Background: Early detection of cerebral ischemia and metabolic crisis is crucial in critically ill subarachnoid hemorrhage (SAH) patients. Variable increases in brain tissue oxygen tension (PbtO 2 ) are observed when the fraction of inspired oxygen (FiO 2 ) is increased to 1.0. The aim of this prospective study was to evaluate whether a 3-minute hyperoxic challenge can identify patients at risk for cerebral ischemia detected by cerebral microdialysis. Methods: Twenty consecutive severe SAH patients undergoing continuous cerebral PbtO 2 and microdialysis monitoring were included. FiO 2 was increased to 1.0 for 3 minutes (the FiO 2 challenge) twice a day and PbtO 2 responses during the FiO 2 challenges were related to cerebral microdialysis–measures, ie, lactate, the lactate-pyruvate ratio, and glycerol. Multivariable linear and logistic regression models were created for each outcome parameter. Results: After predefined exclusions, 274 of 400 FiO 2 challenges were included in the analysis. Lower absolute increases in PbtO 2 (∆PbtO 2 ) during FiO 2 challenges were significantly associated with higher cerebral lactate concentration ( P <0.001), and patients were at higher risk for ischemic lactate levels >4 mmol/L (odds ratio 0.947; P =0.04). Median (interquartile range) ∆PbtO 2 was 7.1 (4.6 to 12.17) mm Hg when cerebral lactate was >4 mmol/L and 10.2 (15.76 to 14.24) mm Hg at normal lactate values (≤4 mmol/L). Median ∆PbtO 2 was significantly lower during hypoxic than during hyperglycolytic lactate elevations (4.6 vs. 10.6 mm Hg, respectively; P <0.001). Lactate-pyruvate ratio and glycerol levels were mainly determined by baseline characteristics. Conclusions: A 3-minute FiO 2 challenge is an easy to perform and feasible bedside diagnostic tool in SAH patients. The absolute increase in PbtO 2 during the FiO 2 challenge might be a useful surrogate marker to estimate cerebral lactate concentrations and might be used to identify patients at risk for impending ischemia.
Brain microdialysis samples of intensive care patients treated with the essential anesthetics ketamine, midazolam and propofol were investigated. Importantly, despite decades of clinical use, comprehensive human cerebral pharmacokinetic data of these drugs is still missing. To encounter this apparent lack of knowledge, we combined cerebral microdialysis with leading-edge analytical instrumentation to monitor the neurochemistry of living human patients. For the quantitative analysis, high performing analytical approaches were developed that can handle minute sample volumes and possible ultralow target analyte levels. The developed methods provided detection limits below 100 ng L−1 for all target analytes and high precision (below 4% RSD intraday). Methods were linear between LODs and 100 μg L−1 for ketamine, 75 μg L−1 for midazolam and 10 μg L−1 for propofol respectively, with coefficients of determination R2≥ 0.999. Further, being aware of the error-prone and demanding translation of microdialysis levels to interstitial concentrations, in vitro approaches for recovery testing of microdialysis probes as well as internal normalization approaches were conducted. Thus, we herein report the first cerebral pharmacokinetic data of ketamine, midazolam and propofol determined in microdialysis samples of 15 neurointensive care patients. We could prove blood-brain barrier penetration of all of the investigated anesthetics and could correlate applied dosages and actual brain exposition of ketamine. However, we emphasize the need of an expanded prospective study including individual microdialysis recovery testing as well as matched serum and/or cerebrospinal fluid collection for a more comprehensive cerebral pharmacokinetic understanding.
Precise tissue sampling during resection of suspected low-grade gliomas (LGG) is the basis for an accurate histopathological diagnosis to enable adequate patient management. In the course of malignant transformation of initial LGG, small intratumoral areas of glioblastoma tissue can potentially arise that might be unrecognized during surgery and thus result in treatment failure. Recently, 5-aminolevulinic acid (5-ALA) induced fluorescence was identified as intraoperative marker for visualization of focal intratumoral WHO grade III areas. The aim of this study is thus to clarify if 5-ALA is also capable to identify areas of unexpected glioblastoma tissue during surgery of radiologically suspected LGG. Our database at the Medical University of Vienna and University of California, San Francisco was screened for adult patients with 5-ALA fluorescence-guided resection of a suspected glioma with non-significant MRI contrast-enhancement (CE; no, patchy/faint or focal CE). In this study, only patients with newly diagnosed lesions were included. In contrast, recurrent gliomas and biopsy only cases were excluded. In all patients, histopathological diagnosis was established according to the WHO classification. Altogether, 7 patients (median age: 53 years, range: 30–66 years) with histological diagnosis of a glioblastoma were identified despite initial radiological suspicion of LGG. Of these, no CE was found on preoperative MRI in two cases (29%), patchy/faint CE in two cases (29%) and focal CE in three cases (42%). During surgery, intratumoral areas with focal 5-ALA induced fluorescence were observed in all 7 patients. In contrast, no visible fluorescence was found in the remaining intratumoral regions. Our study indicates that 5-ALA induced fluorescence is able to identify intratumoral areas containing even focal glioblastoma tissue in radiologically suspected LGG. Thus, the 5-ALA technique will in future markedly improve tissue sampling during resection of suspected LGG to allow a precise histopathological diagnosis and optimized postoperative patient management.
Brain injury is accompanied by neuroinflammation, accumulation of extracellular glutamate and mitochondrial dysfunction, all of which cause neuronal death. The aim of this study was to investigate the impact of these mechanisms on neuronal death. Patients from the neurosurgical intensive care unit suffering aneurysmal subarachnoid hemorrhage (SAH) were recruited retrospectively from a respective database. In vitro experiments were performed in rat cortex homogenate, primary dissociated neuronal cultures, B35 and NG108-15 cell lines. We employed methods including high resolution respirometry, electron spin resonance, fluorescent microscopy, kinetic determination of enzymatic activities and immunocytochemistry. We found that elevated levels of extracellular glutamate and nitric oxide (NO) metabolites correlated with poor clinical outcome in patients with SAH. In experiments using neuronal cultures we showed that the 2-oxoglutarate dehydrogenase complex (OGDHC), a key enzyme of the glutamate-dependent segment of the tricarboxylic acid (TCA) cycle, is more susceptible to the inhibition by NO than mitochondrial respiration. Inhibition of OGDHC by NO or by succinyl phosphonate (SP), a highly specific OGDHC inhibitor, caused accumulation of extracellular glutamate and neuronal death. Extracellular nitrite did not substantially contribute to this NO action. Reactivation of OGDHC by its cofactor thiamine (TH) reduced extracellular glutamate levels, Ca2+ influx into neurons and cell death rate. Salutary effect of TH against glutamate toxicity was confirmed in three different cell lines. Our data suggest that the loss of control over extracellular glutamate, as described here, rather than commonly assumed impaired energy metabolism, is the critical pathological manifestation of insufficient OGDHC activity, leading to neuronal death.
Effective concentrations of antibiotics in brain tissue are essential for antimicrobial therapy of brain infections. However, data concerning cerebral penetration properties of antibiotics for treatment or prophylaxis of central nervous system infections are rare. Six patients suffering subarachnoid hemorrhage and requiring cerebral microdialysis for neurochemical monitoring were included in this study. Free interstitial concentrations of cefuroxime after intravenous application of 1,500 mg were measured by microdialysis in brain tissue, as well as in plasma at steady-state (n = 6) or after single-dose administration (n = 1). At steady state, free area under the concentration-time curve from 0 to 24 h (AUC0-24) values of 389.0 ± 210.3 mg/liter·h and 131.4 ± 72.8 mg/liter·h were achieved for plasma and brain, respectively, resulting in a brain tissue penetration ratio (AUC0-24 brain/AUC0-24 free plasma) of 0.33 ± 0.1. Plasma and brain tissue concentrations at individual time points correlated well (R = 0.59, P = 0.001). At steady-state time over MIC (t>MIC) values of >40% of dosing interval were achieved up to an MIC of 16 mg/liter for plasma and 4 mg/liter for brain tissue. Although MIC90 values could not be achieved in brain tissue for relevant bacteria, current dosing strategies of cefuroxime might be sufficient to treat pathogens with MIC values up to 4 mg/liter. The activity of cefuroxime in brain tissue might be overestimated when relying exclusively on plasma levels. Although currently insufficient data after single dose administration exist, lower brain-plasma ratios observed after the first dose might warrant a loading dose for treatment and perioperative prophylaxis.
The prediction of the individual prognosis of low-grade glioma (LGG) patients is limited in routine clinical practice. Nowadays, 5-aminolevulinic acid (5-ALA) fluorescence is primarily applied for improved intraoperative visualization of high-grade gliomas. However, visible fluorescence is also observed in rare cases despite LGG histopathology and might be an indicator for aggressive tumor behavior. The aim of this study was thus to investigate the value of intraoperative 5-ALA fluorescence for prognosis in LGG patients. We performed a retrospective analysis of patients with newly diagnosed histopathologically confirmed LGG and preoperative 5-ALA administration at two independent specialized centers. In this cohort, we correlated the visible intraoperative fluorescence status with progression-free survival (PFS), malignant transformation-free survival (MTFS) and overall survival (OS). Altogether, visible fluorescence was detected in 7 (12%) of 59 included patients in focal intratumoral areas. At a mean follow-up time of 5.3 ± 2.9 years, patients with fluorescing LGG had significantly shorter PFS (2.3 ± 0.7 vs. 5.0 ± 0.4 years; p = 0.01), MTFS (3.9 ± 0.7 vs. 8.0 ± 0.6 years; p = 0.03), and OS (5.4 ± 1.0 vs. 10.3 ± 0.5 years; p = 0.01) than non-fluorescing tumors. Our data indicate that visible 5-ALA fluorescence during surgery of pure LGG might be an already intraoperatively available marker of unfavorable patient outcome and thus close imaging follow-up might be considered.
Introduction: Commonly effects of resuscitative measures are monitored by peripheral functions like ECG or blood pressure (BP). However, it is unknown if these effects will transfer to the brain, the ultimate target of resuscitation. Therefore we set out to establish a model allowing for concomitant determination of cerebral and peripheral metabolism in a complex cardiac arrest setting in rodents. Methods: In vitro experiments were performed to determine the most reliable flow rate of microdialysis in order to balance temporal resolution and recovery of measures of ischemia, and to specify the inter-assay variability and concentration linearity of our analytic System (CMA600, Sweden). For in vivo testing male Sprague-Dawley rats underwent multimodality monitoring, including ECG, arterial BP, CVP, EtCO2, SpO2 and core temperature. A microdialysis probe (CMA11; 2mm) was introduced into a guide cannula, which was stereotactically implanted 3 days before the experiment into the right hippocampus (histologically verified after necropsy). As reference for peripheral metabolism a second probe was inserted into the right femoral vein. Results: In vitro testing indicated that a flow rate of 1μl/min is sufficient to achieve acceptable recovery values (10-20%) and a temporal resolution of 8 minutes for the most reliable metabolic parameters, i.e. lactate, pyruvate, glutamate and glucose. By introducing this flow rate in our cardiac arrest model we were able to identify 3 main phases: initial surgical trauma, baseline conditions (after preparation and at least 1 hour after probe insertion) and ischemia during cardiac arrest. Compared to peripheral metabolism, cerebrally major deviations were observed during ischemia. Conclusion: Based on this optimized setting we established a reliable and solid model to investigate the impact of resuscitation methods on cerebral metabolism, highlighting the importance of concomitant peripheral and cerebral monitoring.
