Legacy data (Upstate IRB protocol 32-7074) consisting of consecutive transcutaneous Raman spectra obtained over the first hour of a routine dialysis session revealed the presence of different ions and proteins. The “101-7” baseline subtraction algorithm performed on the spectra produces zero mean data for which most of the variance is associated with Raman transitions, i.e., with molecular species in the blood and skin. Raman peaks were identified comprising various molecular anions and other species, and from previous calibration, the concentrations of H2PO4 and HPO4 were determined. It was determined whether these species were increasing or decreasing and were used to calculate the pH of the probed volume of skin and blood. The range for pH varied from 7.21 to 7.09. Temporal pulses were observed in both elastic and inelastic emission induced by the Raman excitation laser, confirming that the spectra have contributions from the blood and skin. Instrumental limitations at the time did not allow data collection over the whole dialysis session. We believe data such as these have not been seen before and can potentially help practitioners improve care for people on dialysis. Combined with FRD/PVOH and other vital sign monitoring that can be calculated directly from the elastic and inelastic emission, these data are sensitive to the individual patient’s autonomic compensation for the dialysis procedure itself, providing feedback to guide adaptation to each patient’s requirements for homeostasis, and hopefully reducing adverse events on the approach to dry weight.

Non-invasive, in vivo, continuous monitoring of vascular volume and electrolytes during dialysis using FRD/PVOH and Raman spectroscopy

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