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Abstract: SA-PO1004

Measurement of Dialysate Sodium: Beware of Assay Artifact

Session Information

Category: Dialysis

  • 701 Dialysis: Hemodialysis and Frequent Dialysis

Authors

  • Brown, Pierre-Antoine, The Ottawa Hospital, Ottawa, Ontario, Canada
  • Hiremath, Swapnil, University of Ottawa, Ottawa, Ontario, Canada
Background

Dialysate sodium is traditionally set at a constant in the range of 136 to 140 mmol/L. However, increasing dialysate sodium, either as a constant, or using sodium ramping, modelling, or using biofeedback systems, can decrease intradialytic hypotension, and symptoms . An individualised dialysate sodium prescription may decrease thirst, interdialytic weight gain and blood pressure. There are some reports that the measured dialysate sodium concentration may vary from the the ordered sodium . This quality assurance study was conducted to measure the bias between machine reported conductivity and the actual delivered dialysate sodium and determine the factors associated with the bias.

Methods

We conducted analyses on 3 different dialysis machines by running patient-free dialysis sessions with varying combinations of sodium and potassium baths. With the different permutations of the 3 machines, sodium and potassium baths.The conductivity meters of the machines were validated prior to each run using a calibrated external handheld conductivity meter. Dialysate samples were sent for measurement of sodium (indirect ion selective [ISE] method) using the Siemens Vista 1500 analyzer in an accredited clinical laboratory, using serum and urine modes. Samples were obtained from the arterial dialyser port. The primary outcome was quantification of the bias between ordered and measured dialysate sodium, defined as the mean difference between the two. The secondary outcome was to measure the variation of the bias based on certain prespecified covariates.

Results

Overall data are available as 230 measurements from 85 sessions. Overall, there was a significant difference between ordered sodium level and measured sodum (mean +5.6, standard deviation [SD] 1.8 mmol/L), with the delivered sodium being higher. There was no significant difference between the different machines, differing sodium ordered (135 or 140), K bath (2 or 3K), time (0, 1, 2, 4 hours). However, there was a marked difference between using serum mode (+ 6.0 SD 1.6) and urine mode (mean 1.5, SD 2.9).

Conclusion

Since serum plasma is composed of 7% solids, the serum measurement has a correction factor that should not be applied when measuring samples with lower amouont of proteins. In the case of the dialysate, using urine mode for measurement of electrolytes corrects the apparent bias in delivered sodium.