Georgios Maragkos

A dynamic approach for the impact of a toxic gas dispersion hazard considering human behaviour and dispersion modelling

The release of toxic gases due to natural/industrial accidents or terrorist attacks in populated areas can have tragic consequences. To prevent and evaluate the effects of these disasters different approaches and modelling tools have been introduced in the literature. These instruments are valuable tools for risk managers doing risk assessment of threatened areas. Despite the significant improvements in hazard assessment in case of toxic gas dispersion, these analyses do not generally include the impact of human behaviour and people movement during emergencies. This work aims at providing an approach which considers both modelling of gas dispersion and evacuation movement in order to improve the accuracy of risk assessment for disasters involving toxic gases. The approach is applied to a hypothetical scenario including a ship releasing Nitrogen dioxide (NO2) on a crowd attending a music festival. The difference between the results obtained with existing static methods (people do not move) and a dynamic approach (people move away from the danger) which considers people movement with different degrees of sophistication (either a simple linear path or more complex behavioural modelling) is discussed.

Large eddy simulations of differential molecular diffusion in non-reacting turbulent jets of H2/CO2 mixing with air

Large eddy simulations of non-reacting H2/CO2 jets mixing with air are performed and the calculations are compared with the experiments reported by Smith et al. [“Laser Raman scattering measurements of differential molecular diffusion in non-reacting turbulent jets of H2/CO2 mixing with air,” Phys. Fluids 7, 1455–1466 (1995)]. The influence of differential diffusion effects for Reynolds numbers Re = 1000–8000 is analyzed and a differential diffusion parameter, ξ, is defined on the basis of normalized H2 and CO2 concentrations in order to quantify the effects of differential diffusion with increasing Reynolds number. The analysis is made not only in physical space but also with scatter plots and histograms. The simulation results reveal that differential diffusion effects are significant at downstream locations (more than 15 nozzle diameters away from the inlet) only for the lower Reynolds numbers (Re = 1000–2000). However, differential diffusion effects are present for all Reynolds numbers examined close to the inlet (closer than 10 nozzle diameters). This is not only confirmed by the mean results of the differential diffusion parameter, ξ, but also by looking at the histograms of ξ. This is an important indication that differential diffusion can be important in turbulent reacting flows if laminarization of the flow or weakening of turbulent diffusion occurs. Including differential diffusion effects in turbulent reactive flows involving mixtures with vastly different mass diffusivities can, therefore, improve the accuracy of numerical simulations. Results obtained assuming equal species mass diffusivities revealed that differential diffusion effects do not have any significant influence in the velocity field.Large eddy simulations of non-reacting H2/CO2 jets mixing with air are performed and the calculations are compared with the experiments reported by Smith et al. [“Laser Raman scattering measurements of differential molecular diffusion in non-reacting turbulent jets of H2/CO2 mixing with air,” Phys. Fluids 7, 1455–1466 (1995)]. The influence of differential diffusion effects for Reynolds numbers Re = 1000–8000 is analyzed and a differential diffusion parameter, ξ, is defined on the basis of normalized H2 and CO2 concentrations in order to quantify the effects of differential diffusion with increasing Reynolds number. The analysis is made not only in physical space but also with scatter plots and histograms. The simulation results reveal that differential diffusion effects are significant at downstream locations (more than 15 nozzle diameters away from the inlet) only for the lower Reynolds numbers (Re = 1000–2000). However, differential diffusion effects are present for all Reynolds numbers examined close ...

Spontaneous Intracranial Hemorrhage in Pregnancy: A Systematic Review of the Literature.

Stroke in pregnant women has a mortality rate of 1.4 deaths per 100,000 deliveries. Vascular malformations are the most common cause of hemorrhagic stroke in this population; preeclampsia and other risk factors have been identified. However, nearly a quarter of strokes have an undeterminable cause. Spontaneous intracranial hemorrhage (ICH) is less frequent but results in significant morbidity. The main objective of this study is to review the literature on pregnant patients who had a spontaneous ICH. A systematic review of the literature was conducted on PubMed and the Cochrane library from January 1992 to September 2016 following the PRISMA guidelines. Studies reporting pregnant patients with spontaneous intraparenchymal hemorrhage (IPH), subarachnoid hemorrhage (SAH), and subdural hemorrhage (SDH) were selected and included if patients had non-structural ICH during pregnancy or up to 6xa0weeks postpartum confirmed by imaging. Twenty studies were included, and 43 patients identified. Twenty-two patients (51.3%) presented with IPH, 15 patients (34.8%) with SAH, and five patients (11.6%) with SDH. The most common neurosurgical management was clinical in 76.7% of patients, and cesarean section was the most common obstetrical management in 28% of patients. The most common maternal outcome was death (48.8%), and fetal outcomes were evenly distributed among term delivery, preterm delivery, and fetal or neonatal death. Spontaneous ICH carries a high maternal mortality with IPH being the most common type, most frequently presenting in the third trimester. Diagnosis and management do not differ for the parturient compared to the non-pregnant woman.

Intraocular Silicone Oil Migration into the Ventricles Resembling Intraventricular Hemorrhage: Case Report and Review of the Literature

BACKGROUNDnIntracranial silicone migration is a rare complication of ocular silicone oil endotamponade and may resemble intraventricular hemorrhage. The etiology of the phenomenon is challenging to understand.nnnCASE DESCRIPTIONnIn an effort to shed light on this phenomenon, we report a case of a 67-year-old woman with ocular silicone oil endotamponade on the left eye due to retinal detachment who presented with headache to the emergency department. The imaging work-up revealed intraventricular silicone oil migration.nnnCONCLUSIONSnThe literature is reviewed through the perspective of pathophysiology. The migration of intraocular silicone oil into the ventricular system provides both an important complication for clinicians to be aware of, as well as a paradigm reminding us that cerebrospinal fluid spaces may have more extensive communications with other body compartments than previously thought.

Statin Therapy and Diabetes Do Not Affect Aneurysm Occlusion or Clinical Outcomes Following Pipeline Embolization Device Treatment: a Preliminary Study

BACKGROUNDnThe effect of statins and diabetes on angiographic and clinical outcomes in aneurysms treated with pipelines has not been adequately reported. Our aim is to assess the effect of concurrent statin medications and diabetes mellitus (DM) on aneurysm occlusion status and outcomes in patients treated with the pipeline embolization device.nnnMETHODSnA retrospective review of our institutions database of aneurysms treated with the pipeline embolization device between 2013 and 2017 was conducted. We collected data about statin therapy status and intensity, and identified patients with a documented history of DM. Our primary outcome was aneurysm obliteration seen on digital subtracted angiography or magnetic resonance angiography at last follow-up.nnnRESULTSnWe identified 151 patients with 182 aneurysms for this cohort, with a median radiographic follow-up time of 7.2 months (6.1-14.5). Thirty-nine patients were taking statins, and 112 patients did not receive statins. Log-rank tests revealed no statistically significant difference in occlusion rates between patients with and without statin therapy (Pxa0= 0.30). A history of DM was documented in 11 patients, with 14 aneurysms in total; 140 patients with 168 aneurysms had no history of DM. Similarly, there were no differences in occlusion rates between the diabetic and nondiabetic groups in multivariate analysis (Pxa0=xa00.24). Only 2 patients showed significant in-stent stenosis on angiographic follow up, and both were diabetic.nnnCONCLUSIONSnOur analysis did not identify a statistically significant association between statin therapy or DM and higher occlusion rates or better outcomes after pipeline embolization. Diabetic patients may have a theoretic risk of significant in-stent stenosis.

Proposal of a Grading System for Predicting Discharge Mortality and Functional Outcome in Patients with Aneurysmal Subarachnoid Hemorrhage

BACKGROUNDnSeveral outcome prediction systems have been developed to evaluate aneurysmal subarachnoid hemorrhage (aSAH). However, they can be difficult to use and can contain subjective elements. We sought to identify the predictors of aSAH outcomes at discharge to provide an accurate and reliable scoring system.nnnMETHODSnA retrospective cohort study of patients with aSAH at an academic institution from 2007 to 2016 was conducted. The primary outcome measure was the modified Rankin scale (mRS) score at discharge, with mRS scores of 0-2 considered favorable and mRS scores of 3-6 considered unfavorable. Factors significant on multivariate regression were used to develop a scale, which was compared with other established grading systems using receiver operating characteristic curves.nnnRESULTSnWe identified 279 patients with aSAH, 37.3% of whom had unfavorable outcomes. The proposed scale assigns 2 points for postresuscitation Glasgow coma scale score of ≤8, 1 point for age ≥70 years, 1 for antiplatelet therapy on admission, and 1 for SAH thickness of ≥10 mm, with a total score of 0-5. The proposed, Subarachnoid Hemorrhage International Trialists, and Hunt and Hess scales had similar areas under the curve (85.2%, 84.8%, and 80.6%, respectively; P > 0.05) but were significantly better than the World Federation of Neurological Surgeons (78.5%; Pxa0= 0.001) and modified Fisher (60.8%; P < 0.001) scales.nnnCONCLUSIONnWe propose a grading scale to predict discharge mortality and functional outcomes in patients with aSAH. The proposed scale outperformed most other outcome prediction scales. The proposed scale contains objective elements, is easy to apply by memory, and can be a useful and effective measure to predict aSAH outcomes.

Quality of Life After Epilepsy Surgery in Children: A Systematic Review and Meta-Analysis

BACKGROUNDnPediatric epilepsy surgery is a treatment modality appropriate for select patients with debilitating medication-resistant seizures. Previous publications have studied seizure freedom as the main outcome of epilepsy surgery. However, there has been no systematic assessment of the postoperative life quality for these children.nnnOBJECTIVEnTo estimate the quality of life (QOL) long-term outcomes after surgery for intractable epilepsy in pediatric patients.nnnMETHODSnA systematic search of the PubMed and Cochrane databases was performed. Studies reporting questionnaire-assessed QOL at least 12 months postoperatively were included. QOL means and standard deviations were compared between surgically and medically managed patients, between the preoperative and postoperative state of each patient, and were further stratified into patients achieving seizure freedom, and those who did not. Meta-analysis was performed using fixed effects models for weighted mean differences (WMD), 95% confidence intervals (CI) and sensitivity analyses. Funnel plots and Beggs tests were utilized to detect publication bias.nnnRESULTSnThe search yielded 18 retrospective studies, reporting 890 surgical patients. Following epilepsy surgery, children had significant QOL improvement compared to their preoperative state (WMD: 16.71, 95% CI: 12.19-21.22, Pxa0<xa0.001) and better QOL than matched medically treated controls (WMD: 12.42, 95% CI: 6.25-18.58, Pxa0<xa0.001). Patients achieving total seizure freedom after surgery had significant postoperative QOL improvement (WMD: 16.12, 95% CI: 7.98-24.25, Pxa0<xa0.001), but patients not achieving seizure freedom did not achieve statistical significance (Pxa0=xa0.79).nnnCONCLUSIONnEpilepsy surgery can effectively improve QOL in children with medication-resistant seizures, through seizure freedom, which was associated with the greatest improvement in life quality.

Accuracy and Safety of External Ventricular Drain Placement by Physician Assistants and Nurse Practitioners in Aneurysmal Acute Subarachnoid Hemorrhage

BackgroundIn the current dynamic health environment, increasing number of procedures are being completed by advanced practitioners (nurse practitioners and physician assistants). This is the first study to assess the clinical outcomes and safety of external ventricular drain (EVD) placements by specially trained advanced practitioners.ObjectiveCompare the safety and outcomes of EVD placement by advanced practitioners in patients with subarachnoid hemorrhage (SAH).MethodsA cohort comparison study was performed from an aneurysmal SAH database selecting patients treated with EVD from a single major academic institution in the USA between June 2007 and June 2017. Safety, accuracy, and complications of EVD placement were compared between advanced practitioners and neurosurgical physicians (attending neurosurgeon and subspecialty clinical fellow). Statistical analysis was performed using the Mann–Whitney test for continuous variables and χ2 test for categorical variables, with p values set atu2009<u20090.05 for significance.ResultsWe identified 203 patients for this cohort with 238 EVD placements; eighty-seven (36.6%) placements were performed by advanced practitioners and 151 (63.4%) by neurosurgeons. Most of the ventriculostomies were placed in the emergency room (nu2009=u2009114; 47.9%). Additional procedures performed concurrently with the EVD placements were significantly higher among the physicians’ group (21.8 vs. 4.6%; pu2009<u20090.001). Bedside placement and usage of Ghajar guide were significantly higher among advanced practitioner’s (58.3 vs. 98.9 and 9.9 vs. 64.4%, respectively, with a pu2009<u20090.001 for both). There were, however, no significant differences in terms ofxa0the number of attempts for insertion, intraprocedural complications, tract hemorrhages, accuracy, infection rates, catheter dislodgments, and need for repositioning/replacement of EVD.ConclusionAfter appropriate training, EVD placement can be safely performed by advanced practitioners with an adequate accuracy of placement.

Proposal of a follow-up imaging strategy following Pipeline flow diversion treatment of intracranial aneurysms

OBJECTIVEThere is currently no standardized follow-up imaging strategy for intracranial aneurysms treated with the Pipeline embolization device (PED). Here, the authors use follow-up imaging data for aneurysms treated with the PED to propose a standardizable follow-up imaging strategy.METHODSA retrospective review of all patients who underwent treatment for ruptured or unruptured intracranial aneurysms with the PED between March 2013 and March 2017 at 2 major academic institutions in the US was performed.RESULTSA total of 218 patients underwent treatment for 259 aneurysms with the PED and had undergone at least 1 follow-up imaging session to assess aneurysm occlusion status. There were 235 (90.7%) anterior and 24 posterior (9.3%) circulation aneurysms. On Kaplan-Meier analysis, the cumulative incidences of aneurysm occlusion at 6, 12, 18, and 24 months were 38.2%, 77.8%, 84.2%, and 85.1%, respectively. No differences in the cumulative incidence of aneurysm occlusion according to aneurysm location (p = 0.39) or aneurysm size (p = 0.81) were observed. A trend toward a decreased cumulative incidence of aneurysm occlusion in patients 70 years or older was observed (p = 0.088). No instances of aneurysm rupture after PED treatment or aneurysm recurrence after occlusion were noted. Sixteen (6.2%) aneurysms were re-treated with the PED; 11 of these had imaging follow-up data available, demonstrating occlusion in 3 (27.3%).CONCLUSIONSThe authors propose a follow-up imaging strategy that incorporates 12-month digital subtraction angiography and 24-month MRA for patients younger than 70 years and single-session digital subtraction angiography at 12 months in patients 70 years or older. For recurrent or persistent aneurysms, re-treatment with the PED or use of an alternative treatment modality may be considered.

Moyamoya disease in pregnancy: a systematic review

BackgroundMoyamoya disease (MMD) management during pregnancy poses a challenge to health care providers, and recommendations are outdated, vague, and controversial. We conducted a systematic review to investigate and present the available evidence.MethodWe searched five online databases and bibliographies of relevant published original studies to identify case reports, case series, cohort studies, and reviews reporting on patients diagnosed with MMD before, during, or shortly after pregnancy. We report and analyze the respective data.ResultsFifty-four relevant articles were identified. In the group of patients with MMD diagnosed prior to pregnancy, 68.7% had previously undergone bypass surgery, 64.5% delivered via cesarean section, 95.2% of mothers had good outcomes, and no bad fetal outcomes were reported. In patients first diagnosed with MMD due to a cerebrovascular accident during pregnancy, the mean gestational age on symptom onset was 28.7xa0weeks and 69.5% presented with cerebral hemorrhage. In this group, 57.2% received neurosurgical operative management, and 80% underwent cesarean section with 13.6% maternal mortality and 23.5% fetal demise. In patients diagnosed with MMD immediately postpartum, 46.6% suffered a cerebrovascular event within 3xa0days of delivery, 78.3% of which were ischemic. Only 15.3% underwent surgical hematoma evacuation and one patient (9%) expired.ConclusionsMMD may coincide with pregnancy, but there is paucity of high-quality data. It appears that MMD is not a contraindication to pregnancy, if blood pressure and ventilation are properly managed. There is no clear evidence that bypass surgery before pregnancy or cesarean mode of delivery improve outcomes.