Extracellular levels of glucose and lactate measured by quantitative microdialysis in the human brain

The aim of this study was to use quantitative microdialysis to estimate the true extracellular concentrations of glucose and lactate in minimally dist urbed human brain. These values are important as criteria for microdialytic al monitoring in critical care patients and for determining therapy. Microd ialysis procedures were carried out during tumor operations, the probe bein g inserted distant from the site of manipulation in minimally disturbed tis sue. Two methods were used 1. The zero net flux method of Lonnroth. 2. The low flow method (10 mm membrane length, flow rate 0.3 mul min(-1), high in vivo recovery). Both methods gave similar values of about 2000 muM for lact ate and slightly less for glucose (1700 muM). Glucose levels correspond wit h those measured by other methods in humans, allowing for the fact that our patients were anesthetised. Extracellular glucose levels were positively c orrelated 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.