title: On-line monitoring of solutes in dialysate using absorption of ultraviolet radiation: technique description.
abstract: OBJECTIVE
  The aim of this work was to describe a new optical method for monitoring solutes in a spent dialysate using absorption of UV radiation.
  
  
  METHODS
  The method utilises UV-absorbance determined in the spent dialysate using a spectrophotometrical set-up. Measurements were performed both on collected dialysate samples and on-line. During on-line monitoring, a spectrophotometer was connected to the fluid outlet of the dialysis machine, with all spent dialysate passing through a specially-designed cuvette for optical single-wavelength measurements. The concentrations of several substances of various molecular sizes, electrical charge, transport mechanism, etc. were determined in the dialysate and in the blood using standard laboratory techniques. The correlation coefficient between UV-absorbance of the spent dialysate and concentration of the substances in the spent dialysate and in the blood was calculated from data based on the collected samples.
  
  
  RESULTS
  The obtained on-line UV-absorbance curve demonstrates the possibility to follow a single hemodialysis session continuously and to monitor deviations in the dialysator performance using UV-absorbance. The experimental results indicate a very good correlation between UV-absorbance and several small waste solutes removed such as urea, creatinine and uric acid in the spent dialysate and in the blood for every individual treatment at a fixed wavelength of 285 nm. Moreover, a good correlation between the UV-absorbance and substances like potassium, phosphate and beta2-microglobulin was obtained. The lowest correlation was achieved for sodium, calcium, glucose, vitamin B12 and albumin.
  
  
  CONCLUSIONS
  A technique for on-line monitoring of solutes in the spent dialysate utilising the UV-absorbance was developed. On-line monitoring during a single hemodialysis session exploiting UV-absorbance represents a possibility to follow a single hemodialysis session continuously and monitor deviations in dialysis efficiency (e.g. changes in blood flow and clearance). The UV-absorbance correlates well to the concentration of several solutes known to accumulate in dialysis patients indicating that the technique can be used to estimate the removal of retained substances.
authors.affiliation: Department of Biomedical Engineering, Linköping University, University Hospital, Sweden. ivofr@imt.liu.se
authors.forename: I
authors.initials: I
authors.lastname: Fridolin
authors.forename: M
authors.initials: M
authors.lastname: Magnusson
authors.forename: L G
authors.initials: LG
authors.lastname: Lindberg
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015314:Dialysis Solutions / Q000737:chemistry*; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000628:therapy; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D009862:Online Systems; D006435:Renal Dialysis; D013056:Spectrophotometry, Ultraviolet; D014508:Urea / Q000032:analysis*
chemical_list: D015314:Dialysis Solutions; D014508:Urea