Frequency-domain broadband near-infrared spectroscopy for noninvasive monitoring of fluid volume status during hemodialysis.

Significance: Poor fluid management during hemodialysis in patients with end-stage kidney disease contributes to adverse clinical outcomes. Current tools for assessing volume status are limited, and there is a need for objective measurement techniques. Aim: We aim to evaluate the ability of a hybrid frequency-domain (FD) and broadband continuous-wave near-infrared spectroscopy (FD-Bb-NIRS) system to monitor tissue changes during hemodialysis and identify markers associated with intradialytic adverse events. Approach: A custom-built FD-Bb-NIRS system was used to acquire continuous optical measurements. The system utilized FD laser diodes (730, 785, 852, and 940 nm) and broadband illumination (700 to 1000 nm). These measurements were integrated using model-based analysis to provide broadband absorption and reduced scattering spectra. Beer's law was used to extract tissue chromophore concentrations. Results: Across 27 subjects, the water ratio ([water]/([water] + [lipid])) showed significant differences between subjects with and without intradialytic adverse events ( Conclusions: The FD-Bb-NIRS device successfully measured changes in tissue fluid dynamics during hemodialysis. Longitudinal water ratio measurements show promise as optical markers for identifying patients at risk of adverse events.