In-vivo microdialysis study of extracellular glutamate response to temperature variance in subarachnoid hemorrhage

Emerging Trends in the Use of Therapeutic Hypothermia as a Method for Neuroprotection in Brain Damage (Review)

The review analyzes current clinical studies on the use of therapeutic hypothermia as a neuroprotective method for treatment of brain damage. This method yields good outcomes in patients with acute brain injuries and chronic critical conditions. There has been shown the interest of researchers in studying the preventive potential of therapeutic hypothermia in secondary neuronal damage. There has been described participation of new molecules producing positive effect on tissues and cells of the central nervous system - proteins and hormones of cold stress - in the mechanisms of neuroprotection in the brain. The prospects of using targeted temperature management in treatment of brain damage are considered.

A New Vision for Therapeutic Hypothermia in the Era of Targeted Temperature Management: A Speculative Synthesis

Three decades of animal studies have reproducibly shown that hypothermia is profoundly cerebroprotective during or after a central nervous system (CNS) insult. The success of hypothermia in preclinical acute brain injury has not only fostered continued interest in research on the classic secondary injury mechanisms that are prevented or blunted by hypothermia but has also sparked a surge of new interest in elucidating beneficial signaling molecules that are increased by cooling. Ironically, while research into cold-induced neuroprotection is enjoying newfound interest in chronic neurodegenerative disease, conversely, the scope of the utility of therapeutic hypothermia (TH) across the field of acute brain injury is somewhat controversial and remains to be fully defined. This has led to the era of Targeted Temperature Management, which emphasizes a wider range of temperatures (33–36°C) showing benefit in acute brain injury. In this comprehensive review, we focus on our current understandings of the novel neuroprotective mechanisms activated by TH, and discuss the critical importance of developmental age germane to its clinical efficacy. We review emerging data on four cold stress hormones and three cold shock proteins that have generated new interest in hypothermia in the field of CNS injury, to create a framework for new frontiers in TH research. We make the case that further elucidation of novel cold responsive pathways might lead to major breakthroughs in the treatment of acute brain injury, chronic neurological diseases, and have broad potential implications for medicines of the distant future, including scenarios such as the prevention of adverse effects of long-duration spaceflight, among others. Finally, we introduce several new phrases that readily summarize the essence of the major concepts outlined by this review—namely, Ultramild Hypothermia, the “Responsivity of Cold Stress Pathways,” and “Hypothermia in a Syringe.”

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.

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.

Neurochemical monitoring of therapeutic effects in large human MCA infarction

BACKGROUND AND PURPOSE

Cerebral microdialysis is an invasive monitoring tool allowing analysis of various substances derived from the extracellular space in brain tissue such as glutamate, glycerol, lactate, and pyruvate. In order to assess the potential effects of hemicraniectomy, hypothermia and conservative therapy on these substances, we used neurochemical monitoring with microdialysis in large human stroke patients.

METHODS

This is an open, prospective observational study in 24 patients with large MCA infarction undergoing either hypothermia (33 degrees C), hemicraniectomy, or maximum conservative therapy. Microdialysis probe placement was aimed at the peri-infarct tissue within 24 h after stroke onset. Glutamate, glycerol, pyruvate, and lactate were analyzed every 60 min. Measurements of two consecutive days were pooled for statistical analysis.

RESULTS

Average glutamate concentrations in patients treated with hemicraniectomy (5.3 +/- 0.5 micromol/l, P < 0.0001; n = 6) and hypothermia (14.5 +/- 3.6 micromol/l, P < 0.0001; n = 14) were significantly lower than in conservatively treated patients (68.3 +/- 5.2 micromol/l; n = 4). Glycerol concentration was significantly lower in patients treated by hypothermia (111 +/- 17 micromol/l; P < 0.0001) and hemicraniectomy (138 +/- 8 micromol/l; P < 0.0001) as compared to conservatively treated patients with 612 +/- 27 micromol/l. The lactate-pyruvate ratio was significantly lower both in the hypothermia (16.2 +/- 3.3) and hemicraniectomy groups (31.3 +/- 1.5) than in the conservative treatment group (56 +/- 2.9).

CONCLUSION

Microdialysis allows bed-side monitoring of neuroprotective effects of stroke rescue therapies such as hypothermia and hemicraniectomy. Rescue of peri-infarct tissue and/or prevention of secondary ischemic injury could be associated with a lower mortality in invasively treated patients.

Cortical brain microdialysis and temperature monitoring during hypothermic circulatory arrest in humans

OBJECTIVES

Critical vascular surgery of the brain or the heart occasionally requires total cessation of the circulatory system. Profound hypothermia is used to protect the brain from ischaemic injury. This study explores the use of microdialysis to measure metabolic indices of ischaemia: glutamate, lactate, and pH, and cerebral temperature during profound hypothermia and circulatory arrest.

METHODS

Effluent from a microdialysis catheter placed in the cerebral cortex of three patients undergoing complete circulatory arrest was continuously sampled. Samples were pooled over 10 minute periods and glutamate and lactate concentrations were measured postoperatively. Brain temperature and pH were measured on line intraoperatively. Electroencephalography and monitoring of somatosensory evoked potentials and brainstem auditory evoked potentials were simultaneously carried out.

RESULTS

Patient 1 had normal glutamate and lactate. PH was 6.75 to 6.85 and increased to 6.9 after warming ensued. Patient 2 had raised glutamate and lactate during most measurements. The glutamate concentrations peaked at 305 microM/l at the start of the measurements and fell below 20 microM/l after warming. The lactate concentrations peaked at 680 microM/l before cooling, rose to 1040 microM/l during the cooling process, decreased to 212 microM/l during circulatory arrest, and rose again to 620 microM/l after warming. The pH started at 7.06 and continued a downward course until stabilising at a pH of 6.5 after circulatory arrest. Patient 3 had a transient, mild increase in glutamate and lactate during the cooling and warming period. pH was stable throughout.

CONCLUSION

Microdialysis combined with temperature and pH measurements of the cerebral cortex promises to be an important tool in detecting cerebral ischaemia. Further studies are needed to validate our findings and test the feasibility of modifying ischaemic changes.