Fluid assessment in dialysis patients by point-of-care magnetic relaxometry

Portable nuclear magnetic resonance (NMR) sensors enable quantitative diagnostic measurements of fluid status in patients with end-stage renal disease. Detecting fluid imbalance The kidneys play an important role in maintaining fluid balance within the body. Patients with end-stage renal disease often experience swelling in the lower limbs due to excess extracellular fluid, and fluid status must be closely monitored during hemodialysis. Colucci and colleagues devised a portable nuclear magnetic resonance (NMR) sensor to assess tissue fluid status. Changes in extracellular fluid space in leg muscles of patients undergoing dialysis detected by the NMR sensor were similar to NMR relaxometry measured by magnetic resonance imaging. Results suggest that the nonimaging NMR sensors can provide objective, rapid bedside evaluation of fluid status in patients. Magnetic resonance imaging (MRI) is a powerful diagnostic tool, but its use is restricted to the scanner suite. Here, we demonstrate that a bedside nuclear magnetic resonance (NMR) sensor can assess fluid status changes in individuals at a fraction of the time and cost compared to MRI. Our study recruited patients with end-stage renal disease (ESRD) who were regularly receiving hemodialysis treatments with intradialytic fluid removal as a model of volume overload and healthy controls as a model of euvolemia. Quantitative T2 measurements of the lower leg of patients with ESRD immediately before and after dialysis were compared to those of euvolemic healthy controls using both a 0.28-T bedside single-voxel NMR sensor and a 1.5-T clinical MRI scanner. In the MRI data, we found that the first sign of fluid overload was an expanded muscle extracellular fluid (ECF) space, a finding undetectable at this stage using physical exam. A decrease in muscle ECF upon fluid removal was similarly detectable with both the bedside sensor and MRI. Bioimpedance measurements performed comparably to the bedside NMR sensor but were generally worse than MRI. These findings suggest that bedside NMR may be a useful method to identify fluid overload early in patients with ESRD and potentially other hypervolemic patient populations.