The aim of this study was to use quantitative microdialysis to estimate the true extracellular concentrations of glucose and lactate in minimally disturbed human brain. These values are important as criteria for microdialytical monitoring in critical care patients and for determining therapy. Microdialysis procedures were carried out during tumor operations, the probe being inserted distant from the site of manipulation in minimally disturbed tissue. Two methods were used: 1. The zero net flux method of Lönnroth. 2. The low flow method (10 mm membrane length, flow rate 0.3 microliter min-1, high in vivo recovery). Both methods gave similar values of about 2000 microM for lactate and slightly less for glucose (1700 microM). Glucose levels correspond with those measured by other methods in humans, allowing for the fact that our patients were anesthetised. Extracellular glucose levels were positively correlated with blood glucose values measured before the operation, and with extracellular lactate. Results confirm that extracellular glucose is zero when blood glucose is about 2 mM.
Although bypass surgery for occlusive cerebrovascular disease is still controversial, our retrospective study suggests both an improvement of symptoms and signs and a risk-reduction for future cerebrovascular events after surgery.
Morbidity and mortality of subarachnoid hemorrhage (SAH) are correlated with the severity of the patient's acute neurological deficit. This initial presentation has been attributed to cerebral hypoperfusion in the acute phase, and we investigated the impact of moderate hypothermia on the early changes in perfusion and metabolism following massive experimental SAH. SAH was induced in 61 anesthetized rats by rapid injection of 0.5 mL of arterial blood into the cisterna magna. In normothermia (NT), animals were kept at 37 degrees C, while in the primary hypothermia (pHT) group, temperature was lowered to 32 degrees C prior to SAH, and in the secondary hypothermia (sHT) group, cooling was started immediately after SAH. From 30 min prior to 180 min after SAH, Laser-Doppler-flowmetry (LDF) probes allowed online recording of cerebral blood flow (CBF) while parenchymal dialysate was collected by microdialysis probes within the frontoparietal cortex. In NT, the acute phase was characterized by impaired autoregulation and prolonged hypoperfusion. In pHT and sHT, autoregulation was preserved and acute hypoperfusion rapidly improved. SAH also caused a highly significant reduction in glucose in NT only. pHT significantly reduced accumulation of lactate, glutamate, and aspartate. Comparable trends were present for histidine, GABA, and taurine, while glutamine consumption was ameliorated. Early perfusion deficits caused by acute hypoperfusion and disruption of cerebral autoregulation can be ameliorated by hypothermia. Also, the acute phase of experimental SAH is characterized by glucose depletion, lactate accumulation, and release of excitatory amino acids, which can be influenced favorably by hypothermia.
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