Management of intracranial hypertension

A teaspoon of sugar and a pinch of salt: Reviewing hyperosmolar therapy

ABSTRACT

The traditional hyperosmolar agents used to treat patients with elevated intracranial pressure are mannitol and hypertonic sodium chloride solution. This article focuses on some of the pros and cons of these treatments for managing cerebral edema.

Modelling glioma progression, mass effect and intracranial pressure in patient anatomy

Increased intracranial pressure is the source of most critical symptoms in patients with glioma, and often the main cause of death. Clinical interventions could benefit from non-invasive estimates of the pressure distribution in the patient's parenchyma provided by computational models. However, existing glioma models do not simulate the pressure distribution and they rely on a large number of model parameters, which complicates their calibration from available patient data. Here we present a novel model for glioma growth, pressure distribution and corresponding brain deformation. The distinct feature of our approach is that the pressure is directly derived from tumour dynamics and patient-specific anatomy, providing non-invasive insights into the patient's state. The model predictions allow estimation of critical conditions such as intracranial hypertension, brain midline shift or neurological and cognitive impairments. A diffuse-domain formalism is employed to allow for efficient numerical implementation of the model in the patient-specific brain anatomy. The model is tested on synthetic and clinical cases. To facilitate clinical deployment, a high-performance computing implementation of the model has been publicly released.

Pentobarbital Coma Use in a Pregnant Patient With Refractory Intracranial Hypertension: A Case Report

OBJECTIVE

Intracranial hypertension is a life-threatening condition that requires emergent diagnosis and management. Although pentobarbital coma for refractory intracranial hypertension has been studied in the general population, this study is the first reported case of pentobarbital coma use in a pregnant patient.

METHODS

We performed a retrospective chart review of a pregnant patient with refractory intracranial hypertension and reviewed the current literature on the role of pentobarbital coma.

RESULTS

We present the case of a 35-year-old woman at 26 weeks of gestation who developed refractory intracranial hypertension secondary to rupture of a dural arteriovenous fistula. The patient was taken to surgery for decompressive hemicraniectomy, clot evacuation, and dural arteriovenous fistula resection. Subsequently, the patient was treated with pentobarbital coma for 5 days and achieved adequate control of her intracranial pressures. The patient and fetus were closely monitored by the obstetrics team with no apparent harm to fetal well-being during her hospital stay. The patient underwent planned cesarean delivery at term, and both the mother and newborn were discharged in stable condition with no known pentobarbital-related complications.

CONCLUSIONS

Thus, we present the first case report demonstrating that pentobarbital coma may be a safe and efficacious option for treating pregnant patients with life-threatening refractory intracranial hypertension. We also provide dosing information for pentobarbital administration. Additional studies and reports involving pregnant patients are needed to better understand the impact of pentobarbital on both the mother and fetus. Furthermore, long-term follow-up of both the mother and newborn is critical to identifying any delayed sequelae of neonatal exposure to pentobarbital.

A comparison of Adult and Pediatric Hydrocephalus

Hydrocephalus is a common clinical problem encountered in neurosurgical practice. With greater subspecialisation, pediatric neurosurgery has emerged as a special discipline in several countries. However, in the developing world, which inhabits a large pediatric population, a limited number of neurosurgeons manage all types of hydrocephalus across all ages. There are some essential differences in pediatric and adult hydrocephalus. The spectrum of hydrocephalus of dysgenetic origin in a neonate and that of normal pressure hydrocephalus of the old age has a completely different strategy of management. Endoscopic third ventriculostomy outcomes are known to be closely associated with age at presentation and surgery. Efficacy of alternative pathways of CSF absorption also differs according to age. Managing this disease in various age groups is challenging because of these differences in etiopathology, tempo of the disease, modalities of investigations and various treatment protocols as well as prognosis.

Signaling Mechanisms and Pharmacological Modulators Governing Diverse Aquaporin Functions in Human Health and Disease

The aquaporins (AQPs) are a family of small integral membrane proteins that facilitate the bidirectional transport of water across biological membranes in response to osmotic pressure gradients as well as enable the transmembrane diffusion of small neutral solutes (such as urea, glycerol, and hydrogen peroxide) and ions. AQPs are expressed throughout the human body. Here, we review their key roles in fluid homeostasis, glandular secretions, signal transduction and sensation, barrier function, immunity and inflammation, cell migration, and angiogenesis. Evidence from a wide variety of studies now supports a view of the functions of AQPs being much more complex than simply mediating the passive flow of water across biological membranes. The discovery and development of small-molecule AQP inhibitors for research use and therapeutic development will lead to new insights into the basic biology of and novel treatments for the wide range of AQP-associated disorders.

Optic Nerve Sheath Diameter Detects Intracranial Hypertension in Acute Malignant Middle Cerebral Artery Infarction

OBJECTIVES

To evaluate optic nerve sheath diameter in the acute phase of patients with malignant ischemic middle cerebral artery stroke submitted or not to decompressive craniectomy surgery.

MATERIALS AND METHODS

Forty patients participated in the study and were evaluated bilaterally by ultrasound on admission and at 24h, 48h and 72 h after admission. Optic nerve sheath diameter values were correlated with tomographic and/or clinical criteria compatible with severe intracranial hypertension.

RESULTS

A Receiver Operating Characteristic curve was drawn for each eye, determining a cut-off value for severe intracranial hypertension in the right eye of 5.4 mm (sensitivity: 62%; specificity: 100%; AUC: 0.82) and in the left eye 5.4 mm (sensitivity: 76%; specificity: 84%; AUC: 0.77). In patients undergoing craniectomy, there was a decrease in the mean value of 1.04mm in the right eye (pre: 5.84 ± 0.47 mm; post: 4.80 ± 0.84 mm; p = 0.001), while in the left, it decreased around 0.86mm (pre: 5.59 ± 0.69 mm; post: 4.73 ± 0.74 mm; p = 0.003). Patients with fatal outcome showed a persistent high mean ocular nerve sheath diameter.

CONCLUSIONS

Monitoring optic nerve sheath by ultrasound can be considered a reliable method for identifying severe intracranial hypertension in patients with large vessel occlusion, as well as for monitoring patients undergoing craniectomy. Additional studies will be necessary to include this parameter in craniectomy indication algorithms in the future.

Hypertonic Saline Compared to Mannitol for the Management of Elevated Intracranial Pressure in Traumatic Brain Injury: A Meta-Analysis

Background: We performed a meta-analysis to evaluate the effect of hypertonic saline compared to mannitol for the management of elevated intracranial pressure in traumatic brain injury.

Methods: A systematic literature search up to July 2021 was performed and 17 studies included 1,392 subjects with traumatic brain injury at the start of the study; 708 of them were administered hypertonic saline and 684 were given mannitol. They were reporting relationships between the effects of hypertonic saline compared to mannitol for the management of elevated intracranial pressure in traumatic brain injury. We calculated the odds ratio (OR) and mean difference (MD) with 95% confidence intervals (CIs) to assess the effect of hypertonic saline compared to mannitol for the management of elevated intracranial pressure in traumatic brain injury using the dichotomous or continuous method with a random or fixed-effect model.

Results: Hypertonic saline had significantly lower treatment failure (OR, 0.38; 95% CI, 0.15–0.98, p = 0.04), lower intracranial pressure 30–60 mins after infusion termination (MD, −1.12; 95% CI, −2.11 to −0.12, p = 0.03), and higher cerebral perfusion pressure 30–60 mins after infusion termination (MD, 5.25; 95% CI, 3.59–6.91, p < 0.001) compared to mannitol in subjects with traumatic brain injury.

However, hypertonic saline had no significant effect on favorable outcome (OR, 1.61; 95% CI, 1.01–2.58, p = 0.05), mortality (OR, 0.59; 95% CI, 0.34–1.02, p = 0.06), intracranial pressure 90–120 mins after infusion termination (MD, −0.90; 95% CI, −3.21–1.41, p = 0.45), cerebral perfusion pressure 90–120 mins after infusion termination (MD, 4.28; 95% CI, −0.16–8.72, p = 0.06), and duration of elevated intracranial pressure per day (MD, 2.20; 95% CI, −5.44–1.05, p = 0.18) compared to mannitol in subjects with traumatic brain injury.

Conclusions: Hypertonic saline had significantly lower treatment failure, lower intracranial pressure 30–60 mins after infusion termination, and higher cerebral perfusion pressure 30–60 mins after infusion termination compared to mannitol in subjects with traumatic brain injury. However, hypertonic saline had no significant effect on the favorable outcome, mortality, intracranial pressure 90–120 mins after infusion termination, cerebral perfusion pressure 90–120 mins after infusion termination, and duration of elevated intracranial pressure per day compared to mannitol in subjects with traumatic brain injury. Further studies are required to validate these findings.

Optimal Mean Arterial Pressure for Favorable Neurological Outcomes in Survivors after Extracorporeal Cardiopulmonary Resuscitation

We evaluated the optimal mean arterial pressure (MAP) for favorable neurological outcomes in patients who underwent extracorporeal cardiopulmonary resuscitation (ECPR). Adult patients who underwent ECPR were included. The average MAP was obtained during 6, 12, 24, 48, 72, and 96 h after cardiac arrest, respectively. Primary outcome was neurological status upon discharge, as assessed by the Cerebral Performance Categories (CPC) scale (range from 1 to 5). Overall, patients with favorable neurological outcomes (CPC 1 or 2) tended to have a higher average MAP than those with poor neurological outcomes. Six models were established based on ensemble algorithms for machine learning, multiple logistic regression and observation times. Patients with average MAP around 75 mmHg had the least probability of poor neurologic outcomes in all the models. However, those with average MAPs below 60 mmHg had a high probability of poor neurological outcomes. In addition, based on an increase in the average MAP, the risk of poor neurological outcomes tended to increase in patients with an average MAP above 75 mmHg. In this study, average MAPs were associated with neurological outcomes in patients who underwent ECPR. Especially, maintaining the survivor’s MAP at about 75 mmHg may be important for neurological recovery after ECPR.

Machine Learning-Based Continuous Intracranial Pressure Prediction for Traumatic Injury Patients

Structured Abstract—Objective: Abnormal elevation of intracranial pressure (ICP) can cause dangerous or even fatal outcomes. The early detection of high intracranial pressure events can be crucial in saving lives in an intensive care unit (ICU). Despite many applications of machine learning (ML) techniques related to clinical diagnosis, ML applications for continuous ICP detection or short-term predictions have been rarely reported. This study proposes an efficient method of applying an artificial recurrent neural network on the early prediction of ICP evaluation continuously for TBI patients. Methods: After ICP data preprocessing, the learning model is generated for thirteen patients to continuously predict the ICP signal occurrence and classify events for the upcoming 10 minutes by inputting the previous 20-minutes of the ICP signal. Results: As the overall model performance, the average accuracy is 94.62%, the average sensitivity is 74.91%, the average specificity is 94.83%, and the average root mean square error is approximately 2.18 mmHg. Conclusion: This research addresses a significant clinical problem with the management of traumatic brain injury patients. The machine learning model data enables early prediction of ICP continuously in a real-time fashion, which is crucial for appropriate clinical interventions. The results show that our machine learning-based model has high adaptive performance, accuracy, and efficiency.

Association of Pre-Hospital Helicopter Transport with Reduced Mortality in Traumatic Brain Injury in Japan: A Nationwide Retrospective Cohort Study

Patients with traumatic brain injury (TBI) are severely injured patients who require timely, efficient, and specialized care. The effectiveness of helicopter emergency medical services (HEMS) for patients with TBI remains unclear. This study aimed to compare the mortality of patients with TBI transported by HEMS and ground ambulance using propensity score-matching analysis, and to analyze the effects of HEMS in various subpopulations. We conducted a retrospective analysis of the Japan Trauma Data Bank. The study period was from January 2004 to December 2018. The participants were divided into two groups: the helicopter group (patients transported by HEMS) and ground group (patients transported by ground ambulance). The principal outcome was death at hospital discharge. In total, 58,532 patients were eligible for analysis (ground group, n = 54,820 [93.7%]; helicopter group, n = 3712 [6.3%]). Helicopter transport decreased patient mortality at hospital discharge (adjusted odds ratio [OR], 0.83; 95% confidence interval [CI], 0.74-0.92). In propensity score-matched patients, the proportion of deaths at hospital discharge was lower in the helicopter (18.76%) than in the ground (21.21%) group (crude OR, 0.86; 95% CI, 0.77-0.96). The mortality rate in the helicopter group was significantly reduced in many subpopulations, especially in cases of severe TBI with a decreased level of consciousness or higher Injury Severity Score (ISS; Japan Coma Scale score 2 [adjusted OR, 0.60; 95% CI, 0.45-0.80] and ISS ≥50 [adjusted OR, 0.69; 95% CI, 0.48-0.99]). Although the study design was non-randomized, our findings in patients with TBI showed that HEMS conferred a mortality benefit over ground ambulance.

Changes in Blood Pressure and Heart Rate during Decompressive Craniectomy

Objective

Rapid increase in intracranial pressure (ICP) can result in hypertension, bradycardia and apnea, referred to as the Cushing phenomenon. During decompressive craniectomy (DC), rapid ICP decreases can cause changes in mean atrial blood pressure (mABP) and heart rate (HR), which may be an indicator of intact autoregulation and vasomotor reflex.

Methods

A total of 82 patients who underwent DC due to traumatic brain injury (42 cases), hypertensive intracerebral hematoma (19 cases), or major infarction (21 cases) were included in this prospective study. Simultaneous ICP, mABP, and HR changes were monitored in one minute intervals during, prior to and 5–10 minutes following the DC.

Results

After DC, the ICP decreased from 38.1±16.3 mmHg to 9.5±14.2 mmHg (p<0.001) and the mABP decreased from 86.4±14.5 mmHg to 72.5±11.4 mmHg (p<0.001). Conversly, overall HR was no significantly changed in HR, which was 100.1±19.7 rate/min prior to DC and 99.7±18.2 rate/min (p=0.848) after DC. Notably when the HR increased after DC, it correlated with a favorable outcome (p<0.001), however mortality was increased (p=0.032) when the HR decreased or remained unchanged.

Conclusion

In this study, ICP was decreased in all patients after DC. Changes in HR were an indicator of preserved autoregulation and vasomotor reflex. The clinical outcome was improved in patients with increased HR after DC.

Peak ependymal cell stretch overlaps with the onset locations of periventricular white matter lesions

Deep and periventricular white matter hyperintensities (dWMH/pvWMH) are bright appearing white matter tissue lesions in T2-weighted fluid attenuated inversion recovery magnetic resonance images and are frequent observations in the aging human brain. While early stages of these white matter lesions are only weakly associated with cognitive impairment, their progressive growth is a strong indicator for long-term functional decline. DWMHs are typically associated with vascular degeneration in diffuse white matter locations; for pvWMHs, however, no unifying theory exists to explain their consistent onset around the horns of the lateral ventricles. We use patient imaging data to create anatomically accurate finite element models of the lateral ventricles, white and gray matter, and cerebrospinal fluid, as well as to reconstruct their WMH volumes. We simulated the mechanical loading of the ependymal cells forming the primary brain-fluid interface, the ventricular wall, and its surrounding tissues at peak ventricular pressure during the hemodynamic cycle. We observe that both the maximum principal tissue strain and the largest ependymal cell stretch consistently localize in the anterior and posterior horns. Our simulations show that ependymal cells experience a loading state that causes the ventricular wall to be stretched thin. Moreover, we show that maximum wall loading coincides with the pvWMH locations observed in our patient scans. These results warrant further analysis of white matter pathology in the periventricular zone that includes a mechanics-driven deterioration model for the ventricular wall.

Non-Invasive Measurement of Intracranial Pressure Through Application of Venous Ophthalmodynamometry

Non-invasive intracranial pressure (ICP) monitoring is possible using venous ophthalmodynamometry to observe a pulsation in retinal blood vessels when intraocular pressure (IOP) exceeds ICP. Here, we identify features in the eye - optic disc and retinal blood vessel locations - and identify pulsation in large retinal blood vessels. The relationship between force and the magnitude of pulsation is used to estimate ICP when force is applied to the eye to gradually increase IOP over time. This approach yields 77% accuracy in automatically observing vessel pulsation.Clinical Relevance - Non-invasive ICP monitoring is desirable to improve patient outcome by reducing potential trauma and complications associated with invasive assessment with intracranial sensors or lumbar puncture.

Fish Gelatin-Based Absorbable Dural Sealant with Anti-inflammatory Properties

Cerebrospinal fluid (CSF) leakage from the dura mater during craniotomy is a common complication, which is associated with infection, meningitis, pneumocephalus, and delayed wound healing. In the present study, we developed an absorbable fish gelatin-based anti-inflammatory sealant for dura mater sealing to prevent CSF leakage. Gelatin derived from Alaska pollock (ApGltn) was modified with α-linolenic acid (ALA), an omega-3 fatty acid that exhibits anti-inflammatory properties, and cross-linked with a poly(ethylene glycol)-based cross-linker to develop ALA-ApGltn sealant (ALA-Seal). ALA-Seal demonstrated a higher storage modulus and tangent delta (tan δ) compared with those of the original ApGltn sealant (Org-Seal). The swelling ratio of ALA-Seal was markedly lower than that of DuraSeal, a commercially available dural sealant. Ex vivo burst strength measurements using porcine dura mater indicated that there was no significant difference between DuraSeal and ALA-Seal, despite ALA-Seal having an order of magnitude lower storage modulus. The anti-inflammatory properties of ALA-Seal, evaluated using brain microglial cells, were considerably higher than those of DuraSeal and Org-Seal, with a minimal adverse effect on cell viability. Therefore, compared to DuraSeal, ALA-Seal is a potential dural sealant with a lower swelling ratio, similar burst strength, and higher anti-inflammatory properties, which may prevent CSF leakage.

Characteristics and Outcomes of the Idiopathic Intracranial Hypertension Treatment in Intrinsic and Extrinsic Stenosis: A Single-Center Experience in China

INTRODUCTION

This study aimed to explore the precipitating factors and evaluate the impact of different stenosis types on treatment outcomes in patients with idiopathic intracranial hypertension (IIH) and venous sinus stenosis (VSS).

METHODS

We recruited patients with IIH who presented with VSS, either intrinsic or extrinsic. We observed the clinical and laboratory findings, and we then compared the outcomes of stenting and medical treatment in different stenosis types.

RESULTS

Among 145 patients with IIH and VSS, 59 were of the intrinsic type and 86 were of the extrinsic type. Patients in the intrinsic group were older (42 vs. 34 years old, P < 0.001) and presented with higher pre-op gradient pressure (15 mmHg vs. 12 mmHg, P < 0.001). There was no significant difference between groups regarding other precipitating factors (P > 0.05). Stenting was significantly associated with complete resolution of the headache and impaired vision both in intrinsic (adjusted OR 0.017, 95% CI 0.001-0.35, P = 0.011; adjusted OR 0.056, 95% CI 0.004-0.697, P = 0.025, respectively) and extrinsic types of stenosis (adjusted OR 0.072, 95% CI 0.015-0.343, P = 0.001; adjusted OR 0.241, 95% CI 0.062-0.931, P = 0.039, respectively). Meanwhile, stenting was significantly associated with improvement of the papilledema in extrinsic-type stenosis compared with medical treatment (adjusted OR 0.017, 95% CI 0.002-0.135, P < 0.001).

CONCLUSION

Stenting may provide substantial clinical improvement in patients with IIH regardless of intrinsic or extrinsic stenosis type in our patient population, as noted in other series.

TRIAL REGISTRATION

Clinical trial registration number ChiCTR-ONN-17010421.

Nonepileptic, Stereotypical, and Intermittent Symptoms After Subdural Hematoma Evacuation

Transient neurological deficits can occur in the setting of subdural hemorrhages with subsequent unremarkable electrodiagnostic and radiological evaluation. This scenario is rare and can be difficult for physicians to interpret. These transient neurological deficits are thought to result from relative ischemia, secondary to a lesser-known concept known as cortical spreading depolarization. These transient neurological deficits are thought to result from relative ischemia, secondary to a lesser-known concept known as cortical spreading depolarization, which may present clinically as nonepileptic, stereotypical, and intermittent symptoms (NESIS). In these instances, patients are often misdiagnosed as epileptics and committed to long-term antiseizure drugs. We present a 51-year-old patient developing acute global aphasia following the evacuation of a subdural hematoma, with no significant findings on laboratory, microbiological, electrodiagnostic, or radiological evaluation. The patient experienced spontaneous improvement and returned to baseline in the subsequent weeks. Increased awareness of NESIS as a cortical spreading depolarization phenomenon can improve patient care and prevent both unnecessary, extended medical evaluations and therapeutic trials.

Development of an In Vitro Hemorrhagic Hydrocephalus Model for Functional Evaluation of Magnetic Microactuators Against Shunt Obstructions

OBJECTIVE

Occlusion of ventriculoperitoneal shunts placed after intraventricular hemorrhage occurs frequently. The objective of this study was to develop a hemorrhagic hydrocephalus model to assess the ability of an oscillating microactuator within the ventricular catheter (VC) to prevent shunt obstruction.

METHODS

An in vitro hydrocephalus model with extreme risk of shunt obstruction was created. Phosphate-buffered saline, blood, and thrombin were driven through ventriculoperitoneal shunts for 8 hours. Five VCs were fitted with a microactuator and compared with 5 control VCs. The microactuator was actuated by an external magnetic field for 30 minutes. Pressure within the imitation lateral ventricle was measured.

RESULTS

In the 5 control shunts, 6 obstructions developed (3 VC, 3 valve-distal catheter) compared with 1 obstruction (VC) in the 5 microactuator shunts. In the control and microactuator groups, the median volume exiting the shunts in 8 hours was 30 mL versus 256 mL. Median time to reach an intraventricular pressure of 40 mm Hg (13.8 minutes vs. >8 hours), median total time >40 mm Hg (6.2 hours vs. 0.0 hours), and median maximum pressure (192 mm Hg vs. 36 mm Hg) were significantly improved in the microactuator group (P < 0.01).

CONCLUSIONS

In addition to protecting the VC, the microactuator appeared to prevent hematoma obstructing the valve or distal catheter, resulting in a much longer duration of low intraventricular pressures. A microactuator activated by placing the patient's head in an external magnetic field could reduce shunt obstructions in hemorrhagic hydrocephalus.

Nanodelivery of traditional Chinese Gingko Biloba extract EGb-761 and bilobalide BN-52021 induces superior neuroprotective effects on pathophysiology of heat stroke

Military personnel often exposed to high summer heat are vulnerable to heat stroke (HS) resulting in abnormal brain function and mental anomalies. There are reasons to believe that leakage of the blood-brain barrier (BBB) due to hyperthermia and development of brain edema could result in brain pathology. Thus, exploration of suitable therapeutic strategies is needed to induce neuroprotection in HS. Extracts of Gingko Biloba (EGb-761) is traditionally used in a variety of mental disorders in Chinese traditional medicine since ages. In this chapter, effects of TiO2 nanowired EGb-761 and BN-52021 delivery to treat brain pathologies in HS is discussed based on our own investigations. We observed that TiO2 nanowired delivery of EGb-761 or TiO2 BN-52021 is able to attenuate more that 80% reduction in the brain pathology in HS as compared to conventional drug delivery. The functional outcome after HS is also significantly improved by nanowired delivery of EGb-761 and BN-52021. These observations are the first to suggest that nanowired delivery of EGb-761 and BN-52021 has superior therapeutic effects in HS not reported earlier. The clinical significance in relation to the military medicine is discussed.

Identification of lymphatic endothelium in cranial arachnoid granulation-like dural gap

The dynamics of cerebrospinal fluid (CSF) are essential for maintaining homeostasis in the central nervous system. Despite insufficiently detailed descriptions of their structural and molecular properties for a century, cranial arachnoid granulations (CAGs) on meninges have been thought to participate in draining CSF from the subarachnoid space into the dural sinuses. However, recent studies have demonstrated the existence of other types of CSF drainage systems, such as lymphatic vessels adjacent to dural sinus and paravascular space in the brain so-called glymphatic system. Therefore, the role of CAGs in CSF drainage has become dubious. To better understand CAG function, we analyzed the ultrastructure and molecular identity of CAG-like structure on meninges adjacent to the superior sagittal sinus of pigs. Transmission electron microscopy analysis revealed that this structure has a reticular conglomerate consisting of endothelial cells that resembles lymphatic linings. Furthermore, immunohistochemistry and immunoelectron microscopy showed that they express molecules specific to lymphatic endothelial cell. We coined a name 'CAG-like dural gap (CAG-LDG)' to this structure and discussed the physiological relevance in terms of CSF drainage.

Tier-three therapies for refractory intracranial hypertension in adult head trauma

Refractory intracranial hypertension after traumatic brain injury (TBI) is defined as recurrent increase of intracranial pressure (ICP) above 20-22 mmHg for sustained period of time (10-15 min), despite conventional therapies, such as osmotic therapy, cerebral spinal fluid drainage and mild hyperventilation. As such, more aggressive treatments should be taken into consideration. In particular, therapeutic hypothermia, barbiturates administration and decompressive craniectomy are considered as tier-three or "salvage" interventions, as they have shown to be able to control refractory hypertension, but are also associated with an increased risk of significant side effects. The aim of this review is therefore to describe the evidence supporting the use of these tier-three therapies in the management of refractory intracranial hypertension in TBI patients.

A bioimpedance-based monitor for real-time detection and identification of secondary brain injury

Secondary brain injury impacts patient prognosis and can lead to long-term morbidity and mortality in cases of trauma. Continuous monitoring of secondary injury in acute clinical settings is primarily limited to intracranial pressure (ICP); however, ICP is unable to identify essential underlying etiologies of injury needed to guide treatment (e.g. immediate surgical intervention vs medical management). Here we show that a novel intracranial bioimpedance monitor (BIM) can detect onset of secondary injury, differentiate focal (e.g. hemorrhage) from global (e.g. edema) events, identify underlying etiology and provide localization of an intracranial mass effect. We found in an in vivo porcine model that the BIM detected changes in intracranial volume down to 0.38 mL, differentiated high impedance (e.g. ischemic) from low impedance (e.g. hemorrhagic) injuries (p < 0.001), separated focal from global events (p < 0.001) and provided coarse 'imaging' through localization of the mass effect. This work presents for the first time the full design, development, characterization and successful implementation of an intracranial bioimpedance monitor. This BIM technology could be further translated to clinical pathologies including but not limited to traumatic brain injury, intracerebral hemorrhage, stroke, hydrocephalus and post-surgical monitoring.

Effects of Venoconstrictive Thigh Cuffs on Dry Immersion-Induced Ophthalmological Changes

Neuro-ophthalmological changes named spaceflight associated neuro-ocular syndrome (SANS) reported after spaceflights are important medical issues. Dry immersion (DI), an analog to microgravity, rapidly induces a centralization of body fluids, immobilization, and hypokinesia similar to that observed during spaceflight. The main objectives of the present study were 2-fold: (1) to assess the neuro-ophthalmological impact during 5 days of DI and (2) to determine the effects of venoconstrictive thigh cuffs (VTC), used as a countermeasure to limit headward fluid shift, on DI-induced ophthalmological adaptations. Eighteen healthy male subjects underwent 5 days of DI with or without VTC countermeasures. The subjects were randomly assigned into two groups of 9: a control and cuffs group. Retinal and optic nerve thickness were assessed with spectral-domain optical coherence tomography (OCT). Optic nerve sheath diameter (ONSD) was measured by ocular ultrasonography and used to assess indirect changes in intracranial pressure (ICP). Intraocular pressure (IOP) was assessed by applanation tonometry. A higher thickness of the retinal nerve fiber layer (RNFL) in the temporal quadrant was observed after DI. ONSD increased significantly during DI and remained higher during the recovery phase. IOP did not significantly change during and after DI. VTC tended to limit the ONSD enlargement but not the higher thickness of an RNFL induced by DI. These findings suggest that 5 days of DI induced significant ophthalmological changes. VTC were found to dampen the ONSD enlargement induced by DI.

The effect of xylazine on intracranial pressure in anesthetized and standing horses

OBJECTIVE

To determine the effect of xylazine on intracranial pressure (ICP) in standing compared to isoflurane-anesthetized horses.

DESIGN

Prospective, crossover study design.

SETTING

University Teaching Hospital.

ANIMALS

Six adult horses donated to the University. Horses were determined to be healthy via physical examination, complete blood count, and neurological evaluation.

INTERVENTIONS

Horses were anesthetized, maintained on isoflurane in oxygen in left lateral recumbency, and ventilated to normocapnia. Horses were instrumented for intraparenchymal measurement of ICP, invasive blood pressure, pulse oximetry, and end tidal gas analyzer. Xylazine 1 mg/kg was administered IV and ICP, systolic arterial pressure, mean arterial pressure (MAP), diastolic arterial pressure, and heart rate were recorded and cerebral perfusion pressure (CPP) was calculated for the following 15 minutes. Twenty-four to 36 hours following anesthetic recovery, xylazine 1 mg/kg was administered IV and ICP, heart rate, and Doppler blood pressure (BPdop) on the tail were monitored for 15 minutes.

MEASUREMENTS AND MAIN RESULTS

There was a decrease in ICP following administration of xylazine in anesthetized horses (P < 0.003) but not standing horses (P = 0.227). There was an increase in systolic arterial pressure, MAP, diastolic arterial pressure (P < 0.001), and BPdop (P = 0.001) following administration of xylazine. As a result, CPP increased in anesthetized horses (P < 0.03). There was a negative association between ICP and MAP in anesthetized horses (P = 0.007) but not ICP and BPdop conscious horses (P = 0.379).

CONCLUSIONS

Administration of xylazine to anesthetized horses resulted in an increased CPP due to decreased ICP with concurrent increased MAP. Administration of xylazine to standing horses did not result in a change in ICP. However, with the increase in BPdop found in awake horses, it is likely that CPP would also increase in awake horses following xylazine administration.

Modified Transpterygoid Approach to Sphenoid Meningoencephaloceles: A Shorter Run for a Longer Slide

OBJECTIVES

Cerebrospinal fluid (CSF) leaks and meningoencephaloceles originating in the lateral recess of the sphenoid sinus can be challenging. The traditional transpterygoid approach through the pterygopalatine fossa (PPF) is time consuming and places important structures at risk, which can lead to significant morbidity. We report a multi-institutional experience using a simplified, endoscopic modified transpterygoid approach (MTPA), which spares the PPF contents in the management of lateral sphenoid sinus meningoencephaloceles and CSF leaks.

STUDY DESIGN

Multi-Institutional, Retrospective Case Series.

METHODS

Patients with lateral sphenoid recess CSF leaks and meningoencephaloceles between 2014 and 2020 who underwent the MTPA at two academic medical centers were identified. Repair techniques and outcomes were evaluated.

RESULTS

Thirty-three patients underwent the MTPA for management. Skull base reconstruction was performed using a free mucosal graft (24/33, 72.7%), nasoseptal flap (4/33, 12.1%), bone grafts (3/33, 9.1%), and abdominal fat grafts (2/33, 6.1%). Lumbar drains and perioperative intracranial pressure measurements were routinely employed. Postoperative complications were uncommon and included three patients (9.7%) with temporary V2 anesthesia, one patient (3.2%) with prolonged V2 anesthesia, and one patient (3.2%) with subjective dry eye, all of which resolved at 9 months postoperatively. There were no recurrent CSF leaks resulting in a 100% success rate. Average follow-up was 13 months.

CONCLUSION

The MTPA reduces morbidity and greatly simplifies access to the lateral sphenoid sinus for the management of CSF leaks and meningoencephaloceles, without compromising exposure. This technique avoids the need for extensive PPF dissection and should be considered for the management of benign lesions involving the lateral sphenoid sinus.

LEVEL OF EVIDENCE

IV Laryngoscope, 2021.

Numerical Models of Spinal Cord Trauma: The Effect of Cerebrospinal Fluid Pressure and Epidural Fat on the Results

Spinal cord injury (SCI) is commonly caused by traumatic mechanical damage. Although numerical models can help predict the mechanics of SCI without putting the subjects in danger, previous studies did not focus on alternations in cerebrospinal fluid (CSF) pressure and did not account for the presence of epidural fat. This study aims to numerically compare the mechanical behavior of the human spine when subjected to contusion and burst fracture with varying CSF pressure, either normal or elevated pressure that represents intracranial hypertension. An additional aim is to find out how the presence of the fat in the model affects the SCI calculations. CSF and epidural fat were modeled as smoothed-particle hydrodynamics (SPH) and the soft tissues were modeled as hyperelastic. This approach made it possible to account for CSF pressure alteration and its effect on the cord. Validation models resulted in good correlation with previous numerical and experimental studies. The results were able to capture the fluid dynamics of the CSF while demonstrating a considerable change in the stresses of the spinal cord. The comparison of the CSF pressures demonstrated that SCI in patients with elevated pressure and in regions where insufficient epidural fat exists might lead to higher spinal cord stresses. Yet, in regions with enough fat, the fat can absorb energy and counteract the effect of the elevated pressure. These results indicate important aspects that need to be accounted for in future numerical models of SCI while also demonstrating how the injury might be aggravated by preexisting conditions.

Evaluation of transpalpebral ultrasonographic measurement of optic nerve sheath diameter for indirect assessment of intracranial pressure in anesthetized and standing healthy adult horses

OBJECTIVE

To determine whether an association exists between direct intracranial pressure (ICP) measurement and ultrasonographic measurement of optic nerve sheath diameter (ONSD) in anesthetized and standing horses.

DESIGN

Cross-sectional study performed on a convenience sample of healthy adult horses.

SETTING

University teaching hospital.

ANIMALS

Eight adult horses donated to the University. Enrolled horses were free of abnormalities on physical examination, CBC, neurological evaluation, and ophthalmological examination.

MEASUREMENTS AND MAIN RESULTS

Horses were anesthetized in lateral recumbency for placement of an ICP transducer. Three head positions (neutral, elevated, and lowered) were used to alter ICP. ICP and ONSD in 2 directions (D1 and D2) were recorded at 5 and 10 minutes after position change to elevated and lowered. ICP and ONSD measurements were repeated in standing sedated horses 24-36 hours after recovery from anesthesia. Linear regressions were performed with ICP as the dependent variable and ONSD as the independent variable by head position and times. Linear regressions were also performed for change from neutral under anesthesia, with ONSD as the independent variable and ICP as the dependent variable, by head position and times. Significance was set at P < 0.05. There was a moderate association between ICP and ONSD in horses with head lowered at 5 and 10 minutes (R² values = 63%-78%) and weak association in head elevated at 10 minutes (R² values = 56%-63%). There was a weak association between change from neutral ICP and change from neutral ONSD in the elevated anesthetized position at 10 minutes for summed D1 + D2 (R²  = 33%).

CONCLUSIONS

Consistent associations between direct ICP and ONSD in anesthetized or standing horses were not observed. This inconsistency limits the clinically utility of transpalpebral ultrasonographic ONSD measurement for ICP monitoring in horses.

Neurologic Assessment of the Neurocritical Care Patient

Sedation is a ubiquitous practice in ICUs and NCCUs. It has the benefit of reducing cerebral energy demands, but also precludes an accurate neurologic assessment. Because of this, sedation is intermittently stopped for the purposes of a neurologic assessment, which is termed a neurologic wake-up test (NWT). NWTs are considered to be the gold-standard in continued assessment of brain-injured patients under sedation. NWTs also produce an acute stress response that is accompanied by elevations in blood pressure, respiratory rate, heart rate, and ICP. Utilization of cerebral microdialysis and brain tissue oxygen monitoring in small cohorts of brain-injured patients suggests that this is not mirrored by alterations in cerebral metabolism, and seldom affects oxygenation. The hard contraindications for the NWT are preexisting intracranial hypertension, barbiturate treatment, status epilepticus, and hyperthermia. However, hemodynamic instability, sedative use for primary ICP control, and sedative use for severe agitation or respiratory distress are considered significant safety concerns. Despite ubiquitous recommendation, it is not clear if additional clinically relevant information is gleaned through its use, especially with the contemporaneous utilization of multimodality monitoring. Various monitoring modalities provide unique and pertinent information about neurologic function, however, their role in improving patient outcomes and guiding treatment plans has not been fully elucidated. There is a paucity of information pertaining to the optimal frequency of NWTs, and if it differs based on type of injury. Only one concrete recommendation was found in the literature, exemplifying the uncertainty surrounding its utility. The most common sedative used and recommended is propofol because of its rapid onset, short duration, and reduction of cerebral energy requirements. Dexmedetomidine may be employed to facilitate serial NWTs, and should always be used in the non-intubated patient or if propofol infusion syndrome (PRIS) develops. Midazolam is not recommended due to tissue accumulation and residual sedation confounding a reliable NWT. Thus, NWTs are well-tolerated in selected patients and remain recommended as the gold-standard for continued neuromonitoring. Predicated upon one expert panel, they should be performed at least one time per day. Propofol or dexmedetomidine are the main sedative choices, both enabling a rapid awakening and consistent NWT.

A constriction channel analysis of astrocytoma stiffness and disease progression

Studies have demonstrated that cancer cells tend to have reduced stiffness (Young's modulus) compared to their healthy counterparts. The mechanical properties of primary brain cancer cells, however, have remained largely unstudied. To investigate whether the stiffness of primary brain cancer cells decreases as malignancy increases, we used a microfluidic constriction channel device to deform healthy astrocytes and astrocytoma cells of grade II, III, and IV and measured the entry time, transit time, and elongation. Calculating cell stiffness directly from the experimental measurements is not possible. To overcome this challenge, finite element simulations of the cell entry into the constriction channel were used to train a neural network to calculate the stiffness of the analyzed cells based on their experimentally measured diameter, entry time, and elongation in the channel. Our study provides the first calculation of stiffness for grades II and III astrocytoma and is the first to apply a neural network analysis to determine cell mechanical properties from a constriction channel device. Our results suggest that the stiffness of astrocytoma cells is not well-correlated with the cell grade. Furthermore, while other non-central-nervous-system cell types typically show reduced stiffness of malignant cells, we found that most astrocytoma cell lines had increased stiffness compared to healthy astrocytes, with lower-grade astrocytoma having higher stiffness values than grade IV glioblastoma. Differences in nucleus-to-cytoplasm ratio only partly explain differences in stiffness values. Although our study does have limitations, our results do not show a strong correlation of stiffness with cell grade, suggesting that other factors may play important roles in determining the invasive capability of astrocytoma. Future studies are warranted to further elucidate the mechanical properties of astrocytoma across various pathological grades.

Modelling physiology of haemodynamic adaptation in short-term microgravity exposure and orthostatic stress on Earth

Cardiovascular haemodynamics alters during posture changes and exposure to microgravity. Vascular auto-remodelling observed in subjects living in space environment causes them orthostatic intolerance when they return on Earth. In this study we modelled the human haemodynamics with focus on head and neck exposed to different hydrostatic pressures in supine, upright (head-up tilt), head-down tilt position, and microgravity environment by using a well-developed 1D-0D haemodynamic model. The model consists of two parts that simulates the arterial (1D) and brain-venous (0D) vascular tree. The cardiovascular system is built as a network of hydraulic resistances and capacitances to properly model physiological parameters like total peripheral resistance, and to calculate vascular pressure and the related flow rate at any branch of the tree. The model calculated 30.0 mmHg (30%), 7.1 mmHg (78%), 1.7 mmHg (38%) reduction in mean blood pressure, intracranial pressure and central venous pressure after posture change from supine to upright, respectively. The modelled brain drainage outflow percentage from internal jugular veins is 67% and 26% for supine and upright posture, while for head-down tilt and microgravity is 65% and 72%, respectively. The model confirmed the role of peripheral veins in regional blood redistribution during posture change from supine to upright and microgravity environment as hypothesized in literature. The model is able to reproduce the known haemodynamic effects of hydraulic pressure change and weightlessness. It also provides a virtual laboratory to examine the consequence of a wide range of orthostatic stresses on human haemodynamics.

Lifesaving Decompressive Craniectomy for High Intracranial Pressure Attributed to Deep-Seated Meningioma: Emergency Management

Objects:

As the most common intracranial extra-axial tumor among adults who tend to grow slowly with minimal clinical manifestation, the patients with meningioma could also fall in neurological emergency and even life-threatening status due to high intracranial pressure (ICP). In those circumstances, decompressive craniectomy (DC) without definitive tumor resection might offer an alternative treatment to alleviate acute increasing of ICP. The current report defines criteria for the indications of lifesaving DC for high ICP caused by deep-seated meningioma as an emergency management.

Patients and Methods:

This study collected the candidates from 2012 to 2018 at Dr. Soetomo General Hospital, Surabaya, Indonesia. The sample included all meningioma patients who came to our ER who fulfilled the clinical (life-threatening decrease in Glasgow Coma Scale [GCS]) and radiography (deep-seated meningioma, midline shift in brain computed tomography [CT] >0.5 cm, and diameter of tumor >4 cm or tumor that involves the temporal lobe) criteria for emergency DC as a lifesaving procedure. GCS, midline shift, tumor diameter, and volume based on CT were evaluated before DC. Immediate postoperative GCS, time to tumor resection, and Glasgow Outcome Scale (GOS) were also assessed postoperation.

Results:

The study enrolled 14 patients, with an average preoperative GCS being 9.29 ± 1.38, whereas the mean midline shift was 15.84 ± 7.02 mm. The average of number of tumor's diameter and volume was 5.59 ± 1.44 cm and 66.76 ± 49.44 cc, respectively. Postoperation, the average time interval between DC and definitive tumor resection surgery was 5.07 ± 3.12 days. The average immediate of GCS postoperation was 10.07 ± 2.97, and the average GOS was 3.93 ± 1.27.

Conclusion:

When emergency tumor resection could not be performed due to some limitation, as in developing countries, DC without tumor resection possibly offers lifesaving procedure in order to alleviate acute increasing ICP before the definitive surgical procedure is carried out. DC might also prevent a higher risk of morbidity and postoperative complications caused by peritumoral brain edema.

What is the Role of Hyperosmolar Therapy in Hemispheric Stroke Patients?

The role of hyperosmolar therapy (HT) in large hemispheric ischemic or hemorrhagic strokes remains a controversial issue. Past and current stroke guidelines state that it represents a reasonable therapeutic measure for patients with either neurological deterioration or intracranial pressure (ICP) elevations documented by ICP monitoring. However, the lack of evidence for a clear effect of this therapy on radiological tissue shifts and clinical outcomes produces uncertainty with respect to the appropriateness of its implementation and duration in the context of radiological mass effect without clinical correlates of neurological decline or documented elevated ICP. In addition, limited data suggest a theoretical potential for harm from the prophylactic and protracted use of HT in the setting of large hemispheric lesions. HT exerts effects on parenchymal volume, cerebral blood volume and cerebral perfusion pressure which may ameliorate global ICP elevation and cerebral blood flow; nevertheless, it also holds theoretical potential for aggravating tissue shifts promoted by significant interhemispheric ICP gradients that may arise in the setting of a large unilateral supratentorial mass lesion. The purpose of this article is to review the literature in order to shed light on the effects of HT on brain tissue shifts and clinical outcome in the context of large hemispheric strokes, as well as elucidate when HT should be initiated and when it should be avoided.

Mechanisms of tracer transport in cerebral perivascular spaces

Tracers infused into the brain appear to be transported along channels surrounding cerebral blood vessels. Bulk fluid flow has been hypothesized in paravascular "glymphatic" channels (outer space between the pial membrane and astrocyte endfeet), as well as in the periarterial space (inner space between smooth muscle cells). The plausibility of net flow in these channels due to steady and oscillatory pressures is reviewed, as is that of transport by oscillatory shear-enhanced dispersion in the absence of net flow. Models including 1D branching networks of annular channels and an expanded compartmental model for humans both predict that flow driven by physiologic steady pressure differences is unlikely in both periarterial and paraarterial spaces, whether the spaces are open or filled with porous media. One exception is that a small additional steady pressure difference could drive paraarterial flow if the space is open. The potential that the tracer injection itself could present such a pressure difference is outlined. Oscillatory (peristaltic) wall motion alone has been found to be insufficient to drive significant forward flow. However, a number of hypothesized mechanisms that have yet to be experimentally verified in the brain may create directional flow in combination with wall motion. Shear-augmented dispersion due to oscillatory pressure in channels with a range of porosity has been modeled analytically. Enhancement of axial dispersion is small for periarterial channels. In open paraarterial channels, dispersion enhancement with optimal lateral mixing is large enough that it may explain observed tracer transport without net forward fluid flow.

Hypertonic saline buffered with sodium acetate for intracranial pressure management

BACKGROUND

3 % hypertonic saline (HS) is a hyperosmolar agent often used to treat elevated intracranial pressure (ICP). However, the resultant hyperchloremia is associated with adverse outcomes in certain patient populations. In this study, HS solution buffered with sodium acetate (HSwSA) is used as an alternative to standard 3 % formulations to reduce overall chloride exposure. Our objectives are to establish whether this alternative agent - with reduced chloride content - is similar to standard 3 % HS in maintaining hyperosmolarity and investigate its effects on hyperchloremia.

METHODS

A retrospective chart review was conducted from August 1, 2014 to August 1, 2017 on patients receiving hypertonic therapies for ICP management. Patients were categorized into three groups, those that received: (1) 3 % HS for at least 72 h, (2) HSwSA for at least 72 h, or (3) were switched from 3 % HS within 72 h of initiating therapy to HSwSA for at least 72 h.

RESULTS

The average increase in serum osmolality after 72 h of therapy was 21.1 moSm/kg for those only on 3 % HS and 20.3 mOsm/kg for those only on HSwSA. Serum chloride levels after 24 h decreased on average by 2.5 mEq/L after switching from 3% HS to HSwSA and stayed below baseline, whereas matched patients only receiving 3% HS on average had serum chloride levels increase 4.3 mEq/L after 24 h and continued to rise.

CONCLUSIONS

Hyperchloremia has been associated with decreased renal perfusion, increasing the risk of acute kidney injury and hyperchloremic metabolic acidosis. Compared to standard 3% HS, our findings suggest an alternative hyperosmolar therapy with less chloride maintains similar hyperosmolarity while reducing overall chloride exposure.

Surgical methodology and protocols for preventing implanted cerebral catheters from becoming obstructed during and after neurosurgery

BACKGROUND

Convection Enhanced Delivery (CED) into targeted brain areas has been tested in animal models and clinical trials for the treatment of various neurological diseases.

NEW METHOD

We used a series of techniques, to in effect, maintain positive pressure inside the catheter relative to the outside, that included a hollow stylet, a high volume bolus of solution to clear the line, a low and slow continuous flow rate during implantation, and heat sealing the catheter at the time of implantation.

RESULTS

120 catheters implanted into brain parenchyma of 89 adult female rhesus monkeys across four sets of experiments. After experiencing a high delivery failure rate - non patent catheters - (19 %) because of tissue entrapment and debris and/or blood clots in the catheter tip, we developed modifications, including increasing the bolus infusion volume from 10 to 20 μl such that by the third experiment, the failure rate was 8 % (1 of 12 implants). Increasing the bolus volume to 100 μl and maintaining positive pressure in the catheter during preparation and implantation yielded a failure rate of 0 % (0/12 implants) by the fourth experiment.

COMPARISON WITH EXISTING METHODS

We provide a retrospective analysis to reveal how several different manipulations affect catheter patency and how post-op MRI examination is essential for assessing catheter patency in situ.

CONCLUSIONS

The results of the present study identified that the main cause of the catheter blockages were clots that rendered the catheter non-patent. We resolved this by modifying the surgical procedures that prevented these clots from forming.

Decompressive Craniectomy for Traumatic Brain Injury: In-hospital Mortality-Associated Factors

Objective  Determine predictors of in-hospital mortality in patients with severe traumatic brain injury (TBI) who underwent decompressive craniectomy. Materials and Methods  This retrospective study reviewed consecutive patients who underwent a decompressive craniectomy between March 2017 and March 2020 at our institution, and analyzed clinical characteristics, brain tomographic images, surgical details and morbimortality associated with this procedure. Results  Thirty-three (30 unilateral and 3 bifrontal) decompressive craniectomies were performed, of which 27 patients were male (81.8%). The mean age was 52.18 years, the mean Glasgow coma scale (GCS) score at admission was 9, and 24 patients had anisocoria (72.7%). Falls were the principal cause of the trauma (51.5%), the mean anterior-posterior diameter (APD) of the bone flap in unilateral cases was 106.81 mm (standard deviation [SD] 20.42) and 16 patients (53.3%) underwent a right-sided hemicraniectomy. The temporal bone enlargement was done in 20 cases (66.7%), the mean time of surgery was 2 hours and 27 minutes, the skull flap was preserved in the subcutaneous layer in 29 cases (87.8%), the mean of blood loss was 636.36 mL,and in-hospital mortality was 12%. Univariate analysis found differences between the APD diameter (120.3 mm vs. 85.3 mm; p = 0.003) and the presence of midline shift > 5 mm ( p = 0.033). Conclusion  The size of the skull flap and the presence of midline shift > 5 mm were predictors of mortality. In the absence of intercranial pressure (ICP) monitoring, clinical and radiological criteria are mandatory to perform a decompressive craniectomy.

Emergency Neuropharmacology

Management of acute neurologic disorders in the emergency department is multimodal and may require the use of medications to decrease morbidity and mortality secondary to neurologic injury. Clinicians should form an individualized treatment approach with regard to various patient specific factors. This review article focuses on the pharmacotherapy for common neurologic emergencies that present to the emergency department, including traumatic brain injury, central nervous system infections, status epilepticus, hypertensive emergencies, spinal cord injury, and neurogenic shock.

Preventing neuronal edema increases network excitability after traumatic brain injury

Edema is an important target for clinical intervention after traumatic brain injury (TBI). We used in vivo cellular resolution imaging and electrophysiological recording to examine the ionic mechanisms underlying neuronal edema and their effects on neuronal and network excitability after controlled cortical impact (CCI) in mice. Unexpectedly, we found that neuronal edema 48 hours after CCI was associated with reduced cellular and network excitability, concurrent with an increase in the expression ratio of the cation-chloride cotransporters (CCCs) NKCC1 and KCC2. Treatment with the CCC blocker bumetanide prevented neuronal swelling via a reversal in the NKCC1/KCC2 expression ratio, identifying altered chloride flux as the mechanism of neuronal edema. Importantly, bumetanide treatment was associated with increased neuronal and network excitability after injury, including increased susceptibility to spreading depolarizations (SDs) and seizures, known agents of clinical worsening after TBI. Treatment with mannitol, a first-line edema treatment in clinical practice, was also associated with increased susceptibility to SDs and seizures after CCI, showing that neuronal volume reduction, regardless of mechanism, was associated with an excitability increase. Finally, we observed an increase in excitability when neuronal edema normalized by 1 week after CCI. We conclude that neuronal swelling may exert protective effects against damaging excitability in the aftermath of TBI and that treatment of edema has the potential to reverse these effects.

The impact of hypertonic saline on cerebrovascular reactivity and compensatory reserve in traumatic brain injury: an exploratory analysis

Background

Intravenous hypertonic saline is utilized commonly in critical care for treatment of acute or refractory elevations of intracranial pressure (ICP) in traumatic brain injury (TBI) patients. Though there is a clear understanding of the general physiological effects of a hypertonic saline solution over long periods of time, smaller epoch effects of hypertonic saline (HTS) have not been thoroughly analyzed. The aim of this study was to perform a direct evaluation of the high-frequency response of HTS on the cerebrovascular physiological responses in TBI.

Methods

We retrospectively reviewed our prospectively maintained adult TBI database for those with archived high-frequency cerebral physiology and available HTS treatment information. We evaluated different epochs of physiology around HTS bolus dosing, comparing pre- with post-HTS. We assessed for changes in slow fluctuations in ICP, pulse amplitude of ICP (AMP), cerebral perfusion pressure (CPP), mean arterial pressure (MAP), cerebrovascular reactivity (as measured through pressure reactivity index (PRx)), and cerebral compensatory reserve (correlation (R) between AMP (A) and ICP (P)). Comparisons of mean measures and percentage time above clinically relevant thresholds for the physiological parameters were compared pre- and post-HTS using descriptive statistics and Mann-Whitney U testing. We assessed for subgroups of physiological responses using latent profile analysis (LPA).

Results

Fifteen patients underwent 69 distinct bolus infusions of hypertonic saline. Apart from the well-documented decrease in ICP, there was also a reduction in AMP. The analysis of cerebrovascular reactivity response to HTS solution had two main effects. For patients with grossly impaired cerebrovascular reactivity pre-HTS (PRx > + 0.30), HTS bolus led to improved reactivity. However, for those with intact cerebrovascular reactivity pre-HTS (PRx < 0), HTS bolus demonstrated a trend towards more impaired reactivity. This indicates that HTS has different impacts, dependent on pre-bolus cerebrovascular status. There was no significant change in metrics of cerebral compensatory reserve. LPA failed to demonstrate any subgroups of physiological responses to HTS administration.

Conclusions

The direct decrease in ICP and AMP confirms that a bolus dose of a HTS solution is an effective therapeutic agent for intracranial hypertension. However, in patients with intact autoregulation, hypertonic saline may impair cerebral hemodynamics. These findings regarding cerebrovascular reactivity remain preliminary and require further investigation.

Electronic supplementary material

The online version of this article (10.1007/s00701-020-04579-0) contains supplementary material, which is available to authorized users.

End-tidal and arterial carbon dioxide gradient in serious traumatic brain injury after prehospital emergency anaesthesia: a retrospective observational study

OBJECTIVES

In the UK, 20% of patients with severe traumatic brain injury (TBI) receive prehospital emergency anaesthesia (PHEA). Current guidance recommends an end-tidal carbon dioxide (ETCO2) of 4.0-4.5 kPa (30.0-33.8 mm Hg) to achieve a low-normal arterial partial pressure of CO2 (PaCO2), and reduce secondary brain injury. This recommendation assumes a 0.5 kPa (3.8 mm Hg) ETCO2-PaCO2 gradient. However, the gradient in the acute phase of TBI is unknown. The primary aim was to report the ETCO2-PaCO2 gradient of TBI patients at hospital arrival.

METHODS

A retrospective cohort study of adult patients with serious TBI, who received a PHEA by a prehospital critical care team in the East of England between 1 April 2015 and 31 December 2017. Linear regression was performed to test for correlation and reported as R-squared (R2). A Bland-Altman plot was used to test for paired ETCO2 and PaCO2 agreement and reported with 95% CI. ETCO2-PaCO2 gradient data were compared with a two-tailed, unpaired, t-test.

RESULTS

107 patients were eligible for inclusion. Sixty-seven patients did not receive a PaCO2 sample within 30 min of hospital arrival and were therefore excluded. Forty patients had complete data and were included in the final analysis; per protocol. The mean ETCO2-PaCO2 gradient was 1.7 (±1.0) kPa (12.8 mm Hg), with moderate correlation (R2=0.23, p=0.002). The Bland-Altman bias was 1.7 (95% CI 1.4 to 2.0) kPa with upper and lower limits of agreement of 3.6 (95% CI 3.0 to 4.1) kPa and -0.2 (95% CI -0.8 to 0.3) kPa, respectively. There was no evidence of a larger gradient in more severe TBI (p=0.29). There was no significant gradient correlation in patients with a coexisting serious thoracic injury (R2=0.13, p=0.10), and this cohort had a larger ETCO2-PaCO2 gradient, 2.0 (±1.1) kPa (15.1 mm Hg), p=0.01. Patients who underwent prehospital arterial blood sampling had an arrival PaCO2 of 4.7 (±0.2) kPa (35.1 mm Hg).

CONCLUSION

There is only moderate correlation of ETCO2 and PaCO2 at hospital arrival in patients with serious TBI. The mean ETCO2-PaCO2 gradient was 1.7 (±1.0) kPa (12.8 mm Hg). Lower ETCO2 targets than previously recommended may be safe and appropriate, and there may be a role for prehospital PaCO2 measurement.

Fluctuations in intracranial pressure can be estimated non-invasively using near-infrared spectroscopy in non-human primates

Intracranial pressure (ICP) is typically measured invasively through a sensor placed inside the brain or a needle inserted into the spinal canal, limiting the patient population on which this assessment can be performed. Currently, non-invasive methods are limited due to lack of sensitivity and thus only apply to extreme cases of increased ICP, instead of use in general clinical practice. We demonstrate a novel application for near-infrared spectroscopy (NIRS) to accurately estimate ICP changes over time. Using a non-human primate (Rhesus Macaque) model, we collected optical data while we induced ICP oscillations at multiple ICP levels obtained by manipulating the height of a fluid column connected via a catheter to the lateral ventricle. Hemodynamic responses to ICP changes were measured at the occipital pole and compared to changes detected by a conventional intraparenchymal ICP probe. We demonstrate that hemoglobin concentrations are highly correlated with induced ICP oscillations and that this response is frequency dependent. We translated the NIRS data into non-invasive ICP measurements via a fitted non-parametric transfer function, demonstrating a match in both magnitude and time alignment with an invasively measured reference. Our results demonstrate that NIRS has the potential for non-invasive ICP monitoring.

Pneumocephalus and air travel: an experimental investigation on the effects of aircraft cabin pressure on intracranial pressure

This study investigates the effects of aircraft cabin pressure on intracranial pressure (ICP) elevation of a pneumocephalus patient. We propose an experimental setup that simulates the intracranial hydrodynamics of a pneumocephalus patient during flight. It consists of an acrylic box (skull), air-filled balloon [intracranial air (ICA)], water-filled balloon (cerebrospinal fluid and blood) and agarose gel (brain). The cabin was replicated using a custom-made pressure chamber. The setup can measure the rise in ICP during depressurization to levels similar to that inside the cabin at cruising altitude. ΔICP, i.e. the difference between mean cruising ICP and initial ICP, was found to increase with ICA volume and ROC. However, ΔICP was independent of the initial ICP. The largest ΔICP was 5 mmHg; obtained when ICA volume and ROC were 20 ml and 1,600 ft/min, respectively. The postulated ICA expansion and the subsequent increase in ICP in pneumocephalus patients during flight were successfully quantified in a laboratory setting. Based on the quantitative and qualitative analyses of the results, an ICA volume of 20 ml and initial ICP of 15 mmHg were recommended as conservative thresholds that are required for safe air travel among pneumocephalus patients. This study provides laboratory data that may be used by doctors to advise post-neurosurgical patients if they can safely fly.

Impacts of Microgravity Analogs to Spaceflight on Cerebral Autoregulation

It is well known that exposure to microgravity in astronauts leads to a plethora physiological responses such as headward fluid shift, body unloading, and cardiovascular deconditioning. When astronauts return to Earth, some encounter problems related to orthostatic intolerance. An impaired cerebral autoregulation (CA), which could be compromised by the effects of microgravity, has been proposed as one of the mechanisms responsible for orthostatic intolerance. CA is a homeostatic mechanism that maintains cerebral blood flow for any variations in cerebral perfusion pressure by adapting the vascular tone and cerebral vessel diameter. The ground-based models of microgravity are useful tools for determining the gravitational impact of spaceflight on human body. The head-down tilt bed rest (HDTBR), where the subject remains in supine position at -6 degrees for periods ranging from few days to several weeks is the most commonly used ground-based model of microgravity for cardiovascular deconditioning. head-down bed rest (HDBR) is able to replicate cephalic fluid shift, immobilization, confinement, and inactivity. Dry immersion (DI) model is another approach where the subject remains immersed in thermoneutral water covered with an elastic waterproof fabric separating the subject from the water. Regarding DI, this analog imitates absence of any supporting structure for the body, centralization of body fluids, immobilization and hypokinesia observed during spaceflight. However, little is known about the impact of microgravity on CA. Here, we review the fundamental principles and the different mechanisms involved in CA. We also consider the different approaches in order to assess CA. Finally, we focus on the effects of short- and long-term spaceflight on CA and compare these findings with two specific analogs to microgravity: HDBR and DI.

Targeted role for sphingosine-1-phosphate receptor 1 in cerebrovascular integrity and inflammation during acute ischemic stroke

Endothelial sphingosine-1-phosphate receptors are emerging as relevant therapeutic targets during acute ischemic stroke (AIS). Physiologically, the cerebrovascular endothelium plays a vital role in maintaining barrier integrity and cerebrovascular homeostasis. During a cerebral ischemic event, products from parenchymal cell death are released and trigger vascular endothelial dysfunction and vascular inflammation leading to barrier integrity disruption. Endothelial dysfunction, inflammation, and a breach in barrier property play a significant role in contributing to a vicious cycle which promotes brain edema formation and exacerbates neuronal injury post stroke. Data from experimental stroke models and clinical trials suggest that selective sphingosine-1-phosphate receptor type 1 (S1PR1) modulation improves endothelial health and function and, as a result, contributes to improved neurological outcome post ischemic injury. This review highlights the impact of sphingosine-1-phosphate (S1P)/S1PR1 signaling involved in blood brain barrier (BBB) integrity and cerebrovascular inflammation following AIS. We focus on the beneficial actions of S1PR1 signaling during ischemic injury including barrier protection to lessen brain edema formation and reduction in the development and progression of vascular inflammation by attenuating endothelial cell activation resulting in reduced neurovascular inflammation. Potential gaps and future directions related to the role of S1PR during AIS are also discussed.