Hemant Desai

Utility of serial EEGs in neonates during extracorporeal membrane oxygenation

We found electroencephalographic (EEG) studies to be useful for monitoring cerebral function, for confirming seizure activity, and for limited prediction of short-term outcome in 145 neonates who required extra-corporeal membrane oxygenation (ECMO) of reversible respiratory failure. The EEG tracings were classified as normal or as mildly, moderately, or markedly abnormal; abnormal recordings were further classified as focal, diffuse, or predominantly lateralized. A significant decrease in frequency and degree of EEG abnormalities was observed in recordings obtained after ECMO compared to those obtained prior to (P = .001) or during ECMO (P = .001). There was no significant increase in marked EEG abnormalities when recordings obtained before and during ECMO were compared (P = 0.41). Of 11 infants with electrographic seizures during ECMO, 7 (64%) either died during their nursery courses or were developmentally handicapped at age 1 year which is a significantly greater adverse outcome than that observed in infants without EEG seizure activity (P less than .003). No consistently lateralized EEG abnormalities were observed during or after ECMO when compared to tracings obtained before cannulation of the right common carotid artery. There was no acute change in EEG rhythm or amplitude over the right cerebral hemisphere during right common carotid artery cannulation. Our observations support the value of serial EEG in the assessment of cerebral function in critically ill infants undergoing ECMO. They further suggest that, in this patient population, cannulation of the right common carotid artery is a safe procedure that does not result in lateralized abnormalities of cerebral electrical activity.

Cranial ultrasound and clinical studies in preterm infants.

Serial ultrasound imaging of the brain was used to determine the ventricular index (VI), and the ratio (VR) of the VI to the cranial hemidiameter during the nursery course and first year post-term in preterm infants of less than 33 weeks gestation. Twenty-nine of the infant survivors with no intracranial hemorrhage or major medical complication during their nursery course composed group 1. Twenty-two survivors with intracranial hemorrhage unassociated with early ventricular dilation composed group 2. Group 3 was comprised of 10 other survivors who had neonatal intraventricular hemorrhage with early ventriculomegaly; all 10 infants had at least one major medical complication during their neonatal course. In groups 1 and 2 the VR decreased and the VI increased significantly with age post-conception. Infants in group 3, compared with those in groups 1 or 2, had decreased occipitofrontal growth during the early postnatal period and increased VR and VI during the neonatal period and first year post-term. These results suggest that the ventriculomegaly associated with neonatal intracranial hemorrhage cannot be explained by posthemorrhagic hydrocephalus alone and may also be related to cerebral atrophy or decreased brain growth or both. Neurodevelopmental assessments at 20 to 30 months of age disclosed significantly lower Bayley Motor Development scores in group 3 compared with groups 1 or 2. Four infants in group 3, but none in groups 1 or 2, had cerebral palsy. The neurodevelopmental deficits in group 3 infants may reflect the complex pathogenesis of the ventriculomegaly as well as the effects of the intraventricular hemorrhage and posthemorrhagic hydrocephalus.

Right common carotid artery reconstruction after extracorporeal membrane oxygenation : vascular imaging, cerebral circulation, electroencephalographic, and neurodevelopmental correlates to recovery

OBJECTIVE Right common carotid artery (RCCA) ligation after extracorporeal membrane oxygenation by venoarterial bypass may contribute to lateralized cerebral injury. Reconstruction of this artery after extracorporeal membrane oxygenation has proved feasible but has not been evaluated for neurologic outcome in any substantial series of infants. METHODS We evaluated RCCA reconstruction in 47 infants treated with ECMO and compared their cerebrovascular and neuroanatomic imaging findings, electroencephalograms, and developmental outcomes with those of 93 infants who had no reconstruction. SUMMARY RESULTS: Color Doppler blood flow imaging revealed that carotid artery patency was usually obtained after RCCA reconstruction. Right internal carotid and bilateral anterior and middle cerebral arterial blood flow velocities were generally higher, and were more symmetrically distributed in infants with reconstructed RCCA. Electroencephalography did not disclose an increased risk of deterioration or marked abnormalities in infants after reconstruction, nor were neuroimaging findings consistent with an increased number of either focal or generalized abnormalities. Neurodevelopmental follow-up revealed no differences in the incidence of delays between those with a reconstructed RCCA and those with a ligated RCCA during the first year of life. CONCLUSIONS Reconstruction of the RCCA after extracorporeal membrane oxygenation may facilitate normal distribution of cerebral blood flow through the circle of Willis, and may augment both left and right middle cerebral artery blood flow immediately after decannulation. The long-term consequences of either ligation or reconstruction of the RCCA will require careful scrutiny, however, before either course is recommended routinely.

Synthesis of narrow molecular weight α,ω-hydroxy telechelic poly(glycidyl nitrate) and estimation of theoretical heat of explosion

Abstract This communication reports the synthetic steps and characterization required to make pure poly(glycidyl nitrate), also known as polyGLYN or POWA3, from cheap commercially available starting materials using dinitrogen pentoxide (N 2 O 5 ) technology. Conditions are given whereby a range of well defined and characterized polyGLYN samples may be safely and reproducibly prepared by the cationic, ring-opening, activated monomer mechanism (AMM). Tetrafluoroboric acid and 1,4-butanediol were used as the catalyst system, and the samples have been characterized by nuclear magnetic resonance spectroscopy, size exclusion chromatography, infra-red spectroscopy and differential scanning calorimetry. The theoretical calculations indicate that the heat of explosion is 2661 kJ kg −1 , this being significantly more energy than for earlier polymers. These materials are currently under assessment in both high-performance explosives and high-energy low-vulnerability propellant systems. Some properties of the material are also shown.

Synthesis and characterization of α,ω-hydroxy and nitrato telechelic oligomers of 3,3-(nitratomethyl) methyl oxetane (NIMMO) and glycidyl nitrate (GLYN)

Abstract The synthesis of α,ω-hydroxy telechelic, low-molecular-weight oligomers (degree of polymerization of less than 10) of glycidyl nitrate (GLYN) and 3,3-(nitratomethyl) methyl oxetane (NIMMO) by the activated monomer mechanism is described. Difunctional and/or trifunctional compounds may be prepared. The end-nitration of these compounds has been investigated using dinitrogen pentoxide in dichloromethane to form α,ω-nitrato telechelic oligomers. The materials were characterized by size exclusion chromatography, infrared and nuclear magnetic resonance spectroscopies. Differential scanning calorimetry was used to study the thermal properties of the compounds as they are envisaged to be energetic and fully compatible (miscible) plasticizers for the new generation of energetic binders such as polyNIMMO or polyGLYN, in propellant and explosive applications.

Synthesis of narrow molecular weight distribution α,ω-hydroxy telechelic polyoxetane by the activated monomer mechanism

Abstract The cationic activated monomer mechanism has been used to prepare polyoxetane (poly(trimethylene oxide)) with low dispersities, hydroxy functional end groups and without significant oligomer contamination. Tetrafluoroboric acid and 1,4-butandiol were used as the catalyst system. The polymer has been characterized by n.m.r. and s.e.c.

Identification of simulants for explosives using pixellated X-ray diffraction

A new method of material identification has been developed utilising pixellated X-ray diffraction (PixD) to probe the molecular structure of hidden items. Since each material has a unique structure, this technique can be used to “fingerprint” items and has significant potential for use in security applications such as airport baggage scanning. The pixellated diffraction technique allows two distinct forms of diffraction, angular-dispersive and energy-dispersive X-ray diffraction, to be combined, exploiting the benefits of both. Thus, fast acquisition times are possible with a small system which contains no moving parts and can be easily implemented. In this work, the capability of the system to identify specific materials within a sample is highlighted. Such an approach would be highly beneficial for detecting explosive materials which are concealed amongst or inside other masking items. The technology could easily be added to existing baggage scanning equipment and would mean that if a suspicious item is seen in a regular X-ray image, the operator of the equipment could analyse the object in detail without opening the bag. The net result would be more accurate analysis of baggage content and faster throughput, as manual searching of suspicious objects would not be required.

Electroencephalographic, neuroradiologic, and neurodevelopmental studies in infants with subclavian steal during ECMO

Color Doppler imaging revealed a subclavian steal--retrograde flow in the right vertebral artery which shunted blood from the brains posterior circulation to the right arm via the subclavian artery--in 17 of 54 infants (31%) during extracorporeal membrane oxygenation (ECMO); right vertebral artery flow returned to antegrade after ECMO and removal of the right common carotid arterial cannula. When subjects with and without a subclavian steal were compared, there were no statistically significant differences in mortality; in the results of neonatal electroencephalograms, cranial ultrasound studies, or computed tomography studies; or in early neurological development. Blood flow patterns and peak systolic velocities in the circle of Willis, middle cerebral arteries, internal carotid arteries, and basilar artery were similar in both groups during ECMO; blood flow velocity in the middle cerebral arteries was slightly but significantly lower on the right than the left in both groups. Our results indicate that increased flow in the left vertebral artery adequately compensated for the effect of a subclavian steal on the basilar and cerebral circulation. The moderate to marked neonatal electroencephalographic abnormalities commonly occurring during ECMO and the approximately 20% incidence of neurodevelopmental deficits among ECMO survivors remain largely unexplained.

Progression of pulmonary cystic disease during ECMO

Only one of the 65 ECMO patients treated at Thomas Jefferson University Hospital to date has shown progression of pulmonary parenchymal cystic change on serial portable chest radiographs while on ECMO. The radiographic and clinical findings of this unique case are presented.

Facile Synthesis and Proposed Mechanism of α,ω‐Oxetanyl-Telechelic Poly(3-nitratomethyl-3-methyl oxetane) by an SN2(i) Nitrato Displacement Method in Basic Media

ABSTRACT The synthesis of a novel heterocyclic–telechelic polymer, α,ω-oxetanyl-telechelic poly(3-nitratomethyl-3-methyl oxetane), is described. Infrared spectroscopy (IR), gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) spectroscopy have been used to confirm the successful synthesis, demonstrating the presence of the telechelic-oxetanyl moieties. Synthesis of the terminal functionalities has been achieved via displacement of nitrato groups, in a manner similar to that employed with other leaving groups such as azido, bromo, and nitro, initiated by nucleophiles. In the present case, displacement occurs on the ends of a nitrato-functionalized polymer driven by the formation of sodium nitrate, which is supported by the polar aprotic solvent N,N-dimethyl formamide. The formation of an alkoxide at the polymer chain ends is favored and allows internal back-biting to the nearest carbon bearing the nitrato group, intrinsically in an SN2(i) reaction, leading to α,ω-oxetanyl functionalization. The telechelic-oxetanyl moieties have the potential to be cross-linked by chemical (e.g., acidic) or radiative (e.g., ultraviolet) curing methods without the use of high temperatures, usually below 100°C. This type of material was designed for future use as a contraband simulant, whereby it would form the predominant constituent of elastomeric composites comprising rubbery polymer with small quantities of solids, typically crystals of contraband substances, such as explosives or narcotics. This method also provides an alternative approach to ring closure and synthesis of heterocycles.