Abstract
In this pilot study, muscle interstitial urea concentrations during hemodialysis (HD) were determined with a microdialysis technique and the results were compared with plasma water urea concentrations. Three patients were investigated during a total of five treatments. Under predialysis steady-state conditions, no difference was observed. During treatment, the muscle interstitial urea concentration was on average 19% higher (range 13–28%, n=4) than the plasma urea concentration after 17±3 min, 29% higher (25–31%, n=3) after 53±10 min, 40% higher (26–50%, n=3) after 117±6 min, 31% higher (26–34%, n= 3) after 179±5 min, and 31% higher (27–36%, n=4) after 231±5 min. The gradient declined after the conclusion of HD, muscle interstitial concentrations being on average 16% (9–26%, n=4) higher than plasma urea concentrations 9±2 min after treatment, and 8% (6–10%, n=3) 25±3 min after treatment. Thus, a urea concentration gradient with a higher concentration in muscle interstitium than in plasma, developed during HD, and dissipated gradually after treatment. This is consistent with blood flow-dependent urea sequestration in muscle tissue, causing intercompartment disequilibrium of urea during HD, and its consequent redistribution after treatment contributing to postdialysis urea rebound.
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