Ischemia monitoring after aneurysmal subarachnoid haemorrhage; contribution of brain tissue oxygen and cerebral microdialysis monitoring


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A Master's thesis.
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Master (thesis) (master)
Ischemia monitoring after aneurysmal subarachnoid haemorrhage; contribution of brain tissue oxygen and cerebral microdialysis monitoring
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Université de Lausanne, Faculté de biologie et médecine
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Introduction: Delayed cerebral ischemia (DCI) is a frequent and serious complication of aneurysmal subarachnoid haemorrhage (SAH). The diagnosis of DCI lies primarily on the deterioration of the clinical state (neurological deficit), but can be difficult to detect in the comatose patient. Transcranial Dopper (TCD) and perfusion Computer Tomography with calculation of cerebral blood flow (CBF) and brain perfusion help with the diagnosis of DCI but their predictive values remain limited. The DCI mechanisms are complex, involving alteration of CBF, impaired cerebral autoregulation, brain energy dysfunction and activation of pro-inflammatory mediators. The use of novel techniques for advanced intracranial monitoring (including brain tissue PO2 and cerebral microdialysis) offer the opportunity to study in detail DCI physiopathology and might help detecting DCI and guiding therapeutic interventions in patients suffering from SAH.
General objectives: The main objective of this study was to examine the relationship between global CBF - measured with TCD and perfusion-CT - and regional brain metabolism, measured with the brain tissue oxygen (PbtO2) probe and the cerebral microdialysis (CMD) technique.
Specific objectives: To examine the relationship between: - DCI and the brain tissue oxygen pressure reactivity index (ORx), which is calculated as the moving linear correlation coefficient between PbtO2 and CPP (=mean arterial pressure - intracranial pressure). The ORx is considered as a surrogate marker of the cerebral autoregulation state; - ORx and CBF, calculated with the perfusion-CT; - ORx and CMD markers of brain energy metabolism (including the lactate/pyruvate ratio and glucose).
Methods: Retrospective analysis of an ongoing cohort database of patients with coma (defined by a Glasgow Coma Scale (GCS) ≤ 8) after aneurysmal SAH, with an abnormal CT-scan (Fisher grade II-IV), who underwent intracranial monitoring with PbtO2 and CMD as part of standard care. Intracranial monitoring was inserted after admission (2 ±1 days). A total of 21 patients were admitted in the Intensive Care Department with poor-grade SAH and underwent imaging and aneurysm securisation (with surgical clipping or endovascular coiling). Cerebral microdialysis allows to measure every hour, through a catheter placed in the cerebral parenchyma (white matter), the extracellular concentration of the main brain metabolites (glucose, lactate, pyruvate, lactate/pyruvate ratio). The DCI is diagnosed with the TCD and the perfusion-CT. The CBF (derived from the cerebral blood volume and the mean transit time) was calculated with the perfusion-CT, with a CBF < 32ml/100g/min that was used as the threshold for brain oligemia. Brain cell hypoxia was defined as a PbtO2 <20mmHg and/or a CMD lactate/pyruvate-ratio >40. The different variables were compared by univariate analysis using a Wilcoxon test for comparisons. The relationship between variables was analysed with the Pearson's R linear correlation coefficient factor.
Expected results: From a clinical standpoint, if a relationship between regional brain physiological variables and global cerebral blood flow can be demonstrated, this could serve as a validation of PbtO2 and cerebral microdialysis monitoring as complementary tools for the diagnosis and the management of DCI in comatose SAH patients. From a pathophysiological standpoint, this study will provide new insights concerning the relationship between cerebral blood flow, brain oxygenation and cerebral energy metabolism in the acute phase of SAH.
subarachnoid haemorrhage, monitoring, cerebral autoregulation, microdialysis
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03/09/2015 8:50
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20/08/2019 14:33
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