I have read that dfr should be twice the blood flow rate re 3x week hemo. Does anyone understand the reasoning behind this and how is the dfr rate determined for SDD and SND?
The dialysate flow rate of twice the blood flow rate theory was developed back in the old days of dialysis (early 70’s) when most patients used Scribner Shunts and had a maximum blood flow rate of about 250 ml/min. There wasn’t definitive science behind it, though it was the golden rule of thumb for many years. When we started using kinetic modeling (Kt/V), we learned that you get great improvements in clearance by increasing blood flow, and small improvements by increasing dialysate flow. You do get higher clearances at higher dialysate flows, but you get less bang for your buck.
For example, a shift from a blood flow rate of 250 up to 400 ml/min would give a 30% increase. An shift in DFR from 500 to 800 ml/min might only increase clearance by 10%. Though many centers use an DFR of 800 ml/min, they could get the same additional clearance by running the patient 15 minutes longer.
In SDD, the blood flow rates usually remain high, in the 500-800 ml/min range. In SND, the number of minutes has increase so much that you can reduce the clearance, which is done by reducing both blood and dialysate flow rates. The low clearances per minute make the dialysis much more gentle, while the total clearances are higher.
Curt
You are also limited by bicarbonate jug capacity with nocturnal to a dfr of about 300 unless you are prepared to respond to a “Low Bicarbonate” warning before morning. We use a bfr of 200 and dfr of 300 which I think is typical.
Jim writes:
An shift in DFR from 500 to 800 ml/min might only increase clearance by 10%. Though many centers use an DFR of 800 ml/min, they could get the same additional clearance by running the patient 15 minutes longer.
When the dfr (Qd) is reduced 25% ( 800 to 600 ml/min) as cost saving measure, how does that affect patients’ health?
If an adjustment is made to the treatment time, it would have no affect whatsoever. In fact, an argument could be made that the patient would be better off getting more time, even at a lower Qd if overall clearance was the same.
If any cost saving measure is implemented without considering the effect on the patient, quality will be reduced. In this case, the difference between an 800 Qd and a 600 Qd would be a relatively small decrease in urea clearance. This decrease may be important if the treatment time is very short.
Curt
Let’s say that by decreasing dfr 25%, labs show a drop in clearance of 1.9 to 1.6. What does this mean in terms of patient’s present and future health?
Jane,
I assume that you mean a drop in Kt/V from 1.9 to 1.6? There are too many variables to say for sure, but more, gentle dialysis is better than less dialysis any way you look at it.
My today’s standards, a Kt/V of 1.6 is adequate dialysis. You can get this with either a high clearance and short time, or a low clearance and a long treatment time.
I do not agree that Kt/V is a good measure of dialysis adequacy, but that is what we use these days. The Featured article by Dr. Kjellstrand is very much to point on this subject.
I am sorry I can’t be more specific because there are so many things to consider, but more dialysis is better than less.
Curt
Yes, I am referring to Kt/V. My question is, if a unit does NOT add tx time and reduces Qd by 25%, how are patients affected? One person told me that patients will not have a loss in clearance ( Kt/V) if their blood pump speed is high enough- only patients with lower blood pump speed would experience loss of clearance. But another individual told me that a 25% loss in Qd without increased tx time could lead to all sorts of physical problems for all patients.
Jane,
Any decrease in Qd will result in a decrease in clearance. This decrease will be more pronounced with a lower blood flow than with a higher Qb because it will have a greater reduction in clearances.
The affect on the patient would be the same as any symptoms of underdialysis: lower energy levels, lower appetite, restless legs, etc. It is hard to say if these symptoms would increase just because the Qd was 600 instead of 800.
I beleive all patients who dialyzer 3 times a week are underdialyzed to some extent. Even with high clearances, this treatment causes such dramatic swings in chemistries and fluid shifts that they still have many of the same symptoms.
Time is more important than high per-minute clearances!
Curt