Microdialysis in equine research: a review of clinical and experimental findings

Microdialysis is a method for sampling compounds from extracellular fluid with minimal tissue trauma. Small hollow probes that are 0.2-0.5mm in diameter are inserted into the tissue and slowly perfused. The probe membrane is semi-permeable and a flux of the solutes occurs exclusively according to the concentration gradients. The recovered dialysate reflects changes in the composition of the extracellular water phase with a minor time delay. Because microdialysis is a continuous sampling method, it differs from point sample methods, such as blood sampling. The ability to obtain local measurements in the tissues has led to important discoveries in the detection of tissue changes within the areas of pharmacokinetics, pharmacodynamics, pathology and pathophysiology. New technological solutions, such as transportable pumps, fluid collectors and bedside analysers, have made microdialysis an indispensable tool for the surveillance of critically ill human patients, such as after brain injuries and reconstructive surgeries. The use of microdialysis in equine medicine has been sparingly described with only 14 published studies within muscle, pulmonary and hoof lamellar tissue, nasal mucosa, intestinal wall, uterine, allantoic and cerebrospinal fluid and blood. Only a few papers have been published within each area, indicating that few equine researchers are aware of the unique opportunities provided by the technique. This review discusses the theory and applications of microdialysis with a special emphasis on clinical and experimental equine studies, which may be useful to veterinary experimental and clinical researchers.