(Stroke. 1998;29:2580-2586.)
© 1998 American Heart Association, Inc.
Original Contributions |
From the Department of Surgery (Neurosurgery) (G.X., R.F.K., J.T.H.), University of Michigan, Ann Arbor, Mich; the Departments of Neurology (K.R.W., Y.H., J.P.B., T.G.B.) and Pathology and Laboratory Medicine (G.M. de C.-M.), University of Cincinnati College of Medicine, Cincinnati, Ohio; and the Medical Research Service (K.R.W.), Department of Veterans Affairs Medical Center, Cincinnati, Ohio.
Correspondence and reprint requests to Kenneth R. Wagner, PhD, Research Service (151), Department of Veterans Affairs Medical Center, 3200 Vine St, Cincinnati, OH 45220.
| Abstract |
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MethodsIn pigs, we infused autologous blood (with or without heparin) into the cerebral white matter to produce lobar hematomas and froze the brains in situ at 1, 4, or 24 hours after ICH. We determined hematomal and perihematomal edema volumes on coronal sections by computer-assisted morphometry. In rats, we infused either blood or thrombin (with or without heparin) into the basal ganglia and measured water, sodium, and potassium contents at 24 hours after ICH.
ResultsIn pigs, unheparinized blood induced rapid (at 1 hour) and prolonged (24 hours) perihematomal edema (average volume, 1.29±0.20 mL; n=6). No perihematomal edema was present following heparinized blood infusions (n=6). In rats, unheparinized blood produced significantly greater edema than heparinized blood infusions. As with whole blood, thrombin-induced gray matter edema at 24 hours was significantly reduced by coinjection of heparin.
ConclusionsAfter ICH, blood clot formation is required for rapid and prolonged edema development in perihematomal white and gray matter. Thrombin also contributes to prolonged edema in gray matter.
Key Words: brain edema cerebral hemorrhage heparinized blood pigs rats
| Introduction |
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The concept that intracerebral blood is itself "toxic" independent of its mass effect was first demonstrated by Suzuki and Ebina,4 who compared intracerebral injections of whole blood with similar infusions of an inert oil-and-wax mixture. They found that blood produced considerably greater histological changes indicative of edema over the first 24 hours compared with the inert substance. On the contrary, mass effect alone, as produced by microballoon inflation, fails to produce edema even though CBF is reduced to <20 mL/100 g/min.5
Recently, new details of the pathophysiological mechanisms involved in edema formation after ICH and the contributions of individual components to the "toxicity" of blood have been demonstrated. Findings by the University of Cincinnati group in a pig ICH model6 provide strong support for several early events in perihematomal edema development.6 7 8 These include (1) clot retraction with decreasing clot volumes and increasing perihematomal edema volumes during the first 4 hours after ICH; (2) plasma protein extravasation that acts oncotically to induce rapid (already at 1 hour) perihematomal edema development; and (3) marked perihematomal immunoreactivity for fibrin(ogen), suggesting the presence of extravascular coagulation and fibrin deposition. Studies of edema development in gray matter in the rat by the University of Michigan group9 10 11 12 have defined the major role of the coagulation cascade and thrombin itself in edema development during the first 24 hours after ICH. Furthermore, the significance of thrombin in this early edema formation is substantiated by the ability of thrombin inhibitors to reduce edema. Other recent findings10 13 also demonstrate that intracerebral infusions of packed red blood cells fail to produce early perihematomal edema.
To further define the importance of blood clotting on early edema development after ICH, we compared heparinized with unheparinized whole-blood infusions in the 2 animal models. Preliminary results from these studies have been presented.14
| Materials and Methods |
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All surgical, blood infusion, and brain freezing methods in pigs have
been described previously in detail.6 Briefly,
pigs (
10 kg) were anesthetized with ketamine (25 to
30 mg/kg IM). After sedation, pentobarbital (35 mg/kg IV) was
administered to achieve deep surgical levels. Anesthesia
was then maintained by continuous pentobarbital infusion (10 mg/kg per
hour). A tracheotomy was performed, and the pigs were intubated and
mechanically ventilated with air (oxygen added at 0.5 L/min). Femoral
vessels were catheterized: arteries to record blood pressure and
measure arterial acid-base status, respiratory gases, and
glucose; veins to infuse saline and drugs. Core temperatures
(38.5±0.5°C) were monitored and controlled. Hematomas were induced
by slowly (over a 15-minute period) infusing 2.5 mL autologous blood
through a 20-gauge Teflon catheter into the frontal cerebral white
matter. Silastic tubing was used to prevent blood clotting. For
heparinized blood infusions, autologous blood (3.5 mL) was withdrawn
into a syringe that had been coated with heparin (approximately 300 U),
and 2.5 mL were infused into the frontal white matter. To test
blood-brain barrier (BBB) permeability to albumin-bound Evans
blue dye, we infused Evans blue intravenously (1 mL/kg of a
2% wt/vol solution) immediately after completion of the
intracerebral blood
infusions.6
In pigs killed at 24 hours, the pentobarbital infusion was stopped, the endotracheal tube and the femoral artery catheter were removed, the femoral vein catheter was left in place, and the incisions were closed with silk sutures after 4 hours following blood infusions. Pigs were cared for in an animal intensive-care unit and were noted to achieve sternal recumbency within a few hours after the pentobarbital infusion was stopped. All pigs were awake and ambulatory the next morning. At 24 hours after blood infusion, the pigs were reanesthetized as described above with ketamine (intramuscular) and pentobarbital (through their indwelling femoral vein catheter). They were prepared for in situ brain freezing as described below.
Brains were frozen in situ with liquid nitrogen at 1, 4, or 24 hours after hematoma induction, as previously described.6 15 Coronal sections were cut with a band saw, and both sides of the coronal sections containing hematomas and/or edema were photographed together with a millimeter ruler. Prints (8x10 inches) were prepared from 2x2-inch photographic slides.
Hematomas and visible perihematomal edema volumes were determined by 1 of the following 2 methods: (1) by outlining the hematomas and visible perihematomal edema on the photographs while directly viewing the frozen slices and then determining the outlined areas by computer-assisted morphometry (Bioquant or NIH Image) or (2) by importing the color images from 2x2-inch color slides (input via Nikon Slide Scanner) and determining hematoma and edema areas by computer-assisted morphometry with use of Image Tool, a freeware image analysis system developed at the University of Texas Health Science Center at San Antonio. Areas determined by Image Tool were identical to those determined with NIH Image. For both methods, areas were corrected for image sizes from the millimeter ruler, the hematoma and edema areas from the 2 sides of each slice were averaged, and the values were multiplied by the slice thickness to calculate volumes and the volumes summed to calculate the total hematoma and edema volumes for each brain. The individual performing the hematoma and edema volume measurements was blinded to the blood-infusion group of the animal being studied.
Studies in Rats
The protocol for these animal studies was approved by The
University of Michigan Committee on the Use and Care of Animals. Thirty
adult male Sprague-Dawley rats (Charles River Laboratories, Portage,
Mich), weighing between 300 and 400 g, were used in this
study. They were anesthetized with an
intraperitoneal injection of pentobarbital (40
mg/kg). A polyethylene catheter (PE-50) was inserted into the right
femoral artery for continuous blood pressure monitoring and blood
sampling. Arterial blood was obtained for analysis
of blood pH, PO2,
PCO2, hematocrit, and blood glucose
and as a source of blood for intracerebral infusion.
Body temperature was maintained at 37.5°C using a feedback-controlled
heating pad.
The rats were positioned in a stereotactic frame (Kopf Instrument), and a cranial burr hole (1 mm) was drilled near the right coronal suture, 4.0 mm lateral to the midline. A needle (26-gauge) was inserted stereotaxically into the right basal ganglia (coordinates: 0.2 mm anterior, 5.5 mm ventral, and 4.0 mm lateral to the bregma). Whole blood, heparinized blood and saline were infused at a rate of 10 µL/min into right basal ganglia with use of a microinfusion pump (Harvard Apparatus Inc.). After infusion, the needle was removed and the skin incisions were closed with sutures. Animals were allowed to recover.
The experiments in rat were divided into 2 parts. Part 1: Three groups of 5 rats each were investigated in this part. The first group received a 50-µL saline infusion. The second group was infused with 50 µL autologous heparinized blood (2.5 U heparin). The third group had 50 µL autologous whole blood. Part 2: Three groups with 5 animals each received a 60-µL infusion of either saline or thrombin (5 U, Sigma Chemical Co) or thrombin (5 U) plus heparin (5 U) into the right basal ganglia. All animals were decapitated at 24 hours.
The rats were decapitated after deep anesthesia (80 mg/kg IP pentobarbital). The brains were removed. A coronal brain slice 4 mm from the frontal pole was cut approximately 3 mm thick. Five tissue samples (ipsilateral cortex and basal ganglia, contralateral cortex and basal ganglia, and cerebellum) were weighed on an electronic analytical balance (model AE 100, Mettler Instrument Co) to obtain the wet weight (WW). The tissue was then dried in a gravity oven at 100°C for 24 hours to obtain the dry weight (DW). Water contents were calculated as follows: Water content (%)=((WW-DW)/WW) * 100.
The dehydrated brain samples were digested in 1 mL of 1 N nitric acid for 1 week. The sodium and potassium ion contents were measured by flame photometry. Ion contents were expressed in milliequivalents per kilogram of dehydrated brain tissue.
Statistical Analysis
All data in the figures and tables are presented as
mean±SD. Data from different animal groups were analyzed with
ANOVA with a Scheffé F test or Student t test. The
differences were considered significant at P<0.05.
| Results |
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The photographs of the coronal brain sections in Figure 1
and the quantitation of the hematoma
and edema volumes in Figure 2
, demonstrate significantly (P=0.01) smaller (
60%)
hematoma volumes in the unheparinized blood infusion group compared
with brains that received heparinized blood infusions. Furthermore,
while perihematomal edema volume in the unheparinized bloodinfused
brains averaged 1.29 mL (Figure 2
), no perihematomal edema was
present in the brains of pigs receiving heparinized blood infusions
(not detectable [ND] in Figure 2
). Thus, unheparinized blood that was
capable of clotting produced perihematomal edema and significantly
smaller hematoma volumes compared with infusions of heparinized
blood.
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Rat ICH Studies
Table 2
presents the
physiological parameters in 6 animal
groups. All physiological variables were within
normal ranges.
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Unheparinized Versus Heparinized Blood Infusions
The infusions of heparinized blood produced slight brain edema,
but the unheparinized blood induced marked water-content increase in
the ipsilateral basal ganglia (Figure 3
).
The water content increase at 24 hours after blood infusion was
associated with accumulation of sodium ions. There was no significant
potassium loss at this time point (Figure 4
).
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Thrombin Versus Thrombin Plus Heparin Infusions
Figure 5
shows the brain water
content after infusions of saline, thrombin (5 U), and thrombin (5 U)
plus heparin (5 U). The thrombin-induced brain edema, sodium ion
accumulation, and potassium loss in ipsilateral cortex and basal
ganglia were significantly reduced by heparin (Figures 5
and 6
).
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| Discussion |
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The anticoagulant effect of heparin is due to its high-affinity binding with antithrombin III (AT III) and the ability of the heparin/AT III complex to inactivate thrombin and other coagulation factors.16 However, the fact that heparin also significantly reduced thrombin-induced edema in the absence of blood and AT III indicates that heparin may also have effects on edema formation not mediated by AT III. Tulinsky found that heparin can bind to the exosite, active site, and fibrinogen recognition exosite of thrombin.17 In addition, heparin may potentiate the effect of serine protease inhibitors that naturally occur in brain. The ability of both protease nexin 1 and plasminogen activator inhibitor-1 to inhibit thrombin is increased in the presence of heparin.18 19
The findings of a blood-fluid level in pig brains with heparinized blood infusions confirm repeated findings on CT scans of ICH patients with coagulopathies that interfere with clot formation or cause lysis of the fibrin matrix.20 Similar blood-fluid levels on CT scans have also been described in patients receiving anticoagulation therapy.21 22 23 24 It is interesting that recent findings from a radiographic evaluation of symptomatic ICH complicating thrombolysis for acute myocardial infarction (GUSTO-1 trial) demonstrate minimal perihematomal edema, particularly in patients with hematoma blood-fluid levels.25 In this trial, all patients received heparin in combination with the thrombolytic agent, which support the importance of blood clot formation in the evolution of early perihematomal edema.
Previously, we demonstrated that autologous blood infused into frontal cerebral white matter in pigs produces rapidly (at 1 hour), developing marked perihematomal edema (>10% increases in water content).6 15 This edema colocalized with interstitial fibrin(ogen) and other plasma protein accumulations despite an intact BBB.6 The present findings support the conclusion that coagulation cascade activation leading to clot formation is necessary for this rapid edema development in perihematomal white matter after ICH.
The present results also further support the role for early
surgical intervention for hematoma removal. The development of
increased BBB permeability after a delay of several hours (Figure 1B
)
suggests that early intervention may also prevent this secondary
pathophysiological event. In this regard, we have
demonstrated that early clot aspiration following lysis with tissue
plasminogen activator not only markedly reduced
(>70%) edema development at 24 hours but also protected the
BBB.7 The edema reduction and BBB protection with
early clot removal using a fibrinolytic agent may be through
"interstitial fibrinolysis" and
reduction of extracellular plasma proteins, including thrombin that may
be retained within the fibrin mesh.26
The present paradigm of using intracerebral infusions of heparinized blood may also provide important information regarding the role of the coagulation cascade and thrombin on long-term neuropathological outcome. Thrombin infusion into rat caudate nucleus did cause inflammation, brain edema, reactive gliosis, and scar formation.9 10 11 12 27 We also demonstrated that at 3 days after lobar ICH, white matter edema is still present and associated with marked astrogliosis and reduced Luxol fast blue staining suggestive of demyelination.28 These results suggest that early and prolonged edema following ICH may contribute to the damage and the long-term morbidity that has been described in ICH patients. The role of early and prolonged edema in this white matter injury could be studied by examining the outcome after heparinized blood infusions.
In conclusion, blood clot formation is a mandatory step for rapid (at 1 hour) and prolonged (24 hours) edema in both white and gray matter after ICH. Furthermore, findings from these and other studies6 7 8 9 10 11 12 13 support the role of plasma proteins (especially thrombin), an activated coagulation cascade, clot retraction, and fibrin deposition in both rapid (at 1 hour) and prolonged (24 hours) edema development adjacent to clots in white and gray matter after ICH. Further studies are required to determine the relative contributions of these various factors and events in perihematomal edema formation following ICH.
| Acknowledgments |
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Received May 29, 1998; revision received August 6, 1998; accepted August 24, 1998.
| References |
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Department of Neurosurgery, University of California, Davis, Sacramento, California
| Introduction |
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Received May 29, 1998; revision received August 6, 1998; accepted August 24, 1998.
| References |
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