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 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.