Hypertonic saline worsens infarct volume after transient focal ischemia in rats

Effectiveness of Continuous Hypertonic Saline in Acute Ischemic Infarcts: A Radiographic and Clinical Evaluation

OBJECTIVE

The role of continuous hypertonic saline (HS) infusion in the management of malignant cerebral edema is controversial. We evaluated patients presenting with large anterior circulation territory infarcts and compared radiographic and clinical outcomes to evaluate the effects of continuous HS.

METHODS

This was a retrospective review of patients with malignant ischemic strokes who were initially managed with continuous HS versus routine medical management. Radiographic parameters of cerebral edema and clinical parameters were collected at different time intervals after admission. Rates and timing of surgery, mortality, and complications were also collected.

RESULTS

The study included 43 patients: 26 in group 1 (HS) and 17 in group 2 (no HS). Both cohorts had comparable baseline clinical and radiographic parameters. There was no difference between rates and timing of surgery, complications, and mortality. Mean midline shift was significantly greater in the HS group at interval 1 (12-36 hours, P = 0.003) and interval 2 (36-60 hours, P = 0.030), and mean change in midline shift from initial interval to interval 1 was significantly greater in the HS group (P = 0.019).

CONCLUSIONS

Despite the widespread use of continuous HS in acute ischemic infarcts, only a limited number of studies have evaluated its efficacy, and virtually no studies have studied its effect on radiographic progression and rates of decompressive surgery. Results of this study indicate that there is no benefit of continuous HS. In fact, there may be worsening of cerebral edema with administration of continuous HS. In addition, there are no differences in prevention or delay of decompressive surgery or in overall mortality.

Osmotherapy for malignant cerebral edema in a phase 2 prospective, double blind, randomized, placebo-controlled study of IV glibenclamide

BACKGROUND/OBJECTIVE

Malignant edema can be a life-threatening complication of large hemispheric infarction (LHI), and is often treated with osmotherapy. In this exploratory analysis of data from the GAMES-RP study, we hypothesized that patients receiving osmotherapy had symptomatic cerebral edema, and that treatment with intravenous (IV) glibenclamide would modify osmotherapy use as compared with placebo.

METHODS

GAMES-RP was a phase 2 multi-center prospective, double blind, randomized, placebo-controlled study in LHI. Patients were randomized to IV glibenclamide (e.g. IV glyburide) or placebo. Cerebral edema therapies included osmotherapy and/or decompressive craniectomy at the discretion of the treating team. Total bolus osmotherapy dosing was quantified by "osmolar load". Radiographic edema was defined by dichotomizing midline shift at 24 h. Clinical changes were defined as any increase in NIHSS1a.

RESULTS

Osmotherapy was administered to 40 of the 77 patients at a median of 39 [27-55] h after stroke onset. The median baseline DWI lesion volume was significantly larger in the osmotherapy treated group (167 [146-211] mL v. 139 [112-170] mL; P=0.046). Adjudicated malignant edema (75% v. 16%; P<0.001) was more common in the osmotherapy treated group. There were no differences in the proportion of patients receiving osmotherapy or the median total osmolar load between treatment arms. Most patients (76%) had a decrease in consciousness (NIHSS item 1A ≥1) on the day they began receiving osmotherapy.

CONCLUSIONS

In the GAMES-RP trial, osmolar therapies were most often administered in response to clinical symptoms of decreased consciousness. However, the optimal timing of administration and impact on outcome after LHI have yet to be defined.

The Effects of Clinically Relevant Hypertonic Saline and Conivaptan Administration on Ischemic Stroke

Cerebral edema after stroke is associated with poor neurological outcomes. Current therapies are limited to osmotic agents, such as hypertonic saline (HS), which reduce intracranial pressure. Although studies have demonstrated edema reductions following HS, tissue survival has not been thoroughly examined. Additionally, the efficacy of promising pharmacological agents has not been evaluated for synergy with osmotic agents. Conivaptan is an FDA-approved vasopressin receptor antagonist that may exert both osmotic and anti-inflammatory effects. In this study, rats were subjected to middle cerebral artery occlusion prior to treatment with 5 % HS bolus +5 % HS maintenance (HS), conivaptan alone (Con), conivaptan +5 % HS maintenance (Con + HS), or conivaptan +5 % HS bolus +5 % maintenance (Con + HSb). Treatments were initiated at six (Early) or 24 h (Late) following stroke and rats were euthanized at 48 h to evaluate infarct volume, brain edema, and microglia/macrophage activation. Infarct volume and brain edema in the Early HS, Early Con, and Late HS groups were significantly reduced compared with controls. Interestingly, only the Early Con group demonstrated reduced microglia/macrophage activation. These data suggest an anti-inflammatory mechanism for conivaptan and provide support for a multipronged approach combining osmotic agents with compounds that inhibit the neuroinflammatory response to stroke.

Hyperosmolar sodium chloride is toxic to cultured neurons and causes reduction of glucose metabolism and ATP levels, an increase in glutamate uptake, and a reduction in cytosolic calcium

Elevation of serum sodium, hypernatremia, which may occur during dehydration or treatment with sodium chloride, may cause brain dysfunction and damage, but toxic mechanisms are poorly understood. We found that exposure to excess NaCl, 10-100mmol/L, for 20h caused cell death in cultured cerebellar granule cells (neurons). Toxicity was due to Na(+), since substituting excess Na(+) with choline reduced cell death to control levels, whereas gluconate instead of excess Cl(-) did not. Prior to cell death from hyperosmolar NaCl, glucose consumption and lactate formation were reduced, and intracellular aspartate levels were elevated, consistent with reduced glycolysis or glucose uptake. Concomitantly, the level of ATP became reduced. Pyruvate, 10mmol/L, reduced NaCl-induced cell death. The extracellular levels of glutamate, taurine, and GABA were concentration-dependently reduced by excess NaCl; high-affinity glutamate uptake increased. High extracellular [Na(+)] caused reduction in intracellular free [Ca(2+)], but a similar effect was seen with mannitol, which was not neurotoxic. We suggest that inhibition of glucose metabolism with ensuing loss of ATP is a neurotoxic mechanism of hyperosmolar sodium, whereas increased uptake of extracellular neuroactive amino acids and reduced intracellular [Ca(2+)] may, if they occur in vivo, contribute to the cerebral dysfunction and delirium described in hypernatremia.

Comparative Analysis of Different Methods of Ischemia/Reperfusion in Hyperglycemic Stroke Outcomes: Interaction with tPA

Acute hyperglycemia (HG) exacerbates reperfusion injury and aggravates tissue plasminogen activator (tPA)-induced hemorrhagic transformation (HT). Previous experimental hyperglycemic stroke studies employed very high blood glucose levels and exclusively used suture occlusion model to induce ischemia. Only few studies evaluated HG in embolic stroke and mostly involving the use of 10-fold higher dose of tPA than that is used in patients. However, the interaction between acute HG and low (human) dose tPA in different experimental models of stroke has never been reported. We first tested the impact of the severity of acute HG on stroke outcome. Building upon our findings, we then compared the impact of mild acute HG on neurovascular injury in rats subjected to suture or thromboembolic occlusion with and without low dose tPA. We assessed cerebral blood flow, neurobehavioral outcomes, infarction, hemorrhage, and edema. tPA did not change the infarct size in either control or hyperglycemic animals when compared to no tPA groups. HG increased HT and worsened functional outcomes in both suture and embolic occlusion models. The combination of HG and tPA exacerbated the vascular injury and worsened the neurological deficits more than each individual treatment in both models. Our findings show that the interaction between HG and even low dose tPA has detrimental effects on the cerebrovasculature and functional outcomes independent of the method of reperfusion.

Infarct volume after hyperacute infusion of hypertonic saline in a rat model of acute embolic stroke

INTRODUCTION

Hypertonic saline (HS) can treat cerebral edema arising from a number of pathologic conditions. However, physicians are reluctant to use it during the first 24 h after stroke because of experimental evidence that it increases infarct volume when administered early after reperfusion. Here, we determined the effect of HS on infarct size in an embolic clot model without planned reperfusion.

METHODS

A clot was injected into the internal carotid artery of male Wistar rats to reduce perfusion in the middle cerebral artery territory to less than 40 % of baseline, as monitored by laser-Doppler flowmetry. After 25 min, rats were randomized to receive 10 mL/kg of 7.5 % HS (50:50 chloride:acetate) or normal saline (NS) followed by a 0.5 mL/h infusion of the same solution for 22 h.

RESULTS

Infarct volume was similar between NS and HS groups (in mm(3): cortex 102 ± 65 mm(3) vs. 93 ± 49 mm(3), p = 0.72; caudoputamenal complex 15 ± 9 mm(3) vs. 21 ± 14, p = 0.22; total hemisphere 119 ± 76 mm(3) vs. 114 ± 62, p = 0.88, respectively). Percent water content was unchanged in the infarcted hemisphere (NS 81.6 ± 1.5 %; HS 80.7 ± 1.3 %, p = 0.16), whereas the HS-treated contralateral hemisphere was significantly dehydrated (NS 79.4 ± 0.8 %; HS 77.5 ± 0.8 %, p < 0.01).

CONCLUSIONS

HS reduced contralateral hemispheric water content but did not affect ipsilateral brain water content when compared to NS. Infarct volume was unaffected by HS administration at all evaluated locations.

Hyperosmolar therapy for intracranial hypertension

The use of hyperosmolar agents for intracranial hypertension was introduced in the early 20th century and remains a mainstay of therapy for patients with cerebral edema. Both animal and human studies have demonstrated the efficacy of two hyperosmolar agents, mannitol and hypertonic saline, in reducing intracranial pressure via volume redistribution, plasma expansion, rheologic modifications, and anti-inflammatory effects. However, because of physician and institutional variation in therapeutic practices, lack of standardized protocols for initiation and administration of therapy, patient heterogeneity, and a paucity of randomized controlled trials have yielded little class I evidence on which clinical decisions can be based, most current evidence regarding the use of hyperosmolar therapy is derived from retrospective analyses (class III) and case series (class IV). In this review, we summarize the available evidence regarding the use of hyperosmolar therapy with mannitol or hypertonic saline for the medical management of intracranial hypertension and present a comprehensive discussion of the evidence associated with various theoretical and practical concerns related to initiation, dosage, and monitoring of therapy.

Managing malignant cerebral infarction

OPINION STATEMENT

Managing patients with malignant cerebral infarction remains one of the foremost challenges in medicine. These patients are at high risk for progressive neurologic deterioration and death due to malignant cerebral edema, and they are best cared for in the intensive care unit of a comprehensive stroke center. Careful initial assessment of neurologic function and of findings on MRI, coupled with frequent reassessment of clinical and radiologic findings using CT or MRI are mandatory to promote the prompt initiation of treatments that will ensure the best outcome in these patients. Significant deterioration in either neurologic function or radiologic findings or both demand timely treatment using the best medical management, which may include osmotherapy (mannitol or hypertonic saline), endotracheal intubation, and mechanical ventilation. Under appropriate circumstances, decompressive craniectomy may be warranted to improve outcome or to prevent death.

Hypertonic saline and mannitol therapy in critical care neurology

Osmotic agents play a vital role in the reduction of elevated intracranial pressure and treatment of cerebral edema in Neurologic critical care. Both mannitol and hypertonic saline reduce cerebral edema in many clinical syndromes, yet there is controversy over agent selection, timing, and dosing regimens. Despite the lack of randomized, controlled trials, our knowledge base on the appropriate clinical use of osmotic agents continues to expand. This review will summarize the evidence for the use of mannitol and hypertonic saline in a variety of disease states causing cerebral edema, as well as outlining monitoring and safety considerations.

A murine model of hypertonic saline as a treatment for acute spinal cord injury: effects on autonomic outcome

Object

Spinal cord injury (SCI) continues to be a problem without a definitive cure. Research based on improved understanding of the immunological aspects of SCI has revealed targets for treating and ameliorating the extent of secondary injury. Hypertonic saline (HTS), a substance both easy to create and to transport, has been investigated as an immunologically active material that can be used in a clinically relevant interval after injury. In this pilot study, HTS was investigated in a murine model for its abilities to ameliorate secondary injury after a severe spinal cord contusion.

Methods

Female C57Bl/6 mice with severe T8–10 contusion injuries were used as the model subjects. A group of 41 mice were studied in a blinded fashion. Mice received treatments with HTS (HTS, 7.5%) or normal saline solution (NSS, 0.9%) at 2 discreet time points (3 and 24 hours after injury.) A separate group of 9 untreated animals were also used as controls. Animals were assessed for autonomic outcome (bladder function). In a group of 33 mice, histological assessment (cellular infiltration) was also measured.

Results

Bladder function was found to be improved significantly in those treated with HTS compared with those who received NSS and also at later treatment times (24 hours) than at earlier treatment times (3 hours). Decreased cellular infiltration in each group correlated with bladder recovery.

Conclusions

The increased effectiveness of later administration time of the more osmotically active and immunomodulatory substance (HTS) suggests that interaction with events occurring around 24 hours after injury is critical. These events may be related to the invasion of leukocytes peaking at 8–24 hours postinjury and/or the peak benefit time of subject rehydration.

[Hypernatremia in neurointensive care]

Hypernatremia invariably denotes hyperosmolarity and, at least transiently, causes cellular dehydration. Because of blood brain barrier properties, cerebral tissue volume is modified by acute changes in osmolarity. An acute hyperosmolarity (by intravenous sodium or mannitol) temporally decreases intracranial pressure. This treatment is thus useful in critical situations, allowing time for diagnosis and, if possible, other treatment. But in cases of sustained hypernatremia, cellular dehydration is rapidly counterbalanced by an increase in cellular osmolarity. For the brain, it has been shown that cerebral volume is restored in a few hours during prolonged hypernatremia. Moreover, the plasmatic osmotic load induces an increase in diuresis and natriuresis. A tight control is then necessary to prevent hypovolemia and electrolytes disorders. Teams using this treatment should undertake controlled randomized studies to ascertain any beneficial effect that cannot be explained by physiology.

Effect of hypernatremia on injury caused by energy deficiency: role of T-type Ca2+ channel

Hypernatremia exerts multiple cellular effects, many of which could influence the outcome of an ischemic event. To further evaluate these effects of hypernatremia, isolated neonatal cardiomyocytes were chronically incubated with medium containing either normal (142 mM) or elevated sodium (167 mM) and then transferred to medium containing deoxyglucose and the electron transport chain inhibitor amobarbital. Chronic hypernatremia diminished the degree of calcium accumulation and reactive oxygen species generation during the period of metabolic inhibition. The improvement in calcium homeostasis was traced in part to the downregulation of the Ca(V)3.1 T-type calcium channel, as deficiency in the Ca(V)3.1 subtype using short hairpin RNA or treatment with an inhibitor of the Ca(V)3.1 variant of the T-type calcium channel (i.e., diphenylhydantoin) attenuated energy deficiency-mediated calcium accumulation and cell death. Although hyperosmotically stressed cells (exposed to 50 mM mannitol) had no effect on T-type calcium channel activity, they were also resistant to death during metabolic inhibition. Both hyperosmotic stress and hypernatremia activated Akt, suggesting that they initiate the phosphatidylinositol 3-kinase/Akt cytoprotective pathway, which protects the cell against calcium overload and oxidative stress. Thus hypernatremia appears to protect the cell against metabolic inhibition by promoting the downregulation of the T-type calcium channel and stimulating cytoprotective protein kinase pathways.

Lack of sex-linked differences in cerebral edema and aquaporin-4 expression after experimental stroke

Aquaporin-4 (AQP4) has been shown to be important in the evolution of stroke-associated cerebral edema. However, the role of AQP4 in stroke-associated cerebral edema as it pertains to sex has not been previously studied. The perivascular pool of AQP4 is important in the influx and efflux of water during focal cerebral ischemia. We used mice with targeted disruption of the gene encoding alpha-syntrophin (alpha-Syn(-/-)) that lack the perivascular AQP4 pool but retain the endothelial pool of this protein. Infarct volume at 72 h after transient focal ischemia (90 mins) in isoflurane-anesthetized mice was attenuated in both sexes with alpha-Syn deletion as compared with their wild-type (WT) counterparts. There were no sex differences in hemispheric water content in WT and alpha-Syn(-/-) mice or regional AQP4 expression in WT mice. In neither sex did alpha-Syn deletion lead to alterations in end-ischemic regional cerebral blood flow (rCBF). These data suggest that after experimental stroke: (1) there is no difference in stroke-associated cerebral edema based on sex, (2) AQP4 does not involve in sex-based differences in stroke volume, and (3) perivascular pool of AQP4 has no significant role in end-ischemic rCBF.

Blood viscosity modulates tissue perfusion: sometimes and somewhere

Each organ possesses specific properties for controlling microvascular perfusion. Such specificity provides an opportunity to design transfusion fluids that target thrombo-embolic or vasospasm-induced ischemia in a particular organ or that optimize overall perfusion from systemic shock. The role of viscosity in the design of these fluids might be underestimated, because viscosity is rarely monitored or considered in critical care decisions. Studies linking viscosity-dependent changes of microvascular perfusion to outcome-relevant data suggest that whole blood viscosity is negligible as a determinant of microvascular perfusion under physiological conditions when autoregulation is effective. Because autoregulation is driven to maintain oxygen supply constant, the organism will compensate for changes in blood viscosity to sustain oxygen delivery. In contrast, under pathological conditions in the brain and elsewhere, increases of overall viscosity should be avoided - including all the situations where vascular autoregulatory mechanisms are inoperative due to ischemia, structural damage or physiologic dysfunction. As latter conditions are not to identify with high certainty, the risks that accompany therapeutic correction of blood viscosity are outweighing the benefits. The ability to bedside monitor blood viscosity and to link changes in viscosity to outcome parameters in various clinical conditions would provide more solid foundation for evidence-based clinical management.

EMS management of acute stroke--out-of-hospital treatment and stroke system development (resource document to NAEMSP position statement)

The American Heart Association estimates an annual incidence of stroke in the United States at 700,000, leading to over 150,000 deaths. Of all strokes, approximately 88% are ischemic and 12% are hemorrhagic. Almost half of all stroke deaths occur in the out-of-hospital environment. Within a given region, the emergency medical services (EMS) system has an important role in the management of the acute stroke patient. Decisions made by EMS personnel can affect treatment and contribute to the immediate, short-term, and long-term outcomes of the patient. Because the patient may require emergent treatment regardless if the stroke is ischemic or hemorrhagic, EMS personnel should manage all potential stroke patients in a time-dependent nature. Proper treatment and disposition of the stroke patient begins in the out-of-hospital environment, continues in the emergency department, and then extends to the inpatient admission. This article reviews the literature on the out-of-hospital treatment of stroke patients and the role of EMS in the development of stroke systems of care.

Hypertonic saline: first-line therapy for cerebral edema?

This article highlights the experimental and clinical data, controversies and postulated mechanisms surrounding osmotherapy with hypertonic saline (HS) solutions in the neurocritical care arena and builds on previous reviews on the subject. Special attention is focused on HS therapy on commonly encountered clinical paradigms of acute brain injury including traumatic brain injury (TBI), post-operative "retraction edema", intracranial hemorrhage (ICH), tumor-associated cerebral edema, and ischemia associated with ischemic stroke.

Clinical review: Therapy for refractory intracranial hypertension in ischaemic stroke

The treatment of patients with large hemispheric ischaemic stroke accompanied by massive space-occupying oedema represents one of the major unsolved problems in neurocritical care medicine. Despite maximum intensive care, the prognosis of these patients is poor, with case fatality rates as high as 80%. Therefore, the term 'malignant brain infarction' was coined. Because conservative treatment strategies to limit brain tissue shift almost consistently fail, these massive infarctions often are regarded as an untreatable disease. The introduction of decompressive surgery (hemicraniectomy) has completely changed this point of view, suggesting that mortality rates may be reduced to approximately 20%. However, critics have always argued that the reduction in mortality may be outweighed by an accompanying increase in severe disability. Due to the lack of conclusive evidence of efficacy from randomised trials, controversy over the benefit of these treatment strategies remained, leading to large regional differences in the application of this procedure. Meanwhile, data from randomised trials confirm the results of former observational studies, demonstrating that hemicraniectomy not only significantly reduces mortality but also significantly improves clinical outcome without increasing the number of completely dependent patients. Hypothermia is another promising treatment option but still needs evidence of efficacy from randomised controlled trials before it may be recommended for clinical routine use. This review gives the reader an integrated view of the current status of treatment options in massive hemispheric brain infarction, based on the available data of clinical trials, including the most recent data from randomised trials published in 2007.

An early bolus of hypertonic saline hydroxyethyl starch improves long-term outcome after global cerebral ischemia

OBJECTIVE

The beneficial effect of hypertonic saline solutions in the emergency treatment of shock and traumatic brain injury is well described. The present study determines effects of a single bolus of hypertonic saline on long-term survival, neurologic function, and neuronal survival 10 days after global cerebral ischemia. In addition, we evaluated the therapeutic window for hypertonic saline treatment (early vs. delayed application).

DESIGN

Laboratory experiment.

SETTING

University laboratory.

SUBJECTS

Male Wistar rats weighing 240-330 g.

INTERVENTIONS

Rats were submitted to temporal global cerebral ischemia using temporary bilateral carotid occlusion combined with hypobaric hypotension. Animals received 7.5% saline/6% hydroxyethyl starch (HHS) or vehicle (NaCl 0.9%) at either 1.5 mins (early treatment) or 31.5 mins (delayed treatment) of reperfusion. Regional cerebral blood flow (rCBF) and physiologic variables were measured during insult and early reperfusion. Animal survival and neurologic function were evaluated throughout the 10-day observation period. Quantification of brain injury was performed on day 10.

MEASUREMENTS AND MAIN RESULTS

Early treatment with HHS resulted in a robust restoration of rCBF after ischemia, reduced postischemic mortality by 77% (9% vs. 39% in vehicle-treated controls), ameliorated neurologic performance (Neuro-Deficit-Score 10 days after insult, 96 +/- 0.7 vs. 85 +/- 1.4, mean +/- se), and almost blunted neuronal cell death (hippocampal CA1, 2150 +/- 191 vs. 884 +/- 141 neurons/mm; cortex, 1746 +/- 91 vs. 1060 +/- 112). In contrast, delayed treatment resulted in no sustained effects.

CONCLUSIONS

Timing of HHS treatment is critical after experimental global cerebral ischemia to reduce mortality, improve neurologic function, and neuronal survival. Our results suggest that early application of HHS may be a potential neuroprotective strategy after global cerebral ischemia.

Effect of duration of osmotherapy on blood-brain barrier disruption and regional cerebral edema after experimental stroke

Osmotherapy is the cornerstone of medical management for cerebral edema associated with large ischemic strokes. We determined the effect of duration of graded increases in serum osmolality with mannitol and hypertonic saline (HS) on blood-brain barrier (BBB) disruption and regional cerebral edema in a well-characterized rat model of large ischemic stroke. Halothane-anesthetized adult male Wistar rats were subjected to transient (2-h) middle cerebral artery occlusion (MCAO) by the intraluminal occlusion technique. Beginning at 6 h after MCAO, rats were treated with either no intravenous fluids or a continuous intravenous infusion (0.3 mL/h) of 0.9% saline, 20% mannitol, 3% HS, or 7.5% HS for 24, 48, 72, and 96 h. In the first series of experiments, BBB permeability was quantified by the Evans blue (EB) extravasation method. In the second series of experiments, water content was assessed by comparing wet-to-dry weight ratios in six predetermined brain regions. Blood-brain barrier disruption was maximal in rats treated with 0.9% saline for 48 h, but did not correlate with increases in serum osmolality or treatment duration with osmotic agents. Treatment with 7.5% HS attenuated water content in the periinfarct regions and all subregions of the contralateral nonischemic hemisphere to a greater extent than mannitol did with no adverse effect on survival rates. These data show that (1) BBB integrity is not affected by the duration and degree of serum osmolality with osmotic agents, and (2) attenuation of increases in brain water content with HS to target levels >350 mOsm/L may have therapeutic implications in the treatment of cerebral edema associated with ischemic stroke.

Osmotic therapy: fact and fiction

This review examines the available data on the use of osmotic agents in patients with head injury and ischemic stroke, summarizes the physiological effects of osmotic agents, and presents the leading hypotheses regarding the mechanism by which they reduce ICP. Finally, it addresses the validity of the following commonly held beliefs: mannitol accumulates in injured brain; mannitol shrinks only normal brain and can increase midline shift; osmolality can be used to monitor mannitol administration; mannitol should be not be administered if osmolality is >320 mOsm; and hypertonic saline is equally effective as mannitol.

Plasma arginine-vasopressin following experimental stroke: effect of osmotherapy

Neurohumoral responses have been implicated in the pathogenesis of ischemia-evoked cerebral edema. In a well-characterized animal model of ischemic stroke, the present study was undertaken to 1) study the profile of plasma arginine-vasopressin (AVP), and 2) determine whether osmotherapy with mannitol and various concentrations of hypertonic saline (HS) solutions influence plasma AVP levels. Halothane-anesthetized adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion with the intraluminal filament technique. Plasma AVP levels (means +/- SD) were significantly elevated at 24 h (42 +/- 21 pg/ml), 48 h (50 +/- 28 pg/ml), and 72 h (110 +/- 47 pg/ml), and returned to baseline at 96 h (22 +/- 15 pg/ml) following middle cerebral artery occlusion compared with sham-operated controls (14 +/- 7 pg/ml). Plasma AVP levels at 72 h were significantly attenuated with 7.5% HS (37 +/- 8 pg/ml; 360 +/- 11 osmol/l) compared with 0.9% saline (73 +/- 6; 292 +/- 6 osmol/l), 3% HS (66 +/- 8 pg/ml; 303 +/- 12 osmol/l), or mannitol (74 +/- 9 pg/ml; 313 +/- 14 osmol/l) treatment. HS (7.5%) significantly attenuated water content in the ipsilateral and contralateral hemispheres compared with surgical shams, 0.9% saline, 3% HS, and mannitol treatments. Peak plasma AVP levels were not associated with direct histopathological injury to the anterior hypothalamus. Attenuation of brain water content with 7.5% HS treatment coincides with attenuated serum AVP levels, and we speculate that this may represent one additional mechanism by which osmotherapy attenuates edema associated with ischemic stroke.

Treatment of massive cerebral infarction

Stroke is the third leading cause of death in the United States, with a person dying every 3 minutes of a stroke. Massive ischemic stroke accounts for 10% to 20% of ischemic strokes, has traditionally been associated with a high mortality and morbidity, and requires a unique management strategy. Recent advances in management, fueled by an increased understanding of the pathophysiology, may help decrease mortality and improve outcomes. Rapid access to reperfusion therapies remains the most critical element of stroke care and the cornerstone of therapy. This article focuses on newer therapies, including osmotic therapy, hypothermia, maintained normothermia, strict glycemic control, induced hypertension, and hemicraniectomy, all of which show promise for reducing mortality and improving functional outcome. These interventions have become integrated into neurologic intensive care units around the world. They are complicated, require a high level of expertise, and carry a significant learning curve. In order for these new management techniques to be effective, an expedited, aggressive, meticulous, and potentially prolonged medical management approach is needed. To accomplish this there is a growing need for focused specialists in the areas of neurointensive care and stroke.

Hyperosmolar Agents in Neurosurgical Practice: The Evolving Role of Hypertonic Saline

Medical management of cerebral edema and elevated intracranial pressure (ICP) is a critical component of perioperative care in neurosurgical practice. Traumatic brain injury, arterial infarction, venous hypertension/infarction, intracerebral hemorrhage, subarachnoid hemorrhage, tumor progression, and postoperative edema can all generate clinical situations in which ICP management is a critical determinant of patient outcomes. Although osmotic agents are among the most fundamental tools to control ICP, prospective data to establish clear guidelines on their use are lacking. Hypertonic saline is emerging as an alternative to mannitol. Early data suggest that indications for each agent may ultimately depend on ICP etiology.

Increases in lung and brain water following experimental stroke: Effect of mannitol and hypertonic saline*

OBJECTIVE

Pulmonary edema is a serious condition following brain injury of diverse etiologies, including large hemispheric infarctions. We have previously shown that treatment with hypertonic saline attenuates cerebral edema associated with experimental ischemic stroke. In a well-characterized animal model of large ischemic stroke, we tested the hypotheses that lung water increases following cerebral ischemia and determined the effects of osmotherapy with hypertonic saline and mannitol on total lung water, as well as on cerebral edema.

DESIGN

Prospective laboratory animal study.

SETTING

Research laboratory in a university teaching hospital.

SUBJECTS

Adult male Wistar rats (300-450 g, n = 103).

INTERVENTIONS

Under controlled conditions of normoxia, normocarbia, and normothermia, spontaneously breathing, halothane-anesthetized (1.0-1.5%) rats were subjected to permanent middle cerebral artery occlusion by the intraluminal occlusion technique.

MEASUREMENTS AND MAIN RESULTS

Cerebral perfusion was monitored by laser-Doppler flowmetry over ipsilateral parietal cortex to ensure adequate vascular occlusion. At 6 hrs following middle cerebral artery occlusion, rats were treated in a blinded randomized fashion with no intravenous fluids (n = 24), a continuous intravenous infusion (0.3 mL/hr) of 0.9% saline (n = 21), 20% mannitol (2 g/Kg) (n = 20), 5% hypertonic saline (n = 20), or 7.5% hypertonic saline (n = 18) as a chloride/acetate mixture (50:50) until the end of the experiment. Brains and lungs were harvested, and tissue water content was estimated by comparing wet-to-dry weight ratios of ipsilateral and contralateral cerebral hemispheres at 48 hrs postischemia. Sham-operated rats served as controls (n = 20). Serum osmolality was determined at the end of the experiment in all animals. Lung water content was increased significantly in rats subjected to middle cerebral artery occlusion and treated with no intravenous fluids (76.7 +/- 0.7%, 317 +/- 7 mOsm/L) (mean +/- sd) and saline (76.8 +/- 1.2%, 311 +/- 10 mOsm/L), compared with sham-operated controls (74.5 +/- 0.9%, 302 +/- 4 mOsm/L). Treatment with 20% mannitol (74.4 +/- 1.2%, 352 +/- 15 mOsm/L), 5% hypertonic saline (75.6 +/- 1.3%, 339 +/- 16 mOsm/L), and 7.5% hypertonic saline (74.9 +/- 0.7%, 360 +/- 23 mOsm/L) significantly attenuated lung water content. Hemispheric brain water content increased both in the ipsilateral ischemic and contralateral hemispheres treated with saline (ipsilateral, 85.1 +/- 1.7%; contralateral, 80.7 +/- 0.7%), compared with sham-operated controls (ipsilateral, 79.6 +/- 0.9%; contralateral, 79.5 +/- 0.9%), as well as in rats that received no fluids (ipsilateral, 84.6 +/- 1.8%; contralateral, 80.4 +/- 0.9%). Treatment with 5% hypertonic saline (ipsilateral, 83.8 +/- 1.0%; contralateral, 79.7 +/- 0.6%) and 7.5% hypertonic saline (ipsilateral, 82.3 +/- 1.3%; contralateral, 78.6 +/- 0.7%) resulted in attenuation of stroke-associated increases in brain water content to a greater extent than mannitol (ipsilateral, 83.6 +/- 1.6%; contralateral, 79.1 +/- 1.0%).

CONCLUSIONS

In a well-characterized animal model of large ischemic stroke, total lung water content increases, which is likely neurogenic in origin. Attenuation of stroke-associated increases in lung and brain water content with continuous infusion of hypertonic saline may have therapeutic implication in the treatment of cerebral and pulmonary edema following ischemic stroke.

Hypertonic saline solutions in brain injury

PURPOSE OF REVIEW

Hypertonic saline solutions have received renewed attention as effective agents for the treatment of cerebral edema and in brain resuscitation in a variety of brain injury paradigms. Although evidence of the beneficial action of hypertonic saline solutions in traumatic brain injury is robust, data supporting use in other conditions are only now mounting.

RECENT FINDINGS

Osmotic properties of hypertonic saline solutions have been well studied in laboratory-based studies in animal models and in patients with acute brain injury. There are, in addition, emerging data on the extraosmotic actions on brain pathophysiology. This review cites baseline literature and provides new evidence of actions of hypertonic saline solutions: (a). in augmenting cerebral blood flow after subarachnoid hemorrhage, (b). as an antiinflammatory adjunct, and (c). utility in chemonucleolysis for intervertebral disc disease and treatment of seizures associated with severe hyponatremia.

SUMMARY

Brain injury from diverse etiologies including trauma, ischemic stroke, global cerebral ischemia from cardiac arrest, intraparenchymal or subarachnoid hemorrhage, infection, or toxic-metabolic derangements are commonly encountered in the clinical setting. Many of these conditions are associated with cerebral edema with or without elevated intracranial pressure. Osmotherapy constitutes the cornerstone of medical therapy for such patients. Hypertonic saline solutions have received renewed attention in clinical practice as osmotic agents for cerebral resuscitation. This article reviews experimental and clinical evidence of the efficacy of hypertonic saline solutions and elaborates on their use in patients with acute neurologic injury. Important areas for current and future research are highlighted before the use of hypertonic saline solutions can be accepted for widespread use.

Effects of Mannitol on Ischemia-Induced Degeneration in Rat Hippocampus

Although mannitol has been used as an osmotherapeutic drug on brain injury, the clinical efficiency of the drug are still controversial. In the present study, we examined the effects of mannitol on the edema in a hippocampal slice due to brief ischemia. To evaluate the effects, we employed an image analysis system that consists of an infrared-differential interference contrast (IR-DIC) microscope, an infrared CCD camera, and a computer with custom-made software. By this system, severity of the edema can be quantified as the coefficient of variation (CV) of digitalized slice images. The dose-dependent improvement on the deteriorated hippocampal slices could be obtained by administration of mannitol (10, 50, and 100 mM) after 10-min ischemia. However, field excitatory postsynaptic potentials (fEPSP) in CA1 stratum radiatum, which disappeared during 10-min ischemia, were never recovered by mannitol after more than 20-min treatment. fEPSP were blocked by the effective dose of mannitol for morphological recovery, but the effects found to be reversible. Although we failed to find positive rescuing effects of mannitol on the synaptic activities after ischemia, the protective effects of the drug on ischemic edema may rescue the secondary damages around the infarct area.

Kappa-Opioid Receptor Selectivity for Ischemic Neuroprotection with BRL 52537 in Rats

Kappa-opioid receptors (KOR) have been implicated in neuroprotection from ischemic neuronal injury, but less work has been performed with transient focal cerebral ischemia to determine the role of KOR during reperfusion. We tested the effects of a selective and specific KOR agonist, BRL 52537 hydrochloride [(+/-)-1-(3,4-dichlorophenyl)acetyl-2-(1-pyrrolidinyl)methylpiperidine], and the standard KOR antagonist, nor-binaltorphimine dihydrochloride [nor-BNI; 17,17'-(dicyclopropylmethyl)-6,6',7,7'-6,6'-imino-7,7'-binorphinan-3,4',14,14'-tetrol], on functional and histological outcome after transient focal ischemia in the rat. By use of the intraluminal filament technique, halothane-anesthetized adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion confirmed by laser Doppler flowmetry. In a blinded, randomized fashion, rats were treated with 1). saline (vehicle) 15 min before reperfusion followed by saline at reperfusion for 22 h, 2). saline 15 min before reperfusion followed by BRL 52537 (1 mg x kg(-1) x h(-1)) at reperfusion for 22 h, 3). saline 15 min before reperfusion followed by nor-BNI (1 mg x kg(-1) x h(-1)) at reperfusion for 22 h, or 4) nor-BNI (1 mg/kg) 15 min before reperfusion followed by BRL 52537 (1 mgx kg(-1)x h(-1)) and nor-BNI (1 mg x kg(-1) x h(-1)) at reperfusion for 22 h. Infarct volume (percentage of ipsilateral structure) analyzed at 4 days of reperfusion was significantly attenuated in saline/BRL 52537 rats (n = 8; cortex, 10.2% +/- 4.3%; caudoputamen [CP], 23.8% +/- 6.7%) (mean +/- SEM) compared with saline/saline treatment (n = 8; cortex, 28.6% +/- 4.9%; CP, 53.3% +/- 5.8%). Addition of the specific KOR antagonist nor-BNI to BRL 52537 completely prevented the neuroprotection (n = 7; cortex, 28.6% +/- 5.3%; CP, 40.9% +/- 6.2%) conferred by BRL 52537. BRL 52537 did not produce postischemic hypothermia. These data demonstrate that KORs may provide a therapeutic target during early reperfusion after ischemic stroke.

IMPLICATIONS

The neuroprotective effect of selective kappa-opioid agonists in transient focal ischemia is via a selective action at the kappa-opioid receptors.

Hypertonic saline for cerebral edema

Raised intracranial pressure (ICP) is a major contributor to the mortality of many conditions encountered in a neurologic intensive care unit. Achieving a sustained reduction in ICP in patients with intracranial hypertension remains a challenge. Treatment with hyperosmolar agents is one of the few options that are available, and mannitol is currently the most commonly used agent. However, hypertonic saline solutions have recently emerged as a potentially safer and more efficacious alternative to mannitol.

Effects of hypertonic/hyperoncotic treatment after rat cortical vein occlusion*

OBJECTIVE

To examine the effects of hypertonic/hyperoncotic treatment on physiologic variables and regional cerebral blood flow and to test its neuroprotective efficiency in a model of permanent venous ischemia.

DESIGN

Randomized prospective study.

SETTING

University research institute.

SUBJECTS

Adult male Wistar rats, weighing 359 +/- 54 g (n = 38).

INTERVENTIONS

Rats were subjected to photochemical occlusion of two adjacent cortical veins. A randomized infusion with vehicle (0.9% NaCl), 10% hydroxyethyl starch 200,000 (HES), or 7.5% saline plus 10% hydroxyethyl starch 200,000 (HHES) was started 30 mins after two-vein occlusion. Effects on physiologic variables and regional cerebral blood flow (assessed by laser Doppler flowmetry) were studied up to 120 mins after two-vein occlusion. Two days after occlusion, the brains were removed for histologic evaluation.

MEASUREMENTS AND MAIN RESULTS

After occlusion, regional cerebral blood flow decreased by 50%, significantly in all groups (from 47.3 +/- 3 to 22.2 +/- 2.2 laser Doppler units). In the vehicle and HES groups, regional cerebral blood flow further decreased to 12.9 +/- 1.9 and 17.8 +/- 2.3 laser Doppler units, respectively. HHES improved regional cerebral blood flow significantly to 27.3 +/- 3.5 laser Doppler units, particularly by reducing no-flow/low-flow areas and reducing infarct size.

CONCLUSION

We found that HHES reduced infarct size as a consequence of an improved regional cerebral blood flow and reduced no-flow/low-flow areas in the tissue at risk in the two-vein occlusion model.

Treatment of space-occupying cerebral infarction

OBJECTIVE

Patients with a hemispheric infarct accompanied by massive edema have a poor prognosis; the case fatality rate may be as high as 80%, and most survivors are left severely disabled. Various treatment strategies have been proposed to limit brain tissue shifts and to reduce intracranial pressure, but their use is controversial. We performed a systematic search of the literature to review the evidence of efficacy of these therapeutic modalities.

DATA SOURCES

Literature searches were carried out on MEDLINE and PubMed.

STUDY SELECTION

Studies were included if they were published in English between 1966 and February 2002 and addressed the effect of osmotherapy, hyperventilation, barbiturates, steroids, hypothermia, or decompressive surgery in supratentorial infarction with edema in animals or humans.

DATA SYNTHESIS

Animal studies of medical treatment strategies in focal cerebral ischemia produced conflicting results. If any, experimental support for these strategies is derived from studies with animal models of moderately severe focal ischemia instead of severe space-occupying infarction. None of the treatment options have improved outcome in randomized clinical trials. Two large nonrandomized studies of decompressive surgery yielded promising results in terms of reduction of mortality and improvement of functional outcome.

CONCLUSIONS

There is no treatment modality of proven efficacy for patients with space-occupying hemispheric infarction. Decompressive surgery might be the most promising therapeutic option. For decisive answers, randomized, controlled clinical trials are needed.

Chemical shift imaging of mannitol in acute cerebral ischemia. Case report

The effectiveness of mannitol for the treatment of cerebral edema after stroke has long been debated, and the diffusion of mannitol through a disrupted blood-brain barrier has been the focus of many contradictory studies. The authors present a unique case in which chemical shift imaging was used to demonstrate the accumulation of mannitol in an area of stroke underlying a subdural hematoma in a patient with end-stage renal disease being treated with hemodialysis. A metabolite map for the xenobiotic mannitol was created from the data and demonstrated the accumulation of mannitol when hemodialysis was interrupted prematurely. Metabolite maps were also used to show removal of the mannitol with the reestablishment of hemodialysis. It is concluded that mannitol can accumulate in an area of infarction, and that chemical shift imaging can be used to illustrate this process.

Hypertonic saline ameliorates cerebral edema associated with experimental brain tumor

Cerebral edema commonly accompanies brain tumors and frequently leads to lethal intracranial compartmental shifts and elevated intracranial pressure. Therapeutic modalities for tumor-associated cerebral edema include diuretics, osmotherapy, and corticosteroids. Recently, hypertonic saline (HS) has received attention as an osmotic agent in the treatment of cerebral edema from diverse causes. The effects of continuous HS infusion in brain tumor-associated edema have not been previously reported. Therefore, we tested the hypothesis that HS given as a continuous intravenous infusion ameliorates tumor-associated edema in a rat model of brain tumor. 9L gliosarcoma, propagated as a solid flank tumor, was implanted intracranially over the left hemisphere in adult female Fischer 344 rats (180-220 g). On day 11 after implantation, rats were divided in a blinded, randomized fashion into groups that received no treatment or continuous infusion of 0.9% saline (NS) (0.3 mL/h) and in a subsequent series that included NS + intravenous furosemide 2.5 mg/kg every six hours, NS + intravenous mannitol 2.5 g/kg every six hours, or continuous infusion 7.5% HS (chloride:acetate 50:50) (0.3 mL/h). Hemispheric water content ipsilateral (IH) and contralateral to tumor implantation was determined at day 13 by wet-to-dry weight ratio after 48 hours of therapy. Ipsilateral hemispheric water content (mean +/- SEM) was significantly increased in rats with intracranial tumor on day 11 (80.3 +/- 0.5%) (n = 7) and day 13 (81.4 +/- 0.3%) (n = 10), as compared to naive weight-matched rats without tumor implant (79.3 +/- 0.1%) (n = 13) (P <.05). After 48 hours of treatment, IH water content was attenuated with continuous HS (n = 15) (79.3 +/- 0.2%), mannitol (n = 14) (80.1 +/- 0.2%), and furosemide (n = 15) (79.9 +/- 0.2%) as compared to NS (n = 7) (80.8 +/- 0.5%). Continuous HS infusion attenuated cerebral edema in the affected hemisphere as well as the contralateral noninjured hemisphere to a larger extent than was observed with furosemide or mannitol. These findings suggest a potential new treatment strategy for tumor-associated cerebral edema.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Global brain water increases after experimental focal cerebral ischemia: effect of hypertonic saline

OBJECTIVE

Isolated experiments suggest that global cerebral edema is a sequela of large hemispheric ischemic lesions, presumably as an extension of the initial ischemic insult into areas of vital, noninjured tissue. Diuretics and osmotic agents are controversial and poorly defined therapeutic modalities after large infarction. By using a rat model of middle cerebral artery occlusion (MCAO), we tested the hypothesis that significant edema occurs in the contralateral uninjured hemisphere and that this postischemic complication can be manipulated by hypertonic saline therapy.

DESIGN

Prospective laboratory animal study.

SETTING

Research laboratory in a teaching hospital.

SUBJECTS

Halothane-anesthetized, male Wistar rats.

INTERVENTIONS

Under controlled conditions of normoxia, normocarbia, and normothermia, rats were subjected to 2 hrs of MCAO.

MEASUREMENTS AND MAIN RESULTS

Adequacy of MCAO and reperfusion was assessed by laser Doppler flowmetry. All animals except naive rats received continuous infusion of 0.9% saline at 0.5 mL/hr throughout the experiment. Brains were harvested, and tissue water content was estimated by comparing the wet-to-dry weight ratios of ipsilateral and contralateral cerebral hemispheres at 12 hrs, 24 hrs, or 2, 3, or 7 days postischemia. Naive and sham-operated rats served as control cohorts. In a second series of randomized experiments, wet-to-dry weight ratios were determined in rats treated with continuous intravenous infusion of 7.5% hypertonic saline (0.5 mL/hr; acetate/chloride, 50:50) and were compared with well-studied antiedema therapy: 20% mannitol (2.5 g/kg bolus every 6 hrs) or furosemide (2.5 mg/kg bolus every 6 hrs). Treatments were started at 24 hrs of reperfusion, and brain water was assessed at 2 days of reperfusion. In a third series of experiments, wet-to-dry ratios were determined in brains harvested at 2 days of reperfusion from rats that were subjected to 2 hrs of MCAO and did not receive any intravenous fluids. All values are mean +/- SEM. There were no differences between sham-operated and naive control cohorts. At 24 hrs of reperfusion, water content was higher in both ipsilateral ischemic (82.80 +/- 0.86%) and contralateral hemispheres (80.53 +/- 0.29%), compared with naive animals (ipsilateral, 79.62 +/- 0.12%; contralateral, 79.53 +/- 0.13%). Maximal cerebral edema was measured at 2 days in both hemispheres (ipsilateral, 83.94 +/- 0.47%; contralateral, 80.63 +/- 0.13%). Edema was present for up to 3 days in contralateral tissue (80.27 +/- 0.26%) and persisted to 7 days in the injured hemisphere (81.07 +/- 0.34%). Maximal edema (as assessed at 2 days postocclusion) was robustly attenuated with hypertonic saline therapy (ipsilateral, 81.59 +/- 0.52%; contralateral, 78.44 +/- 0.22%). The efficacy of hypertonic saline was equivalent to furosemide (ipsilateral, 82.09 +/- 0.50%; contralateral, 79.13 +/- 0.17%) but less robust than mannitol (ipsilateral, 79.89 +/- 0.36%; contralateral, 78.73 +/- 0.17%).

CONCLUSIONS

These data demonstrate that cerebral edema persists in both injured and contralateral hemispheres for days after MCAO. The global, maximal increase in brain water is responsive to continuous 7.5% hypertonic saline treatment begun at 24 hrs postischemia and to standard diuretic/osmotic agents. These results may have implications for diuretic and osmotic therapy in clinical ischemic stroke.

Pyruvate improves cerebral metabolism during hemorrhagic shock

Pyruvate (PYR) improves cellular and organ function hypoxia and ischemia by stabilizing the reduced nicotinamide adenine dinucleotide redox state and cytosolic ATP phosphorylation potential. In this in vivo study, we evaluated the effects of intravenous pyruvate on neocortical function, indexes of the cytosolic redox state, cellular energy state, and ischemia during a prolonged (4 h) controlled arterial hemorrhage (40 mmHg) in swine. Thirty minutes after the onset of hemorrhagic shock, sodium PYR (n = 8) was infused (0.5 g x kg(-1) x h(-1)) to attain arterial levels of 5 mM. The volume and osmotic effects were matched with 10% NaCl [hypertonic saline (HTS)] (n = 8) or 0.9% NaCl [normal saline (NS)] (n = 8). During the hemorrhage protocol, the time to peak hemorrhage volume was significantly delayed in the PYR group compared with the HTS and NS groups (94 +/- 5 vs. 73 +/- 6 and 72 +/- 4 min, P < 0.05). In addition to the early onset of the decompensatory phase of hemorrhagic shock, the complete return of the hemorrhage volume during decompensatory shock resulted in the death of five and four animals, respectively, in the HTS and NS groups. In contrast, in the PYR group, reinfusion of the hemorrhage volume was slower and all animals survived the 4-h hemorrhage protocol. During hemorrhage, the PYR group also exhibited improved cerebral cortical metabolic and function status. PYR slowed and reduced the rise in neocortical microdialysis levels of adenosine, inosine, and hypoxanthine and delayed the loss of cerebral cortical biopsy ATP and phosphocreatine content. This improvement in energetic status was evident in the improved preservation of the electrocorticogram in the PYR group. PYR also prevented the eightfold increase in the excitotoxic amino acid glutamate observed in the HTS group. The findings show that PYR administered after the onset of hemorrhagic shock markedly improves cerebral metabolic and functional status for at least 4 h.