Manny (not his real name) started BigD about two months ago. And contrary to common experience, he feels just as lousy as when he started: weak, tired, generally unwell and incapable of doing much at all. These are classic symptoms of insufficient dialysis, where not enough toxins are being removed by the membrane filter.
Why? Like all new BigD members, his fistula was soft and fragile and initially couldn’t handle blood pump speeds higher than about 200 milliLitres per minute (mL/min). But rather than his fistula gradually maturing over time to become capable of faster blood flows, it had some kind of blockage (maybe it was clotted or had a narrowing that impeded the blood flow). So staff couldn’t get the blood pump speed past the 200 mL/min mark, which is not really enough dialysis to make a difference.
Manny has since had a fistulagram, an X-ray procedure to look at the blood flow and check for clots or other blockages. There was narrowing, and a balloon was placed into the narrow area and blown up with sterile water: the balloon expanded and enlarged the narrow area of his fistula.
He is now dialysis with a higher blood flow. He should start feeling better within a couple of weeks. I’ll let you know.
So what is a good pump speed? Can you pump too fast and damage your fistula or maybe your heart?
Put simply, within limits the faster the pump speed the better. Over a run, a faster blood pump speed increases the volume of blood running past the membrane, and thus the more toxins are removed.
Two of things affect blood pump speed: the state of our fistula and needle size.
State of the Fistula
Fistulas are created by joining a major artery with a nearby vein to provide sufficient blood flow in the vein for the dialysis machine to operate. The newly created fistula typically needs several months for the draining vein to expand and the blood flow to increase to a point where dialysis is possible. The ideal dialysis starting point is when the fistula has a minimum venous diameter of 0.4 cm (0.16in) or greater at its narrowest point and a blood flow rate of 500 mL/min or greater. Both of these measures tend to increase further as the fistula matures, as does the ability of the fistula to handle increasingly greater pump speeds.
If the fistula is robust and stable and blood is flowing freely with no blockages (eg if you hold your fistula arm vertically above your head and it ‘empties’ quickly), it is a likely candidate for a high pump speed (obviously you should clear it with your nephrologist before making any pump speed changes).
Many people are started on dialysis with 17 gauge needles and a pump speed of up to 250 mL/min. as the fistula matures, they gradually move to 15g needles (the smaller the gauge the bigger the needle) with pump speeds of around 300 – 350 mL/min. For pumps speeds above about 360 mL/min, 14g needles are used.
If the speed is too high for the needle size there is a danger of recirculation and possible damage to red blood cells. In all cases, both needles must be the same size.
Several people in my unit use 14g needles, with pump speeds up to 460 mL/min. All are getting good quality dialysis and many feel well enough to work nearly full time. Other units, especially in the US, use pump speeds of 500 mL/min and higher.
With regard to damaging the fistula, there is no evidence that fast blood pump speeds damage a mature fistula. Fistulas are engineered to create blood flows of at least 500 mL/min and some larger older fistulas manage flows of 1000 mL/min or more. The speeds achieved using 14 g needles are well within this range.
Similarly, there is little evidence that blood pumps running at high speed cause any damage to the heart. Most BigD heart problems are associated with the left ventricle, which is the largest and strongest chamber in the heart. For us, the left ventricle becomes enlarged, due to the extra fluid we carry before we start dialysis, and between BigD sessions. This is true for all BigDers, on HD and PD. The extra fluid increases the volume of blood in the body and the heart has to work harder to pump the blood. The extra work causes the left ventricle to increase in size. Pump speed does not have any effect on increasing the size of the heart.
(This is not true of the extra fluid: most hearts can handle it for a short period, but if it becomes part of our routine over the years on BigD, the heart becomes weak and heart attack or stroke becomes likely. The key to long life is to keep fluid gain to between 1 and 2 litres between runs.)
I have used 15g needles for the past 17 years and have had no thought of going higher. However, after researching this article, I can see no reason why I shouldn’t move to 14g and raise my pump speed. Apart from the initial discomfort of expanding my buttonholes, I can see only benefits. I am keen to see how much better I will feel.
I will certainly let you know.