A Modified in vivo Flow Variation Technique of Microdialysis for Sampling Uremic Toxins in the Subcutaneous Interstitial Compartment

BACKGROUND: Uremic toxins are typically measured in plasma and little is known of their interstitial concentrations. We undertook experiments to validate a microdialysis technique for simultaneous recovery of small and large uremic toxins in the subcutaneous interstitial fluid (ISF). METHODS: Microdialysis catheters were inserted into the subcutaneous interstitium of 8 subjects (controls and uremic patients) and perfused using two different solutions at incremental flow rates to determine analyte recovery and ISF concentrations of urea and protein. RESULTS: 10% dextran-40 perfusate allowed the determination of interstitial concentrations of urea and protein reliably, by virtue of the exponential decay of their concentrations in the microdialysate with incremental flow rates (R(2) = 0.63-0.99). Interstitial and plasma urea correlated well (r = 0.95), as did interstitial urea from distant anatomical sites (r = 0.96). CONCLUSION: Cutaneous microdialysis with dextran-40 allows measurement of small and large molecule concentrations in ISF, creating an opportunity to characterize ISF in uremia.