Respiratory Support in Meconium Aspiration Syndrome: A Practical Guide

Meconium aspiration syndrome (MAS) is a complex respiratory disease of the term and near-term neonate. Inhalation of meconium causes airway obstruction, atelectasis, epithelial injury, surfactant inhibition, and pulmonary hypertension, the chief clinical manifestations of which are hypoxaemia and poor lung compliance. Supplemental oxygen is the mainstay of therapy for MAS, with around one-third of infants requiring intubation and mechanical ventilation. For those ventilated, high ventilator pressures, as well as a relatively long inspiratory time and slow ventilator rate, may be necessary to achieve adequate oxygenation. High-frequency ventilation may offer a benefit in infants with refractory hypoxaemia and/or gas trapping. Inhaled nitric oxide is effective in those with pulmonary hypertension, and other adjunctive therapies, including surfactant administration and lung lavage, should be considered in selected cases. With judicious use of available modes of ventilation and adjunctive therapies, infants with even the most severe MAS can usually be supported through the disease, with an acceptably low risk of short- and long-term morbidities

A Radiological Study of the Intracranial Arteriovenous Malformations

(1) A series of 32 cases form the basis of a radiological investigation of the intracranial arteriovenous malformations. (2) The incidence of the intracranial arterio- venous malformations has been estimated at one% of the neurological admissions to hospital (Mackenzie 1953). They comprise two to five% of the reported cases examined by cerebral angiography (4.8% in the present series). (3) The pathology of the lesion is described and its relationship to the other vascular anomalies is defined. Arteriovenous malformation is considered to be the most suitable terminology. (4) Abnormal appearances in the preliminary skull radiographs, attributable to the presence of an arteriovenous malformation, may be seen in approximately 30% of the cases. They are as follows: (a) Enlargement of foramina and grooves for the meningeal vessels and occasionally anomalous vascular channels. Perforations in the skull due to communications between branches of the external carotid artery in the scalp and the meningeal vessels. Thickening of the skull, when the vascularity of the hone is greatly increased, which may simulate the hyperostosis of a meningioma. (b) Enlarged and pulsating drainage veins or the malformation itself may lead to localised areas of erosion of the inner table of the skull. Enlargement of the sagittal sinus groove may be demonstrable when there is a large shunt situated so that its effluents drain into the sinus. This observation may be of some value, since it may be the only visible radiographic change occurring with a lesion confined to the intracerebral circulation. Pour of the present cases showed marked widening and deepening of the sinus groove and in three others enlargement was probable. (c) Calcification may be found in the walls of the vessels of the malformation or in adjacent haematomata. It is present in approximately 15% of cases. (5) Ventriculography and encephalography have been superseded by cerebral angiography in the investigation of intracranial vascular lesions. In approximately 70% of cases of arteriovenous malformation plain radiography and ventriculography combined show some abnormality. An undulating, serrated or ripple contour of the walls of the lateral ventricle, without shift of the ventricular system has been considered typical of the conditions. Other changes result from cerebral atrophy, organisation of blood clot in the ventricle leading to coarctation, or to filling of a porencephalic cyst with air. Hydrocephalus commonly occurs with mid-brain lesions. (6) The technique of cerebral angiography as it applies to the demonstration of the arteriovenous malformations is described. Possible pitfalls in diagnosis are considered. (7) The angiographic appearances of the arteriovenous malformations, their feeding arteries and drainage veins are described. There were 17 large lesions, 10 small and 5 of intermediate size. The middle cerebral artery was the feeding vessel in 75% of cases. (8) A case is presented to support the hypothesis that a true increase in size of the arteriovenous malformations occurs. (9) Epilepsy was the presenting symptom in 25% and present eventually in 44 cent. of the present cases. The attacks were mainly focal in type and in those presenting with epilepsy the common situation of the lesion was fronto-parietal. If haemorrhage proceeded the onset of the attacks the lesion was elsewhere in the brain. (10) Headache was a presenting feature in 44% of the cases. It was commoner with the large (11 of 17 cases) than with the small (3 of 10 cases). Six lesions in relation to the occipital lobe were associated with headache of a migrainous type. (11) Haemorrhage occurred from 41% of the large, 70% of the small and all 5 lesions of medium size. It is suggested that the difference in incidence in bleeding from the small and large malformations, is due to the fact that the large ones are found during the course of investigation for symptoms such as headache and epilepsy, whereas small lesions are frequently asymptomatic until bleeding occurs. The relative liability of the small and large lesions to bleed cannot however be assessed until the number of small lesions at risk is known. The possibility that the small lesions are in fact more liable to haemorrhage than the large is not excluded. There are no characteristic angiographic features whereby the liability of a particular lesion to haemorrhage can be forecast. (12) The frequency with which an intracranial bruit can be heard on auscultation of the skull has varied widely in different reports. It was present in 8 cases (25% ), all large lesions, of the author's series. In 5 of the cases there was clinical or radiographic evidence of hypertrophy of branches of the external carotid artery. (13) The differentiating features between highly vascular tumours such as glioblastoma multiforme and meningioma and the arteriovenous malformations are described. There were no difficulties of this type in the present series of cases. (14) The value of cerebral angiography in the assessment of the operability of a lesion and in showing the results of excision are exemplified

Poly(2-oxazoline) hydrogels : state-of-the-art and emerging applications

The synthesis of poly(2-oxazoline)s has been known since the 1960s. In the last two decades, they have risen in popularity thanks to improvements in their synthesis and the realization of their potential in the biomedical field due to their stealth properties, stimuli responsiveness, and tailorable properties. Even though the bulk of the research to date has been on linear forms of the polymer, they are also of interest for creating network structures due to the relatively easy introduction of reactive functional groups during synthesis that can be cross-linked under a variety of conditions. This opinion article briefly reviews the history of poly(2-oxazoline)s and examines the in vivo data on soluble poly(2-oxazoline)s to date in an effort to predict how hydrogels may perform as implantable materials. This is followed by an overview of the most recent hydrogel synthesis methods and emerging applications, and is concluded with a section on the future directions predicted for these fascinating yet underutilized polymers

Angular adaptivity with spherical harmonics for Boltzmann transport

This paper describes an angular adaptivity algorithm for Boltzmann transport applications which uses Pn and filtered Pn expansions, allowing for different expansion orders across space/energy. Our spatial discretisation is specifically designed to use less memory than competing DG schemes and also gives us direct access to the amount of stabilisation applied at each node. For filtered Pn expansions, we then use our adaptive process in combination with this net amount of stabilisation to compute a spatially dependent filter strength that does not depend on a priori spatial information. This applies heavy filtering only where discontinuities are present, allowing the filtered Pn expansion to retain high-order convergence where possible. Regular and goal-based error metrics are shown and both the adapted Pn and adapted filtered Pn methods show significant reductions in DOFs and runtime. The adapted filtered Pn with our spatially dependent filter shows close to fixed iteration counts and up to high-order is even competitive with P0 discretisations in problems with heavy advection.Comment: arXiv admin note: text overlap with arXiv:1901.0492

Scalable angular adaptivity for Boltzmann transport

This paper describes an angular adaptivity algorithm for Boltzmann transport applications which for the first time shows evidence of $\mathcal{O}(n)$ scaling in both runtime and memory usage, where $n$ is the number of adapted angles. This adaptivity uses Haar wavelets, which perform structured $h$-adaptivity built on top of a hierarchical P$_0$ FEM discretisation of a 2D angular domain, allowing different anisotropic angular resolution to be applied across space/energy. Fixed angular refinement, along with regular and goal-based error metrics are shown in three example problems taken from neutronics/radiative transfer applications. We use a spatial discretisation designed to use less memory than competing alternatives in general applications and gives us the flexibility to use a matrix-free multgrid method as our iterative method. This relies on scalable matrix-vector products using Fast Wavelet Transforms and allows the use of traditional sweep algorithms if desired

AIR multigrid with GMRES polynomials (AIRG) and additive preconditioners for Boltzmann transport

We develop a reduction multigrid based on approximate ideal restriction (AIR) for use with asymmetric linear systems. We use fixed-order GMRES polynomials to approximate $A_\textrm{ff}^{-1}$ and we use these polynomials to build grid transfer operators and perform F-point smoothing. We can also apply a fixed sparsity to these polynomials to prevent fill-in. When applied in the streaming limit of the Boltzmann Transport Equation (BTE), with a P$^0$ angular discretisation and a low-memory spatial discretisation on unstructured grids, this "AIRG" multigrid used as a preconditioner to an outer GMRES iteration outperforms the lAIR implementation in hypre, with two to three times less work. AIRG is very close to scalable; we find either fixed work in the solve with slight growth in the setup, or slight growth in the solve with fixed work in the setup when using fixed sparsity. Using fixed sparsity we see less than 20% growth in the work of the solve with either 6 levels of spatial refinement or 3 levels of angular refinement. In problems with scattering AIRG performs as well as lAIR, but using the full matrix with scattering is not scalable. We then present an iterative method designed for use with scattering which uses the additive combination of two fixed-sparsity preconditioners applied to the angular flux; a single AIRG V-cycle on the streaming/removal operator and a DSA method with a CG FEM. We find with space or angle refinement our iterative method is very close to scalable with fixed memory use