Neurochemical monitoring using intracerebral microdialysis in patients with subarachnoid hemorrhage

Cerebral microdialysis demonstrates improvements in brain metabolism with cerebrospinal fluid diversion in spontaneous intracerebral hemorrhage

Background

Cerebral microdialysis (CMD) is an FDA-approved multimodal invasive monitoring technique that provides local brain metabolism measurements through continuous interstitial brain fluid sampling at the bedside. The past applications in traumatic brain injury and subarachnoid hemorrhage show that acute brain injury (ABI) can lead to a metabolic crisis reflected by changes in cerebral glucose, pyruvate, and lactate. However, limited literature exists on CMD in spontaneous intracerebral hemorrhage (ICH).

Case Description

A 45-year-old woman presented with a Glasgow Coma Scale of 8T and left frontal ICH with a 6 mm midline shift. She underwent craniotomy and ICH evacuation. Intraoperatively, CMD, brain tissue oxygenation (PbtO2), intracranial pressure (ICP), and cerebral blood flow (CBF) catheters were placed, targeted toward the peri-hematoma region. Postoperatively, ICP was normal; however, PbtO2, CBF, glucose, and lactate/ pyruvate ratio were abnormal. Due to concern for the metabolic crisis, poor examination, and hydrocephalus on computed tomography of the head (CTH), she underwent external ventricular drainage (EVD). Post-EVD, all parameters normalized (P < 0.05 on Student's t-test). Monitors were removed, and she was discharged to a nursing facility with a modified Rankin scale of 4.

Conclusion

Here, we demonstrate the safe implementation of CMD in ICH and the use of CMD in tandem with PbtO2/ICP/CBF to guide treatment in ICH. Despite a normal ICP, numerous cerebral metabolic derangements existed and improved after cerebrospinal fluid diversion. A normal ICP may not reflect underlying metabolic-substrate demands of the brain during ABI. CMD and PbtO2/CBF monitoring augment traditional ICP monitoring in brain injury. Further prospective studies will be needed to understand further the interplay between ICP, PbtO2, CBF, and CMD values in ABI.

Early brain metabolic disturbances associated with delayed cerebral ischemia in patients with severe subarachnoid hemorrhage

Delayed cerebral ischemia (DCI) is a devastating complication of aneurysmal subarachnoid hemorrhage (ASAH) causing brain infarction and disability. Cerebral microdialysis (CMD) monitoring is a focal technique that may detect DCI-related neurochemical changes as an advance warning. We conducted retrospective analyses from 44 poor-grade ASAH patients and analyzed glucose, lactate, pyruvate, and glutamate concentrations in control patients without DCI (n = 19), and in patients with DCI whose CMD probe was located within (n = 17) or outside (n = 8) a new infarct. When monitored from within a lesion, DCI was preceded by a decrease in glucose and a surge in glutamate, accompanied by increases in lactate/pyruvate and lactate/glucose ratios whereas these parameters remained stable in control patients. When CMD monitoring was performed outside the lesion, the glutamate surge was absent, but glucose and L/G ratio were still significantly altered. Overall, glucose and L/G ratio were significant biomarkers of DCI (se96.0, spe73.7-68.4). Glucose and L/G predicted DCI 67 h before CT detection of a new infarct. The pathogenesis of DCI therefore induces early metabolic disturbances that can be detected by CMD as an advance warning. Glucose and L/G could provide a trigger for initiating further examination or therapy, earlier than when guided by other monitoring techniques.

Meta-analysis of the effects of inert gases on cerebral ischemia-reperfusion injury

Recently, noble gas has become a hot spot within the medical field like respiratory organ cerebral anemia, acute urinary organ injury and transplantation. However, the shield performance in cerebral ischemia-reperfusion injury (CIRI) has not reached an accord. This study aims to evaluate existing evidence through meta-analysis to determine the effects of inert gases on the level of blood glucose, partial pressure of oxygen, and lactate levels in CIRI. We searched relevant articles within the following both Chinese and English databases: PubMed, Web of science, Embase, CNKI, Cochrane Library and Scopus. The search was conducted from the time of database establishment to the end of May 2023, and two researchers independently entered the data into Revman 5.3 and Stata 15.1. There were total 14 articles were enclosed within the search. The results showed that the amount of partial pressure of blood oxygen in the noble gas cluster was beyond that in the medicine gas cluster (P < 0.05), and the inert gas group had lower lactate acid and blood glucose levels than the medical gas group. The partial pressure of oxygen (SMD = 1.51, 95% CI 0.10 ~ 0.91 P = 0.04), the blood glucose level (SMD = - 0.59, 95% CI - 0.92 ~ - 0.27 P = 0.0004) and the lactic acid level (SMD = - 0.42, 95% CI - 0.80 ~ - 0.03 P = 0.03) (P < 0.05). These results are evaluated as medium-quality evidence. Inert gas can effectively regulate blood glucose level, partial pressure of oxygen and lactate level, and this regulatory function mainly plays a protective role in the small animal ischemia-reperfusion injury model. This finding provides an assessment and evidence of the effectiveness of inert gases for clinical practice, and provides the possibility for the application of noble gases in the treatment of CIRI. However, more operations are still needed before designing clinical trials, such as the analysis of the inhalation time, inhalation dose and efficacy of different inert gases, and the effective comparison of the effects in large-scale animal experiments.

Clinical protocol: Feasibility of evaluating abemaciclib neuropharmacokinetics of diffuse midline glioma using intratumoral microdialysis

Diffuse midline gliomas (DMG) are the most aggressive brain tumors of childhood and young adults, with documented 2-year survival rates <10%. Treatment failure is due in part to the function of the BBB. Intratumoral microdialysis sampling is an effective tool to determine brain entry of varied agents and could help to provide a better understanding of the relationship of drug permeability to DMG treatment responsivity. This is a non-randomized, single-center, phase 1 clinical trial. Up to seven young adult (18-39 years) patients with recurrent high-grade or diffuse midline glioma will be enrolled with the goal of 5 patients completing the trial over an anticipated 24 months. All patients will take abemaciclib pre-operatively for 4.5 days at twice daily dosing. Patients will undergo resection or biopsy, placement of a microdialysis catheter, and 48 hours of dialysate sampling coupled with timed plasma collections. If intratumoral tumor or brain dialysate sampling concentrations are >10nmol/L, or tumor tissue studies demonstrate CDK inhibition, then restart of abemaciclib therapy along with temozolomide will be administered for maintenance therapy and discontinued with evidence of radiologic or clinical disease progression. The poor survival associated with diffuse midline gliomas underscore the need for improved means to evaluate efficacy of drug delivery to tumor and peritumoral tissue. The findings of this novel study, will provide real-time measurements of BBB function which have the potential to influence future prognostic and diagnostic decisions in such a lethal disease with limited treatment options. Trial registration: Clinicaltrials.gov, NCT05413304. Registered June 10, 2022, Abemaciclib Neuropharmacokinetics of Diffuse Midline Glioma Using Intratumoral Microdialysis.

Neuropharmacological Study of Posaconazole for Glioblastoma: A Phase 0 Clinical Trial Protocol

BACKGROUND

Glioblastoma (GBM) is the most common malignant primary brain tumor with a universally poor prognosis. GBMs express elevated levels of hexokinase 2 (HK2), catalyzing the critical step in glycolysis and influencing several oncogenic pathways. Previous preclinical work has suggested a role for repurposed posaconazole (PCZ) in downregulating HK2 activity, reducing lactate and pyruvate production, interfering with tumor cell metabolism, and increasing mouse survival.

OBJECTIVE

To establish brain tumor penetrance, neuropharmacokinetic profile, and mechanistic effect on tumor cell metabolism of PCZ in adults with GBM.

METHODS

This is an open label, nonrandomized, parallel arm trial involving patients with GBM. Cohorts will receive PCZ (intervention, n = 5) or will not receive PCZ (control, n = 5), followed by tumor resection and microdialysis catheter placement. Dialysate, plasma, and tumor samples will be analyzed for lactate and pyruvate concentrations. Tumor samples will also be assessed for PCZ concentration, HK2 expression, angiogenesis, and apoptosis. PCZ's neuropharmacokinetics will be determined based on the concentration vs time profile and area under the curve 0 to 24 hours of PCZ concentration in the brain interstitium.

EXPECTED OUTCOMES

(1) Increased PCZ concentration in contrast-enhancing brain regions compared with nonenhancing regions; (2) inverse correlation between lactate/pyruvate and PCZ concentrations in dialysate samples from treated patients, over time; and (3) decreased HK2 activity in PCZ-treated tumor samples.

DISCUSSION

A successful trial will support the decision to proceed to advanced phase trials. Any tumor penetration by PCZ, with concomitant effect on glycolysis, warrants further in-depth analysis, as therapeutic options for these deadly tumors are currently limited.

Invasive Multimodal Neuromonitoring in Aneurysmal Subarachnoid Hemorrhage: A Systematic Review

BACKGROUND AND PURPOSE

Aneurysmal subarachnoid hemorrhage is a devastating disease leaving surviving patients often severely disabled. Delayed cerebral ischemia (DCI) has been identified as one of the main contributors to poor clinical outcome after subarachnoid hemorrhage. The objective of this review is to summarize existing clinical evidence assessing the diagnostic value of invasive neuromonitoring (INM) in detecting DCI and provide an update of evidence since the 2014 consensus statement on multimodality monitoring in neurocritical care.

METHODS

Three invasive monitoring techniques were targeted in the data collection process: brain tissue oxygen tension (p_tiO₂), cerebral microdialysis, and electrocorticography. Prospective and retrospective studies as well as case series (≥10 patients) were included as long as monitoring was used to detect DCI or guide DCI treatment.

RESULTS

Forty-seven studies reporting INM in the context of DCI were included (p_tiO₂: N=21; cerebral microdialysis: N=22; electrocorticography: N=4). Changes in brain oxygen tension are associated with angiographic vasospasm or reduction in regional cerebral blood flow. Metabolic monitoring with trend analysis of the lactate to pyruvate ratio using cerebral microdialysis, identifies patients at risk for DCI. Clusters of cortical spreading depolarizations are associated with clinical neurological worsening and cerebral infarction in selected patients receiving electrocorticography monitoring.

CONCLUSIONS

Data supports the use of INM for the detection of DCI in selected patients. Generalizability to all subarachnoid hemorrhage patients is limited by design bias of available studies and lack of randomized trials. Continuous data recording with trend analysis and the combination of INM modalities can provide tailored treatment support in patients at high risk for DCI. Future trials should test interventions triggered by INM in relation to cerebral infarctions.

Multimodality Monitoring in Neurocritical Care: Decision-Making Utilizing Direct And Indirect Surrogate Markers

Substantial progress has been made to create innovative technology that can monitor the different physiological characteristics that precede the onset of secondary brain injury, with the ultimate goal of intervening prior to the onset of irreversible neurological damage. One of the goals of neurocritical care is to recognize and preemptively manage secondary neurological injury by analyzing physiologic markers of ischemia and brain injury prior to the development of irreversible damage. This is helpful in a multitude of neurological conditions, whereby secondary neurological injury could present including but not limited to traumatic intracranial hemorrhage and, specifically, subarachnoid hemorrhage, which has the potential of progressing to delayed cerebral ischemia and monitoring postneurosurgical interventions. In this study, we examine the utilization of direct and indirect surrogate physiologic markers of ongoing neurologic injury, including intracranial pressure, cerebral blood flow, and brain metabolism.

Can Amantadine Ameliorate Neurocognitive Functions After Subarachnoid Haemorrhage? A Preliminary Study

OBJECTIVE

Aneurysmal subarachnoid haemorrhage (SAH) may have devastating effects on patients. Motor and neurocognitive impairments may arise depending on the location and grade of the SAH. Although the effects of amantadine on neurocognitive function after traumatic brain injury have been widely studied to the best of our knowledge, their effects on recovery from SAH in humans have not been studied. The present study aimed to evaluate how amantadine influences improvement in neurocognitive function in patients with aneurysmal SAH over a period of six months.

METHODS

This preliminary study included 12 patients with aneurysmal SAH who were admitted to the neurointensive care unit of Cerrahpasa Faculty of Medicine. Patients in Group A (n=5) received the standard treatment for SAH and amantadine for 30 days after admission, and those in Group C (n=7) received only the standard treatment. Neurocognitive function was evaluated using the Coma Recovery Scale-Revised and Disability Rating Scale on the first and fifth days and at the third and sixth months after admission. The primary endpoint of the present study was to compare the effects of amantadine in combination with the standard treatment to those of the standard treatment alone on the neurocognitive function of patients with SAH for over 6 months.

RESULTS

Compared to the standard treatment alone, amantadine administration with the standard treatment during the early period of SAH may improve recovery.

CONCLUSION

Amantadine along with the standard treatment can ameliorate neurocognitive function after SAH.

Concentrations of Cefuroxime in Brain Tissue of Neurointensive Care Patients

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 (AUC_0-24) 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 (AUC_0-24 brain/AUC_{0-24 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.

Endovascular Rescue Therapies for Refractory Vasospasm After Subarachnoid Hemorrhage: A Prospective Evaluation Study Using Multimodal, Continuous Event Neuromonitoring

BACKGROUND

Critical hypoperfusion and metabolic derangement are frequently encountered with refractory vasospasm. Endovascular rescue therapies (ERT) have proven beneficial in selected cases. However, angioplasty (AP) and intraarterial lysis (IAL) are measures of last resort and prospective, quantitative results regarding the efficacy (cerebral oxygenation, metabolism) are largely lacking.

OBJECTIVE

To evaluate the efficacy of ERTs for medically refractory vasospasm using multimodal, continuous event neuromonitoring.

METHODS

To detect cerebral compromise in a timely fashion, sedated patients with aneurysmal subarachnoid hemorrhage received continuous neuromonitoring (p ti O 2 measurement, intraparenchymal microdialysis). ERT (AP and/or IAL) was considered in cases of clinically relevant vasospasm refractory to conservative treatment measures. Oxygen saturation and cerebral and systemic metabolism before and after events of ERT was recorded.

RESULTS

We prospectively included 13 consecutive patients and recorded a total of 25 ERT events: AP (n = 10), IAL (n = 11), or both (AP + IAL, n = 4). Average cerebral p ti O 2 was 10 ± 11 torr before and 49 ± 22 torr after ERT ( P < .001), with a lactate-pyruvate ratio decreasing from 146.6 ± 119.0 to 27.9 ± 10.7 after ERT ( P < .001). Comparable improvement was observed for each type of intervention (AP, IAL, or both). No significant alterations in systemic metabolism could be detected after ERT.

CONCLUSION

Multimodal event neuromonitoring is able to quantify treatment efficacy in subarachnoid hemorrhage-related vasospasm. In our small cohort of highly selected cases, ERT was associated with improvement in cerebral oxygenation and metabolism with reasonable outcome. Event neuromonitoring may facilitate individual and timely optimization of treatment modality according to the individual clinical course.

Clinical Use of Cerebral Microdialysis in Patients with Aneurysmal Subarachnoid Hemorrhage-State of the Art

Objective

To review the published literature on the clinical application of cerebral microdialysis (CMD) in aneurysmal subarachnoid hemorrhage (SAH) patients and to summarize the evidence relating cerebral metabolism to pathophysiology, secondary brain injury, and outcome.

Methods

Study selection: Two reviewers identified all manuscripts reporting on the clinical use of CMD in aneurysmal SAH patients from MEDLINE. All identified studies were grouped according to their focus on brain metabolic changes during the early and subacute phase after SAH, their association with mechanisms of secondary brain injury and outcome.

Results

The review demonstrated: (1) limited literature is available in the very early phase before the aneurysm is secured. (2) Brain metabolic changes related to early and delayed secondary injury mechanisms may be used in addition to other neuromonitoring parameters in the critical care management of SAH patients. (3) CMD markers of ischemia may detect delayed cerebral ischemia early (up to 16 h before onset), underlining the importance of trend analysis. (4) Various CMD-derived parameters may be associated with patient outcome at 3–12 months, including CMD-lactate-to-pyruvate-ratio, CMD-glucose, and CMD-glutamate.

Conclusion

The clinical use of CMD is an emerging area in the literature of aneurysmal SAH patients. Larger prospective multi-center studies on interventions based on CMD findings are needed.

First Description of Reduced Pyruvate Dehydrogenase Enzyme Activity Following Subarachnoid Hemorrhage (SAH)

Object: Several previous studies reported metabolic derangements and an accumulation of metabolic products in the early phase of experimental subarachnoid hemorrhage (SAH), which may contribute to secondary brain damage. This may be a result of deranged oxygen utilization due to enzymatic dysfunction in aerobic glucose metabolism. This study was performed to investigate, if pyruvate dehydrogenase enzyme (PDH) is affected in its activity giving further hints for a derangement of oxidative metabolism.

Methods: Eighteen male Sprague-Dawley rats were randomly assigned to one of two experimental groups (n = 9): (1) SAH induced by the endovascular filament model and (2) sham-operated controls. Mean arterial blood pressure (MABP), intracranial pressure (ICP), and local cerebral blood flow (LCBF; laser-Doppler flowmetry) were continuously monitored from 30 min before until 3 h after SAH. Thereafter, the animals were sacrificed and PDH activity was measured by ELISA.

Results: PDH activity was significantly reduced in animals subjected to SAH compared to controls.

Conclusion: The results of this study demonstrate for the first time a reduction of PDH activity following SAH, independent of supply of substrates and may be an independent factor contributing to a derangement of oxidative metabolism, failure of oxygen utilization, and secondary brain damage.

Intracranial Multimodality Monitoring for Delayed Cerebral Ischemia

Management of patients with aneurysmal subarachnoid hemorrhage focuses on prevention of rebleeding by early treatment of the aneurysm, as well as detection and management of neurologic and medical complications. Early detection of delayed cerebral ischemia and management of modifiable contributing causes such as vasospasm take a central role, with the goal of preventing irreversible cerebral injury. In efforts to prevent delayed cerebral ischemia, multimodality monitoring has emerged as a promising tool in detecting subclinical physiologic changes before infarction occurs. However, there has been much variability in the utilization of this technology. Recent consensus guidelines discuss the role of multimodality monitoring in acute brain injury. In this review, we evaluate these guidelines and the utility of each modality of multimodality monitoring in aneurysmal subarachnoid hemorrhage.

Excitotoxicity and Metabolic Crisis Are Associated with Spreading Depolarizations in Severe Traumatic Brain Injury Patients

Cerebral microdialysis has enabled the clinical characterization of excitotoxicity (glutamate >10 μM) and non-ischemic metabolic crisis (lactate/pyruvate ratio [LPR] >40) as important components of secondary damage in severe traumatic brain injury (TBI). Spreading depolarizations (SD) are pathological waves that occur in many patients in the days following TBI and, in animal models, cause elevations in extracellular glutamate, increased anaerobic metabolism, and energy substrate depletion. Here, we examined the association of SD with changes in cerebral neurochemistry by placing a microdialysis probe alongside a subdural electrode strip in peri-lesional cortex of 16 TBI patients requiring neurosurgery. In 107 h (median; range: 76-117 h) of monitoring, 135 SDs were recorded in six patients. Glutamate (50 μmol/L) and lactate (3.7 mmol/L) were significantly elevated on day 0 in patients with SD compared with subsequent days and with patients without SD, whereas pyruvate was decreased in the latter group on days 0 and 1 (two-way analysis of variance [ANOVA], p values <0.05). In patients with SD, both glutamate and LPR increased in a dose-dependent manner with the number of SDs in the microdialysis sampling period (0, 1, ≥2 SD) [glutamate: 2.1→7.0→52.3 μmol/L; LPR: 27.8→29.9→45.0, p values <0.05]. In these patients, there was a 10% probability of SD occurring when glutamate and LPR were in normal ranges, but a 60% probability when both variables were abnormal (>10 μmol/L and >40 μmol/L, respectively). Taken together with previous studies, these preliminary clinical results suggest SDs are a key pathophysiological process of secondary brain injury associated with non-ischemic glutamate excitotoxicity and severe metabolic crisis in severe TBI patients.

Perihemorrhagic ischemia occurs in a volume-dependent manner as assessed by multimodal cerebral monitoring in a porcine model of intracerebral hemorrhage

BACKGROUND

Changes in the perihemorrhagic zone (PHZ) of intracerebral hemorrhage (ICH) are variable. Different mechanisms contribute to secondary neuronal injury after ICH. This multimodal monitoring study investigated early changes in the PHZ of ICH.

METHODS

Twenty-four swine were anesthetized, ventilated, and underwent monitoring of vital parameters. Next to an intracranial pressure-probe (ICP), microdialysis (MD), thermodiffusion cerebral blood flow (td-CBF), and oxygen probes (PbrO2) were placed into the gray white matter junction for 12 h of monitoring. ICH was induced using the autologous blood injection model. Pre-defined volumes were 0 ml (sham), 1.5 ml ipsilateral (1.5 ml), 3.0 ml ipsilateral (3.0 ml), and 3.0 ml contralateral (3.0 ml contra).

RESULTS

ICP equally increased in all groups after ICH. In the 3.0 ml group tissue oxygenation decreased to ischemic values of 9 ± 7 mmHg early after 6 h of monitoring. This decrease was associated with a significant perfusion reduction from 36 ± 8 ml/100 g/min to 20 ± 10 ml/100 g/min. MD correlated with a threefold lactate/pyruvate ratio increase. Measurements in all other groups were unchanged.

CONCLUSION

Multimodal monitoring demonstrates volume-dependent changes of tissue oxygenation, blood flow, and ischemic MD markers in the PHZ independent of increased ICP suggesting early moderate ischemia. No evidence was found for the existence of a perihemorrhagic ischemia in the small hematoma groups.

The neurological wake-up test does not alter cerebral energy metabolism and oxygenation in patients with severe traumatic brain injury

BACKGROUND

The neurological wake-up test (NWT) is used to monitor the level of consciousness in patients with traumatic brain injury (TBI). However, it requires interruption of sedation and may elicit a stress response. We evaluated the effects of the NWT using cerebral microdialysis (MD), brain tissue oxygenation (PbtiO2), jugular venous oxygen saturation (SjvO2), and/or arterial-venous difference (AVD) for glucose, lactate, and oxygen in patients with severe TBI.

METHODS

Seventeen intubated TBI patients (age 16-74 years) were sedated using continuous propofol infusion. All patients received intracranial pressure (ICP) and cerebral perfusion pressure (CPP) monitoring in addition to MD, PbtiO2 and/or SjvO2. Up to 10 days post-injury, ICP, CPP, PbtiO2 (51 NWTs), MD (49 NWTs), and/or SjvO2 (18 NWTs) levels during propofol sedation (baseline) and NWT were compared. MD was evaluated at a flow rate of 1.0 μL/min (28 NWTs) or the routine 0.3 μL/min rate (21 NWTs).

RESULTS

The NWT increased ICP and CPP levels (p < 0.05). Compared to baseline, interstitial levels of glucose, lactate, pyruvate, glutamate, glycerol, and the lactate/pyruvate ratio were unaltered by the NWT. Pathological SjvO2 (<50 % or >71 %; n = 2 NWTs) and PbtiO2 (<10 mmHg; n = 3 NWTs) values were rare at baseline and did not change following NWT. Finally, the NWT did not alter the AVD of glucose, lactate, or oxygen.

CONCLUSIONS

The NWT-induced stress response resulted in increased ICP and CPP levels although it did not negatively alter focal neurochemistry or cerebral oxygenation in TBI patients.

Perioperative microdialysis in meningioma surgery: correlation of cerebral metabolites with clinical outcome

BACKGROUND

Brain tumour resection requires surgical manoeuvres that may cause an ischaemic injury to peritumoral tissue. The aim of the present study was to examine whether putative alterations in peritumoral tissue biochemistry, monitored by microdialysis, correlate with clinical outcome in patients undergoing craniotomy for meningioma resection.

METHODS

In 34 patients undergoing meningioma resection (35 % male; mean age ± SD: 54.3 ± 12.1 years), microdialysis measurements were taken perioperatively from peritumoral brain parenchyma. Standard metabolites (glucose, lactate, pyruvate, glycerol and the lactate:pyruvate ratio) were quantified in relation to clinical outcome assessed by the Glasgow Coma Scale (GCS) and the Karnofsky Performance Status scale.

RESULTS

Higher postoperative glucose and pyruvate levels were found in patients with a favourable outcome (GCS not deteriorated or Karnofsky score > 80). Multiple logistic regression analysis (age, preoperative physical status, metabolite levels as independent variables) showed that lower postoperative glucose and pyruvate levels as well as higher lactate:pyruvate ratio values were independently associated with an unfavourable outcome as defined by Karnofsky score <80 [(OR: 0.084, 95 % CI: 0.01-0.98, p = 0.049), (OR: 0.97, 95 % CI: 0.95-0.99, p = 0.050), (OR: 1.21, 95 % CI: 1.04-1.42, p = 0.015) respectively], as well as with death [(OR: 0.08, 95 % CI: 0.01-0.97, p = 0.046), (OR: 0.94, 95 % CI: 0.89-0.99, p = 0.016), (OR: 1.07, 95 % CI: 1.00-1.15, p = 0.05) respectively].

CONCLUSIONS

Postoperative levels of glucose and pyruvate and the lactate:pyruvate ratio appear to correlate with clinical outcome in patients undergoing meningioma resection. The present findings provide support for the utility of microdialysis as a prognostic tool in brain tumour surgery.

Glucose and the injured brain-monitored in the neurointensive care unit

Brain has a continuous demand for energy that is met by oxidative metabolism of oxygen and glucose. This demand is compromised in the injured brain and if the inadequate supply persists it will lead to permanent tissue damage. Zero values of cerebral glucose have been associated with infarction and poor neurological outcome. Furthermore, hyperglycemia is common in patients with neurological insults and associated with poor outcome. Intensive insulin therapy (IIT) to control blood glucose has been suggested and used in neurointensive care with conflicting results. This review covers the studies reporting on monitoring of cerebral glucose with microdialysis in patients with traumatic brain injury (TBI), subarachnoid hemorrhage (SAH) and ischemic stroke. Studies investigating IIT are also discussed. Available data suggest that low cerebral glucose in patients with TBI and SAH provides valuable information on development of secondary ischemia and has been correlated with worse outcome. There is also indication that the location of the catheter is important for correlation between plasma and brain glucose. In conclusion considering catheter location, monitoring of brain glucose in the neurointensive care not only provides information on imminent secondary ischemia it also reveals the effect of peripheral treatment on the injured brain.

Monitoring of Cerebral Blood Flow and Metabolism Bedside in Patients with Subarachnoid Hemorrhage - A Xenon-CT and Microdialysis Study

Cerebral ischemia is the leading cause of morbidity and mortality following aneurysmal subarachnoid hemorrhage (SAH). Although 70% of the patients show angiographic vasospasm only 30% develop symptomatic vasospasm defined as delayed cerebral ischemia (DCI). Early detection and management of reversible ischemia is of critical importance in patients with SAH. Using a bedside Xenon enhanced computerized tomography (Xenon-CT) scanner makes it possible to measure quantitative regional Cerebral blood flow (CBF) bedside in the neurointensive care setting and intracerebral microdialysis (MD) is a method that offers the possibility to monitor the metabolic state of the brain continuously. Here, we present results from nine SAH patients with both MD monitoring and bedside Xenon-CT measurements. CBF measurements were performed within the first 72 h following bleeding. Six out of nine patients developed DCI at a later stage. Five out of six patients who developed DCI had initial global CBF below 26 ml/100 g/min whereas one had 53 ml/100 g/min. The three patients who did not develop clinical vasospasm all had initial global CBF above 27 ml/100 g/min. High lactate/pyruvate (L/P) ratio was associated with lower CBF values in the area surrounding the catheter. Five out of nine patients had L/P ratio ≥25 and four of these patients had CBF ≤ 22 ml/100 g/min. These preliminary results suggest that patients with initially low global CBF on Xenon-CT may be more likely to develop DCI. Initially low global CBF was accompanied with metabolic disturbances determined by the MD. Most importantly, pathological findings on the Xenon-CT and MD could be observed before any clinical signs of DCI. Combining bedside Xenon-CT and MD was found to be useful and feasible. Further studies are needed to evaluate if DCI can be detected before any other signs of DCI to prevent progress to infarction.

Brain tissue oxygenation and cerebral metabolic patterns in focal and diffuse traumatic brain injury

INTRODUCTION

Neurointensive care of traumatic brain injury (TBI) patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted protocols. There are reasons to believe that knowledge of brain tissue oxygenation (BtipO2) would add information with the potential of improving patient outcome. The aim of this study was to examine BtipO2 and cerebral metabolism using the Neurovent-PTO probe and cerebral microdialysis (MD) in TBI patients.

METHODS

Twenty-three severe TBI patients with monitoring of physiological parameters, ICP, CPP, BtipO2, and MD for biomarkers of energy metabolism (glucose, lactate, and pyruvate) and cellular distress (glutamate, glycerol) were included. Patients were grouped according to injury type (focal/diffuse) and placement of the Neurovent-PTO probe and MD catheter (injured/non-injured hemisphere).

RESULTS

We observed different patterns in BtipO2 and MD biomarkers in diffuse and focal injury where placement of the probe also influenced the results (ipsilateral/contralateral). In all groups, despite fairly normal levels of ICP and CPP, increased MD levels of glutamate, glycerol, or the L/P ratio were observed at BtipO2 <5 mmHg, indicating increased vulnerability of the brain at this level.

CONCLUSION

Monitoring of BtipO2 adds important information in addition to traditional ICP and CPP surveillance. Because of the different metabolic responses to very low BtipO2 in the individual patient groups we submit that brain tissue oximetry is a complementary tool rather than an alternative to MD monitoring.

Cerebral microdialysis in glioma studies, from theory to application

Despite recent advances in the treatment of solid tumors, there are few effective treatments for malignant gliomas due to the infiltrative nature, and the protective shield of blood-brain barrier or blood-tumor barriers that restrict the passage of chemotherapy drugs into the brain. Imaging techniques, such as PET and MRI, have allowed the assessment of tumor function in vivo, but they are indirect measures of activity and do not easily allow continuous repeated evaluations. Because the biology of glioma on a cellular and molecular level is fairly unknown, especially in relation to various treatments, the development of novel therapeutic approaches to this devastating condition requires a strong need for a deeper understanding of the tumor's pathophysiology and biochemistry. Cerebral microdialysis, a probe-based sampling technique, allows a discrete volume of the brain to be sampled for neurochemical analysis of neurotransmitters, metabolites, biomarkers, and chemotherapy drugs, which has been employed in studying brain tumors, and is significant for improving the treatment of glioma. In this review, the current concepts of cerebral microdialysis for glioma are elucidated, with a special emphasis on its application to neurochemistry and pharmacokinetic studies.

(13)C-labelled microdialysis studies of cerebral metabolism in TBI patients

Human brain chemistry is incompletely understood and better methodologies are needed. Traumatic brain injury (TBI) causes metabolic perturbations, one result of which includes increased brain lactate levels. Attention has largely focussed on glycolysis, whereby glucose is converted to pyruvate and lactate, and is proposed to act as an energy source by feeding into neurons’ tricarboxylic acid (TCA) cycle, generating ATP. Also reportedly upregulated by TBI is the pentose phosphate pathway (PPP) that does not generate ATP but produces various molecules that are putatively neuroprotective, antioxidant and reparative, in addition to lactate among the end products.

We have developed a novel combination of ¹³C-labelled cerebral microdialysis both to deliver ¹³C-labelled substrates into brains of TBI patients and recover the ¹³C-labelled metabolites, with high-resolution ¹³C NMR analysis of the microdialysates. This methodology has enabled us to achieve the first direct demonstration in humans that the brain can utilise lactate via the TCA cycle. We are currently using this methodology to make the first direct comparison of glycolysis and the PPP in human brain.

In this article, we consider the application of ¹³C-labelled cerebral microdialysis for studying brain energy metabolism in patients. We set this methodology within the context of metabolic pathways in the brain, and ¹³C research modalities addressing them.

[Multimodal monitoring in neurointensive care medicine: state of the art]

The prognosis of neurointensive care patients depends largely on the occurrence of secondary ischemic/hypoxic tissue damage, which is mediated by different pathomechanisms, such as edema formation or increased intracranial pressure. Due to the cerebral damage and need for sedation as well as intubation, clinical assessment of these patients is limited. Furthermore, clinical signs of secondary damage, such as advanced herniation syndromes are often delayed and therefore mostly indicate irreversible brain damage. To adequately predict and detect secondary neuronal damage, various neuromonitoring techniques have been developed in recent years with ongoing technical refinement. These can be used for bedside and ideally continuous monitoring of various functional systems of the brain. Neuromonitoring is used to implement early therapeutic measures before irreversible brain damage has occurred, to monitor therapeutic effects, for evaluation of the prognosis and to improve the neurological outcome of patients. Different monitoring techniques are often combined in multimodal neuromonitoring. This article gives an overview of the most promising neuromonitoring techniques available.

Evidence-based cerebral vasospasm surveillance

Subarachnoid hemorrhage related to aneurysmal rupture (aSAH) carries significant morbidity and mortality, and its treatment is focused on preventing secondary injury. The most common—and devastating—complication is delayed cerebral ischemia resulting from vasospasm. In this paper, the authors review the various surveillance technologies available to detect cerebral vasospasm in the days following aSAH. First, evidence related to the most common modalities, including transcranial doppler ultrasonography and computed tomography, are reviewed. Continuous electroencephalography and older instruments such as positron emission tomography, xenon-enhanced CT, and single-photon emission computed tomography are also discussed. Invasive strategies including brain tissue oxygen monitoring, microdialysis, thermal diffusion, and jugular bulb oximetry are examined. Lastly, near-infrared spectroscopy, a recent addition to the field, is briefly reviewed. Each surveillance tool carries its own set of advantages and limitations, and the concomitant use of multiple modalities serves to improve diagnostic sensitivity and specificity.

Clipping versus coiling for ruptured intracranial aneurysms: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Endovascular treatment has increasingly been used for aneurismal subarachnoid aneurismal hemorrhage. The aim of this analysis is to assess the current evidence regarding safety and efficiency of clipping compared with coiling.

METHODS

We conducted a meta-analysis of studies that compared clipping with coiling between January 1999 and July 2012. Comparison of binary outcomes between treatment groups was described using odds ratios (OR; clip versus coil).

RESULTS

Four randomized controlled trials and 23 observational studies were included. Randomized controlled trials showed that coiling reduced the 1-year unfavorable outcome rate (OR, 1.48; 95% confidence interval [CI], 1.24-1.76). However, there was no statistical deference in nonrandomized controlled trials (OR, 1.11; 95% CI, 0.96-1.28). Subgroup analysis revealed coiling yielded better outcomes for patients with good preoperative grade (OR, 1.51; 95% CI, 1.24-1.84) than for poor preoperative patients (OR, 0.88; 95% CI 0.56-1.38). Additionally, the incidence of rebleeding is higher after coiling (OR, 0.43; 95% CI, 0.28-0.66), corresponding to a better complete occlusion rate of clipping (OR, 2.43; 95% CI, 1.88-3.13). The 1-year mortality showed no significant difference (OR, 1.07; 95% CI, 0.88-1.30). Vasospasm was more common after clipping (OR, 1.43; 95% CI, 1.07-1.91), whereas the ischemic infarct (OR, 0.74; 95% CI, 0.52-1.06), shunt-dependent hydrocephalus (OR, 0.84; 95% CI, 0.66-1.07), and procedural complication rates (OR, 1.19; 95% CI, 0.67-2.11) did not differ significantly between techniques.

CONCLUSIONS

Coiling yields a better clinical outcome, the benefit being greater in those with a good preoperative grade than those with a poor preoperative grade. However, coiling leads to a greater risk of rebleeding. Well-designed randomized trials with special considerations to the aspect are needed.

Pilot investigation on long-term subcutaneous microdialysis: proof of principle in humans

Reliable drug concentration measurements at the target site are increasingly demanded and can be achieved by microdialysis. The aim of this pilot study was to demonstrate the proof of principle of long-term subcutaneous microdialysis in humans. For long-term microdialysis, a special setting implementing both concentric and linear catheters has been developed ensuring good clinical practice compliance, tolerability, and convenience for participants and personnel. As a model compound, moderately lipophilic voriconazole was selected as a well-characterized drug in in vitro microdialysis experiments. Multiple in vivo relative recovery (RR) determinations for microdialysis were performed by retrodialysis during the entire study (n = 48 samples). Continuous microdialysis was successfully applied and well tolerated over 87 h in three adults for the first time. RR revealed low intra-individual (coefficient of variation (CV) = 4.4-12.5%) and inter-individual variability (CV = 4.3-12.5%) across all samples and catheters. Lower RR values were consistently determined for linear catheters. One catheter leakage was managed without an impact on the reliability of the RR values. Overall, RR values were calculated to be 73.3% (linear: CV = 18.5%, n = 23) and 84.9% (concentric: CV = 5.6%, n = 23). Long-term microdialysis application over almost 4 days was feasible by reliable multiple RR (proof of principle), well tolerated, and reduced the burden in humans avoiding several catheter insertions, thereby allowing to monitor concentration-time courses continuously. Moreover, a moderately lipophilic drug has been proven suitable for in vivo microdialysis, as previously suggested by in vitro microdialysis.

Advances in gas chromatographic methods for the identification of biomarkers in cancer

Screening complex biological specimens such as exhaled air, tissue, blood and urine to identify biomarkers in different forms of cancer has become increasingly popular over the last decade, mainly due to new instruments and improved bioinformatics. However, despite some progress, the identification of biomarkers has shown to be a difficult task with few new biomarkers (excluding recent genetic markers) being considered for introduction to clinical analysis. This review describes recent advances in gas chromatographic methods for the identification of biomarkers in the detection, diagnosis and treatment of cancer. It presents a general overview of cancer metabolism, the current biomarkers used for cancer diagnosis and treatment, a background to metabolic changes in tumors, an overview of current GC methods, and collectively presents the scope and outlook of GC methods in oncology.

Brain tissue oxygenation and cerebral perfusion pressure thresholds of ischemia in a standardized pig brain death model

BACKGROUND

Neurointensive care of traumatic brain injury (TBI) patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted protocols. Monitoring brain tissue oxygenation (BtipO2) is of considerable clinical interest, but the exact threshold level of ischemia has been difficult to establish due to the complexity of the clinical situation. The objective of this study was to use the Neurovent-PTO (NV) probe, and to define critical cerebral oxygenation- and CPP threshold levels of cerebral ischemia in a standardized brain death model caused by increasing the ICP in pig. Ischemia was defined by a severe increase of cerebral microdialysis (MD) lactate/pyruvate ratio (L/P ratio > 30).

METHODS

BtipO2, L/P ratio, Glucose, Glutamate, Glycerol and CPP were recorded using NV and MD probes during gradual increase of ICP by inflation of an epidural balloon catheter with saline until brain death was achieved.

RESULTS

Baseline level of BtipO2 was 22.9 ± 6.2 mmHg, the L/P ratio 17.7 ± 6.1 and CPP 73 ± 17 mmHg. BtipO2 and CPP decreased when intracranial volume was added. The L/P ratio increased above its ischemic levels, (>30)when CPP decreased below 30 mmHg and BtipO2 to <10 mmHg.

CONCLUSIONS

A severe increase of ICP leading to CPP below 30 mmHg and BtipO2 below 10 mmHg is associated with an increase of the L/P ratio, thus seems to be critical thresholds for cerebral ischemia under these conditions.

Monitoring and detection of vasospasm II: EEG and invasive monitoring

Several non-invasive and invasive modalities have been used to monitor patients for cerebral ischemia after subarachnoid hemorrhage. A literature search was performed to identify original research studies testing monitors that may be used in addition to the standard measures of brain function and cerebral blood flow. Fifty observational studies were identified that evaluated the role of electroencephalography, brain tissue oxygenation monitoring, cerebral microdialysis, thermal diffusion flowmetry, or near-infrared spectroscopy in patients after subarachnoid hemorrhage.

Cerebral perfusion pressure thresholds for brain tissue hypoxia and metabolic crisis after poor-grade subarachnoid hemorrhage

BACKGROUND AND PURPOSE

To identify a minimally acceptable cerebral perfusion pressure threshold above which the risks of brain tissue hypoxia (BTH) and oxidative metabolic crisis are reduced for patients with subarachnoid hemorrhage (SAH).

METHODS

We studied 30 poor-grade SAH patients who underwent brain multimodality monitoring (3042 hours). Physiological measures were averaged over 60 minutes for each collected microdialysis sample. Metabolic crisis was defined as a lactate/pyruvate ratio>40 with a brain glucose concentration≤0.7 mmol/L. BTH was defined as PbtO2<20 mm Hg. Outcome was assessed at 3 months with the Modified Rankin Scale.

RESULTS

Multivariable analyses adjusting for admission Hunt-Hess grade, intraventricular hemorrhage, systemic glucose, and end-tidal CO2 revealed that cerebral perfusion pressure≤70 mm Hg was significantly associated with an increased risk of BTH (OR, 2.0; 95% CI, 1.2-3.3; P=0.007) and metabolic crisis (OR, 2.1; 95% CI, 1.2-3.7; P=0.007). Death or severe disability at 3 months was significantly associated with metabolic crisis (OR, 5.4; 95% CI, 1.8-16; P=0.002) and BTH (OR, 5.1; 95% CI, 1.2-23; P=0.03) after adjusting for admission Hunt-Hess grade.

CONCLUSIONS

Metabolic crisis and BTH are associated with mortality and poor functional recovery after SAH. Cerebral perfusion pressure levels<70 mm Hg was associated with metabolic crisis and BTH, and may increase the risk of secondary brain injury in poor-grade SAH patients.

Analytical validation of microdialysis analyzer for monitoring glucose, lactate and pyruvate in cerebral microdialysates

BACKGROUND

Cerebral microdialysis is a valuable tool for neurochemical monitoring of acute brain injury. We performed an independent analytical validation of glucose, lactate and pyruvate methods on the new ISCUS(flex) new analyzer developed by CMA Microdialysis.

METHODS

Evaluation of analytical parameters included limit of detection, limit of quantification, linearity, intra- and inter-assay imprecision expressed as the coefficient of variation (CV), recovery, inter-sample and inter-reagent contamination, drug and bilirubin interferences, sample stability, method comparison.

RESULTS

Linearity ranges were 0.1-25 mmol/L, 0.2-12 mmol/L and 19-1500 μmol/L for glucose, lactate and pyruvate respectively. For critical threshold, intra- and inter-assay CVs were 3.1/4.5% for glucose (1 mmol/L), 3.5/4% for lactate (4 mmol/L) and 3.3/4.3% for pyruvate (100 μmol/L). Inter-assay CVs for lactate/pyruvate (LPR) and lactate/glucose (LGR) ratios were 5.9% and 6.0% respectively. For glucose, lactate, pyruvate, LPR and LGR, the reference change values (RCV) were 20%, 26%, 20%, 27% and 28% respectively. Practically, variations below 27% between two successive LPR values could not be interpreted as significant.

CONCLUSION

These data prove that ISCUS(flex) has the qualities required for clinical application in neuro-intensive care. Correct clinical interpretation of data need the implementation of a strict quality control program and strong cooperation between clinicians and biologists.

A prospective, randomized clinical trial to compare the effect of hyperbaric to normobaric hyperoxia on cerebral metabolism, intracranial pressure, and oxygen toxicity in severe traumatic brain injury

Object

Oxygen delivered in supraphysiological amounts is currently under investigation as a therapy for severe traumatic brain injury (TBI). Hyperoxia can be delivered to the brain under normobaric as well as hyperbaric conditions. In this study the authors directly compare hyperbaric oxygen (HBO2) and normobaric hyperoxia (NBH) treatment effects.

Methods

Sixty-nine patients who had sustained severe TBIs (mean Glasgow Coma Scale Score 5.8) were prospectively randomized to 1 of 3 groups within 24 hours of injury: 1) HBO2, 60 minutes of HBO2 at 1.5 ATA; 2) NBH, 3 hours of 100% fraction of inspired oxygen at 1 ATA; and 3) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Brain tissue PO2, microdialysis, and intracranial pressure were continuously monitored. Cerebral blood flow (CBF), arteriovenous differences in oxygen, cerebral metabolic rate of oxygen (CMRO2), CSF lactate and F2-isoprostane concentrations, and bronchial alveolar lavage (BAL) fluid interleukin (IL)–8 and IL-6 assays were obtained pretreatment and 1 and 6 hours posttreatment. Mixed-effects linear modeling was used to statistically test differences among the treatment arms as well as changes from pretreatment to posttreatment.

Results

In comparison with values in the control group, the brain tissue PO2 levels were significantly increased during treatment in both the HBO2 (mean ± SEM, 223 ± 29 mm Hg) and NBH (86 ± 12 mm Hg) groups (p < 0.0001) and following HBO2 until the next treatment session (p = 0.003). Hyperbaric O2 significantly increased CBF and CMRO2 for 6 hours (p ≤ 0.01). Cerebrospinal fluid lactate concentrations decreased posttreatment in both the HBO2 and NBH groups (p < 0.05). The dialysate lactate levels in patients who had received HBO2 decreased for 5 hours posttreatment (p = 0.017). Microdialysis lactate/pyruvate (L/P) ratios were significantly decreased posttreatment in both HBO2 and NBH groups (p < 0.05). Cerebral blood flow, CMRO2, microdialysate lactate, and the L/P ratio had significantly greater improvement when a brain tissue PO2 ≥ 200 mm Hg was achieved during treatment (p < 0.01). Intracranial pressure was significantly lower after HBO2 until the next treatment session (p < 0.001) in comparison with levels in the control group. The treatment effect persisted over all 3 days. No increase was seen in the CSF F2-isoprostane levels, microdialysate glycerol, and BAL inflammatory markers, which were used to monitor potential O2 toxicity.

Conclusions

Hyperbaric O2 has a more robust posttreatment effect than NBH on oxidative cerebral metabolism related to its ability to produce a brain tissue PO2 ≥ 200 mm Hg. However, it appears that O2 treatment for severe TBI is not an all or nothing phenomenon but represents a graduated effect. No signs of pulmonary or cerebral O2 toxicity were present.

Cerebral microdialysis and intracranial pressure monitoring in patients with idiopathic normal-pressure hydrocephalus: association with clinical response to extended lumbar drainage and shunt surgery

OBJECT

This study was performed in patients with idiopathic normal-pressure hydrocephalus (iNPH) to monitor cerebral metabolism with microdialysis (MD) and intracranial pressure (ICP) readings, and relate to the clinical responses to extended lumbar drainage (ELD) and shunt surgery.

METHODS

The baseline levels of MD metabolites and ICP were monitored overnight in 40 consecutive patients with iNPH. In a subset of 28 patients, monitoring was continued during 3 days of ELD. Thirty-one patients received a ventriculoperitoneal shunt. The clinical severity of iNPH was determined before and then 3 and 6-12 months after shunt surgery.

RESULTS

Altered levels of MD markers (lactate, pyruvate, lactate/pyruvate ratio, glutamate, and/or glycerol) were seen in all patients at baseline; these improved during ELD. Despite normal static ICP (mean ICP), the pulsatile ICP (the ICP wave amplitude) was increased in 24 patients (60%). Only the level of the ICP wave amplitude differentiated the ELD and/or shunt responders from nonresponders.

CONCLUSIONS

The MD monitoring indicated low-grade cerebral ischemia in patients with iNPH; during ELD, cerebral metabolism improved. The pulsatile ICP (the ICP wave amplitude) was the only variable differentiating the clinical responders from the nonresponders. The authors suggest that the pulsatile ICP reflects the intracranial compliance and that CSF diversion improves the biophysical milieu of the nerve cells, which subsequently may improve their biochemical milieu.

Intracerebral microdialysis in children

INTRODUCTION

Cerebral microdialysis is a relatively new, minimally invasive technique that permits sampling and analyzing the chemical constituents of the extracellular fluid. Although mainly used as a research tool, it is also used in the neurointensive care, in combination with other monitoring methods, in patients with severe traumatic brain injury and subarachnoid hemorrhage. Its main clinical utility is the identification of markers of ischemia and cell damage with the ultimate goal of preventing any secondary insults to the brain by instituting early appropriate treatment measures. With few exceptions, all the available data on intracerebral microdialysis in humans comes from studies performed in adults.

OBJECTIVE

The purpose of this report is to provide a brief review of the intracerebral microdialysis studies performed in children.

CONCLUSION

Differences in trends of concentrations of structural and excitatory amino acids have been identified in children, in comparison to those observed in adults, the significance of which remains unknown at present.

Use of magnesium in traumatic brain injury

Depletion of magnesium is observed in animal brain and in human blood after brain injury. Treatment with magnesium attenuates the pathological and behavioral changes in rats with brain injury; however, the therapeutic effect of magnesium has not been consistently observed in humans with traumatic brain injury (TBI). Secondary brain insults are observed in patients with brain injury, which adversely affect clinical outcome. Systemic administration studies in rats have shown that magnesium enters the brain; however, inducing hypermagnesemia in humans did not concomitantly increase magnesium levels in the CSF. We hypothesize that the neuroprotective effects of magnesium in TBI patients could be observed by increasing its brain bioavailability with mannitol. Here, we review the role of magnesium in brain injury, preclinical studies in brain injury, clinical safety and efficacy studies in TBI patients, brain bioavailability studies in rat, and pharmacokinetic studies in humans with brain injury. Neurodegeneration after brain injury involves multiple biochemical pathways. Treatment with a single agent has often resulted in poor efficacy at a safe dose or toxicity at a therapeutic dose. A successful neuroprotective therapy needs to be aimed at homeostatic control of these pathways with multiple agents. Other pharmacological agents, such as dexanabinol and progesterone, and physiological interventions, with hypothermia and hyperoxia, have been studied for the treatment of brain injury. Treatment with magnesium and hypothermia has shown favorable outcome in rats with cerebral ischemia. We conclude that coadministration of magnesium and mannitol with pharmacological and physiological agents could be an effective neuroprotective regimen for the treatment of TBI.

Microdialysis: is it ready for prime time?

PURPOSE OF REVIEW

This review highlights recent advances in cerebral microdialysis for investigational and clinical neurochemical monitoring in patients with critical neurological conditions.

RECENT FINDINGS

Use of microdialysis with other methods, including PET, electrophysiological monitoring and brain tissue oximetry in traumatic brain injury, subarachnoid hemorrhage with vasospasm, and infarction with refractory increased intracranial pressure have been reported. Potentially adverse neurochemical effects of nonconvulsive status epilepticus and cortical slow depolarization waves, both of which are increasingly recognized in traumatic brain injury and stroke patients, have been reported. The explosive growth in the use of cerebral oximetry with targeted management of brain tissue oxygen levels is leading to greater understanding of derangements of cerebral bioenergetics in the critically ill brain, but there remain unresolved basic issues. Understanding of the analytes that are measurable at the bedside - glucose, lactate, pyruvate, glutamate and glycerol - continues to evolve with glucose, lactate, pyruvate and the lactate-pyruvate ratio taking center stage. Analytes including inflammatory biomarkers such as cytokines and metabolites of nitric oxide are presently investigational, but hold promise for future application in advancing our understanding of basic pathophysiology, therapeutic target selection and prognostication. Growing consensus on indications for use of clinical microdialysis and advances in commercially available equipment continue to make microdialysis increasingly 'ready for prime time.'

SUMMARY

Cerebral microdialysis is an established tool for neurochemical research in the ICU. This technique cannot be fruitfully used in isolation, but when combined with other monitoring methods provides unique insights into the biochemical and physiological derangements in the injured brain.