Intracranial pressure changes and outcomes in the early phase of experimental subarachnoid hemorrhage: severity of subarachnoid hemorrhage and maximum intracranial pressure

Intracranial pressure changes and outcomes in the early phase of experimental subarachnoid hemorrhage: severity of subarachnoid hemorrhage and maximum intracranial pressure | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Intracranial pressure changes and outcomes in the early phase of experimental subarachnoid hemorrhage: severity of subarachnoid hemorrhage and maximum intracranial pressure Kazuya Fujii, Satoru Takeuchi, Terushige Toyooka, Arata Tomiyama, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9175606/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 8 You are reading this latest preprint version Abstract Purpose To investigate the correlation between intracranial pressure (ICP) and the outcomes in rat subarachnoid hemorrhage (SAH) model and determine whether maximum ICP can predict severity of SAH. Methods Sprague-Dawley rats underwent the monofilament puncture procedure to induce SAH, and were divided into 4 groups according to the maximum ICP for survival prediction: sham group, mild ICP group (ICP < 50 mmHg), moderate ICP group (ICP 50–149 mmHg), and severe ICP group (ICP ≥ 150 mmHg). Results Maximum ICP showed strong correlations with the neurological score, SAH grade at 24 hours after induction, and mortality. Histological study demonstrated that greater increase in maximum ICP was associated with worse outcome and more severe neuronal damage, apoptosis, and oxidative stress in the brain cortex and hippocampus at 24 hours after induction. Conclusion The present study demonstrates that monitoring the ICP can confirm the induction of SAH and classify individual cases into severity grade. Animals with maximum ICP of 50–149 mmHg may be the most suitable for the experimental study of SAH. Subarachnoid hemorrhage Rat Monofilament perforation Intracranial pressure Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Recent clinical and experimental investigations into subarachnoid hemorrhage (SAH) have demonstrated the importance of the rapid pathophysiological changes occurring during the acute phase of SAH. In particular, early brain injury (EBI), which occurs within 72 hours after SAH, is very important in determining the outcome of SAH [ 2 ]. However, other pathological changes such as microvascular filling defects, cortical spreading depolarization, and vasospasm may also be important. Investigation of the pathophysiological mechanisms and development of new therapeutic strategies for the acute phase of SAH require experimental methods that can provide reproducible induction of SAH under similar conditions to those found in humans. In addition, a consistent method to evaluate the severity of SAH is necessary to accurately predict the outcome [ 1 , 6 , 14 , 24 , 30 , 33 ]. The endovascular monofilament puncture method is one of the most common methods used to induce SAH in rat or mouse models [ 3 , 8 , 15 , 17 , 22 , 25 , 27 , 28 , 29 ]. This method is effective for investigating SAH because the induced severity and conditions in the acute phase are quite similar to SAH caused by ruptured aneurysm in humans. These conditions are induced by the rapid increase in intracranial pressure (ICP) that leads to global ischemia [ 5 ]. However, this method causes high mortality rates in the experimental animals due to the inability to control the bleeding volume into the subarachnoid space, which leads to immediate extreme elevation of the ICP [ 5 , 24 ]. In addition, the SAH grade cannot be determined before tissue preparation, although an SAH grading system for classifying the bleeding scale has been proposed [ 31 ]. Nevertheless, most experimental studies using the endovascular monofilament puncture method have been conducted without any consideration of these problems. The present study investigated the correlation between the maximum ICP and the outcomes in the rat SAH model using the endovascular monofilament puncture method, to determine whether ICP monitoring can estimate the severity of SAH before tissue preparation. Materials and methods Materials All experimental procedures were approved by the Animal Care and Use Committee of the National Defense Medical College (approval number: 14006). Sprague-Dawley rats (male, 280350 g; 8–10 weeks of age) were housed in individual cages under controlled environmental conditions (12/12 h light/dark cycle, 22–24°C; room temperature) with food and water freely available, for one week before the experimental surgery. Throughout the study, extreme care was taken to minimize any pain and discomfort to the animals. Experimental procedures General anesthesia was induced with 3% isoflurane. The rats were intubated, and maintained on a mechanical ventilator after infusion of pancuronium bromide (0.1 mg/kg, tidal volume 2.5–3.0 mL/kg, respiratory rate 60/min). The tail artery was cannulated with a polyethylene catheter. Blood pressure was monitored throughout the procedure, and arterial blood samples were analyzed before induction of SAH and 30 minutes after induction (PaCO 2 was controlled at 30–40 mmHg). Isoflurane concentration was titrated between 0.5% and 3% to maintain mean arterial blood pressure (MABP) of 80 to 130 mmHg. The rectal temperature was measured with a rectal probe and was maintained strictly at 36.5–37.5°C with a heating pad and heating lamp. ICP monitoring The ICP was continuously measured using a Codman Microsensor (Johnson & Johnson Medical Ltd., Tokyo, Japan). After intubation and initiation of mechanical ventilation, the rats were fixed in a stereotaxic frame in the head-down position. A linear incision was made into the parietal bone. The transducer was inserted through a burr hole 1 mm lateral and rostral to the bregma on the right side, and was placed into the epidural space. ICP was measured until 60 minutes after SAH induction. Induction of SAH and experimental groups SAH was induced by endovascular perforation of the internal carotid artery (ICA) bifurcation with a sharpened 4 − 0 monofilament nylon suture, as reported previously [ 3 , 16 ]. Briefly, after making a midline incision, the left common carotid artery (CCA), external carotid artery (ECA), and ICA were exposed, and the ECA was ligated and cut to a 4 mm stump. The pterygopalatine artery was then ligated. A monofilament suture was inserted through the ECA stump and advanced into the intracranial ICA until resistance was felt (15 to 18 mm from the CCA bifurcation) and then pushed 2 mm further to penetrate the wall of the bifurcation of the anterior and middle cerebral arteries. Immediately after the puncture, the suture was withdrawn, and the clamp on the CCA was released. After the operation, the surgical wound was closed and the rat was allowed to recover from anesthesia, then returned to the home cage, with food and water freely available. The rats were divided into the groups according to the results of the maximum ICP for survival prediction: mild, moderate, severe ICP, and sham group. Mortality and neurological scoring Mortality rate and neurological scores were evaluated 24 hours after SAH induction. Neurological scores were evaluated with a modification of the previously reported scoring system [ 10 , 31 ]. Grading of SAH SAH was evaluated in 25 rats (mild ICP group 10, moderate ICP group 15). No rats in the severe ICP group were evaluated because all surviving rats were used for water content measurement. Under deep anesthesia, the rats were perfused transcardially with 0.9% saline solution, followed by 4% buffered paraformaldehyde. After removing the brain, the base of the brain was imaged to show the circle of Willis and basilar arteries. SAH grade was evaluated with the reported scoring system [ 31 ]. Immunohistochemistry Histopathological analysis examined a total of 18 rats (mild ICP group 6, moderate ICP group 6, sham group 6). Rats were deeply anesthetized and transcardially perfused with 0.9% saline solution, followed by 4% buffered paraformaldehyde. After fixation for 24 hours at 4˚C, the brains were removed and embedded in paraffin. Coronal sections were cut to 8 µm thickness at the level 3.8 mm posterior to the bregma. Each series of sections was used for Nissl staining, 8-hydroxy-2-deoxyguanosine (8-OHdG) staining, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL). Nissl staining was performed to detect injured or intact neurons. Brain sections were stained with 0.2% cresyl violet [ 20 ]. The right parietal cortex and the cornu ammonis 1 (CA1) of the hippocampus were imaged using an all-in-one fluorescence microscope (BZ-X700; Keyence, Osaka, Japan). Histological changes were evaluated by an investigator unaware of the group classification. For each section, three fields of view (×400) were sequentially selected, and the numbers of intact pyramidal cells in each field were counted. 8-OHdG staining was performed to detect oxidative damage (35, 36). Serial coronal sections were stained overnight at 4˚C with mouse monoclonal antibody against 8-OHdG (1:100; Japan Institute for the Control of Aging, Fukuroi, Shizuoka, Japan). Then the sections were treated with secondary antibodies (Vectastain ABC Kit; Vector Laboratories, Burlingame, CA). Immunoreactivity was visualized by the ABC (avidin-biotin complex) method according to the manufacturer’s instructions. The right parietal cortex and the hippocampal CA1 were imaged using an all-in-one fluorescence microscope (BZ-X700). For each section, three fields of view (×400) were sequentially selected, and the numbers of positive cells in each field were counted. TUNEL staining was performed to detect apoptotic cells [ 17 ] with a kit for detection of apoptotic cells (Apoptosis in situ Detection Kit; Wako Pure Chemical Industries, Tokyo, Japan) according to the manufacturer’s instructions. The right parietal cortex and the hippocampal CA1 were imaged using an all-in-one fluorescence microscope (BZ-X700). For each section, three fields of view (×400) were sequentially selected, and the numbers of TUNEL-positive cells in each field were counted. Brain water content Brain water content was measured using the wet/dry method to assess brain edema in a total of 24 rats, 6 rats from each group [ 32 ]. After deep anesthesia, the brain of each rat was removed. The cortex of the right frontal lobe was separated and weighed, then the tissue was placed in an oven at 95˚C for 24 hours and reweighed. The brain water content was calculated using the following formula: (wet weight - dry weight)/wet weight × 100%. Statistical analysis All values are presented as mean ± standard deviation. Spearman’s rank correlation coefficient and regression analysis were performed to assess the correlation between the maximum ICP and neurological score, and SAH grade. Logistic univariate regression analysis was performed to assess the inverse correlation between the maximum ICP and mortality rate. One-way analysis of variance followed by Tukey’s honestly significant difference test or Games-Howell’s method for post-hoc analysis was performed to assess differences between multiple groups, or the Kruskal-Wallis test followed by Steel-Dwass post-hoc analysis according to the distribution of the values. P 0.7 was considered to indicate strong correlation. Results Blood gas analysis was performed before and 30 minutes after SAH induction. Values were controlled within the normal ranges and showed no significant changes in any group at all times (Table 1 ). Table 1 Parameters of blood gas analysis before and 30 minutes after SAH induction Sham group, n = 20 Before SAH 30 min after SAH pH (units) 7.39 ± 0.04 7.40 ± 0.03 PaCO 2 (mmHg) 37.7 ± 4.2 37.4 ± 3.8 PaO 2 (mmHg) 132.1 ± 15.9 138.5 ± 14.3 HCO 3 (mmol/L) 22.8 ± 2.4 22.8 ± 2.3 Base excess (mmol/L) -1.2 ± 1.9 -1.7 ± 1.8 Lactate (mmol/L) 1.5 ± 0.7 1.5 ± 0.7 Mild ICP group, n = 27 pH (units) 7.39 ± 0.04 7.39 ± 0.03 PaCO 2 (mmHg) 37.3 ± 4.3 38.1 ± 3.6 PaO 2 (mmHg) 131.6 ± 12.9 136.9 ± 11.7 HCO 3 (mmol/L) 23.6 ± 2.2 23.3 ± 2.1 Base excess (mmol/L) -1.0 ± 1.8 -0.9 ± 2.3 Lactate (mmol/L) 1.5 ± 0.5 1.5 ± 0.5 Moderate ICP group, n = 35 pH (units) 7.41 ± 0.04 7.39 ± 0.04 PaCO 2 (mmHg) 36.3 ± 3.9 36.3 ± 4.0 PaO 2 (mmHg) 138.2 ± 13.9 136.6 ± 16.2 HCO 3 (mmol/L) 22.9 ± 2.1 21.9 ± 4.2 Base excess (mmol/L) -1.6 ± 1.8 -1.9 ± 1.8 Lactate (mmol/L) 1.5 ± 0.5 1.6 ± 0.6 Severe ICP group, n = 23 pH (units) 7.38 ± 0.05 7.40 ± 0.04 PaCO 2 (mmHg) 35.3 ± 4.0 34.6 ± 3.0 PaO 2 (mmHg) 127.0 ± 12.7 139.2 ± 12.3 HCO 3 (mmol/L) 22.5 ± 3.0 22.4 ± 2.2 Base excess (mmol/L) -1.7 ± 1.9 -1.6 ± 1.3 Lactate (mmol/L) 1.4 ± 0.5 2.5 ± 2.8 No significant differences were found between the groups Values are expressed as mean ± standard deviation Classification by maximum ICP for survival prediction Receiver operating characteristic curve analysis demonstrated high discriminatory performance (area under the curve = 0.853, 95% confidence interval [CI] = 0.775–0.931), with sensitivity and specificity reaching maximum values at ICP = 89 mmHg (Fig. 1 a). The equilibrium of sensitivity was 0.909 and specificity was 0.611 at an ICP of 50 mmHg, and sensitivity was 0.515 and specificity was 0.917 at an ICP of 150 mmHg (Fig. 1 b). Therefore, the rats were divided into the following 4 groups according to the results of the maximum ICP for survival prediction: mild ICP group (ICP < 50 mmHg, n = 27), moderate ICP group (ICP 50–149 mmHg, n = 35), severe ICP group (ICP ≥ 150 mmHg, n = 23), and sham group (normal ICP, n = 20). Mortality rates and ICP, MABP, and cerebral perfusion pressure (CPP) Table 2 summarizes maximum ICP, minimum CPP, mortality rate, SAH grade, and neurological score in each group. Maximum ICP was significantly associated with mortality, with higher values correlating with increased risk of death by univariate logistic analysis (odds ratio 1.02, 95% CI 1.010–1.030, p < 0.01). The mortality rate was 0% in the sham group, and 38.8% in the induced SAH group. Further analysis showed that the mortality rate was 11.1% in the mild ICP group, 37.1% in the moderate ICP group, and 73.9% in the severe ICP group (Fig. 1 c). ICP, MABP, and CPP were controlled within the normal ranges and showed no significant changes in any group before induction of SAH. ICP elevated immediately after the monofilament suture punctured the intracranial artery, and peaked within approximately 30 seconds to 1 minute. Thereafter, ICP fell within 5 minutes but remained clearly higher than before SAH. MABP increased and then decreased in reaction to the increase and decrease in ICP (Fig. 1 d). ICP and MABP did not change at all throughout the procedure in the sham group. Correlation between maximum ICP and neurological score/SAH grade Maximum ICP showed a strong correlation (|r| = 0.859, p < 0.01) with the neurological score and SAH grade (|r| = 0.859, p < 0.01) at 24 hours after SAH induction (Fig. 2 ). Intergroup comparison showed significant differences between all groups except between the moderate and severe ICP groups (Table 2 ). Table 2 Summary of the clinical characteristics of each group Maximum ICP (mmHg) Sham group (n = 20) Mild ICP group (n = 27) Moderate ICP group (n = 35) Severe ICP group (n = 23) 9.3 ± 3.0 35.2 ± 11.3 103.3 ± 26.7 174.4 ± 14.7 Minimum CPP (mmHg) 98.2 ± 8.8 82.5 ± 17.2 30.2 ± 19.5 11.6 ± 6.7 Mortality rate (%) 0 11.1 37.1* 73.9* Neurological score 17.8 ± 0.4 16.3 ± 1.2 11.6 ± 3.0 9 ± 1.9 SAH grade 0 6.5 ± 2.2 11.0 ± 2.5 not aggregated *Significantly higher in the moderate and severe ICP groups, and lower in the mild ICP and sham groups ( p < 0.001) Values are mean ± standard deviation Neuronal injury in the parietal cortex and hippocampal CA1 No obvious neuronal injury was detected in the sham group (Fig. 3 a and d). Severe neuronal injury was observed in the moderate ICP group (Fig. 3 c and f). In addition, many pyramidal neurons exhibited pyknotic, shrunken nuclei. Fewer injured neurons were observed in the mild ICP group (Fig. 3 b and e). Quantitative comparison of the numbers of intact neurons in the three groups found that the mild and moderate ICP groups showed significant decreases in intact neuronal cells compared to the sham group, and the moderate ICP group exhibited significantly lower number of intact neurons than the mild ICP group (Fig. 3 g and h). Oxidative damage in the parietal cortex and hippocampal CA1 Oxidative damage was detected in a few cells in the sham group (Fig. 3 i and l). In contrast, oxidative damage was observed in many cells in the moderate ICP group (Fig. 3 k and n ). Few damaged cells were observed in the mild ICP group, with obviously less damage than in the moderate ICP group (Fig. 3 j and m). Quantitative comparison found that the moderate ICP group showed significant increase in oxidative damage in the cortex and hippocampal CA1 compared to the sham and mild ICP groups (Fig. 3 o and p). Apoptosis in the parietal cortex and hippocampal CA1 Only a few apoptotic cells were detected in the sham group (Fig. 3 q and t). In contrast, many neuronal apoptotic cells were observed in the moderate ICP group (Fig. 3 s and v). Few apoptotic cells were observed in the mild ICP group (Fig. 3 r and u). Quantitative comparison found that the moderate ICP group showed significant increase in neuronal apoptosis in the cortex compared to both the sham and mild ICP groups (Fig. 3 w), whereas the moderate ICP group showed significant increase in the hippocampal CA1 compared only with the sham group (Fig. 3 x). Extent of brain edema Brain water content was measured to assess the extent of brain edema at 24 hours after induction of SAH. Brain water content increased with greater ICP elevation, according to the maximum ICP. The moderate ICP group showed significant increase in brain water content compared to the sham, mild ICP, and severe ICP groups (Fig. 4 ). Discussion The present study used the rat perforation SAH model to evaluate the SAH grade, mortality rate, neurological score, neuronal damage, and brain edema in groups classified according to the maximum ICP. In the moderate ICP group (maximum ICP 50–149 mmHg), the mortality rate was 37.1%, and prominent oxidative damage and apoptotic cells were observed in the parietal cortex and hippocampal CA1 in the brain of surviving rats. Death caused by SAH The global mortality rate of SAH ranges from 32% to 67%, and approximately 20% of patients die before arriving at the hospital [ 7 , 13 , 23 ]. Sudden death may be caused by acute cardiac failure, arrhythmia, or global brain ischemia and edema as a result of sudden increase in ICP and decrease in CPP and cerebral blood flow [ 2 , 26 ]. The present study found the mortality rate at 24 hours after SAH induction was 38.8% (33/85) in the SAH group. Fourteen of the 33 animals died very soon (within 1 hour) after perforation, and 12 of these 14 animals were classified in the severe ICP group. For comparison with the mortality rate of SAH in humans, the mild ICP group may correspond to World Federation of Neurosurgical Societies (WFNS) grade II or III, whereas the moderate ICP group may correspond to WFNS grade IV [ 11 ]. Neuronal damage during the acute phase of SAH EBI is a general term that refers to the global brain damage which occurs from 24 to 72 hours after SAH [ 4 , 12 , 21 , 34 , 36 ]. Recent clinical and basic investigations have demonstrated the importance of EBI in determining the outcome after SAH. The pathogenesis of EBI is multifactorial and includes complex pathways which lead to neuronal cell death. Rapid increase in ICP and decrease in CPP are perhaps the most immediate and important events in the occurrence of EBI, and are followed by global perfusion deficits. Physiological compensatory mechanisms may prevent sudden death, but the ICP still remains higher than normal [ 4 , 21 ]. Global brain ischemia occurring in the initial phase after SAH causes energy failures in the neurons and glia, and initiates the cascade which leads to cytotoxic edema. This ischemic status also results in apoptosis, and initiates the cascade that disrupts the blood-brain barrier, which leads to vasogenic edema. The present histological study demonstrated diffusely distributed neuronal damage and apoptosis in the cortex and hippocampus, similar to previous findings [ 5 , 17 , 18 , 28 ]. Furthermore, the damage level was greater in the groups with higher ICP, which supports the pathophysiological explanation of transient global ischemia occurring immediately after SAH. Oxidative stress and EBI Oxidative stress is well known to be important in EBI [ 2 , 19 , 36 ]. Excess production of reactive oxygen species exceeding the capacity of the neutralization systems of antioxidants in the brain following SAH results in the release of strong oxidizing agents. Free radicals directly damage the neurovascular complex and neurons, leading to neuronal apoptosis, endothelial injury, and blood-brain barrier disruption [ 35 , 36 ]. The present study demonstrated high levels of oxidative damage in the cerebral cortex and hippocampus, which was more significant in the groups with higher ICP. Recently, basic research has shown that antioxidant therapy against EBI, based on agents such as hydrogen or edaravone, is effective, but clinical studies found that the effect was poor or limited [ 9 , 19 ]. The present study indicates that oxidative stress is significantly stronger in severe cases, so the ameliorative effect may be limited to cases of severe SAH. The present study demonstrated that greater increase in ICP in the hyperacute phase of SAH was correlated with worse outcome and more severe neuronal damage and apoptosis in the brain cortex and hippocampus. One of the problems with the endovascular perforation model is the instability of the pathophysiological parameters after induction of SAH. Therefore, classification of the animals based on the severity of brain injury is important to compare the effects and results more accurately. Maximum ICP was correlated with the extent of subarachnoid blood clots, neurological function, survival rate, and neuronal damage, so measurement of the ICP can estimate the severity of SAH before sacrificing the animal. Our present findings indicate the use of animals with maximum ICP of 50–149 mmHg to study the pathophysiology and therapeutic effects on EBI after experimental SAH. In addition, real time information about the ICP confirms reliable perforation of the vessel wall, and can be helpful to avoid multiple perforations, or excess penetration of the monofilament suture, which will cause extra damage to the brain. Conclusions The present study demonstrates the importance of monitoring ICP during the induction of SAH and observation period of endovascular perforation models. Monitoring the ICP can confirm the induction of SAH and classify individual cases into severity grade. Animals with maximum ICP of 50–149 mmHg may be the most suitable for the experimental study of SAH. Abbreviations CA1: cornu ammonis 1, CCA: common carotid artery, CI: confidence interval, CPP: cerebral perfusion pressure EBI: early brain injury, ECA: external carotid artery, ICA: internal carotid artery, ICP: intracranial pressure, MABP: mean arterial blood pressure, 8-OHdG: 8-hydroxy-2-deoxyguanosine, SAH: subarachnoid hemorrhage, TUNEL: terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling, WFNS: World Federation of Neurosurgical Societies Declarations Ethics approval: This study was performed in line with the approval of the Institutional Animal Ethics Committee, National Defense Medical College (approval no-14006). Conflict of interest: The authors declare no conflict of interest. Author Contribution Author contributions to the study and manuscript preparation include the following. Conception and design: K.M.Acquisition of data: K.F., S.T.Drafting the article: K.F., S.T.Preparing Tables: K.F.Preparing Figures: K.F., S.T., T.T.Statistical Analyses: S.T., T.T.Critically revising the article: A.T., T.T., K.W.Approved the final version of the manuscript on behalf of all authors: T.T., K.W.Study supervision: K.M. Data Availability The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request, in accordance with institutional guidelines. References Aladag MA, Turkoz Y, Sahna E, Parlakpinar H, Gul M (2003) The attenuation of vasospasm by using a SOD mimetic after experimental subarachnoidal haemorrhage in rats. Acta Neurochir (Wien) 145:673–677 Ayer R, Zhang J (2010) Connecting the early brain injury of aneurysmal subarachnoid hemorrhage to clinical practice. 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Stroke 36:2220–2225 Zhang ZY, Sun BL, Yang MF, Li DW, Fang J, Zhang S (2015) Carnosine attenuates early brain injury through its antioxidative and anti-apoptotic effects in a rat experimental subarachnoid hemorrhage model. Cell Mol Neurobiol 35:147–157 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 12 May, 2026 Reviews received at journal 27 Apr, 2026 Reviewers agreed at journal 07 Apr, 2026 Reviewers agreed at journal 06 Apr, 2026 Reviewers invited by journal 24 Mar, 2026 Editor assigned by journal 23 Mar, 2026 Submission checks completed at journal 23 Mar, 2026 First submitted to journal 20 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9175606","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":611547871,"identity":"1f5cb3f5-1077-463b-b2ec-7c2ab8ef86cd","order_by":0,"name":"Kazuya Fujii","email":"","orcid":"","institution":"National Defense Medical College","correspondingAuthor":false,"prefix":"","firstName":"Kazuya","middleName":"","lastName":"Fujii","suffix":""},{"id":611547876,"identity":"8fde61f9-c077-4015-acd4-f3790695bf7b","order_by":1,"name":"Satoru Takeuchi","email":"","orcid":"","institution":"National Defense Medical College","correspondingAuthor":false,"prefix":"","firstName":"Satoru","middleName":"","lastName":"Takeuchi","suffix":""},{"id":611547878,"identity":"8c862651-6279-469f-971e-ebe7c63181a8","order_by":2,"name":"Terushige Toyooka","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIiWNgGAWjYBADHn5m/o8PQAw+gkpBxAEGBjnJ9gZjA5AAG7FajA3OHDCTAHEIarFn730m/aHicOLMGQlplV9z7GTYGJgfPrqBzxae42YSB84cTuyXSDh2W3ZbMtBhbMbGOfi0SKSxSRxsA9mS2HZbchszUAsPmzReLfLPIFo23EhmK5bcVk+EFgk2sBag94+xMX7cdpgILWfSmC3OnEkHBnIPszTjtuM8bMwE/MLefozxRkWFNTAqeRg//txWbc/P3vzwMT4tUNAMJpnBscRMWDkI1IFJxh/EqR4Fo2AUjIIRBgDRcUVVS2Gg9QAAAABJRU5ErkJggg==","orcid":"","institution":"National Defense Medical College","correspondingAuthor":true,"prefix":"","firstName":"Terushige","middleName":"","lastName":"Toyooka","suffix":""},{"id":611547885,"identity":"e64251d3-f446-422c-9875-6d739137ebd4","order_by":3,"name":"Arata Tomiyama","email":"","orcid":"","institution":"National Defense Medical College","correspondingAuthor":false,"prefix":"","firstName":"Arata","middleName":"","lastName":"Tomiyama","suffix":""},{"id":611547887,"identity":"8e4b8e8c-3b40-4861-a7d8-6d44d3ceddbb","order_by":4,"name":"Kentaro Mori","email":"","orcid":"","institution":"Tokyo General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Kentaro","middleName":"","lastName":"Mori","suffix":""},{"id":611547890,"identity":"e2c6fde3-2ebb-4b01-97fc-232729b21be2","order_by":5,"name":"Kojiro Wada","email":"","orcid":"","institution":"National Defense Medical College","correspondingAuthor":false,"prefix":"","firstName":"Kojiro","middleName":"","lastName":"Wada","suffix":""}],"badges":[],"createdAt":"2026-03-20 06:39:05","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9175606/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9175606/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105566873,"identity":"79302fdb-574f-405c-ab84-b17b4b805f17","added_by":"auto","created_at":"2026-03-27 12:57:37","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1506717,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e:\u003cstrong\u003e \u003c/strong\u003eMaximum intracranial pressure (ICP) for survival prediction in rat subarachnoid hemorrhage (SAH) model. Receiver operating characteristic curve demonstrated high discriminatory performance (area under the curve = 0.853, 95% confidence interval [CI] = 0.775–0.931), with sensitivity and specificity reaching maximum values at ICP = 89 mmHg. \u003cstrong\u003eb\u003c/strong\u003e: Equilibrium of sensitivity was 0.909 and specificity was 0.611 at an ICP of 50 mmHg, and sensitivity was 0.515 and specificity was 0.917 at an ICP of 150 mmHg. \u003cstrong\u003ec\u003c/strong\u003e: Maximum ICP was significantly associated with mortality, with higher values correlating with increased risk of death by univariate logistic analysis (odds ratio 1.02, 95% CI 1.010–1.030, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01). The mortality rate was 0% in the sham group, 11.1% in the mild ICP group, 37.1% in the moderate ICP group, and 73.9% in the severe ICP group. \u003cstrong\u003ed\u003c/strong\u003e:\u003cstrong\u003e \u003c/strong\u003eGraphs showing changes in ICP, mean arterial blood pressure (MABP), and cerebral perfusion pressure (CPP) during the initial 60 minutes after SAH induction. *\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05, **\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01, ***\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001 vs. mild ICP group. #\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01, ##\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001 vs. moderate ICP group\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9175606/v1/074bd189dace4e833063bab9.jpeg"},{"id":105497567,"identity":"e8b16c78-be3e-494f-9ba1-f42cb93cb391","added_by":"auto","created_at":"2026-03-26 16:46:07","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":204326,"visible":true,"origin":"","legend":"\u003cp\u003eRegression analysis showing a strong correlation between the maximum ICP and the neurological score (a, |r| = 0.859, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01) and SAH grade (b, |r| = 0.859, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01) at 24 hours after SAH induction\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9175606/v1/55f5c2ef268e438cbaec27b2.jpeg"},{"id":105728535,"identity":"53761cf3-5e67-4731-9fc5-7f6fdb834bcd","added_by":"auto","created_at":"2026-03-30 11:12:06","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":750400,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea–f\u003c/strong\u003e: Representative photomicrographs of Nissl staining of the cerebral cortex (a–c) and the cornu ammonis 1 (CA1) hippocampal neurons (d–f). Arrowheads indicate injured neurons. Scale bar = 100 µm. \u003cstrong\u003eg and h\u003c/strong\u003e: Quantitative evaluation of intact pyramidal neurons in the cerebral cortex (g) and hippocampal CA1 (h). \u003cstrong\u003ei–n\u003c/strong\u003e: Representative photomicrographs of 8-hydroxy-2-deoxyguanosine (8-OHdG) staining of the cerebral cortex (i–k) and the hippocampal CA1 neurons (l–n). Arrowheads indicate 8-OHdG-positive cells. \u003cstrong\u003eo and p\u003c/strong\u003e: Quantitative evaluation of 8-OHdG-positive cells in the cerebral cortex (o) and hippocampal CA1 (p). \u003cstrong\u003eq–v\u003c/strong\u003e: Representative photomicrographs of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) staining of the cerebral cortex (q–s) and the hippocampal CA1 neurons (t–v). Arrowheads indicate apoptotic cells. \u003cstrong\u003ew and x\u003c/strong\u003e: Quantitative evaluation of TUNEL-positive cells in the cerebral cortex (w) and hippocampal CA1 (x). Scale bar = 100 µm. *\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01, **\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001 vs. sham group. #\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01, ##\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001 vs. mild ICP group\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9175606/v1/42194d4dbfc752b0ba61020d.jpeg"},{"id":105497563,"identity":"c2b64f89-27c8-4e54-a8f4-3dc2d14bbe52","added_by":"auto","created_at":"2026-03-26 16:46:05","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":146670,"visible":true,"origin":"","legend":"\u003cp\u003eBrain edema formation after SAH. Brain water content was measured to assess the extent of brain edema. The brain water content increased as the severity of ICP increased. Values are expressed as mean ± standard deviation (n = 6 per group). *\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9175606/v1/0a9760fbe400678ec8b1ab98.jpeg"},{"id":105729872,"identity":"6073f2ee-84f0-421f-9388-2d76d07f6d87","added_by":"auto","created_at":"2026-03-30 11:21:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3573775,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9175606/v1/d46fe29f-90fb-42f6-b293-cb47ef04d432.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Intracranial pressure changes and outcomes in the early phase of experimental subarachnoid hemorrhage: severity of subarachnoid hemorrhage and maximum intracranial pressure","fulltext":[{"header":"Introduction","content":"\u003cp\u003eRecent clinical and experimental investigations into subarachnoid hemorrhage (SAH) have demonstrated the importance of the rapid pathophysiological changes occurring during the acute phase of SAH. In particular, early brain injury (EBI), which occurs within 72 hours after SAH, is very important in determining the outcome of SAH [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. However, other pathological changes such as microvascular filling defects, cortical spreading depolarization, and vasospasm may also be important. Investigation of the pathophysiological mechanisms and development of new therapeutic strategies for the acute phase of SAH require experimental methods that can provide reproducible induction of SAH under similar conditions to those found in humans. In addition, a consistent method to evaluate the severity of SAH is necessary to accurately predict the outcome [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe endovascular monofilament puncture method is one of the most common methods used to induce SAH in rat or mouse models [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. This method is effective for investigating SAH because the induced severity and conditions in the acute phase are quite similar to SAH caused by ruptured aneurysm in humans. These conditions are induced by the rapid increase in intracranial pressure (ICP) that leads to global ischemia [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, this method causes high mortality rates in the experimental animals due to the inability to control the bleeding volume into the subarachnoid space, which leads to immediate extreme elevation of the ICP [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In addition, the SAH grade cannot be determined before tissue preparation, although an SAH grading system for classifying the bleeding scale has been proposed [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Nevertheless, most experimental studies using the endovascular monofilament puncture method have been conducted without any consideration of these problems.\u003c/p\u003e \u003cp\u003eThe present study investigated the correlation between the maximum ICP and the outcomes in the rat SAH model using the endovascular monofilament puncture method, to determine whether ICP monitoring can estimate the severity of SAH before tissue preparation.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eAll experimental procedures were approved by the Animal Care and Use Committee of the National Defense Medical College (approval number: 14006). Sprague-Dawley rats (male, 280350 g; 8\u0026ndash;10 weeks of age) were housed in individual cages under controlled environmental conditions (12/12 h light/dark cycle, 22\u0026ndash;24\u0026deg;C; room temperature) with food and water freely available, for one week before the experimental surgery. Throughout the study, extreme care was taken to minimize any pain and discomfort to the animals.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eExperimental procedures\u003c/h3\u003e\n\u003cp\u003eGeneral anesthesia was induced with 3% isoflurane. The rats were intubated, and maintained on a mechanical ventilator after infusion of pancuronium bromide (0.1 mg/kg, tidal volume 2.5\u0026ndash;3.0 mL/kg, respiratory rate 60/min). The tail artery was cannulated with a polyethylene catheter. Blood pressure was monitored throughout the procedure, and arterial blood samples were analyzed before induction of SAH and 30 minutes after induction (PaCO\u003csub\u003e2\u003c/sub\u003e was controlled at 30\u0026ndash;40 mmHg). Isoflurane concentration was titrated between 0.5% and 3% to maintain mean arterial blood pressure (MABP) of 80 to 130 mmHg. The rectal temperature was measured with a rectal probe and was maintained strictly at 36.5\u0026ndash;37.5\u0026deg;C with a heating pad and heating lamp.\u003c/p\u003e\n\u003ch3\u003eICP monitoring\u003c/h3\u003e\n\u003cp\u003eThe ICP was continuously measured using a Codman Microsensor (Johnson \u0026amp; Johnson Medical Ltd., Tokyo, Japan). After intubation and initiation of mechanical ventilation, the rats were fixed in a stereotaxic frame in the head-down position. A linear incision was made into the parietal bone. The transducer was inserted through a burr hole 1 mm lateral and rostral to the bregma on the right side, and was placed into the epidural space. ICP was measured until 60 minutes after SAH induction.\u003c/p\u003e\n\u003ch3\u003eInduction of SAH and experimental groups\u003c/h3\u003e\n\u003cp\u003eSAH was induced by endovascular perforation of the internal carotid artery (ICA) bifurcation with a sharpened 4\u0026thinsp;\u0026minus;\u0026thinsp;0 monofilament nylon suture, as reported previously [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Briefly, after making a midline incision, the left common carotid artery (CCA), external carotid artery (ECA), and ICA were exposed, and the ECA was ligated and cut to a 4 mm stump. The pterygopalatine artery was then ligated. A monofilament suture was inserted through the ECA stump and advanced into the intracranial ICA until resistance was felt (15 to 18 mm from the CCA bifurcation) and then pushed 2 mm further to penetrate the wall of the bifurcation of the anterior and middle cerebral arteries. Immediately after the puncture, the suture was withdrawn, and the clamp on the CCA was released. After the operation, the surgical wound was closed and the rat was allowed to recover from anesthesia, then returned to the home cage, with food and water freely available. The rats were divided into the groups according to the results of the maximum ICP for survival prediction: mild, moderate, severe ICP, and sham group.\u003c/p\u003e\n\u003ch3\u003eMortality and neurological scoring\u003c/h3\u003e\n\u003cp\u003eMortality rate and neurological scores were evaluated 24 hours after SAH induction. Neurological scores were evaluated with a modification of the previously reported scoring system [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eGrading of SAH\u003c/h2\u003e \u003cp\u003eSAH was evaluated in 25 rats (mild ICP group 10, moderate ICP group 15). No rats in the severe ICP group were evaluated because all surviving rats were used for water content measurement. Under deep anesthesia, the rats were perfused transcardially with 0.9% saline solution, followed by 4% buffered paraformaldehyde. After removing the brain, the base of the brain was imaged to show the circle of Willis and basilar arteries. SAH grade was evaluated with the reported scoring system [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eImmunohistochemistry\u003c/h3\u003e\n\u003cp\u003eHistopathological analysis examined a total of 18 rats (mild ICP group 6, moderate ICP group 6, sham group 6). Rats were deeply anesthetized and transcardially perfused with 0.9% saline solution, followed by 4% buffered paraformaldehyde. After fixation for 24 hours at 4˚C, the brains were removed and embedded in paraffin. Coronal sections were cut to 8 \u0026micro;m thickness at the level 3.8 mm posterior to the bregma. Each series of sections was used for Nissl staining, 8-hydroxy-2-deoxyguanosine (8-OHdG) staining, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL).\u003c/p\u003e \u003cp\u003eNissl staining was performed to detect injured or intact neurons. Brain sections were stained with 0.2% cresyl violet [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The right parietal cortex and the cornu ammonis 1 (CA1) of the hippocampus were imaged using an all-in-one fluorescence microscope (BZ-X700; Keyence, Osaka, Japan). Histological changes were evaluated by an investigator unaware of the group classification. For each section, three fields of view (\u0026times;400) were sequentially selected, and the numbers of intact pyramidal cells in each field were counted. 8-OHdG staining was performed to detect oxidative damage (35, 36). Serial coronal sections were stained overnight at 4˚C with mouse monoclonal antibody against 8-OHdG (1:100; Japan Institute for the Control of Aging, Fukuroi, Shizuoka, Japan). Then the sections were treated with secondary antibodies (Vectastain ABC Kit; Vector Laboratories, Burlingame, CA). Immunoreactivity was visualized by the ABC (avidin-biotin complex) method according to the manufacturer\u0026rsquo;s instructions. The right parietal cortex and the hippocampal CA1 were imaged using an all-in-one fluorescence microscope (BZ-X700). For each section, three fields of view (\u0026times;400) were sequentially selected, and the numbers of positive cells in each field were counted. TUNEL staining was performed to detect apoptotic cells [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] with a kit for detection of apoptotic cells (Apoptosis in situ Detection Kit; Wako Pure Chemical Industries, Tokyo, Japan) according to the manufacturer\u0026rsquo;s instructions. The right parietal cortex and the hippocampal CA1 were imaged using an all-in-one fluorescence microscope (BZ-X700). For each section, three fields of view (\u0026times;400) were sequentially selected, and the numbers of TUNEL-positive cells in each field were counted.\u003c/p\u003e\n\u003ch3\u003eBrain water content\u003c/h3\u003e\n\u003cp\u003eBrain water content was measured using the wet/dry method to assess brain edema in a total of 24 rats, 6 rats from each group [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. After deep anesthesia, the brain of each rat was removed. The cortex of the right frontal lobe was separated and weighed, then the tissue was placed in an oven at 95˚C for 24 hours and reweighed. The brain water content was calculated using the following formula: (wet weight - dry weight)/wet weight \u0026times; 100%.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eAll values are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. Spearman\u0026rsquo;s rank correlation coefficient and regression analysis were performed to assess the correlation between the maximum ICP and neurological score, and SAH grade. Logistic univariate regression analysis was performed to assess the inverse correlation between the maximum ICP and mortality rate. One-way analysis of variance followed by Tukey\u0026rsquo;s honestly significant difference test or Games-Howell\u0026rsquo;s method for post-hoc analysis was performed to assess differences between multiple groups, or the Kruskal-Wallis test followed by Steel-Dwass post-hoc analysis according to the distribution of the values. \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant. |r| \u0026gt; 0.7 was considered to indicate strong correlation.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eBlood gas analysis was performed before and 30 minutes after SAH induction. Values were controlled within the normal ranges and showed no significant changes in any group at all times (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eParameters of blood gas analysis before and 30 minutes after SAH induction\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSham group, n\u0026thinsp;=\u0026thinsp;20\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBefore SAH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30 min after SAH\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH (units)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e7.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e37.7\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e37.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e132.1\u0026thinsp;\u0026plusmn;\u0026thinsp;15.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e138.5\u0026thinsp;\u0026plusmn;\u0026thinsp;14.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHCO\u003csub\u003e3\u003c/sub\u003e (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e22.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e22.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBase excess (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLactate (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMild ICP group, n\u0026thinsp;=\u0026thinsp;27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH (units)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e7.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e37.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e38.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e131.6\u0026thinsp;\u0026plusmn;\u0026thinsp;12.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e136.9\u0026thinsp;\u0026plusmn;\u0026thinsp;11.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHCO\u003csub\u003e3\u003c/sub\u003e (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e23.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e23.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBase excess (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-1.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLactate (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eModerate ICP group, n\u0026thinsp;=\u0026thinsp;35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH (units)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e7.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e36.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e36.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e138.2\u0026thinsp;\u0026plusmn;\u0026thinsp;13.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e136.6\u0026thinsp;\u0026plusmn;\u0026thinsp;16.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHCO\u003csub\u003e3\u003c/sub\u003e (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e22.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e21.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBase excess (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-1.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLactate (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSevere ICP group, n\u0026thinsp;=\u0026thinsp;23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH (units)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e7.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e35.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e34.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e127.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e139.2\u0026thinsp;\u0026plusmn;\u0026thinsp;12.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHCO\u003csub\u003e3\u003c/sub\u003e (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e22.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e22.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBase excess (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e-1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e-1.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLactate (mmol/L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e2.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eNo significant differences were found between the groups\u003c/p\u003e \u003cp\u003eValues are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation\u003c/p\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eClassification by maximum ICP for survival prediction\u003c/h2\u003e \u003cp\u003eReceiver operating characteristic curve analysis demonstrated high discriminatory performance (area under the curve\u0026thinsp;=\u0026thinsp;0.853, 95% confidence interval [CI]\u0026thinsp;=\u0026thinsp;0.775\u0026ndash;0.931), with sensitivity and specificity reaching maximum values at ICP\u0026thinsp;=\u0026thinsp;89 mmHg (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The equilibrium of sensitivity was 0.909 and specificity was 0.611 at an ICP of 50 mmHg, and sensitivity was 0.515 and specificity was 0.917 at an ICP of 150 mmHg (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Therefore, the rats were divided into the following 4 groups according to the results of the maximum ICP for survival prediction: mild ICP group (ICP\u0026thinsp;\u0026lt;\u0026thinsp;50 mmHg, n\u0026thinsp;=\u0026thinsp;27), moderate ICP group (ICP 50\u0026ndash;149 mmHg, n\u0026thinsp;=\u0026thinsp;35), severe ICP group (ICP\u0026thinsp;\u0026ge;\u0026thinsp;150 mmHg, n\u0026thinsp;=\u0026thinsp;23), and sham group (normal ICP, n\u0026thinsp;=\u0026thinsp;20).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eMortality rates and ICP, MABP, and cerebral perfusion pressure (CPP)\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes maximum ICP, minimum CPP, mortality rate, SAH grade, and neurological score in each group. Maximum ICP was significantly associated with mortality, with higher values correlating with increased risk of death by univariate logistic analysis (odds ratio 1.02, 95% CI 1.010\u0026ndash;1.030, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). The mortality rate was 0% in the sham group, and 38.8% in the induced SAH group. Further analysis showed that the mortality rate was 11.1% in the mild ICP group, 37.1% in the moderate ICP group, and 73.9% in the severe ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003eICP, MABP, and CPP were controlled within the normal ranges and showed no significant changes in any group before induction of SAH. ICP elevated immediately after the monofilament suture punctured the intracranial artery, and peaked within approximately 30 seconds to 1 minute. Thereafter, ICP fell within 5 minutes but remained clearly higher than before SAH. MABP increased and then decreased in reaction to the increase and decrease in ICP (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). ICP and MABP did not change at all throughout the procedure in the sham group.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eCorrelation between maximum ICP and neurological score/SAH grade\u003c/h2\u003e \u003cp\u003eMaximum ICP showed a strong correlation (|r| = 0.859, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) with the neurological score and SAH grade (|r| = 0.859, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) at 24 hours after SAH induction (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Intergroup comparison showed significant differences between all groups except between the moderate and severe ICP groups (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of the clinical characteristics of each group\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMaximum ICP (mmHg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSham group\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;20)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMild ICP group\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;27)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eModerate ICP group\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;35)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSevere ICP group\u003c/p\u003e \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;23)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35.2\u0026thinsp;\u0026plusmn;\u0026thinsp;11.3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e103.3\u0026thinsp;\u0026plusmn;\u0026thinsp;26.7\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e174.4\u0026thinsp;\u0026plusmn;\u0026thinsp;14.7\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimum CPP (mmHg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e98.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e82.5\u0026thinsp;\u0026plusmn;\u0026thinsp;17.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30.2\u0026thinsp;\u0026plusmn;\u0026thinsp;19.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.6\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMortality rate (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e37.1*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e73.9*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNeurological score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSAH grade\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003enot aggregated\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e*Significantly higher in the moderate and severe ICP groups, and lower in the mild ICP and sham groups (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eValues are mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eNeuronal injury in the parietal cortex and hippocampal CA1\u003c/h2\u003e \u003cp\u003eNo obvious neuronal injury was detected in the sham group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and d). Severe neuronal injury was observed in the moderate ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec and f). In addition, many pyramidal neurons exhibited pyknotic, shrunken nuclei. Fewer injured neurons were observed in the mild ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and e). Quantitative comparison of the numbers of intact neurons in the three groups found that the mild and moderate ICP groups showed significant decreases in intact neuronal cells compared to the sham group, and the moderate ICP group exhibited significantly lower number of intact neurons than the mild ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg and h).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eOxidative damage in the parietal cortex and hippocampal CA1\u003c/h2\u003e \u003cp\u003eOxidative damage was detected in a few cells in the sham group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei and l). In contrast, oxidative damage was observed in many cells in the moderate ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ek and \u003cb\u003en\u003c/b\u003e). Few damaged cells were observed in the mild ICP group, with obviously less damage than in the moderate ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej and m). Quantitative comparison found that the moderate ICP group showed significant increase in oxidative damage in the cortex and hippocampal CA1 compared to the sham and mild ICP groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eo and p).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eApoptosis in the parietal cortex and hippocampal CA1\u003c/h2\u003e \u003cp\u003eOnly a few apoptotic cells were detected in the sham group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eq and t). In contrast, many neuronal apoptotic cells were observed in the moderate ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003es and v). Few apoptotic cells were observed in the mild ICP group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003er and u). Quantitative comparison found that the moderate ICP group showed significant increase in neuronal apoptosis in the cortex compared to both the sham and mild ICP groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ew), whereas the moderate ICP group showed significant increase in the hippocampal CA1 compared only with the sham group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ex).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eExtent of brain edema\u003c/h2\u003e \u003cp\u003eBrain water content was measured to assess the extent of brain edema at 24 hours after induction of SAH. Brain water content increased with greater ICP elevation, according to the maximum ICP. The moderate ICP group showed significant increase in brain water content compared to the sham, mild ICP, and severe ICP groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe present study used the rat perforation SAH model to evaluate the SAH grade, mortality rate, neurological score, neuronal damage, and brain edema in groups classified according to the maximum ICP. In the moderate ICP group (maximum ICP 50\u0026ndash;149 mmHg), the mortality rate was 37.1%, and prominent oxidative damage and apoptotic cells were observed in the parietal cortex and hippocampal CA1 in the brain of surviving rats.\u003c/p\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eDeath caused by SAH\u003c/h2\u003e \u003cp\u003eThe global mortality rate of SAH ranges from 32% to 67%, and approximately 20% of patients die before arriving at the hospital [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Sudden death may be caused by acute cardiac failure, arrhythmia, or global brain ischemia and edema as a result of sudden increase in ICP and decrease in CPP and cerebral blood flow [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The present study found the mortality rate at 24 hours after SAH induction was 38.8% (33/85) in the SAH group. Fourteen of the 33 animals died very soon (within 1 hour) after perforation, and 12 of these 14 animals were classified in the severe ICP group. For comparison with the mortality rate of SAH in humans, the mild ICP group may correspond to World Federation of Neurosurgical Societies (WFNS) grade II or III, whereas the moderate ICP group may correspond to WFNS grade IV [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eNeuronal damage during the acute phase of SAH\u003c/h2\u003e \u003cp\u003eEBI is a general term that refers to the global brain damage which occurs from 24 to 72 hours after SAH [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Recent clinical and basic investigations have demonstrated the importance of EBI in determining the outcome after SAH. The pathogenesis of EBI is multifactorial and includes complex pathways which lead to neuronal cell death. Rapid increase in ICP and decrease in CPP are perhaps the most immediate and important events in the occurrence of EBI, and are followed by global perfusion deficits. Physiological compensatory mechanisms may prevent sudden death, but the ICP still remains higher than normal [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Global brain ischemia occurring in the initial phase after SAH causes energy failures in the neurons and glia, and initiates the cascade which leads to cytotoxic edema. This ischemic status also results in apoptosis, and initiates the cascade that disrupts the blood-brain barrier, which leads to vasogenic edema. The present histological study demonstrated diffusely distributed neuronal damage and apoptosis in the cortex and hippocampus, similar to previous findings [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Furthermore, the damage level was greater in the groups with higher ICP, which supports the pathophysiological explanation of transient global ischemia occurring immediately after SAH.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eOxidative stress and EBI\u003c/h2\u003e \u003cp\u003eOxidative stress is well known to be important in EBI [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Excess production of reactive oxygen species exceeding the capacity of the neutralization systems of antioxidants in the brain following SAH results in the release of strong oxidizing agents. Free radicals directly damage the neurovascular complex and neurons, leading to neuronal apoptosis, endothelial injury, and blood-brain barrier disruption [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The present study demonstrated high levels of oxidative damage in the cerebral cortex and hippocampus, which was more significant in the groups with higher ICP. Recently, basic research has shown that antioxidant therapy against EBI, based on agents such as hydrogen or edaravone, is effective, but clinical studies found that the effect was poor or limited [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The present study indicates that oxidative stress is significantly stronger in severe cases, so the ameliorative effect may be limited to cases of severe SAH.\u003c/p\u003e \u003cp\u003eThe present study demonstrated that greater increase in ICP in the hyperacute phase of SAH was correlated with worse outcome and more severe neuronal damage and apoptosis in the brain cortex and hippocampus. One of the problems with the endovascular perforation model is the instability of the pathophysiological parameters after induction of SAH. Therefore, classification of the animals based on the severity of brain injury is important to compare the effects and results more accurately. Maximum ICP was correlated with the extent of subarachnoid blood clots, neurological function, survival rate, and neuronal damage, so measurement of the ICP can estimate the severity of SAH before sacrificing the animal. Our present findings indicate the use of animals with maximum ICP of 50\u0026ndash;149 mmHg to study the pathophysiology and therapeutic effects on EBI after experimental SAH. In addition, real time information about the ICP confirms reliable perforation of the vessel wall, and can be helpful to avoid multiple perforations, or excess penetration of the monofilament suture, which will cause extra damage to the brain.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe present study demonstrates the importance of monitoring ICP during the induction of SAH and observation period of endovascular perforation models. Monitoring the ICP can confirm the induction of SAH and classify individual cases into severity grade. Animals with maximum ICP of 50\u0026ndash;149 mmHg may be the most suitable for the experimental study of SAH.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCA1: cornu ammonis 1, CCA: common carotid artery, CI: confidence interval, CPP: cerebral perfusion pressure EBI: early brain injury, ECA: external carotid artery, ICA: internal carotid artery, ICP: intracranial pressure, MABP: mean arterial blood pressure, 8-OHdG: 8-hydroxy-2-deoxyguanosine, SAH: subarachnoid hemorrhage, TUNEL: terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling, WFNS: World Federation of Neurosurgical Societies\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis study was performed in line with the approval of the Institutional Animal Ethics Committee, National Defense Medical College (approval no-14006).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthor contributions to the study and manuscript preparation include the following. Conception and design: K.M.Acquisition of data: K.F., S.T.Drafting the article: K.F., S.T.Preparing Tables: K.F.Preparing Figures: K.F., S.T., T.T.Statistical Analyses: S.T., T.T.Critically revising the article: A.T., T.T., K.W.Approved the final version of the manuscript on behalf of all authors: T.T., K.W.Study supervision: K.M.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request, in accordance with institutional guidelines.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAladag MA, Turkoz Y, Sahna E, Parlakpinar H, Gul M (2003) The attenuation of vasospasm by using a SOD mimetic after experimental subarachnoidal haemorrhage in rats. 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Cell Mol Neurobiol 35:147\u0026ndash;157\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"acta-neurochirurgica","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"anch","sideBox":"Learn more about [Acta Neurochirurgica](http://link.springer.com/journal/701)","snPcode":"701","submissionUrl":"https://submission.springernature.com/new-submission/701/3","title":"Acta Neurochirurgica","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Subarachnoid hemorrhage, Rat, Monofilament perforation, Intracranial pressure","lastPublishedDoi":"10.21203/rs.3.rs-9175606/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9175606/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eTo investigate the correlation between intracranial pressure (ICP) and the outcomes in rat subarachnoid hemorrhage (SAH) model and determine whether maximum ICP can predict severity of SAH.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eSprague-Dawley rats underwent the monofilament puncture procedure to induce SAH, and were divided into 4 groups according to the maximum ICP for survival prediction: sham group, mild ICP group (ICP\u0026thinsp;\u0026lt;\u0026thinsp;50 mmHg), moderate ICP group (ICP 50\u0026ndash;149 mmHg), and severe ICP group (ICP\u0026thinsp;\u0026ge;\u0026thinsp;150 mmHg).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eMaximum ICP showed strong correlations with the neurological score, SAH grade at 24 hours after induction, and mortality. Histological study demonstrated that greater increase in maximum ICP was associated with worse outcome and more severe neuronal damage, apoptosis, and oxidative stress in the brain cortex and hippocampus at 24 hours after induction.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThe present study demonstrates that monitoring the ICP can confirm the induction of SAH and classify individual cases into severity grade. Animals with maximum ICP of 50\u0026ndash;149 mmHg may be the most suitable for the experimental study of SAH.\u003c/p\u003e","manuscriptTitle":"Intracranial pressure changes and outcomes in the early phase of experimental subarachnoid hemorrhage: severity of subarachnoid hemorrhage and maximum intracranial pressure","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-26 16:46:00","doi":"10.21203/rs.3.rs-9175606/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-12T14:53:46+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-27T11:02:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"213633584516821475189437987839677619874","date":"2026-04-07T07:19:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"16496067090226332377252096122692456034","date":"2026-04-06T21:31:42+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-24T17:25:10+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-23T07:49:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-23T07:48:34+00:00","index":"","fulltext":""},{"type":"submitted","content":"Acta Neurochirurgica","date":"2026-03-20T06:35:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"acta-neurochirurgica","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"anch","sideBox":"Learn more about [Acta Neurochirurgica](http://link.springer.com/journal/701)","snPcode":"701","submissionUrl":"https://submission.springernature.com/new-submission/701/3","title":"Acta Neurochirurgica","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"308272fc-2dd6-4db9-a18b-6c3c4eb56466","owner":[],"postedDate":"March 26th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-12T14:53:46+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-19T07:08:50+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-26 16:46:00","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9175606","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9175606","identity":"rs-9175606","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}