How should dialysis dose be measured?
Since the establishment of a link between dialysis dose measured by urea clearance and clinical outcomes in patients with ESRD, the clearance of urea adjusted for the volume of distribution of water has been used as an index of dialysis adequacy (Kt/V).
Although widely used for chronic patients, the use of this dose assessment parameter in Acute Kidney Injury is not clear.
In Acute Kidney Injury, the changes in body water volumes and urea generation rates result in inaccuracy of these formulas.
The calculated Kt/V in Acute Kidney Injury patients has been shown to be 30% higher than the measured clearance in the dialysate because of episodes of hypotension, dialyzer clotting, and vascular access recirculation.
In CRRT, we also overestimate the true solute clearance by using the effluent volume as a surrogate marker of the delivered dose.
Treatment interruptions, progressive decreased filter efficacy, and, consequently, reduced clearance over time result in a gap between the prescribed and the delivered dialysis dose.
The use of dialysate-side measurements provides more accurate dose information (actual solute removal), as it accounts for the loss of filter efficacy.
Thus, measuring the actual solute removal in the effluent, and calculating the clearance based on the mass extract, could dramatically improve the way we assess the effect of dose on outcomes in critically ill patients.
