Title:
KINETIC STUDIES ON UREA EXTRACTION WITH HAEMODIALYSIS IN CHILDREN AND ADOLSCENTS BY ON-LINE MONITORING OF DIALYSATE UREA

Adela Della Marina^none ;Adela Della Marina^none ;Adela Della Marina^none ;Adela Della Marina^none ;Adela Della Marina^none ;Adela Della Marina^none ;Adela Della Marina^none

Germany' ne ''

E-mail address corresponding author:
klaus-eugen.bonzel@uni-essen.de

Background:
Kinetics of urea extraction during a single hemodialysis session in children are unknown, because analysis of dialysate solutes is difficult due to the extreme dilution of dialysate. Because of the small size of children good vascular access is difficult to achieve and blood flow sometimes is low. Therefore more information on changes in urea clearance and extraction during time elapsing with one dialysis session is needed especially for reasons of quality assessment in children on regular hemodialysis treatment.

Methods:
We studied 160 urea kinetics in 9 children and adolescents aged 13 to 19 years weighing 26 to 58 kg and looked for influences of membrane size, blood flow and duration of dialysis session. Bicarbonate dialysis regimen was 4 to 5 hours each 3 times weekly using polysulfone high flux dialysers (Fresenius F60 and F80 depending on body size). For continuous urea measurement in the dialysate we used DQM urea monitor from Gambro. Urea measurement applies to the change of electrical dialysate conductivity due to ionisation because of urea splitting by urease.

Results:
Kt/V accumulation during one dialysis session was linear. Average 4 hrs Kt/V for F60 was 1.69±0.53 and for F80 1.63±0.25, extracted urea mass was 16.0±5.4g and 32.5±5.4g, respectively (p<0.05); Kt/V for blood flows of 180–220ml/min was 1.36±0.52 and for <180ml/min 1.10±0.43, extracted urea mass was 21±8 g and 16±5g, respectively (p<0.05). - Urea mass transfer was exponential and showed saturation kinetics. Total average urea elimination ratio per patient after only 2hrs of dialysis was 62.8±3,3%. Extraction ratio during the 4th hr of dialysis was only 15.3±4.1% and during the 5th hr not more than 9.0+3.6% of total urea extraction. Intraindividual variation was smaller than interindividual variation. Urea mass transfer varied a lot mostly depending on body size of patients, much more than Kt/V showing to be roughly independent from body size if corrected for body surface area.

Conclusion:
Kinetics of urea extraction helps understanding dialyis processes in children. Adapting the size of dialyser in proportion to body size raises urea extraction and maintains urea clearance Kt/V at the desired quality level. An inadequate blood flow lowers both urea extraction and urea clearance Kt/V. Prolonging dialysis beyond 4 hrs is a rather ineffective means for urea kinetic modelling. We speculate that children with blood flow problems should be dialysed more often.

Subject:
Monitoring of Dialysis

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