeutic efficacy of hemodilution-induced increases in CBF are offset by concomitant decreases in oxygen content. The effect of hemodilution, with diaspirin alpha-alpha cross-linked hemoglobin (DCLHb), on CBF during middle cerebral artery occlusion was assessed. Rats were hemodiluted to one of the following hematocrits (Hct): (a) 44/Hct, (b) 37/Hct, (c) 30/Hct, (d) 23/Hct, (e) 16/Hct, or (f) 9/Hct. After 10 min of ischemia, CBF was determined with 14C-iodoantipyrine. Coronal brain sections were evaluated for areas with a CBF of 0-10 and 11-20 ml 100 g-1 min-1. In addition, oxygen delivery was calculated. In the center of the ischemic zone, both areas of low CBF were less in the 30/Hct, 23/Hct, and 16/Hct groups compared with the 44/Hct and 37/Hct groups; and both areas were less in the 9/Hct group compared with the other five groups (p < 0.05). For the hemisphere contralateral to occlusion, there was a direct correlation between hematocrit and oxygen delivery. However, for the hemisphere ipsilateral to occlusion, oxygen delivery increased as hematocrit decreased (44/Hct, 8.6 +/- 0.3 vs. 9/Hct, 13.6 +/- 0.4 [mean +/- SD, ml 100 g-1 min-1]). The results of this study support a hypothesis that hemodilution with DCLHb decreases the extent of focal cerebral ischemia.

Mechanism of cerebral blood flow augmentation by hemodilution in rabbits

BACKGROUND AND PURPOSE

Hemodilution is known to increase cerebral blood flow, but it is not known whether the increase in flow is a direct result of a decrease in viscosity or whether it may be due to compensatory vasodilatation in response to the decrease in oxygen carrying capacity that results from hemodilution. This study is designed to investigate this question.

METHODS

Changes in regional cerebral blood flow were studied in normal and ischemic brains of 15 and 18 rabbits, respectively. In one group of rabbits graded hemodilution was used to reduce arterial oxygen content progressively in stages; in the second group the arterial oxygen content was reduced in similar stages by progressively larger reductions in the concentration of inspired oxygen (hypoxic hypoxia). In the ischemic animals focal ischemia was produced by embolic occlusion of the right middle cerebral artery.

RESULTS

In the normal rabbits, hypoxic hypoxia and hemodilution resulted in similar progressive increases in cerebral blood flow as arterial oxygen content fell. In the ischemic animals, there was a significant fall in cerebral blood flow in the ischemic region in all groups after arterial occlusion. Hemodilution resulted in a progressive increase in cerebral blood flow in both ischemic and nonischemic regions. With hypoxic hypoxia, however, cerebral blood flow in the ischemic region showed no increase or a slight decrease.

CONCLUSIONS

Even though hypoxic hypoxia results in a marked increase in cerebral blood flow in normal brain, it does not significantly change cerebral blood flow in ischemic brain. In contrast, hemodilution resulting in a comparable degree of hypoxemia is capable of significantly increasing cerebral blood flow in ischemic brain. Therefore, the mechanism of blood flow augmentation by hemodilution in ischemic brain is probably related to a direct hemorheologic effect rather than to the resulting hypoxemia.

What have drugs to offer the patient with acute stroke?

1. Drug treatment for acute stroke is designed to salvage neuronal tissue, and to prevent complications of stroke, which are often non-neurological. This review addresses the areas of recent advance in treatment designed to reduce the size of the cerebral infarct. With the exception of cardiac-source embolism, for which anticoagulation in the acute phase is sometimes considered, prevention of recurrent events is not discussed. 2. It is to be hoped that pharmaceutical developments will improve the current bleak picture in which there are no proven treatments for ischaemic stroke or intracerebral haemorrhage. To meet this challenge will require careful, controlled evaluation of treatment early after acute stroke in large scale clinical studies.

Time course of the impairment of cerebral autoregulation during chronic cerebral vasospasm after subarachnoid hemorrhage in primates

The time course of the impairment of cerebral autoregulation during chronic cerebral vasospasm after subarachnoid hemorrhage was studied in 18 monkeys. Changes in cerebral blood flow (CBF) at the regional level and central conduction times during either graded hypo- or hypertension were evaluated in these animals at three stages (3, 7, and 14 days) following the introduction of an autologous blood clot around the right middle cerebral artery (MCA). Angiograms revealed a reduction in vessel caliber (compared to the baseline level in the involved MCA) of 30% at 3 days, 50% at 7 days, and 10% at 14 days. At all stages, CBF remained constant at mean arterial blood pressures (MABP) of 60 to 160 mm Hg in the noninvolved hemisphere. In contrast, at the 3- and 7-day stages, there was an impairment of autoregulation in the involved hemisphere at MABP of 40 to 180 mm Hg. The right hemispheric CBF was significantly (p less than 0.05) lower than that in the left throughout the period of investigation at MABP below 120 mm Hg, but rose to exceed the left CBF at MABP above 180 mm Hg at the 7-day stage and 160 mm Hg at the 14-day stage. The right-sided central conduction time showed significant (p less than 0.05) prolongation at MABP below 60 mm Hg at the 3-day stage and 40 mm Hg at the 7-day stage. It is suggested that these results may help to develop guidelines for hemodynamic therapy for vasospasm in its various stages.

Prevention of post-ischemic brain lipid conjugated diene production and neurological injury by hydroxyethyl starch-conjugated deferoxamine

Hydroxyethyl starch conjugated deferoxamine (DFO) was administered to rats following resuscitation from 6.5 min cardiac arrest (CA) in an attempt to prevent the iron-catalyzed production of oxygen free radicals which may lead to neurologic injury and ultimately death following restoration of spontaneous circulation (ROSC). Brain conjugated dienes were analyzed spectrophotometrically 4 and 24 hr following ROSC, and were found to be significantly elevated when compared to non-ischemic controls. Hydroxyethyl starch-DFO treated rats demonstrated no increased conjugated diene production at either period. Neurologic injury was significantly less in drug treated rats surviving 24 or 72 hours when compared to controls. While mortality was similar in drug treated or control rats for the first 24 hours following ROSC, delayed mortality (days 1-10) was significantly less in drug treated animals, presumably as a result of neurologic protection afforded by post-ischemic drug administration. Administration of DFO conjugated to hydroxyethyl starch appears to modulate the neurologic injury which occurs during brain ischemia and reperfusion.

[In vivo rheologic studies of plasma substitutes]

The aim of this study was to compare in 60 ASA1 patients, the rheological effects of a 500 ml plasma substitute infusion at induction of general anaesthesia. The 60 patients were allocated into 6 groups of 10. Each group received either albumin 4%, or dextran 40 3.5%, or dextran 60 6%, or hydroxyethylstarch (HES) 200 6%, or modified fluid gelatin or Ringer lactate. The infusion extended over 30 minutes. In blood samples obtained before infusion, immediately after the end, three and 24 hours after the end of infusion, osmotic pressure, oncotic pressure, proteins and fibrinogen concentration were measured. Following rheological parameters were also assessed: plasma viscosity, blood viscosity at two shear rates (0.5 and 128 s-1), erythrocyte aggregation by primary and final aggregation times as well as total and partial dissociation thresholds. The determinations were carried out at haematocrit corrected to 40%. At intergroup analysis of the different substitutes compared to albumin 4%, with the exception of Ringer lactate, there was no significant modification of osmotic and oncotic pressures or fibrinogen concentrations. Only gelatin and dextran 60 modified the rheological parameters. The intragroup comparison did not demonstrate significant variations of osmotic and oncotic pressures. Fibrinogen concentrations remained unchanged up to the 24th hours, where they increased as a reaction to surgery. Similar changes of rheological parameters occurred for Ringer lactate, albumin 4% and dextran 40: decrease of plasma viscosity (< 10%) and blood viscosity (< 20% at shear rate of 0.5 s-1), increase of primary aggregation time (30-50%) with decrease of total dissociation threshold (10-20%). These changes ended 24 hours after infusion. Dextran 60 and gelatin elicited a modification of blood rheology until the 24th hour after the end of infusion. Such modifications did not occur with HES. It is concluded that when a rheological effect is required albumin 4% or dextran 40 3.5% should be used.

Hypertension with hemodilution prevents multifocal cerebral hypoperfusion after cardiac arrest in dogs

BACKGROUND

Improved neurological outcome with postarrest hypertensive hemodilution in an earlier study could be the result of more homogeneous cerebral perfusion and improved O2 delivery. We explored global, regional, and local cerebral blood flow by stable xenon-enhanced computed tomography and global cerebral metabolism in our dog cardiac arrest model.

METHODS

Ventricular fibrillation cardiac arrest of 12.5 minutes was reversed by brief cardiopulmonary bypass, followed by life support to 4 hours postarrest. We compared control group I (n = 5; mean arterial blood pressure, 100 mm Hg; hematocrit, greater than or equal to 35%) with immediately postarrest reflow-promoted group II (n = 5; mean arterial blood pressure, 140-110 mm Hg; hypervolemic hemodilution with plasma substitute to hematocrit, 20-25%).

RESULTS

After initial hyperemia in both groups, during the "delayed hypoperfusion phase" at 1-4 hours postarrest, global cerebral blood flow was 51-60% of baseline in group I versus 85-100% of baseline in group II (p less than 0.01). Percentages of brain tissue voxels with no flow, trickle flow, or low flow were lower (p less than 0.01) and mean regional cerebral blood flow values were higher in group II (p less than 0.01). Global cerebral oxygen uptake recovered to near baseline values at 3-4 hours postarrest in both groups. Postarrest arterial O2 content, however, in hemodiluted group II was 40-50% of that in group I. Thus, the O2 uptake/delivery ratio was increased (worsened) in both groups at 2-4 hours postarrest.

CONCLUSIONS

After prolonged cardiac arrest, immediately induced moderate hypertensive hemodilution to hematocrit 20-25% can normalize cerebral blood flow patterns (improve homogeneity of cerebral perfusion), but does not improve cerebral O2 delivery, since the flow benefit is offset by decreased arterial O2 content. Individualized titration of hematocrit or hemodilution with acellular O2 carrying blood substitute (stroma-free hemoglobin or fluorocarbon solution) would be required to improve O2 uptake/delivery ratio.

Relationship between the timing of aneurysm surgery and the development of delayed cerebral ischemia

A consecutive series of 145 patients with acute aneurysmal subarachnoid hemorrhage (SAH) were operated on within 7 days of SAH and were prospectively evaluated over a 4-year period to determine if the timing of aneurysm surgery influenced the development of delayed cerebral ischemia. All patients were managed with a standardized policy of urgent surgical clipping and treatment with aggressive prophylactic postoperative volume expansion. Patients with delayed ischemic symptoms were additionally treated with induced hypertension. Forty-nine patients underwent surgery on Day 0 or 1 (Group 1) post-SAH, 60 patients on Day 2 or 3 (Group 2), and 36 patients on Days 4 through 7 (Group 3). Postoperative delayed cerebral ischemia developed in 16% of (Group 1) patients, in 22% of Group 2 patients, and in 28% of Group 3 patients. Cerebral infarction resulting from delayed cerebral ischemia developed in only 4% of Group 1 patients, 10% of Group 2 patients, and 11% of Group 3 patients. A bad clinical outcome as a result of delayed cerebral ischemia occurred in one Group 1 patient (2%), two Group 2 patients (3%), and one Group 3 patient (3%). Preoperative grade was not significantly correlated with the incidence or severity of delayed cerebral ischemia at any time interval except that patients in modified Hunt and Hess Grade I or II who underwent surgery on Day 0 or 1 after SAH had no strokes or bad outcomes from delayed cerebral ischemia. This study demonstrates that there is no rationale for delaying aneurysm surgery based on the time interval between SAH and patient evaluation.

Hypervolemic-hemodilution and hypertension during temporary middle cerebral artery occlusion in rats: the effect on blood-brain barrier permeability

The effect of hypervolemic-hemodilution, with and without hypertension, on blood-brain barrier permeability was investigated in rats, after 180 minutes of middle cerebral artery occlusion (MCAo), and 60 minutes of reperfusion. One of the following conditions was maintained during MCAo: 1) Control--hematocrit and blood pressure were not manipulated; 2) Hypervolemic-Hemodilution/Normotension--the hematocrit was decreased to 30%; 3) Hypervolemic-Hemodilution/Hypertension--the hematocrit was decreased to 30% and mean arterial pressure increased by 30 mmHg with phenylphrine. In all groups, Evans Blue was administered, and its concentration determined by spectrophotometric assay. Evans Blue (micrograms (g-1 of brain tissue [mean +/- SD]) was greater in the Hypervolemic-Hemodilution/Hypertension group (71 +/- 20) versus the Control (13 +/- 9) and Hypervolemic-Hemodilution/Normotension (17 +/- 10) groups (p less than 0.05). No other differences were present. These results support the hypothesis that during MCAo, hypervolemic-hemodilution/hypertensive therapy effects an increase in blood-brain barrier permeability in the early period of reperfusion.