Indicator microdialysis technique employs microdialysis for quantitative assessment of regional tissue perfusion. A special slim probe with a semi-permeable membrane at the tip is inserted into the tissue where small molecules are interchanged between the fluid inside the probe and the interstitial tissue. The indicator substance is supplied to the probe where it partly diffuses into the interstitial fluid and gets drawn into blood capillaries. In steady state diffusion of the indicator out of the probe is proportional to tissue perfusion. It is also influenced by many other factors such as tissue diffusibility of the indicator, intensity of probe perfusion, ultrafiltration of the fluid out of the probe, movement of the tissue or probe, spatial heterogeneity of the tissue etc. The first studies with artificial perfusion of tissues displayed a good correlation between tissue perfusion and tissue extraction of the indicator but later in-vivo studies showed little or no changes of indicator extraction with gross changes in tissue perfusion. The question of validity of indicator microdialysis technique for quantitative assessment of tissue perfusion is not finally answered yet. Because of the requirement for maximal precision when performing this technique to gain valid results, the use of this technique is almost excluded from clinical practice.

        Key words: microdialysis – indicator – ethanol – tissue perfusion