Kai Lauri

Optical Online Monitoring of Uric Acid Removal during Dialysis

This study estimates the total removal of uric acid (TRUA) by online UV absorbance measurements in the spent dialysate in two different dialysis centers in Estonia and Sweden. Sixteen dialysis patients were included. All dialysate was collected that gave the reference for TRUA. Two regression models were investigated: one for each patient (UV1) and one for the entire material (UV2). TRUA from the three methods was in the same order but showed a statistically significant difference when the UV2 model was built on data from both centers together. TRUA, (n = 56) was (mean ± SD, µmol): 5,854 ± 1,377 for reference, 6,117 ± 1,795 for UV1 and 5,762 ± 1,591 for UV2. Six patients were monitored 1 year after the first study session, using the same models as the previous year, still having a nonsignificant difference. The results show the possibility of estimating TRUA by using UV absorbance. The method appeared to be reliable also in long-term patient monitoring.

Dialysis dose and nutrition assessment by optical on-line dialysis adequacy monitor.

AIM In light of the variability of dialysis sessions, on-line monitoring could improve hemodialysis (HD) adequacy. A new optical Dialysis Adequacy Monitor (DIAMON) prototype enables to estimate dialysis dose and protein nitrogen appearance (PNA) at every dialysis session. The aim of this study was to compare the adequacy of dialysis treatment and the patients nutritional status by pre-and post-dialysis blood samples, the DIAMON prototype and Total Dialysate Collection (TDC). MATERIAL AND METHODS Ten patients were monitored during three consecutive hemodialysis sessions during one week. Blood samples were drawn before the start of dialysis and at the end of dialysis. The DIAMON prototype was connected to the fluid outlet of the dialysis machine with all spent dialysate passing through during the on-line experiments, and TDC was performed for all dialysis treatments. Equilibrated Kt/V (eKt/V) values were estimated from blood-urea (eKt/Vb) and from DIAMON (eKt/Va), and normalized PNA (nPNA) values from TDC and DIAMON, respectively. The variable volume single pool urea kinetic modeling (VVSP UKM) was also utilized for single-pool Kt/V (spKt/V) and nPNA estimation. RESULTS The mean +/- SD given by eKt/Vb was 1.08 +/- 0.22 (n = 30), and eKt/Va 1.05 +/- 0.21 (n = 28). The mean +/- SD of nPNA was 0.73 +/- 0.15 g/kg/day (n = 29) from TDC, and 0.73 +/- 0.14 g/kg/day (n = 28) using DIAMON prototype. The mean values of eKt/V from blood samples and nPNA from TDC were not statistically different from the corresponding values estimated by DIAMON (p < 0.05). Generally the delivered dialysis dose and dietary protein intake of the patients observed during the study using the DIAMON prototype was very similar to that obtained by TDC and VVSP UKM. CONCLUSION The optical dialysis adequacy sensor, DIAMON, provides continuous, on-line measurements of dialysis adequacy and permits longitudinal analysis of the delivered dialysis dose and patients nutritional status, and can immediately identify, and alert to, any deviations in dialysis treatment.

Optical Method for Cardiovascular Risk Marker Uric Acid Removal Assessment during Dialysis

The aim of this study was to estimate the concentration of uric acid (UA) optically by using the original and processed ultraviolet (UV) absorbance spectra of spent dialysate. Also, the effect of using several wavelengths (multi-wavelength algorithms) for estimation was examined. This paper gives an overview of seven studies carried out in Linköping, Sweden, and Tallinn, Estonia. A total of 60 patients were monitored over their 188 dialysis treatment procedures. Dialysate samples were taken and analysed by means of UA concentration in a chemical laboratory and with a double-beam spectrophotometer. The measured UV absorbance spectra were processed. Three models for the original and three for the first derivate of UV absorbance were created; concentrations of UA from the different methods were finally compared in terms of mean values and SD. The mean concentration (micromol/L) of UA was 49.7 ± 23.0 measured in the chemical laboratory, and 48.9 ± 22.4 calculated with the best estimate among all models. The concentrations were not significantly different (P ≥ 0.17). It was found that using a multi-wavelength and processed signal approach leads to more accurate results, and therefore these approaches should be used in future.

HPLC study of uremic fluids related to optical dialysis adequacy monitoring

PURPOSE The aim of this study was to investigate uremia-related high-performance liquid chromatography (HPLC) ultraviolet (UV) absorbance profiles of serum and spent dialysate and to study the removal of uremic retention solutes in connection with optical dialysis adequacy monitoring. METHODS 10 uremic patients were investigated using online spectrophotometry at a wavelength of 280 nm over the course of 30 hemodialysis treatments. The dialysate and blood samples were taken and analyzed simultaneously using standard biochemical methods and reversed-phase HPLC. Filters with cutoff at 3 kDa and 70 kDa were used for the pre-treatment of the serum. The chromatographic peaks were detected by a UV detector at wavelengths of 254 and 280 nm. RESULTS This study indicated that the main solute responsible for UV absorbance in the spent dialysate is a low-molecular-weight, water-soluble, non-protein-bound compound uric acid (UA). Three additional uremic retention solutes - creatinine (CR), indoxyl sulphate (IS) and hippuric acid (HA) - were identified from the HPLC profiles. The number of detected HPLC peaks was not significantly different for a serum filtered through the 3 kDa or 70 kDa cutoff filters, and was lower for the spent dialysate, indicating that the molecular weight (MW) of the main UV chromophores in the uremic fluids did not exceed 3 kDa. The reduction ratio (RR) estimated by the total area of HPLC peaks at 254 nm and 280 nm in the serum and by the online UV absorbance at 280 nm was best related to the removal of small water-soluble non-protein bound solutes like urea (UR), CR and UA. CONCLUSIONS The present study contributes new information on the removal of uremic retention solutes during hemodialysis and on the origin of the optical dialysis adequacy monitoring signal.

Optical measurement of creatinine in spent dialysate

AIM The aim of the study was to develop an optical method for the estimation of creatinine (Cr) removal during dialysis using UV-absorbance. MATERIAL AND METHODS 29 hemodialysis patients on chronic 3-times-a-week hemodialysis were studied in 6 separate studies. Double-beam pectrophotometer was used for the determination of UV-absorbance in the collected spent dialysate samples. A single wavelength (SW) and a multi-wavelength (MW) model were developed using stepwise regression utilizing Cr values from the laboratory as the dependent parameter. The reduction ratio (RR) and total removed Cr (TRCr) were estimated. RESULTS For blood-Cr RRb (mean ± SD) was 60.9 ± 5.0% (calibration set) and 58.1 ± 6.0% (validation set), for SW UVabsorbance RR_SW was 61.5 ± 5.9% and 57.3 ± 6.0%, and for MW UV-absorbance RR_MW was 65.8 ± 5.8% and 61.7 ± 6.4% respectively. RR_SW and RRb were not statistically different. RR_MW was higher compared to RRb (p < 0.05). TRCr_lab was 13.8 ± 3.8 mmol, TRCr_SW 14.5 ± 2.5 mmol and TRCr_MW 13.8 ± 2.6 mmol, being not statistically different. CONCLUSION In summary, creatinine removal during dialysis can be estimated as reduction ratio and total removed creatinine with the UV-absorbance technique.

Optical dialysis adequacy sensor: contribution of chromophores to the ultra violet absorbance in the spent dialysate

Several on-line methods have been developed to standardize the assessment of dialysis adequacy. Earlier studies have demonstrated that on-line monitoring of total ultra violet (UV) absorbance in spent dialysate can be utilized to follow continuously a single hemodialysis session. The aim of this study was to investigate the contribution of different compounds, acting as chromophores, to the UV-absorbance in the spent dialysate in order to explain origin of the cumulative and integrated UV-absorbance measured by the optical dialysis adequacy sensor. Four uremic patients, during 12 hemodialysis treatments, were followed by the optical dialysis adequacy sensor using the wavelength of 280 mn. The dialysate samples were taken and analyzed using reversed phase high performance liquid chromatography (HPLC). The total number of detected peaks from the HPLC gradient separation profiles measured at the wavelength 280 nm for the samples collected 10 mm after the start of hemodialysis (MeanplusmnSD) was 38plusmn6. The relative contribution from the area of 10 main peaks to the total area of all detected peaks in percentage was 91.01plusmn2.52 %. The optical dialysis adequacy sensor provides continuous, on-line hemodialysis measurements and may immediately identify and alert to any deviations in the dialysis. Our study indicates that there exists a number of prevalent compounds that are the main cause of the cumulative and integrated UV- absorbance

Concentration of uric acid removed during dialysis. estimated by multi wavelength and processed ultra violet absorbance spectra

The aim of this study was to estimate the concentration of uric acid (UA) optically by using original and processed ultra violet (UV) absorbance spectras of the spent dialysate. Also the effect of using several wavelengths for estimation was examined.

Improved Optical Method for Measuring Concentration of Uric Acid Removed during Dialysis

The aim of this study was to compare concentration measurements of uric acid (UA) removed during dialysis. Algorithms based on ultraviolet (UV) absorbance and 1st derivate of UV-absorbance whereby single and multi-wavelength was used.

A multicentre study of an enhanced optical method for measuring concentration of uric acid removed during dialysis

The aim of this study was to compare concentration measurements of uric acid (UA) removed during dialysis by two algorithms based on UV-absorbance and the 1st derivate of UV absorbance. Ten uremic patients from Tallinn and ten from Linköping, during 30+40 haemodialysis treatments, were followed at the Departments of Dialysis and Nephrology at North-Estonian Medical Centre and at Linköping University Hospital. The dialysate samples were taken and analyzed by means of UA concentration at the chemical laboratory and with a double-beam spectrophotometer. UV absorbance and derivate of UV absorbance was transformed into UA concentration in the spent dialysate using the regression models from the calibration set of material, noted as UV-absorbance (UV_A) and the 1st derivate of UV absorbance (UV_D) method. These models were tested on validation set of material and concentrations of UA from the two methods were compared regarding mean values and SD. Mean concentration of UA were 52.7 ± 25.0 micromol/l measured at the chemical laboratory (UA_Lab), 54.9 ± 23.8 micromol/l determined by UV_A and 52.9 ± 23.0 micromol/l determined by UV_D. The results of mean concentrations were not significantly different (p ≥ 0.54). The systematic errors were -7.8 % and -3.3% and random errors were 15.8 % and 10.4 % using UV_A and UV_D respectively. The systematic and random errors were significantly different (p < 0.05) indicating that the new algorithm enables more accurate UA estimation.

A New Optical Method for Measuring Creatinine Concentration During Dialysis.

The aim of this study was to compare creatinine (Cr) concentration measurements removed during dialysis by two optical algorithms based on single wavelength and multiwavelength UV-absorbance.