How Does My Doctor Know if Dialysis is Working?

When you begin dialysis treatments, whether hemodialysis or peritoneal dialysis (PD), you should begin to feel better as your blood is getting cleaned. To make sure you are getting adequate dialysis, your nephrologist will order lab work to see how well dialysis is working for you. If your doctor sees that your blood is not being adequately cleaned, changes can be made to help you get better treatments.

URR

The urea reduction ratio (URR) is one way of measuring dialysis adequacy—how much waste is removed by hemodialysis. If you receive hemodialysis three times a week, each treatment should reduce your urea level (also called BUN or blood urea nitrogen) by at least 65 percent.

Kt/V

Kt/V, like URR, is a measure of dialysis adequacy.

  • K = clearance—the amount of urea your dialyzer can remove (liters/minute)
  • t = time—the duration of treatment (minutes)
  • V = volume—the amount of body fluid (liters)

For hemodialysis three times a week, K/DOQI (Kidney Disease Outcomes Quality Initiative) national guidelines recommend a delivered Kt/V of at least 1.2.

In continuous ambulatory peritoneal dialysis (CAPD), the guidelines recommend a weekly Kt/V of at least 2.0, taking into account any remaining kidney function along with the CAPD treatment. In PD, Kt/V is measured by collecting drained dialysate along with any urine you produce in a 24-hour period.

URR and Kt/V tests

These lab tests are drawn monthly. For PD, the Kt/V is usually done quarterly. Ask your dialysis nurse what your values are each time. If your values do not reach adequate numbers, work with your healthcare team to raise your dialysis dose.

Ideal blood flow rate for hemodialysis

During hemodialysis, a blood pump is set to a constant speed to push your blood through the dialyzer and back to your body. Your doctor prescribes the blood flow rate. It’s usually between 300 and 500 mL/min (milliliters per minute). Ask your technician to show you how to see the blood flow rate on your machine. With many dialyzers, blood flow rates greater than 400 mL/min can increase the removal of toxins. Blood flow rate is limited by the size of your access, the tubing and the needles.

Arterial pressure and venous pressure on the hemodialysis machine

A hemodialysis machine monitors the pressure of your blood inside the tubing and dialyzer. Depending on the machine, arterial pressure is measured in one of two places. One is between your access and the blood pump (pre-pump arterial pressure). The other is between the blood pump and the dialyzer (post-pump arterial pressure).

An alarm will go off if the pressure is too high or too low, due to:

  • Infiltration of the access (bleeding inside the access arm)
  • Clotting in the access or needle
  • A needle against the access wall
  • A kink in the blood tubing
  • Low blood pressure
  • Too-fast or too-slow blood pump speed
  • Separation of the blood tubing from the access or dialyzer

In the hemodialysis machine, venous pressure is measured between the dialyzer and your access. If your venous pressure rises from week to week, it could mean a narrowing of the blood vessels in your access. Caught early, this can be fixed.

A venous pressure alarm will go off it:

  • A needle against the blood vessel wall
  • A kink in the blood tubing
  • Separation of the blood tubing from the dialyzer
  • A blood clot in the dialyzer or tubing
  • Narrowing of the blood vessel in the access
  • Too-fast or too-slow blood pump speed
  • An infiltration
  • Needle dislodgement

Ask your dialysis team what your arterial and venous pressure numbers should be.

The best judge of how you feel is you, but your doctor will also review your lab tests to see if you are receiving the most effective dialysis treatments.

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