Enterococci enhance Clostridioides difficile pathogenesis.

Enteric pathogens are exposed to a dynamic polymicrobial environment in the gastrointestinal tract1. This microbial community has been shown to be important during infection, but there are few examples illustrating how microbial interactions can influence the virulence of invading pathogens2. Here we show that expansion of a group of antibiotic-resistant, opportunistic pathogens in the gut-the enterococci-enhances the fitness and pathogenesis of Clostridioides difficile. Through a parallel process of nutrient restriction and cross-feeding, enterococci shape the metabolic environment in the gut and reprogramme C. difficile metabolism. Enterococci provide fermentable amino acids, including leucine and ornithine, which increase C. difficile fitness in the antibiotic-perturbed gut. Parallel depletion of arginine by enterococci through arginine catabolism provides a metabolic cue for C. difficile that facilitates increased virulence. We find evidence of microbial interaction between these two pathogenic organisms in multiple mouse models of infection and patients infected with C. difficile. These findings provide mechanistic insights into the role of pathogenic microbiota in the susceptibility to and the severity of C. difficile infection.

Structural Elucidation of Ubiquitin via Gas-Phase Ion/Ion Cross-Linking Reactions Using Sodium-Cationized Reagents Coupled with Infrared Multiphoton Dissociation.

Accurate structural determination of proteins is critical to understanding their biological functions and the impact of structural disruption on disease progression. Gas-phase cross-linking mass spectrometry (XL-MS) via ion/ion reactions between multiply charged protein cations and singly charged cross-linker anions has previously been developed to obtain low-resolution structural information on proteins. This method significantly shortens experimental time relative to conventional solution-phase XL-MS but has several technical limitations: (1) the singly deprotonated N-hydroxysulfosuccinimide (sulfo-NHS)-based cross-linker anions are restricted to attachment at neutral amine groups of basic amino acid residues and (2) analyzing terminal cross-linked fragment ions is insufficient to unambiguously localize sites of linker attachment. Herein, we demonstrate enhanced structural information for alcohol-denatured A-state ubiquitin obtained from an alternative gas-phase XL-MS approach. Briefly, singly sodiated ethylene glycol bis(sulfosuccinimidyl succinate) (sulfo-EGS) cross-linker anions enable covalent cross-linking at both ammonium and amine groups. Additionally, covalently modified internal fragment ions, along with terminal b-/y-type counterparts, improve the determination of linker attachment sites. Molecular dynamics simulations validate experimentally obtained gas-phase conformations of denatured ubiquitin. This method has identified four cross-linking sites across 8+ ubiquitin, including two new sites in the N-terminal region of the protein that were originally inaccessible in prior gas-phase XL approaches. The two N-terminal cross-linking sites suggest that the N-terminal half of ubiquitin is more compact in gas-phase conformations. By comparison, the two C-terminal linker sites indicate the signature transformation of this region of the protein from a native to a denatured conformation. Overall, the results suggest that the solution-phase secondary structures of the A-state ubiquitin are conserved in the gas phase. This method also provides sufficient sensitivity to differentiate between two gas-phase conformers of the same charge state with subtle structural variations.

Multimodal Image Fusion Workflow Incorporating MALDI Imaging Mass Spectrometry and Microscopy for the Study of Small Pharmaceutical Compounds.

Multimodal imaging analyses of dosed tissue samples can provide more comprehensive insights into the effects of a therapeutically active compound on a target tissue compared to single-modal imaging. For example, simultaneous spatial mapping of pharmaceutical compounds and endogenous macromolecule receptors is difficult to achieve in a single imaging experiment. Herein, we present a multimodal workflow combining imaging mass spectrometry with immunohistochemistry (IHC) fluorescence imaging and brightfield microscopy imaging. Imaging mass spectrometry enables direct mapping of pharmaceutical compounds and metabolites, IHC fluorescence imaging can visualize large proteins, and brightfield microscopy imaging provides tissue morphology information. Single-cell resolution images are generally difficult to acquire using imaging mass spectrometry but are readily acquired with IHC fluorescence and brightfield microscopy imaging. Spatial sharpening of mass spectrometry images would thus allow for higher fidelity coregistration with other higher-resolution microscopy images. Imaging mass spectrometry spatial resolution can be predicted to a finer value via a computational image fusion workflow, which models the relationship between the intensity values in the mass spectrometry image and the features of a high-spatial resolution microscopy image. As a proof of concept, our multimodal workflow was applied to brain tissue extracted from a Sprague-Dawley rat dosed with a kratom alkaloid, corynantheidine. Four candidate mathematical models, including linear regression, partial least-squares regression, random forest regression, and two-dimensional convolutional neural network (2-D CNN), were tested. The random forest and 2-D CNN models most accurately predicted the intensity values at each pixel as well as the overall patterns of the mass spectrometry images, while also providing the best spatial resolution enhancements. Herein, image fusion enabled predicted mass spectrometry images of corynantheidine, GABA, and glutamine to approximately 2.5 µm spatial resolutions, a significant improvement compared to the original images acquired at 25 µm spatial resolution. The predicted mass spectrometry images were then coregistered with an H&E image and IHC fluorescence image of the µ-opioid receptor to assess colocalization of corynantheidine with brain cells. Our study also provides insights into the different evaluation parameters to consider when utilizing image fusion for biological applications.

Divergent Metabolic Fates of Aromatic Amino Acid-Derived Isomers: Insights from Ex Vivo Metabolomics and HDX-HRMS/MS-Based Resolution of Tautomers.

Tautomers are one of the many types of isomers, and differences in tautomeric structures confer altered chemical and biological properties. Using ultrahigh-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) ex vivo metabolomics, we investigate, in whole blood, the divergent metabolism of enol and keto forms of indole-3-pyruvate (IPyA), a tautomeric product of aromatic amino acid metabolism. Two new compounds resulting from IPyA metabolism were discovered, 3-(1H-indol-3-yl)-2,3-dioxopropanoic acid or "indole-3-oxopyruvic acid" and glutathionyl-indole pyruvate (GSHIPyA), which were characterized via ultraviolet photodissociation (UVPD) and higher-energy collisional dissociation (HCD). Computational calculations support the hypothesis that GSHIPyA forms specifically through the enol form of IPyA. GSHIPyA is also hypothesized to be tautomeric, and a hydrogen-deuterium exchange-high-resolution tandem mass spectrometry (HDX-HRMS/MS) approach is developed to prove the presence of an enol and keto tautomer. HDX of GSHIPyA labels the keto form with an additional deuterium, relative to the enol form. HRMS/MS of the labeled isomers is employed to leverage the relationship of resolving power scaling inversely with the square root of m/z, for Orbitrap mass analyzers. HRMS/MS yields a smaller-molecular-weight deuterated tautomeric product ion, reducing the analyte ion m/z and thus lowering the resolving power necessary to separate the deuterated keto tautomer product ion from the [13]C product ion.

Indole-3-pyruvate: Analysis and Control of Tautomerism and Reactivity.

It is well-known in biochemistry that structure confers function, meaning that chemical structural elucidation is critical to truly understanding the function of a given metabolite. Indole-3-pyruvate (IPyA) exists in an equilibrium between the keto and enol tautomeric forms. IPyA is suggested to play a role in immune function; however, determining whether the tautomeric forms function differently can only be studied if an analytical method is capable of distinguishing between the two forms. Herein, we describe the use of UHPLC-HRMS to gain insight into the physical variables that govern IPyA tautomer equilibrium, reactivity, and detection limit. We use hydrogen-deuterium exchange (HDX) to identify enol and keto peaks, and we show that tautomers exhibit a valley of fronting followed by a tailing peak shape (though separation is still attainable) and identical MS/MS spectra. We observed drastically different ratios of keto and enol forms in different solvents, which is an important consideration for in vitro studies. IPyA was found to be highly unstable with accelerated reactivity in peroxides. Through in vitro reactivity studies, IPyA produced a myriad of known and unknown metabolites via nonenzymatic processes, many of which were mapped in vivo via the analysis of human plasma. Finally, we show that vitamin C (ascorbic acid) can slow this reactivity and enable sensitive detection in whole blood.

Structural characterization of sphingomyelins from tissue using electron-induced dissociation.

RATIONALE: Sphingomyelins (SMs) and resulting metabolic products serve important functional and cell signaling roles and can act as potential biomarkers and therapeutic targets in many pathological disorders. SMs each contain a sphingoid base, an amide-linked fatty acyl chain, and a phosphocholine headgroup. Despite these simple building blocks, variations and modifications of both the sphingoid base and the fatty acyl chain result in a diverse array of structurally complicated SM compounds. Conventional tandem mass spectrometry (MS/MS) using the collision-induced dissociation (CID) method only provides limited structural information, necessitating other tools to unravel the structural complexity of these lipids. METHODS: We utilize electron-induced dissociation (EID) and sequential CID/EID approaches to elucidate detailed structural features of SMs. Integrating the CID/EID method into an imaging MS workflow enables accurate identification of SMs directly from kidney tissue. RESULTS: The application of EID enables identification of SMs at the molecular species level, identifying the sphingosine base and the amide-linked fatty acyl chains. Furthermore, removal of the phosphocholine headgroup via CID followed by sequential EID in an MS3 analysis (CID/EID) enhances the structural information obtained. CID/EID provides diagnostic fragmentation patterns revealing the hydroxylation site and double bond position in both the sphingosine base and amide-linked fatty acyl chains. CONCLUSIONS: Detailed structural information of SMs from synthetic standards and biological tissue samples is obtained using an alternative electron-based dissociation method. Accurate characterization of SMs promises to better inform studies of tissue biochemistry, lipid metabolism, and molecular pathology.

Multiple ion isolation and accumulation events for selective chemical noise reduction and dynamic range enhancement in MALDI imaging mass spectrometry.

Abundant chemical noise in MALDI imaging mass spectrometry experiments can impede the detection of less abundant compounds of interest. This chemical noise commonly originates from the MALDI matrix as well as other endogenous compounds present in high concentrations and/or with high ionization efficiencies. MALDI imaging mass spectrometry of biological tissues measures numerous biomolecular compounds that exist in a wide range of concentrations in vivo. When ion trapping instruments are used, highly abundant ions can dominate the charge capacity and lead to space charge effects that hinder the dynamic range and detection of lowly abundant compounds of interest. Gas-phase fractionation has been previously utilized in mass spectrometry to isolate and enrich target analytes. Herein, we have characterized the use of multiple continuous accumulations of selected ions (Multi CASI) to reduce the abundance of chemical noise and diminish the effects of space charge in MALDI imaging mass spectrometry experiments. Multi CASI utilizes the mass-resolving capability of a quadrupole mass filter to perform multiple sequential ion isolation events prior to a single mass analysis of the combined ion population. Multi CASI was used to improve metabolite and lipid detection in the MALDI imaging mass spectrometry analysis of rat brain tissue.

Imaging and Structural Characterization of Phosphatidylcholine Isomers from Rat Brain Tissue Using Sequential Collision-Induced Dissociation/Electron-Induced Dissociation.

The chemical complexity of biological tissues creates challenges in the analysis of lipids via imaging mass spectrometry. The presence of isobaric and isomeric compounds introduces chemical noise that makes it difficult to unambiguously identify and accurately map the spatial distributions of these compounds. Electron-induced dissociation (EID) has previously been shown to profile phosphatidylcholine (PCs) sn-isomers directly from rat brain tissue in matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry. However, the acquisition of true pixel-by-pixel images, as opposed to regional profiling measurements, using EID is difficult due to low fragmentation efficiency and precursor ion signal dilution into multiple fragment ion channels, resulting in low sensitivity. In this work, we have developed a sequential collision-induced dissociation (CID)/EID method to visualize the distribution of sn-isomers in MALDI imaging mass spectrometry experiments. Briefly, CID is performed on sodium-adducted PCs, which results in facile loss of the phosphocholine headgroup. This ion is then subjected to an EID analysis. Since the lipid headgroup is removed prior to EID, a major fragmentation pathway common to EID ion activation is eliminated, resulting in a more sensitive analysis. This sequential CID/EID workflow generates sn-specific fragment ions allowing for the assignment of the sn-positions. Carbon-carbon double-bond (C═C) positions are also localized along the fatty acyl tails by the presence of a 2 Da shift pattern in the fragment ions arising from carbon-carbon bond cleavages. Moreover, the integration of the CID/EID method into MALDI imaging mass spectrometry enables the mapping of the absolute and relative distribution of sn-isomers at every pixel. The localized relative abundances of sn-isomers vary throughout brain substructures and likely reflect different biological functions and metabolism.

Relative Quantification of Lipid Isomers in Imaging Mass Spectrometry Using Gas-Phase Charge Inversion Ion/Ion Reactions and Infrared Multiphoton Dissociation.

Accurate structural identification of lipids in imaging mass spectrometry is critical to properly contextualizing spatial distributions with tissue biochemistry. Gas-phase charge inversion ion/ion reactions alter the ion type prior to dissociation to allow for more structurally informative fragmentation and improve lipid identification at the isomeric level. In this work, infrared multiphoton dissociation (IRMPD) was interfaced with a commercial hybrid Qh-FT-ICR mass spectrometer to enable the rapid fragmentation of gas-phase charge inversion ion/ion reaction products at every pixel in imaging mass spectrometry experiments. An ion/ion reaction between phosphatidylcholine (PC) monocations generated from rat brain tissue via matrix-assisted laser desorption/ionization (MALDI) and 1,4-phenylenediproprionic acid reagent dianions generated via electrospray ionization (ESI) followed by IRMPD of the resulting product ion complex produces selective fatty acyl chain cleavages indicative of fatty acyl carbon compositions in the lipid. Ion/ion reaction images using this workflow allow for mapping of the relative spatial distribution of multiple PC isomers under a single sum composition lipid identification. Lipid isomers display significantly different relative spatial distributions within rat brain tissue, highlighting the importance of resolving isomers in imaging mass spectrometry experiments.

Selective Schiff base formation via gas-phase ion/ion reactions to enable differentiation of isobaric lipids in imaging mass spectrometry.

The separation and identification of lipids in complex mixtures are critical to deciphering their cellular functions. Failure to resolve isobaric compounds (e.g., via high mass resolution or tandem mass spectrometry) can result in incorrect identifications in mass spectrometry experiments. In imaging mass spectrometry, unresolved peaks can also result in composite images of multiple compounds, giving inaccurate depictions of molecular distributions. Gas-phase ion/ion reactions can be used to selectively react with specific chemical functional groups on a target analyte, thereby extracting it from a complex mixture and shifting its m/z value to an unobstructed region of the mass range. Herein, we use selective Schiff base formation via a novel charge inversion ion/ion reaction to purify phosphatidylserines from other isobaric (i.e., same nominal mass) lipids and reveal their singular distributions in imaging mass spectrometry. The selective Schiff base formation between singly deprotonated phosphatidylserine (PS) lipid anions and doubly charged N,N,N',N'-tetramethyl-N,N'-bis(6-oxohexyl)hexane-1,6-diaminium (TMODA) cations is performed using a modified commercial dual source hybrid Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. This process is demonstrated using the isobaric lipids [PS 40:6 - H]- (m/z 834.528) and [SHexCer d38:1 - H]- (m/z 834.576), which produces [PS 40:6 + TMODA - H - H2O]+ (m/z 1186.879), and [SHexCer d38:1 + TMODA - H]+ (m/z 1204.938) product ions following the gas-phase charge inversion reaction. These product ions differ by roughly 18 Da in mass and are easily separated by low mass resolution analysis, while the isobaric precursor ions require roughly 45,000 mass resolving power (full-width at half maximum) to separate. Imaging mass spectrometry using targeted gas-phase ion/ion reactions shows distinct spatial distributions for the separated lipid product ions relative to the composite images of the unseparated precursor ions.

Structural Elucidation and Relative Quantification of Sodium- and Potassium-Cationized Phosphatidylcholine Regioisomers Directly from Tissue Using Electron Induced Dissociation.

Comprehensive structural characterization of phosphatidylcholines (PCs) is essential to understanding their biological functions and roles in metabolism. Electron induced dissociation (EID) of protonated PCs directly generated from biological tissues has previously been shown to provide in-depth structural information on the lipid headgroup, regiosiomerism of fatty acyl tails and double bond positions. Although phosphatidylcholine ions formed via alkali metal cationization (i.e., [M + Na]+ and [M + K]+) are commonly generated during matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry experiments, the gas-phase ion chemistry behavior of EID on sodium- and potassium-cationized phosphatidylcholine ion types has not been studied for ions generated directly from tissue. Herein, we demonstrate EID on [M + Na]+ and [M + K]+ ion types in a MALDI imaging mass spectrometry workflow for lipid structural characterization. Briefly, near-complete structural information can be obtained upon EID of sodium- and potassium-cationized PCs, including diagnostic fragmentation of the lipid headgroup as well as identification of fatty acyl chain positions and double bond position. EID of cationized lipids generates sn-specific glycerol backbone cleavages as well as a favorable combined loss of sn-2 fatty acid with choline over sn-1, allowing for facile differentiation and relative quantification of PC regioisomers. Moreover, relative quantification of sn-positional isomers from biological tissue reveals that the relative percentages of sodium- and potassium-cationized sn-positional isomers varies significantly in different regions of rat brain tissue.

Nationwide Clinical Practice Patterns of Anesthesiology Critical Care Physicians: A Survey to Members of the Society of Critical Care Anesthesiologists.

BACKGROUND: Despite the growing contributions of critical care anesthesiologists to clinical practice, research, and administrative leadership of intensive care units (ICUs), relatively little is known about the subspecialty-specific clinical practice environment. An understanding of contemporary clinical practice is essential to recognize the opportunities and challenges facing critical care anesthesia, optimize staffing patterns, assess sustainability and satisfaction, and strategically plan for future activity, scope, and training. This study surveyed intensivists who are members of the Society of Critical Care Anesthesiologists (SOCCA) to evaluate practice patterns of critical care anesthesiologists, including compensation, types of ICUs covered, models of overnight ICU coverage, and relationships between these factors. We hypothesized that variability in compensation and practice patterns would be observed between individuals. METHODS: Board-certified critical care anesthesiologists practicing in the United States were identified using the SOCCA membership distribution list and invited to take a voluntary online survey between May and June 2021. Multiple-choice questions with both single- and multiple-select options were used for answers with categorical data, and adaptive questioning was used to clarify stem-based responses. Respondents were asked to describe practice patterns at their respective institutions and provide information about their demographics, salaries, effort in ICUs, as well as other activities. RESULTS: A total of 490 participants were invited to take this survey, and 157 (response rate 32%) surveys were completed and analyzed. The majority of respondents were White (73%), male (69%), and younger than 50 years of age (82%). The cardiothoracic/cardiovascular ICU was the most common practice setting, with 69.5% of respondents reporting time working in this unit. Significant variability was observed in ICU practice patterns. Respondents reported spending an equal proportion of their time in clinical practice in the operating rooms and ICUs (median, 40%; interquartile range [IQR], 20%-50%), whereas a smaller proportion-primarily those who completed their training before 2009-reported administrative or research activities. Female respondents reported salaries that were $36,739 less than male respondents; however, this difference was not statistically different, and after adjusting for age and practice type, these differences were less pronounced (-$27,479.79; 95% confidence interval [CI], -$57,232.61 to $2273.03; P = .07). CONCLUSIONS: These survey data provide a current snapshot of anesthesiology critical care clinical practice patterns in the United States. Our findings may inform decision-making around the initiation and expansion of critical care services and optimal staffing patterns, as well as provide a basis for further work that focuses on intensivist satisfaction and burnout.

Processed intraoperative burst suppression and postoperative cognitive dysfunction in a cohort of older noncardiac surgery patients.

Postoperative cognitive dysfunction (POCD) is a decline in cognitive test performance which persists months after surgery. There has been great interest in the anesthesia community regarding whether variables generated by commercially available processed EEG monitors originally marketed to prevent awareness under anesthesia can be used to guide intraoperative anesthetic management to prevent POCD. Processed EEG monitors represent an opportunity for anesthesiologists to directly monitor the brain even if they have not been trained to interpret EEG waveforms. There is continued equipoise regarding whether any of the variables generated by the machines' interpretation of raw data are associated with POCD. Most literature has focused on the depth of anesthesia number, however recent studies have shown that processed depth may not be accurate in older age groups due to reduced alpha band power. Burst suppression is an encephalographic pattern of high voltage activity alternating with periods of electrical silence and is another marker of depth which can be obtained from commercial processed EEG monitors. We performed a prospective cohort study to determine whether burst suppression and burst suppression ratio as measured by the BIS Monitor (Bispectral Index, BIS Medtronic, Boulder CO), is associated with cognitive dysfunction 3 months after surgery. We recruited 167 elective surgery patients, 65 years of age and older, anticipated to require at least 2 day inpatient admission. Our main outcome measure was cognitive decline in composite z-score on the Alzheimer's Disease Research Center UDS Battery of at least 1 standard deviation 3 months after surgery relative to preoperative baseline. 14% experienced POCD, this group was older (72 [70, 74] versus 70 [67, 75] years), and had frailty scores as measured by the FRAIL Scale (2 [0, 3] versus 1 [0, 2]) and lower baseline z-scores (- 0.2 [- 0.6, 0.5] versus 0.1 [- 0.3, 0.5]). There was a univariable association between suppression ratio > 10 (SR > 10) and POCD (4.8 [0, 37.3] versus 15.4 [4.0-142.4] min), p = .038. However, after adjustment this relationship did not persist, only anesthetic technique, age, and pain remained in the model. In our cohort of older elective noncardiac surgery patients we found a marginal association between processed burst suppression (total burst suppression p = .067, SR > 5 p = .052, SR > 10.038) which did not persist in a multivariable model. Patients with POCD had almost twice the number of minutes of burst suppression, and three times the amount of time for SR > 5 and > 10. Our finding may be a limitation of the monitor's ability to detect burst suppression. The consistent trend towards more intraoperative burst suppression in patients who developed POCD suggests that future studies are needed to investigate the relationship of raw intraoperative burst suppression and POCD.Trial registry Clinical trial number and registry URL: Optimizing Postoperative Cognitive Dysfunction in the Elderly-PRESERVE, Clinical Trials Gov# NCT02650687; https://clinicaltrials.gov/ct2/show/NCT02650687 .

Perspective on Emerging Mass Spectrometry Technologies for Comprehensive Lipid Structural Elucidation.

Lipids and metabolites are of interest in many clinical and research settings because it is the metabolome that is increasingly recognized as a more dynamic and sensitive molecular measure of phenotype. The enormous diversity of lipid structures and the importance of biological structure-function relationships in a wide variety of applications makes accurate identification a challenging yet crucial area of research in the lipid community. Indeed, subtle differences in the chemical structures of lipids can have important implications in cellular metabolism and many disease pathologies. The speed, sensitivity, and molecular specificity afforded by modern mass spectrometry has led to its widespread adoption in the field of lipidomics on many different instrument platforms and experimental workflows. However, unambiguous and complete structural identification of lipids by mass spectrometry remains challenging. Increasingly sophisticated tandem mass spectrometry (MS/MS) approaches are now being developed and seamlessly integrated into lipidomics workflows to meet this challenge. These approaches generally either (i) alter the type of ion that is interrogated or (ii) alter the dissociation method in order to improve the structural information obtained from the MS/MS experiment. In this Perspective, we highlight recent advances in both ion type alteration and ion dissociation methods for lipid identification by mass spectrometry. This discussion is aimed to engage investigators involved in fundamental ion chemistry and technology developments as well as practitioners of lipidomics and its many applications. The rapid rate of technology development in recent years has accelerated and strengthened the ties between these two research communities. We identify the common characteristics and practical figures of merit of these emerging approaches and discuss ways these may catalyze future directions of lipid structural elucidation research.

Neurophysiologic Intraoperative Monitoring for Spine Surgery: A Practical Guide From Past to Present.

Intraoperative neuromonitoring was introduced in the second half of the 20th century with the goal of preventing patient morbidity for patients undergoing complex operations of the central and peripheral nervous system. Since its early use for scoliosis surgery, the growth and utilization of IOM techniques expanded dramatically over the past 50 years to include spinal tumor resection and evaluation of cerebral ischemia. The importance of IOM has been broadly acknowledged, and in 1989, the American Academy of Neurology (AAN) released a statement that the use of SSEPs should be standard-of-care during spine surgery. In 2012, both the AAN and the American Clinical Neurophysiology Society (ACNS) recommended that: "Intraoperative monitoring (IOM) using SSEPs and transcranial MEPs be established as an effective means of predicting an increased risk of adverse outcomes, such as paraparesis, paraplegia, and quadriplegia, in spinal surgery." With a multimodal approach that combines SSEPs, MEPs, and sEMG with tEMG and D waves, as appropriate, sensitivity and specificity can be maximized for the diagnosis of reversible insults to the spinal cord, nerve roots, and peripheral nerves. As with most patient safety efforts in the operating room, IOM requires contributions from and communication between a number of different teams. This comprehensive review of neuromonitoring techniques for surgery on the central and peripheral nervous system will highlight the technical, surgical and anesthesia factors required to optimize outcomes. In addition, this review will discuss important trouble shooting measures to be considered when managing ION changes concerning for potential injury.

Hemorrhagic Complications of Invasive Intracranial Pressure Monitor Placement in Acute Liver Failure: Outcomes of a Single-Center Protocol and Comprehensive Literature Review.

BACKGROUND: Elevated intracranial pressure due to cerebral edema is associated with very poor survival in patients with acute liver failure (ALF). Placing an intracranial pressure monitor (ICPm) aids in management of intracranial hypertension, but is associated with potentially fatal hemorrhagic complications related to the severe coagulopathy associated with ALF. METHODS: An institutional Acute Liver Failure Clinical Protocol (ALF-CP) was created to correct ALF coagulopathy prior to placing parenchymal ICP monitoring bolts. We aimed to investigate the frequency, severity, and clinical significance of hemorrhagic complications associated with ICPm bolt placement in the setting of an ALF-CP. All assessed patients were managed with the ALF-CP and had rigorous radiologic follow-up allowing assessment of the occurrence and chronology of hemorrhagic complications. We also aimed to compare our outcomes to other studies that were identified through a comprehensive review of the literature. RESULTS: Fourteen ALF patients were included in our analysis. There was no symptomatic hemorrhage after ICP monitor placement though four patients were found to have minor intraparenchymal asymptomatic hemorrhages after liver transplant when the ICP monitor had been removed, making the rate of radiographically identified clinically asymptomatic hemorrhage 28.6%. These results compare favorably to those found in a comprehensive review of the literature which revealed rates as high as 17.5% for symptomatic hemorrhages and 30.4% for asymptomatic hemorrhage. CONCLUSION: This study suggests that an intraparenchymal ICPm can be placed safely in tertiary referral centers which utilize a protocol such as the ALF-CP that aggressively corrects coagulopathy. The ALF-CP led to advantageous outcomes for ICPm placement with a 0% rate of symptomatic and low rate of asymptomatic hemorrhagic complications, which compares well to results reported in other series. A strict ICPm placement protocol in this setting facilitates management of ALF patients with cerebral edema during the wait time to transplantation or spontaneous recovery.

Identification of Phosphatidylcholine Isomers in Imaging Mass Spectrometry Using Gas-Phase Charge Inversion Ion/Ion Reactions.

Gas-phase ion/ion reactions have been enabled on a commercial dual source, hybrid QhFT-ICR mass spectrometer for use during imaging mass spectrometry experiments. These reactions allow for the transformation of the ion type most readily generated from the tissue surface to an ion type that gives improved chemical structural information upon tandem mass spectrometry (MS/MS) without manipulating the tissue sample. This process is demonstrated via the charge inversion reaction of phosphatidylcholine (PC) lipid cations generated from rat brain tissue via matrix-assisted laser desorption/ionization (MALDI) with 1,4-phenylenedipropionic acid (PDPA) reagent dianions generated via electrospray ionization (ESI). Collision-induced dissociation (CID) of the resulting demethylated PC product anions allows for the determination of the lipid fatty acyl tail identities and positions, which is not possible via CID of the precursor lipid cations. The abundance of lipid isomers revealed by this workflow is found to vary significantly in different regions of the brain. As each isoform may have a unique cellular function, these results underscore the importance of accurately separating and identifying the many isobaric and isomeric lipids and metabolites that can complicate image interpretation and spectral analysis.

Dynamic Range Expansion by Gas-Phase Ion Fractionation and Enrichment for Imaging Mass Spectrometry.

In the analysis of biological tissue by imaging mass spectrometry (IMS), the limit of detection and dynamic range are of paramount importance in obtaining experimental results that provide insight into underlying biological processes. Many important biomolecules are present in the tissue milieu in low concentrations and in complex mixtures with other compounds of widely ranging abundances, challenging the limits of analytical technologies. In many IMS experiments, the ion signal can be dominated by a few highly abundant ion species. On trap-based instrument platforms that accumulate ions prior to mass analysis, these high abundance ions can diminish the detection and dynamic range of lower abundance ions. Herein, we describe two strategies for combating these challenges during IMS experiments on a hybrid QhFT-ICR MS. In one iteration, the mass resolving capabilities of a quadrupole mass filter are used to selectively enrich ions of interest via a technique previously termed continuous accumulation of selected ions. Second, we have introduced a supplemental dipolar AC waveform to the quadrupole mass filter of a commercial QhFT-ICR mass spectrometer to perform selected ion ejection prior to the ion accumulation region. This setup allows the selective ejection of the most abundant ion species prior to ion accumulation, thereby greatly improving the molecular depth with which IMS can probe tissue samples. The gain in sensitivity of both of these approaches roughly scales with the number of accumulated laser shots up to the charge capacity of the ion accumulation cell. The efficiencies of these two strategies are described here by performing lipid imaging mass spectrometry analyses of a rat brain.

Innovations in laboratory-based dynamic micro-CT to accelerate in situ research.

In the past few years, dynamic computed tomography (CT) approaches or uninterrupted acquisitions of deforming materials have rapidly emerged as an essential technique to understand material evolution, facilitating in situ investigations ranging from mechanical deformation to fluid flow in porous materials and beyond. Developments at synchrotron facilities have led this effort, pointing to the future of the technique. In the laboratory, recent developments at TESCAN XRE have made it possible to image, reconstruct and inspect dynamic processes in the laboratory with a temporal resolution below 10 s, meaning that an entire acquisition from 0 to 360° is completed within 10 s. The aim of this study is to explore the challenges and innovations that have led to the ability to perform high speed, dynamic acquisitions. A unique horizontally rotating gantry based micro-CT system was developed to facilitate complex in situ experiments. In doing so, the sample stays fixed while source and detector are uninterruptedly rotating around a vertical axis. In this work, the dynamic CT method with this rotating gantry based system will be described by two application examples: (1) deformation and collapse of a delicate beer foam and (2) in situ baking process of pastry. For the pastry baking process, an oven was needed to reach baking temperature. In a conventional micro-CT system, where the sample rotates, it is not so obvious to rotate an oven with sensor and heating cables. On the other hand, the delicate foam of a collapsing beer head is able to rotate, but because of the tangential convection during fast rotation (<10 s), it could influence the bubble detachment and liquid drainage and thus also the foam degradation. To investigate both processes, a horizontally rotating gantry based micro-CT is required. For both examples it was possible to quantify the key parameters such as pore size and distribution to better understand the rise and fall of porous foams. These examples will highlight the recent progress in adapting micro-CT workflows to accommodate uninterrupted imaging of dynamic events and point to opportunities for future continued development. LAY DESCRIPTION: Micro-CT allows the nondestructive visualisation of internal structures and is being used routinely in the field of Material Science, Geoscience, Life Science and more. Because of its nondestructive aspect, micro-CT is optimal to take repetitive scans of the same sample over time. The combination of taking different scans over time is so called time-resolved CT. By doing so, crucial insights can be obtained on how materials form, deform and perform over time or under certain external conditions. TESCAN XRE have made it possible to image, reconstruct and inspect dynamic processes in the laboratory with a temporal resolution below 10 s. The dynamic CT method will be described through the lens of two application examples: (1) deformation and collapse of a delicate beer foam and (2) in situ baking process of pastry. These examples will highlight the recent progress in adapting micro-CT workflows to accommodate imaging of dynamic events and point to opportunities for future continued development.

Repeat Cooled Radiofrequency Ablation Is Beneficial for Chronic Posterior Sacroiliac Joint Pain.

OBJECTIVE: This study aimed to investigate the effectiveness of repeat cooled radiofrequency ablation (CRFA) in chronic posterior sacroiliac joint (SIJ) pain. DESIGN: The electronic records of 41 adult patients who had successful CRFA were reviewed for duration of pain relief and utilization of medical care for six months before and after each CRFA procedure. SETTING: Academic, tertiary medical center. PATIENTS: Forty-one adult patients who had CRFA for chronic posterior SIJ pain. RESULTS: A repeat ipsilateral CRFA ablation procedure provided 9.0 months of pain relief compared with 5.5 months after the first CRFA procedure (P = 0.0378). The total number of medical treatments decreased after the first CRFA procedure (from 343 to 201). The medical cost decreased by 51.0% after the first CRFA and by 70.4% after the repeated CRFA procedure. CONCLUSIONS: Using repeated nonsurgical, minimally invasive approach, CRFA relieves chronic posterior SIJ pain and reduces patients' utilization of medical services.