Online measurement of urea concentration in spent dialysate during hemodialysis.
BACKGROUND
We describe online optical measurements of urea in the effluent dialysate line during regular hemodialysis treatment of several patients. Monitoring urea removal can provide valuable information about dialysis efficiency.


METHODS
Spectral measurements were performed with a Fourier-transform infrared spectrometer equipped with a flow-through cell. Spectra were recorded across the 5000-4000 cm(-1) (2.0-2.5 microm) wavelength range at 1-min intervals. Savitzky-Golay filtering was used to remove baseline variations attributable to the temperature dependence of the water absorption spectrum. Urea concentrations were extracted from the filtered spectra by use of partial least-squares regression and the net analyte signal of urea.


RESULTS
Urea concentrations predicted by partial least-squares regression matched concentrations obtained from standard chemical assays with a root mean square error of 0.30 mmol/L (0.84 mg/dL urea nitrogen) over an observed concentration range of 0-11 mmol/L. The root mean square error obtained with the net analyte signal of urea was 0.43 mmol/L with a calibration based only on a set of pure-component spectra. The error decreased to 0.23 mmol/L when a slope and offset correction were used.


CONCLUSIONS
Urea concentrations can be continuously monitored during hemodialysis by near-infrared spectroscopy. Calibrations based on the net analyte signal of urea are particularly appealing because they do not require a training step, as do statistical multivariate calibration procedures such as partial least-squares regression.
Olesberg
Jonathon T
JT
Optical Science and Technology Center and the Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA.
Arnold
Mark A
MA
Flanigan
Michael J
MJ
D002138:Calibration; D015314:Dialysis Solutions / Q000737:chemistry*; D006801:Humans; D016018:Least-Squares Analysis; D006435:Renal Dialysis; D017550:Spectroscopy, Fourier Transform Infrared; D014508:Urea / Q000032:analysis*
D015314:Dialysis Solutions; D014508:Urea