Cutaneous microdialysis in the rat: insertion trauma studied by ultrasound imaging

Microdialysis is a method by which compounds can be studied in the extracellular space in skin, in vivo. The microdialysis probe is inserted in the dermis using a guide cannula. It is expected that intradermal oedema associated with insertion trauma as well as the probe depth can influence the results of microdialysis studies. The aim of the present study was to assess the effects of insertion trauma and, additionally, the probe depth by ultrasound. High-frequency (20 MHz) ultrasound is a noninvasive method for measuring the thickness and echostructure of skin. Hairless rats were anaesthetized with either halothane (n = 7) or pentobarbital sodium (n = 6). The insertion of the microdialysis probe resulted in a 38% relative increase in skin thickness. At 120 min the skin thickness had not reached the pre-insertion value. Thus, significant skin thickening, representing traumatic oedema, developed due to insertion of the microdialysis probe in the skin. The microdialysis probe could be inserted reproducibly in the lower dermis.