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Prescribed versus delivered dialysis: Importance of dialysis time

Robert Hootkins, MD, PhD, FACP, FAHA, FASN
William L Henrich, MD, MACP
Richard A Sherman, MD
Section Editor
Steve J Schwab, MD
Deputy Editor
Alice M Sheridan, MD


Adequacy of hemodialysis is an important issue since it appears to be an important determinant of patient survival (see "Patient survival and maintenance dialysis"). One method of assessing the amount of dialysis prescribed is to assess urea removal normalized for a measure of body size, the Kt/V. This parameter can be estimated from the dialyzer urea clearance data supplied by the manufacturer (K), the duration of dialysis in minutes (t), and the patient's urea space (V) as derived from a standard height/weight nomogram.

A number of the major factors contributing to K are:

The size of the dialysis membrane since larger surface area membranes can remove more urea per unit time.

The blood flow rate to the dialyzer (Qb) since presenting new plasma with a high urea concentration maintains the favorable gradient for urea removal (figure 1).

The dialysate flow rate (Qd) since delivering new fluid containing no urea also maintains the urea concentration gradient.

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Literature review current through: Oct 2017. | This topic last updated: Mar 11, 2016.
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