The microdialysis technique is based on a thin probe with a semipermeable membrane being inserted in affected brain tissue, collecting interstitial fluid from a small area surrounding the probe. The fluid is analysed for metabolites, proteins or pharmacological substances and has earlier been shown to be of great value in guiding NICU care and prognostication. One problem with the technique is, however, that the measurements are regional and limited to the very small sampling volume of the probe. Another obstacle is that the technique is intracranial invasive.