Dialysis Dose & Adequacy

Haemodialysis Dose & Adequacy

When kidneys fail, dialysis is necessary to remove waste products such as urea from the blood. By itself, urea is only mildly toxic, but a high urea level means that the levels of many other waste products that are more harmful and not as easily measured are also building up.

To see the actual clearance through the dialysis procedure, we should test the blood once in a month. Blood is sampled at the start of dialysis and at the end. The levels of urea in the two blood samples are then compared. Two methods are generally used to assess dialysis adequacy, URR and Kt/V.

How is the dose of dialysis determined?

The dose of dialysis is determined by measuring the urea concentration in the blood at the start and end of the dialysis procedure to determine the amount of urea that is removed during the dialysis session and concurrently determining the amount of fluid removed during a single haemodialysis session. Once these values are available, a variety of techniques can be used to determine the dose of dialysis provided to the patient.

What technical factors should be considered when measuring the dose of dialysis?

The method by which the pre-dialysis and post-dialysis blood samples are obtained is important in ensuring accurate results. Blood urea nitrogen (BUN) levels are subject to rebound of three different types, including access recirculation, cardiopulmonary recirculation, and remote compartment rebound. By following a specific technique for blood drawing, the effect of access recirculation on the post-dialysis BUN sample is minimized. Both the pre-dialysis and post-dialysis samples should be drawn during the same dialysis session. The post-dialysis BUN samples should be obtained using either the slow flow or stop flow technique. With the slow flow technique, the dialysate flow is turned off and the blood pump is slowed to about 100 mL/min for about 15 seconds prior to obtaining the sample from the sampling port. Alternatively, with the stop flow technique, after the aforementioned procedures are performed, the blood pump is stopped and the arterial and venous blood lines are clamped prior to obtaining the sample.

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