Dialysis functions as a very effective but partial replacement for the processes of the kidneys. The main capability is the removal of waste products (e.g. see Creatinine above) from the blood supply. A secondary capability is the removal of water from the blood supply, and through that, from areas water is over-accumulating.
If you do dialysis in a clinic you spend many hours a week sitting next to a dialysis machine. It is possible you never need to concern yourself with how it works: it can be treated as just a black box that the RNs and technicians take care of. It may also be out of your view, so if you do want a look, you may need to ask to have it turned a bit.
Understanding what the dialysis machine is doing can relieve boredom, provide education, and help avoid problems. Potentially very painful and health-threatening problems. Your doctor's prescription and the clinic technicians enter the values for dialysis, and these may be the correct values. In two years of dialysis, the values were mostly right for me. In the last few months though (at a different dialysis center), "mistakes were made". By understanding the machine's display I caught the errors at the start of the treatment.
My dialysis machine when I started dialysis in 2021 looked like this:
Later the machine was updated to a new model and the display looked like this (the pump rate moved up onto the display), which makes it a bit easier to read and explain.
The dashboard ('Home') mode is only one state of the machine, but it is the one you are most likely to see.
Using a diagram from the Fresenius Technical Documentation, you can see they agree with how it looks in real life (without the glare and perspective effects).
There are more than twenty values displayed on this screen. The following aspects are the most critical:
The core value driving dialysis session length is in the initial value of the ‹RTD› (Remaining Time on Dialysis) field (e.g. '0:56' in the diagram).
This is a countdown timer, so if you have a four hour session, it starts at four hours. Initially it will match a clock time countdown (say a four-hour session starting at 2:00, after an hour should be 3-hours remaining), but as the session progresses dialysis could be paused. The clock time will stop matching the RTD counter any time the dialysis session pauses. Dialysis could be paused because you needed to leave the chair, but for me it was mostly based on whether my blood pressure dropped too low. My session length was pretty much always four hours, although it could be reduced to 3.5 if there was a scheduling issue.
The ‹Blood Pump Rate› (e.g. '200') is the speed the pump is pulling blood out of the catheter or fistula . When I had a catheter it was 350 and with a matured fistula it went up to 400.
The session length and pump rate should be values you expect. If the pump rate is too low the dialysis will be less effective. If the session length is too short, you may be happy it ended early (but likely not because of the water effect), but they aren't going to just let you go. Or your doctor will be unhappy you are not following the prescription.
The ‹UF Goal› (e.g. '3000') is the amount of water they expect to remove (through ‹Ultrafiltration›) during the dialysis session. This should match the amount that your ‹Wet Weight› is above your ‹Dry Weight› as long as that isn't too much for you to handle. Values above 3 liters are risky for most people. I could 'try for' as much as 4 but usually would cramp out and fail.
If the ‹UF Goal› is too small, you will be water-heavy leaving from dialysis and are going to have to get rid of that water eventually (with more diuretics, paracentisis, or in subsequent dialysis sessions). So that is not ideal.
The ‹UF Time› (e.g. '0:56') is a countdown timer for ultrafilteration, which will match the RTD countdown initially.
This is a second reason you want the RTD value to not be too short. If the UF Time value is too short and the goal is correct, the machine is going to quickly pull a lot of water. And you will likely have increased chances and severity for cramping.
Beyond the above values, the rest are mostly 'just interesting'.
Over a two year period I had a bit less than 300 4-hour dialysis sessions. Or more than 1000 hours of dialysis. These varied from being in the hospital, where the machine came to me and attached to my neck catheter, through having dialysis in a Satellite Healthcare center where the machine attached to a chest catheter, and finished with fistula-based dialysis where two large (15-gauge) needles are put into my upper left-arm. I was approved for solo home dialysis, but while preparing for that new approach, I was given a third kidney via transplant. So I missed out on the experience of putting two fat needles into my arm and taking them out four hours later.
As an ICU patient in need of dialysis, I have only vague memories of my first session. Late in the evening, a technician wheeled in a large machine and parked it near my bed. They then hooked up a bunch of tubing into the bathroom and did something to my right-side neck that I couldn’t see. I was already trapped in the bed by being feeble and many other machine connections, so being attached to yet another machine had no impact on me.
The machine running all night also had no impact on me physically. I believe this is a general advantage of the slow flow rate of overnight dialysis, which stresses the heart less and also gives more time for the body to rebalance any water drawn during dialysis.
The next form of dialysis I had was during the day. A machine was again wheeled into my M5 (Liver and Kidney ward) room, which this time came along with a nurse overseeing the process. Other than having someone to talk with, this felt the same as the overnight dialysis. I believe the continual nurse oversight prevents cramping and other common dialysis symptom: the nurse can adjust the flow rate dynamically based on physical measurements.
Changing to a dialisys clinic was a dramatic adjustment to having dialysis as just one of many procedures within the hospital. Clinic dialysis involves:
Preparing for dialysis is partially dealing with physical things. It is common to have a bag containing blankets, cushions, entertainment, and possibly some amount of food to take to dialysis. If you need walkers for movement, they need to be available for transport.
Additionally, there are bodily preparations. Dialysis can pull water from the body: the goal is to have a constant ‹dry weight› (say 75Kg) by the end of the session, so during a session they could pull up to 4 liters (4Kg) of water from you if you weigh more than 75Kg. This water draw alleviates Ascites and other water gain issues that are caused by damaged kidneys and livers. Unfortunately, that water draw can also cause severe cramping. For me, it happened mostly in my legs and hands, but more extreme versions can happen in my stomach muscles. You can’t (easily) stand up during dialysis, so cramping can be very painful and not quickly alleviated.
One self-preparation is to decide how much water is within you. Ideally you keep as close to the dry weight as possible between sessions. But in preparation for the dialysis session, you may want to add some “inbound” water to your stomach. You may also want to have some amount of fluid to drink during the session. Unfortunately these increase either your ‹wet weight› or your post-dialysis ‹dry weight› There is so much variation that I don’t believe any recommendation is right for everyone at any given moment. I experimented over two years and came up with different conclusions at different times.
I always tried to empty my bladder and bowels (as needed) before the session so I didn’t need to be temporarily unhooked during dialysis.
Initially I was not allowed to drive, so I was dependent on others to drive me the ten miles from my home to the dialysis center. My family was available to drive me, but the reliability of family members to get me to dialysis on time varied a bit. And it always felt like an imposition on them. There are also ParaTransit services, public transport, and Uber/Lyft/Taxi services. It appeared that some patients had a lot of issues with these other services in terms of reliability (e.g. a Taxi leaving without waiting for the dialysis patient to be medically released). I only used them sporadically and did not encounter any problems although they can be expensive when you use them six times a week (two trips every other day).
Within about a month I was able to drive myself, so that alleviated most of the transportation concerns. Eventually I moved to within reasonable walking/biking distance of the nearest dialysis center, which meant I could potentially get to dialysis even when I was unable to drive.
The dialysis facilities I went to had 24 chairs, and I tended to have appointments for the 2PM shift. The length of dialysis varies but is limited to 4 hours of dialysis itself. Setting up and disconnecting from dialysis can take about fifteen minutes each. So there is some chance of delays where a previous patient is still using a chair. I probably waited at most an hour for a chair, but was normally more like ten minutes.
To prepare for dialysis you need to weigh yourself and transport everything to the dialysis chair. When I had a walker, this was fairly involved, but eventually I could just carry a bag and wheelchair cushion to the scale (for the ‹wet weight›) and to the chair.
With a catheter, the RN does all the work of cleaning and connecting the dialysis tubes. The patient just has to have clothing that enables easy reach of the chest area.
Assuming you feel comfortable, you now need to spend four hours sitting in a relatively comfortable chain, in a room with a couple dozen other people, and where there are televisions displayed over every chair. Unfortunately at my center, the televisions display daytime (2PM) shows that are not of any interest to me. And the twenty four people are all spaced far enough away that you can't talk to them. Only in one case did I have someone near me physically (or really near my sister that was sitting next to me) and that discussion did not go well. It is easier to talk to the staff, but they are busy. Finally the chair is probably objectively comfortable but your body is very frail and you can't get up at all, so for me I needed an extra cushion, and some people brought pillows and other comfort improvements.
The room is noisy — the machines make standard noise, and alarms go off intermittently — so you need headphones to either overlay the noise or to cancel the noise. The room is somewhat cold and the procedure draws heat from you, so you need blankets to stay warm. Finally, you are pinned by either the chest catheter or arm fistula, so you need to work around those constraints.
Ultimately I fell into using good noise canceling headphones, a personal electronic device to watch movies or join meetings, talking to staff, and an ability to sleep for part of the time. Most patients seem to simply zone out and watch the television.
Dialysis is not just sitting in a chair. It is sitting in a chair where 5% or more of you blood is flowing into an external machine every minute. At the same time dialysis may be pulling a lot of water from your body. For me it was up to a liter per hour. The stress of dialysis caused me to severely cramp sporadically: eventually I would figure out indicators before the cramps occurred and could get assistance to adjust the machine settings or do more active recovery techniques. Other times the machine would complain (and the nurses respond) when my pulse or blood pressure dropped but without me be aware of any significant symptoms. I may have lost consciousness beyond just sleeping.
Other patients had more severe symptoms, including excruciating cramps and loss of consciousness. Every once in a while parametics would be called to transfer the patient to the nearby hospital. Beyond empathy for the person, it does make you worry about the future on dialysis.
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Having a fistula makes scheduling dialysis much easier. Only RNs can deal with chest catheters, and in California there is one RN for every twelve patients. So arrival times need to be staggered and there is a limit to which sessions a patient could go to. Many more technicians are present in a clinic, and most of these are allowed to insert and remove the dialysis needles. So the bottleneck on starting and ending a dialysis session is a bit easier.
Most of the technicians are also very skilled at ‹needle work›, but that leads to the biggest fistula drawback: it hurts both putting in and pulling out a 15-gauge needle. And you can bleed significantly after you pull a needle out. And you can miss (infiltrate) when putting a needle in. And it is just generally scary. But the benefits are eventually the needle wound closes up and so the risk of infection is less than a catheter. And you can shower, swim, get sweaty, and various other activities without concern.
I never had home dialysis but I prepared for it, up to the point of rearranging my furniture and scheduling training sessions with Outset (for the Tablo machine). The main advantage of home dialysis was an ability to schedule sessions outside of normal clinic times. Most obviously, having dialysis late at night would enable me to leverage the daylight hours without interruption. Patients can also control dialysis session duration and frequency more easily, although I found my schedule to be acceptable.
Tradeoff for home dialysis is dealing with insertion and withdrawal of needles, a lot of required supplies, water and power usage, and distance of any emergency services.
Many people have found home dialysis to be great, but I never experienced it to confirm whether it would have worked for me.
I was about a month for an elbow AVF. Infiltrated once but that was at three months and more a technician problem than an AVF issue. They started with a larger gauge needle but migrated within a week.
«Maturation mostly occurs 4 to 6 weeks after the initial fistula surgery but that timeframe can vary with the average time ranging from 1 to 4 months. » • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5989091/
I believe they did a second vein mapping (dynamic ultrasound of the blood flow) that needed to reach a particular flow rate and possibly diameter before approving use.
Something like «The Rules of 6 (flow volume >600 mL/min, vein diameter >6 mm, vein depth <6 mm) » • https://pubmed.ncbi.nlm.nih.gov/35227801/
Presumably if it failed to mature sufficiently they would follow up in another month or so.
A 'Fistula' is like a surfaced artery, except it immediately goes back to your heart. Like a highway loop with no stops in between.
Apparently, this can happen naturally: some people have an artery that connects to a vein directly instead of going through capillaries first. It can cause several problems due to the abnormal blood flow and pressures. Large fistulas can be surgically fixed and removed.
Somehow nature inspired a doctor to do the opposite: create a fistula where none existed before. Usually this is done in your arm, near your wrist or elbow. The surgeon shunts an artery to the returning vein, so some of the blood flow immediately loops back through the shunt instead of continuing to your hand. Since veins are on the surface and the blood is headed back to the heart, this creates an unusually good blood access point. A vein on steroids.
