Treatment of experimental focal cerebral ischemia with mannitol. Assessment by intracellular brain pH, cortical blood flow, and electroencephalography

Comparison of endoscope- versus microscope-assisted resection of deep-seated intracranial lesions using a minimally invasive port retractor system

OBJECT

Tubular brain retractors may improve access to deep-seated brain lesions while potentially reducing the risks of collateral neurological injury associated with standard microsurgical approaches. Here, microscope-assisted resection of lesions using tubular retractors is assessed to determine if it is superior to endoscope-assisted surgery due to the technological advancements associated with modern tubular ports and surgical microscopes.

METHODS

Following institutional approval of the tubular port, data obtained from the initial 20 patients to undergo transportal resection of deep-seated brain lesions were analyzed in this study. The pathological entities of the resected tissues included metastatic tumors (8 patients), glioma (7), meningioma (1), neurocytoma (1), radiation necrosis (1), primitive neuroectodermal tumor (1), and hemangioblastoma (1). Surgery incorporated endoscopic (5 patients) or microscopic (15) assistance. The locations included the basal ganglia (11 patients), cerebellum (4), frontal lobe (2), temporal lobe (2), and parietal lobe (1). Cases were reviewed for neurological outcomes, extent of resection (EOR), and complications. Technical data for the port, surgical microscope, and endoscope were analyzed.

RESULTS

EOR was considered total in 14 (70%), near total (> 95%) in 4 (20%), and subtotal (< 90%) in 2 (10%) of 20 patients. Incomplete resection was associated with the basal ganglia location (p < 0.05) and use of the endoscope (p < 0.002). Four of 5 (80%) endoscope-assisted cases were near-total (2) or subtotal (2) resection. Histopathological diagnosis, presenting neurological symptoms, and demographics were not associated with EOR. Complication rates were low and similar between groups.

CONCLUSIONS

Initial experience with tubular retractors favors use of the microscope rather than the endoscope due to a wider and 3D field of view. Improved microscope optics and tubular retractor design allows for binocular vision with improved lighting for the resection of deep-seated brain lesions.

Flow Augmentation in Acute Ischemic Stroke

There is an urgent need for additional therapeutic options for acute ischemic stroke considering the major pitfalls of the options available. Herein, we briefly review the role of cerebral blood flow, collaterals, vasoreactivity, and reperfusion injury in acute ischemic stroke. Then, we reviewed pharmacological and interventional measures such as volume expansion and induced hypertension, intra-aortic balloon counterpulsation, partial aortic occlusion, extracranial-intracranial carotid bypass surgery, sphenopalatine ganglion stimulation, and transcranial laser therapy with regard to their effects on flow augmentation and neuroprotection.

Combination of therapeutic hypothermia and other neuroprotective strategies after an ischemic cerebral insult

Abrupt deprivation of substrates to neuronal tissue triggers a number of pathological events (the “ischemic cascade”) that lead to cell death. As this is a process of delayed neuronal cell death and not an instantaneous event, several pharmacological and non-pharmacological strategies have been developed to attenuate or block this cascade. The most promising neuroprotectant so far is therapeutic hypothermia and its beneficial effects have inspired researchers to further improve its protective benefit by combining it with other neuroprotective agents. This review provides an overview of all neuroprotective strategies that have been combined with therapeutic hypothermia in rodent models of focal cerebral ischemia. A distinction is made between drugs interrupting only one event of the ischemic cascade from those mitigating different pathways and having multimodal effects. Also the combination of therapeutic hypothermia with hemicraniectomy, gene therapy and protein therapy is briefly discussed. Furthermore, those combinations that have been studied in a clinical setting are also reviewed.

Brain retraction injury

This paper reviews the literature of the brain retraction injury during the last century. The review focused on the instrument characteristic as well as the physiopathological and histopathological damage of the brain induced by brain retraction. It was found that lesions were induced by cerebral ischemia. We conclude that a better monitoring system needs to be developed to avoid brain injury.

Cerebral hemodynamic and metabolic effects of equi-osmolar doses mannitol and 23.4% saline in patients with edema following large ischemic stroke

INTRODUCTION

Cerebral edema after ischemic stroke is frequently treated with mannitol and hypertonic saline (HS); however, their relative cerebrovascular and metabolic effects are incompletely understood, and may operate independent of their ability to lower intracranial pressure.

METHODS

We compared the effects of 20% mannitol and 23.4% saline on cerebral blood flow (CBF), blood volume (CBV), oxygen extraction fraction (OEF), and oxygen metabolism (CMRO(2)), in nine ischemic stroke patients who deteriorated and had >2 mm midline shift on imaging. (15)O-PET was performed before and 1 h after administration of randomly assigned equi-osmolar doses of mannitol (1.0 g/kg) or 23.4% saline (0.686 mL/kg).

RESULTS

Baseline CBF values (ml/100g/min) in the infarct core, periinfarct region, remaining ipsilateral hemisphere, and contralateral hemisphere in the mannitol group were 5.0 ± 3.9, 25.6 ± 4.4, 35.6 ± 8.6, and 45.5 ± 2.2, respectively, and in the HS group were 8.3 ± 9.8, 35.3 ± 10.9, 38.2 ± 15.1, and 35.2 ± 12.4, respectively. There was a trend for CBF to rise in the contralateral hemisphere after mannitol from 45.5 ± 12.2 to 57.6 ± 21.7, P = 0.098, but not HS. CBV, OEF, and CMRO(2) did not change after administration of either agent. Change in CBF in the contralateral hemisphere after osmotic therapy was strongly correlated with baseline blood pressure (R (2)= 0.879, P = 0.002).

CONCLUSIONS

We conclude that at higher perfusion pressures, osmotic agents may raise CBF in non-ischemic tissue. We conclude that at higher perfusion pressures, osmotic agents may raise CBF in non-ischemic tissue.

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.

Effects of mannitol and glycerol on cerebral energy metabolism in gerbils

OBJECTIVES

To evaluate the effects of infusion with hyperosmolar solutions, mannitol and glycerol on the recovery of cerebral energy metabolism during ischemia and reperfusion in the gerbil brain.

MATERIALS AND METHODS

Sequential changes in cerebral energy metabolism following 90-min ischemia and up to 8 h after reperfusion were measured in 15 gerbils using 31P nuclear magnetic resonance (NMR) spectroscopy after 60-min infusion of 10% glycerol (0.5 g/kg; n=5), or 20% mannitol (1.0 g/kg; n=5), and compared with those gerbils receiving with saline (n=5). Gerbils were anesthetized by intraperitoneal injection of pentobarbital. Forebrain ischemia was induced by clipping of bilateral common carotid arteries for 90 min and reperfused. NMR spectroscopy was measured by a 6.34-Tesla JEOL spectrometer, before administration, 2, 4, 6, and 8 h after 90-min ischemia and reperfusion. Areas of inorganic phosphate (Pi), phosphocreatine (PCr), and beta-ATP peaks were measured to calculate parameters of cerebral energy metabolism, i.e., PCr/Pi and beta-ATP/Pi ratios. Intracellular pH (pHi) was calculated from chemical shifts of Pi relative to PCr.

RESULTS

PHi was higher in the mannitol group than in the glycerol and saline groups (P<0.05) 2 h after reperfusion. PCr/Pi ratio was higher 2, 4, and 8 h after reperfusion (P<0.01, P<0.05, P<0.01) in the mannitol group; and 6 h after reperfusion (P<0.05) in the glycerol group; than in the saline group. Beta-ATP/Pi ratio was higher 2 and 8 h after reperfusion (P<0.05) in the glycerol group; and 2 h after reperfusion (P<0.01) in the mannitol group, than in the saline group.

CONCLUSIONS

The mannitol group had improved pHi higher than the glycerol group 2 h after reperfusion (P<0.05), while the glycerol group had improved beta-ATP/Pi ratio higher than the mannitol group 6 h after reperfusion (P<0.05). Both mannitol and glycerol groups had improved parameters of cerebral energy metabolism during ischemia and up to 8 h after reperfusion in the gerbil brain.

Early effects of mannitol in patients with head injuries assessed using bedside multimodality monitoring

OBJECTIVE

We have employed bedside multimodality methods to assess the influence of a slow (20 min) bolus of hypertonic mannitol on cerebral hemodynamics in comatose patients with head injuries.

METHODS

Middle cerebral artery flow velocities (FV) and cortical microcirculatory flows were measured in comatose patients with head injuries after the administration of 200 ml of 20% mannitol. A comparison was made with the effects of an identical bolus of isotonic saline. Fourteen patients with diffuse head injuries and with raised intracranial pressure were selected, and mannitol infusion studies were conducted when clinically indicated (n = 23). Using transcranial doppler and laser doppler flowmetry (LDF), indices of estimated cerebrovascular resistance (eCVR) were calculated for the macro- (eCVR-FV) and micro- (eCVR-LDF) circulation.

RESULTS

During mannitol infusion, a significant rise in cerebral perfusion pressure was detected (+10%, P = 0.03) as a result of a fall in intracranial pressure (-21%, P = 0.001). Increases in both FV (+13%, P < 0.001) and LDF (+14%, P = 0.002) occurred only after the administration of mannitol and persisted beyond completion of infusion. The effect on FV and LDF decayed exponentially, with a time constant of 34.0 and 38.0 minutes, respectively, and was independent of the pressure autoregulatory status. There was a tendency for eCVR-FV and eCVR-LDF to decrease. No significant effects resulted from the administration of saline.

CONCLUSION

Bedside multimodality monitoring may provide a useful means for assessing the effects of therapy in the comatose patient. The mechanisms by which mannitol reduces intracranial pressure in patients with head injuries are discussed.

Mild hypothermia, hypertension, and mannitol are protective against infarction during experimental intracranial temporary vessel occlusion

A rabbit model of focal temporary ischemia was used to test the protection provided by mild hypothermia, hypertension, mannitol and the combination of the three methods. Twenty-four New Zealand White rabbits were divided into five groups as follows: a control group, a hypertension group (mean arterial blood pressure increased by 42 mm Hg), a hypothermic group (rectal temperature decreased by 6 degrees C), a mannitol group (1 g/kg of body weight, administered intravenously), and the triple-therapy group. The intracranial internal carotid artery, the middle cerebral artery, and the anterior cerebral artery were clipped for 2 hours and then underwent 4 hours of reperfusion. Blood pressure, rectal and brain temperature, blood glucose level, hematocrit, and arterial blood gases were monitored during the experiment. For measuring the infarction size, the brain was divided into 4-mm slices and stained with 2,3,5-triphenyltetrazolium chloride. The severity of the neuronal damage was also evaluated by conventional histological examination with hematoxylin and eosin staining. The infarct volume was 193.2 +/- 34.8 (standard error of the mean) mm3 for the control group, 32.3 +/- 22.6 mm3 for the hypertension group (P < 0.0005 versus control), 40.9 +/- 17.6 mm3 for the hypothermia group (P < 0.0005), 58.0 +/- 41.0 mm3 for the mannitol group (P < 0.005), and 0.9 +/- 0.9 mm3 for the triple-therapy group (P < 0.0001). The infarct volume of the triple-therapy group was smaller than that of the hypertension, hypothermia, and mannitol groups but the difference was not statistically significant. The combination of hypertension, mild hypothermia, and mannitol to protect against temporary focal ischemia provides a set of manipulations that is readily available for neurovascular procedures.

The effect of mannitol on experimental cerebral ischemia, revisited

The effect of 20% mannitol on ischemic neuronal injury was examined in male Wistar rats (n = 80) that were randomly divided into forebrain and focal ischemia groups. The animals were further subdivided into control, treatment with mannitol before ischemia (1 g/kg of body weight, 12 min before ischemia), and treatment with mannitol after ischemia (0.25 g/kg of body weight, beginning 20 min after ischemia and then every 6 h for 48 h) groups. Physiological parameters were carefully monitored and maintained within normal limits. The administration of mannitol after ischemia was found to produce a statistically significant improvement in ischemic neocortical injury and selective neuronal necrosis in the neocortex in the forebrain and focal models, respectively. However, treatment with mannitol after ischemia was shown not to favorably alter histopathological outcome in hippocampal levels 2 through 7 in the forebrain model nor did not reduce infarct volume in the focal ischemia group. Treatment with mannitol before ischemia did not produce statistically significant reductions in neuronal injury in either model. These results do not support the findings of previous investigations, which have demonstrated that mannitol affords a significant degree of neuroprotection when administered either before or immediately after vessel occlusion in models of forebrain and focal cerebral ischemia. The neuroprotective effect of mannitol demonstrated in the neocortex of both forebrain and focally ischemic rats may support the theory that the main mechanisms responsible for neocortical injury in ischemia differ from those in the striatum hippocampus. Finally, mannitol's ability to reduce ischemic neuronal injury most effectively when administered after rather than before the production of ischemia is consistent with a possible beneficial influence on the development of delayed cerebral edema.

Decreased cerebral blood flow during acute hyperglycemia

Cerebral blood flow (CBF) decreases during acute hyperglycemia but the mechanism of this change is unknown. The role that plasma osmolality plays in this effect was reexamined in pentobarbital-anesthetized rats using a continuous measure of CBF, laser-Doppler flowmetry. CBF decreased 25% during acute elevation of plasma osmolality induced by intraperitoneal injection of concentrated solutions of glucose or mannitol. In addition there were brief transient increases of CBF with peak magnitude 2-4-times the baseline level that were not accompanied by transient depression of electroencephalographic activity. These transient CBF increases may explain why discontinuous methods of CBF measurement fail to detect flow decreases after mannitol injection. Decreased CBF measured during acute hyperglycemia may be the result of increased plasma osmolality.

Effect of mannitol on focal cerebral ischemia evaluated by somatosensory-evoked potentials and magnetic resonance imaging

BACKGROUND

Mannitol has been used in routine neurosurgical practice for the control of increased intracranial pressure. The effect of mannitol on focal cerebral ischemia was evaluated by somatosensory-evoked potentials (SEP) and magnetic resonance imaging (MRI).

METHODS

The left middle cerebral artery (MCA) was exposed via the superomedial transorbital approach and occluded proximal to the origin of the perforating arteries. Ten cats received mannitol (0.5 g/kg IV) immediately, 6, 12, and 18 hours after MCA occlusion. The other 10 cats received saline solution and served as control. The animals were initially prepared to measure SEP before and 15, 30, and 60 minutes after MCA occlusion. Following SEP measurement, all cats were prepared for MRI. Sequential MRI of both intravoxel incoherent motion (IVIM) and T2-weighted spin echo techniques were obtained at 2, 4, 6, and 24 hours after MCA occlusion. The animals were sacrificed after the last MRIs for histologic study.

RESULTS

The SEP amplitude decreased to about 10% at 15 minutes after MCA occlusion and then gradually recovered to 38% at 60 minutes in the mannitol group, and 21% in the control group. In MRI study, IVIM imaging demonstrated ischemic cerebral injury as a sharply demarcated area at 2 hours after MCA occlusion, while T-2 weighted imaging failed to show clear evidence of injury until 2-6 hours. High-signal intensity areas on both IVIM and T2-weighted images were smaller in the mannitol group than those in the control group. Histologic study demonstrated that infarction size was 36.9% +/- 7.7% of the left hemisphere in the mannitol group and 57.3% +/- 5.3% in the control group (p < 0.05).

CONCLUSIONS

Mannitol is effective for acute cerebral ischemia, and SEP and MRI are useful for monitoring it.

Use of mild intraischemic hypothermia versus mannitol to reduce infarct size after temporary middle cerebral artery occlusion in rats

To determine which of two treatments for reducing ischemic injury after temporal focal ischemia is more effective, the effects of mild (33 degrees C) intraischemic hypothermia were compared with those of mannitol, the most commonly used neuroprotective agent. Four groups of Sprague-Dawley rats underwent 1 hour of endovascular middle cerebral artery occlusion followed by 23 hours of normothermic reperfusion. The four experimental groups were as follows: Group A, saline control; Group B, mannitol (25%, 1 g/kg); Group C, hypothermia; and Group D, hypothermia plus man-nitol. Laser-Doppler estimates of cortical blood flow showed that hypothermia did not affect blood flow during ischemia or reperfusion. Mannitol increased cortical blood flow during ischemia and reperfusion under both normothermic and hypothermic conditions (p < 0.05). Neurological deficit was significantly less severe in treated rats (Group B, p < 0.05; Group C or D, p < 0.01) than in controls (Group A). Infarct volume, measured on semiserial Nissl-stained sections, was significantly smaller in treated rats (p < 0.01) than in controls. Infarct volume was also significantly smaller in rats treated with hypothermia than in those treated with mannitol (Group C vs. Group B, p < 0.05); there was no difference between rats treated with mannitol and those treated with mannitol and hypothermia. All three treatments reduced infarct area in the ischemic penumbra; hypothermia with or without mannitol also reduced infarct area in the ischemic core. These results demonstrate that both mild intraischemic hypothermia and mannitol reduce infarct size and neurological deficit: hypothermia reduces infarct size more effectively than mannitol, and mannitol adds no significant protection to hypothermia, whereas hypothermia adds significant protection beyond that afforded by mannitol after brief focal ischemia followed by reperfusion in rats. The results suggest that mild intraischemic hypothermia alone, or in combination with mannitol, may be useful in avoiding ischemic injury from temporary vessel occlusion during cerebrovascular surgery.

The therapeutic value of naloxone and mannitol in experimental focal cerebral ischemia. Neurological outcome, histopathological findings, and tissue concentrations of Na+, K+ and water

In this study, the effect of naloxone and mannitol was investigated on focal cerebral ischemia induced by middle cerebral artery occlusion with the transorbital approach in the rabbit model. Rabbits were randomly and blindly assigned to one of three groups (six animals in each): (1) a control group that received equal volumes of physiological saline solution; (2) a naloxone group that received a 5 mg/kg bolus of naloxone i.v. 1 h after occlusion, followed by 2 mg/kg per hour i.v. infusion for 5 h; (3) a mannitol group that received 0.2 g/kg twice with an interval of 10 min at 5 h. The neurological outcome was better in rabbits treated with naloxone than in the others. The ratio of ischemic to total neurons in the cortex was smaller in the naloxone group than in the control and mannitol groups (P < 0.05). In addition, there was a statistically significance reduction in infarct size in the naloxone group compared with the other groups (P < 0.05). Edema was severe in the control and mannitol groups, but moderate in the naloxone group. There was no statistically significant difference in Na+, K+, and water content between groups. Our data provide evidence for the beneficial effects of naloxone on promoting neurological recovery and preserving the ischemic area.

Closed head injury and the treatment of sequelae after a motor vehicle accident

Approximately 2 million closed head injuries (CHIs) occur yearly in the United States. Twenty-five percent of these injuries require hospitalization, and 70,000 to 90,000 of those hospitalized suffer long-term disability. This case conference details one such case of CHI in which the patient ultimately died. Close attention is given to the pathophysiology and treatment of this process. Commonly accepted, as well as investigational, modalities of therapy are discussed.

U50488 reduces the severity of tissue damage in a rabbit model of focal cerebral ischemia

Many pharmacotherapies for stroke that have been successful in the laboratory have proven to be ineffective in the clinical setting, often because patients do not arrive for treatment until hours after the onset of the ischemic insult. Kappa opioid treatment of cerebral ischemia has been successful in the cat and mouse with treatment delays of up to 6 h. The purpose of the present study was to develop a model of delayed kappa opioid treatment of cerebral ischemia in the rabbit. Fourteen rabbits underwent permanent, unilateral occlusion of the internal carotid, middle cerebral, and anterior cerebral arteries via a transorbital, microsurgical approach. At 6 h postocclusion, animals received a blinded bolus injection and continuous infusion of either saline or the kappa agonist, U50488. Survival was not improved after U50488 treatment. U50488 treatment did, however, reduce areas of severe tissue damage and increase areas of modest tissue damage. This suggests U50488 arrested the progression of damage from noninfarcted to fully infarcted tissue. The present results show beneficial effects of delayed treatment with kappa agonists in a species similar in vasculature to humans, and much less costly than primates or cats.

A review of brain retraction and recommendations for minimizing intraoperative brain injury

Brain retraction is required for adequate exposure during many intracranial procedures. The incidence of contusion or infarction from overzealous brain retraction is probably 10% in cranial base procedures and 5% in intracranial aneurysm procedures. The literature on brain retraction injury is reviewed, with particular attention to the use of intermittent retraction. Intraoperative monitoring techniques--brain electrical activity, cerebral blood flow, and brain retraction pressure--are evaluated. Various intraoperative interventions--anesthetic agents, positioning, cerebrospinal fluid drainage, operative approaches involving bone resection or osteotomy, hyperventilation, induced hypotension, induced hypertension, mannitol, and nimodipine--are assessed with regard to their effects on brain retraction. Because brain retraction injury, like other forms of focal cerebral ischemia, is multifactorial in its origins, a multifaceted approach probably will be most advantageous in minimizing retraction injury. Recommendations for operative management of cases involving significant brain retraction are made. These recommendations optimize the following goals: anesthesia and metabolic depression, improvement in cerebral blood flow and calcium channel blockade, intraoperative monitoring, and operative exposure and retraction efficacy. Through a combination of judicious retraction, appropriate anesthetic and pharmacological management, and aggressive intraoperative monitoring, brain retraction should become a much less common source of morbidity in the future.

Management of raised intracranial pressure

This review has been written at an unfortunate time. Novel questions are being asked of the old therapies and there is an abundance of new strategies both to lower ICP and protect the brain against cerebral ischaemia. In the United Kingdom, the problem is to ensure that appropriate patients continue to be referred to centres where clinical trials of high quality can be undertaken. One of the success stories of the past decade has been the decline in the number of road accidents as a result of seat belt legislation, improvements in car design and the drink/driving laws. Hence, fortunately there are fewer patients with head injuries to treat and it is even more important that patients are appropriately referred if studies to assess efficacy of the new strategies are not to be thwarted. The nihilistic concept that intensive investigation with ICP monitoring for patients with diffuse head injury or brain swelling following evacuation of a haematoma or a contusion has no proven beneficial effect on outcome, requires revision. A cocktail of therapies may be required that can be created only when patients are monitored in sufficient detail to reveal the mechanisms underlying their individual ICP problem. Ethical problems may arise over how aggressively therapy for intracranial hypertension should be pursued and for how long. There has always been the concern that cranial decompression or prolonged barbiturate coma may preserve patients but with unacceptably severe disability. Some patients may be salvaged from herniating with massive cerebral infarction with the use of osmotherapy but is the outcome acceptable? Similar considerations apply to some children with metabolic encephalopathies. Where such considerations have been scrutinised in patients with severe head injury, the whole spectrum of outcomes appears to be shifted so that the number of severe disabilities and persistent vegetative states are not increased. However, it is important to be sensitive to such issues based on experience of the particular cause of raised intracranial pressure in a given age group.

Effects of mannitol on cerebral blood flow, blood pressure, blood viscosity, hematocrit, sodium, and potassium

In our miniature swine model of brain retraction ischemia under conditions simulating the neurosurgical operating room, we studied the effects of bolus mannitol (2 g/kg) administration on cerebral blood flow, blood pressure, blood viscosity, hematocrit, sodium, and potassium serially for 4 hours following administration, at which time a second bolus was administered. Both viscosity and hematocrit were significantly decreased transiently following both the first and second boluses. Sodium was decreased for 30 minutes following the first bolus, 15 minutes following the second bolus, and increased at 150 minutes and later following the second bolus. There was a mild decrease in blood pressure and a mild increase in cerebral blood flow following mannitol, but little difference between the first hour following a bolus (when the viscosity and hematocrit were decreased) and hours 2-4 (when they were near baseline). Mannitol's effects on blood pressure and cerebral blood flow probably depend on factors in addition to its effects on blood viscosity and hematocrit. The results are discussed in light of previous findings that bolus mannitol administration may improve cerebral blood flow in ischemia, but does not appear to benefit the preservation of brain electrical activity.

Effects of retrograde perfusion of the brain with combined drug therapy after focal ischemia in rat brain

BACKGROUND AND PURPOSE

The ischemic edema associated with blood-brain barrier permeability changes and the excess production of free radicals are serious complications in prolonged cerebral ischemia. We examined the efficacy of transvenous perfusion of the brain, starting treatment 5 hours after occlusion of the middle cerebral artery for a period of 2 hours in rats with the combined agents mannitol (10 ml/2 hr) and dexamethasone (1 mg/2 hr) to counter edema and verapamil (0.05 mg/kg/2 hr) for vasodilation.

METHODS

In experiment 1, blood-brain barrier permeability changes were examined in five groups with six rats each: group C rats underwent 7 hours of middle cerebral artery occlusion with no treatment; group V, treatment with verapamil alone; group VD, treatment with verapamil and dexamethasone; group VM, treatment with verapamil and mannitol; and group VDM, treatment with verapamil, dexamethasone, and mannitol. In experiment 2, we examined local cerebral blood flow, ischemic tissue damage volume, and water content of cerebral hemispheres in two groups of 16 rats each subjected to the same treatment as groups C and VDM rats in experiment 1.

RESULTS

There was a significant reduction of blood-brain barrier permeability changes in the ischemic cortex of rats in group VDM compared with rats in the other groups. In the group undergoing transvenous perfusion of the brain with the three combined agents, there was a significant improvement of cerebral blood flow (39-58%, p < 0.05) in the ischemic cortex and reduction of ischemic cerebral damage volume (22%, p < 0.01) and water content of the ischemic hemisphere (p < 0.05) compared with the control group.

CONCLUSIONS

The therapeutic approach using combined agents is effective treatment when initiated within 5 hours of focal cerebral ischemia in rats.

Effect of mannitol on local cerebral blood flow after temporary complete cerebral ischemia in rats

The effects of pretreatment with mannitol on local cerebral blood flow (CBF) after permanent or temporary global cerebral ischemia were evaluated with 14C-iodoantipyrine autoradiography in rats under halothane-N2O endotracheal anesthesia. Blood pressure, pulse rate, arterial blood gas levels, and electroencephalographic (EEG) tracings were monitored throughout the experiments. After permanent occlusion of the basilar artery and both external carotid and pterygopalatine arteries, severe global ischemia was induced by permanent occlusion of the common carotid arteries (CCA's) or by a 30-minute temporary CCA occlusion followed by 5 minutes of reperfusion. Intravenous mannitol (25%, 1 gm/kg) or saline solution was administered 5 minutes before occlusion of the CCA's. Cerebral blood flow was measured in 24 anatomical regions. The EEG tracings flattened within 2 to 3 minutes after the onset of ischemia, and no recovery was observed during reperfusion. In the mannitol-treated rats and the saline-treated controls, autoradiographic studies after permanent occlusion showed no CBF in the forebrain or cerebellum, although brain-stem and spinal cord CBF values were normal. After 5 minutes of reperfusion, CBF in the cortex, basal ganglia, and white matter was 100% to 200% higher in mannitol-treated rats and 50% to 100% higher in saline-injected rats than in the nonischemic anesthetized control group. Heterogeneously distributed areas of no-reflow were seen in all saline-injected rats but were observed in none of the mannitol-treated rats. Pretreatment with mannitol prevented postischemic obstruction of the microcirculation during 5 minutes of recirculation after 30 minutes of severe temporary ischemia, but the EEG signals did not recover. Further studies of the functional and morphological responses to longer periods of postischemic recirculation are needed to verify the extent to which these mannitol-induced effects are protective.

Temporary clipping in aneurysm surgery: technique and results

The use of temporary clipping has become an established tool in the armamentarium of the aneurysm surgeon. Our experience with 62 consecutive patients is presented, detailing operative protocols and results. Twenty-two had unruptured aneurysms (35%), 15 were grade I (24%), 16 grade II (25%), five grade III (8%), and four grade IV (7%). The aneurysms were mainly located in the middle cerebral artery (29 patients) and the anterior communicating artery (13 patients). Eleven of our 62 patients (17%) developed a new, persistent postoperative deficit. However, in only one case (2%) was temporary clipping felt to be implicated in the development of the deficit. In three other patients (5%), the effect of temporary clipping, although unlikely, could not be excluded. Overall, 92% of our patients with temporary clipping had good to excellent outcome, with 3% mortality and 5% morbidity. We believe that temporary clipping is a safe procedure that contributes significantly to a better outcome.

Management of cerebral aneurysms: further facts and additional myths

In 1985 we reviewed 17 misconceptions or myths surrounding the treatment of aneurysmal subarachnoid hemorrhage that may contribute to the dismal outcome from these lesions. Since that time, significant new data, or facts, have become available regarding the influence of early aneurysm surgery on rebleeding, the efficacy of treatments for symptomatic arterial narrowing, improvements in surgical techniques such as temporary arterial clipping, and measures to protect the brain from ischemic injury. However, additional myths have become apparent which continue to limit our ability to improve the outcome of these patients. We review these facts and myths and discuss management of the patient with aneurysmal subarachnoid hemorrhage.

The risk of ischaemic brain damage during the use of self-retaining brain retractors

Self-retaining brain retractors (SRBR) are commonly used during intracranial surgery and they are indispensable during microneurosurgery. To evaluate limitations in the employment of SRBR, as well animal as human studies have been performed. In the animal studies, male Wistar rats were used for measurements of regional cerebral blood flow (rCBF) changes during brain retractor pressure (BRP) provided by lead weights. These weights, corresponding to different levels of mm Hg, were applicated for different periods of time on the parietal cortex after craniotomy. In one part of the animal studies different profiles of the application surface of the weights were evaluated. For measurement of the rCBF (n = 41) autoradiography with carbon-14(14C)iodoantipyrine was used as described by Gjedde et al (1980). A neuropathological method (n = 30) was used to reveal possible brain damage after graded BRP. In the rats the thresholds of rCBF, regional cerebral perfusion pressure (rCPP) and time were 20-25 ml/100 g/min, 20 mm Hg and 7-10 minutes respectively. In the human studies only alert patients without neurological deficits (except defects of the visual fields) and in whom preoperative CT-scans did not disclose any sign of infarction were included. BRP beneath as well the tip as the centre of the SRBR and the MABP were recorded continuously. Patients with peroperative complications were excluded. During the operations induced hypotension (n = 20) and mannitol (n = 6) were administrated. The patients (n = 23) had a 3-month follow-up examination. In man the thresholds of rCPP and time were found to be 10 mm Hg and 6-8 minutes, respectively. Other authors have found a rCBF threshold of 10-13 ml/100 g/min (Astrup 1982, Iannotti & Hoff 1983). It is concluded that the results obtained in the rat studies are comparable to the human situation if reservations are made concerning the differences in the thresholds of rCBF and rCPP. The time threshold of cerebral ischaemia seems to be rather equal in rat and in man. If these thresholds are reached, intermittent BRP is absolutely recommendable. It was also found that the most easily-handled retractors, those with a flat profile, did not decrease the rCBF further than other types of retractors.

Intraoperative use of laser Doppler in the study of cerebral microvascular circulation

Laser Doppler (LD) flowmetry has been used for evaluation of microcirculatory flow in a variety of human tissues, including skin, muscle, retina and recently the brain. In the present paper, intraoperative Laser Doppler recordings have been performed in 72 cases, in basal conditions and after stimulation. The morphology of basal recordings obtained from normal cortical areas were analyzed and three different rhythmical variations were identified; these rhythmical variations are described and explained. Several kinds of stimulation have been used: hypotensive drugs, mannitol, nimodipine, eupaverine, hypercapnia, decompressive manoeuvres and temporary occlusion of the ICA in the neck. Laser Doppler recordings obtained during and after these stimulations are reported and explained. The results have been evaluated in order to verify the reliability and the reproducibility of this technique in the study of the cerebral microvascular circulation intraoperatively.