Dialysis 101 for Home Hemodialysis (HD)
In my 47 years in nephrology, I must have “sentenced” many hundreds of ordinary and fearful people to life with dialysis. Yet, I have not been immunized against the trauma each new patient must feel when meeting the machine for the first time. I still share their sense of dread—despite all the preparation and education we try to give—when I say…”I think it is time you started.”
This is why experienced patients, educators, and moderators at the Home Dialysis Central Discussion Group try to answer your questions as best they can, gently and respectfully trying to help you understand home dialysis.
To thrive at home, you need to understand some basic dialysis principles. This article seeks to address some of these.
1. We are all different
No two of us are exactly the same. Even identical twins—while physically very close—will become individuals. This means that each of us will respond in a unique way to any given “event,” and in never quite the same way as someone else would.
Machines, on the other hand, are engineered to be safe, reliable, and predictable. They do the same thing, each time. A machine is—and must be—the opposite of individual. It needs to reliably do just what we ask (and expect) it to do.
But—and here’s the challenge—a dialysis machine must deliver a predictable treatment to unpredictable you. Each dialysis patient will react differently (sometimes just a little, but sometimes quite a lot) even if the treatment is identical.
To make matters worse, you can respond differently to the same mechanical “event” at different times. So, your responses may be quite varied with the same HD prescription. A key benefit of home HD is the freedom to add sensible flexibility into a dialysis prescription. More of this later.
The best defense against changing circumstances is to learn to:
Recognize your own responses.
Listen to your own rhythms and limits.
Learn how your own body speaks.
Find out your own circulation signals.
Feel your own emotions.
Good, unrushed, repetitive, empathetic, but firm and structured training should equip you to safely and optimally self-dialyse. Only you—no-one else—can know you. In Australia where I am from, this is why we prefer to train you, not a carer. Even the very best carer cannot feel what you feel, cannot read your body signals, cannot “be” you.
When you are new to dialysis, it can be comforting to ask questions in the Facebook group and get answers from other patients like you. But, bear in mind that, while similar, they are not you. So, while others’ experiences can be helpful, they can also be contradictory, or even harmful. They react differently to you, and their circumstances are always different to your own.
Good training will teach you to know yourself, not others. And, learning about yourself takes time, patience, and practice. Once you learn and understand how you respond, your HD practice can be subtly varied in ways that are less possible in centre-based programs.
But never forget: we are all different, no two of us are exactly the same. And, beyond that, no two HD treatments are ever quite the same, either.
2. Where we went wrong
In the early days, as we sought to understand the impact of renal failure on human wellbeing, it was clear that waste buildup or, better, the loss of adequate waste excretion was a key factor. Most of the signs and symptoms of renal failure were thought of as a failure of waste clearance. This was how I was first taught to think of renal failure, or as it was then called “uraemia”—an accumulation of urea in the blood.
It seemed natural to study (and focus on) wastes, or, as they are often called, solutes. So, a failure of waste excretion, wastes (solutes) dominated our early thinking. Many HD professionals still focus mainly on solutes, today. That is not all their fault.
Mid/late 20th century teaching emphasized measurable chemistry: removal of urea, sodium, potassium, bicarbonate, phosphate, calcium, magnesium, albumin, parathyroid hormone (PTH), haemoglobin, urine protein, and a raft of other tests (“labs”). We nephrologists were seduced into thinking that these were what mattered most.
Even the measure that follows the decline of kidney function through the arbitrary stages of chronic kidney disease from CKD1-2 into CKD3 —> CKD4—> CKD5, is a solute: a muscle “waste” called creatinine. Creatinine is now used to calculate a key marker of kidney function, the estimated glomerular filtration rate (eGFR).
Once dialysis begins, we cast creatinine aside in favour of another solute: urea. In the early days of HD, urea was cheap and easy to measure and thought to be a good marker for the dose of HD. While this is clearly not true, urea has somehow managed to stick in the mind of most dialysis professionals. In some countries—like the U.S.—urea has even been given regulatory status as the solute. The “adequacy” of an HD treatment has become enshrined in a complex mathematical equation (called Kt/Vurea) that seeks to assure that enough urea has been removed.
In some jurisdictions – like the UK, Australia and New Zealand – a simpler assessment, the percentage reduction in urea (or PRU) is used, but the PRU, too, is based (1) on a solute, and (2) on a poorly chosen solute (urea).
Solute (urea) removal is used as ‘the yardstick’ for ‘adequate dialysis in both peritoneal dialysis and haemodialysis, though at least in peritoneal dialysis, the clearance of creatinine – a more representative waste than urea – still plays a major monitoring role.
But, solute removal is the easy side of the coin to read.
What really matters
If we had thought about dialysis more carefully at the start, we might have come to different conclusions, and developed a different set of measures.
We might have realized that:
Urea rarely – if ever – kills
Creatinine – a rather gentle toxin – never makes us sick, and does not kill.
Potassium can kill – absolutely – but dialysis patients can tolerate wild shifts in the blood concentration of potassium (a interesting fact in and of itself) and nowadays, even potassium rarely kills.
PTH may do ultimate slow and unseen harm to bone, but takes years to do so – and it rarely kills.
Anaemia makes people feel horrible, and makes things harder for the heart – but of itself, it rarely kills.
While these are clearly over-simplifications, and yes … at least the last two on this list can and do cause long-term damage … they still pale into insignificance against the ‘elephant in the room’.
The ‘elephant in the room’ – the number one killer – is fluid overload … excess blood and tissue fluid volume … and its surrogate clinical measure, the blood pressure.
How fluid is moved from the cells, from between the cells (the interstitium), and from the blood circulation itself, is what really matters as a marker of dialysis morbidity and mortality.
Fluid volume as it reflects …
the total body fluid load
the rate of change of fluid volume between the three main body compartments – the cells, the interstitial fluid and the blood volume
… is the primary determinant of health, or ill-health, in dialysis patients.
Fluid volume – and especially if it rapidly changes during dialysis – is what kills.
Our blind devotion to numbers, our insistence on endless ‘lab’ tests, and our fear-tactic to ‘get the numbers right’ … these are what have allowed us to ‘sell our patients short’!
What has really mattered – all along – has been blood, tissue, and cellular volume. Fluid – either in excess or in deficit – and especially the rate at which dialysis changes its balance across all three main body compartments – is the key and prime factor will determine which dialysis patients will likely live, live well, and live long … and those who likely will not.
Correcting a wrong
Dialysis professionals must say ‘mea culpa’, then re-orient, and re-educate. First with themselves, and then with their patients, they must alter the emphasis.
Dialysis professionals have slaved for decades to ‘get the numbers right’. At the same time, they have puzzled why this approach has made such little difference to patient wellbeing and survival.
It is past time to alter the order, to put solutes second, and talk first and foremost about volume!
When explaining complex physiology, simple analogies can help.
Think of a river system.
The headwaters are in the mountains, far away. The river winds through upland and lowland plains, then past a town half way between the mountains and the sea. After a further distance, it then enters a small lake near the river mouth. Finally, this lake drains directly into the sea.
Suddenly, there is a huge storm in the mountains and on the upland plains. The headwaters and plains flood. Upstream, everything is drenched and sodden, the fields and crops are awash, roads are cut, and people are scrambling to save their belongings. This is where all the water is.
Meanwhile, down by the sea, the sun is shining and the little lake – as always – is nice for boating, and good for fishing. It will take ages for the flood waters to make their way to the lake downstream, and flood the houses on the lake shore.
As the flood moves slowly down the river, the waters will rise at the town then subside again as the flood waters pass. Meanwhile, the lake remains perfect for boating – and the fish are biting.
Someone who lives beside the little lake suggests a solution to the impending flooding of their lakeside houses. If the lake is drained dry by pumping all its’ water into the sea, the lake won’t flood when the floodwaters finally arrive from the mountains and plains far away.
But … this is a false security.
Draining the lake will not ‘draw’ the floodwaters down the river any faster. They will still come, when they come. But, that will take time! Floods do not move very fast.
Meanwhile, draining the little lake will leave all its fish high and dry. The things that depend on a healthy lake will be ruined. Everything will die. And, despite destroying the health of the little lake, the flood will still eventually come.
The lake is small, but the flood is large. Although draining the lake will make little eventual difference to the flooding of the houses on the shore, the ecology of the lake will be damaged beyond repair.
Let us now fit fluid overload and dialysis into that example.
The mountains and the upland plains far away represents the cells where the majority of the fluid in the body collects.
The lowland plains and the town represent the interstitium – the ‘half-way house’ between the cells and the circulation.
The small lake represents our circulation – the blood volume – the smallest fluid volume in the body.
Dialysis is the drain – a drain that can only access the small lake – but no further.
Sucking the circulation dry will have a huge effect on the blood volume (the lake), but will have no significant effect on the fluid in the interstitium (the lowland plains and the town) upstream. And, it will be of no benefit to the cells (the flooded upland plains). The only outcome will be to destroy the lake, and all that depends on it, is nourished by it, or lives within it.
And so it is with dialysis.
If the blood volume is aggressively contracted, all those structures that depend on a well preserved blood volume for their healthy function are put at risk. The heart, the brain, and all the other organs that are sustained by a healthy blood volume will be damaged.
There are two better options:
Reduce the amount of water that makes up the flood! Clearly this can’t be done in the weather analogy … we can’t control the weather … but it can be done in the human body by imposing restrictions on fluid intake … ie: reducing the size of the storm! In practice, this is not simple as it seems, for many find it difficult to reduce their fluid intake enough to prevent at least some degree of flooding.
Slowly remove fluid from the circulation at – or as close as possible to – the same rate as the fluid is arriving from the interstitium (ie: drain water from the lake at the same rate as water arrives from upstream). This will ensure that the circulating blood volume (the lake) will stay stable, but that the excess water load is still ‘managed’ as effectively as possible. Doing this is a slower process, but a far more effective (and safe) one.
Better still, if the flood can be made less severe (ie: fluid intake restriction is applied) … and if the lake downstream is slowly drained at the same rate as the flood slowly arrives from upstream (ie: fluid is removed from the blood volume at the same rate as the interstitium replenishes it) … then major damage – both upstream and downstream – will be minimised.
This is simple fluid mechanics!
Slow, gentle dialysis – dialysis that minimally disturbs the blood volume, but that ultimately removes far more fluid than fast, damaging, self-limiting ‘drying’ ever can – is what I would describe as ‘optimum dialysis’.
Dialysis should be all about ensuring stable fluid mechanics.
Solute removal takes second place. While solute removal matters, it matters less. And … modern dialysis equipment copes quite easily with the clearance of most (though not all) solutes.
Either we have forgotten this, or, perhaps we never properly understood it in the first place.
Finally, how does all this apply to Home Haemodialysis
A home dialysis patient is (or very much should be) the master of his/her own dialysis settings.
A well trained home patient can (and should) be able to ‘read the tea leaves’ of their own physiology and make adjustments in treatment duration and frequency to offset any alteration in circumstance.
More fluid to remove? … ANSWER = dialyse longer, and/or pop in an extra treatment if or where needed.
Match the rate of fluid removal (the draining of the lake to the sea) to the influx of tissue fluid as tissue fluid is moved across all three compartments (the flood as it moves downstream) to ensure the circulation (the lake) remains ideally filled, even as fluid is being removed? … ANSWER = match dialysis duration to the rate of fluid removal to ensure fluid removal remains (preferrably) less than 6 ml/kg of body weight/hour of dialysis … though the lower the rate, the better.
Some (but not all) patients will sustain a residual urine output and, where this is so, the ultra-filtration rate can be kept at (or towards) zero. If fluid doesn’t need to be removed, then the UF rate can be set to ‘iso-volaemic’ (or fluid-neutral) dialysis.
In centre-based pateints, the concept of ultrafiltration ‘profiling’ where the ultrafiltration rate maybe varied during dialysis – greater at the start, lower towards the end – is a current hot topic. But, this is neither necessary nor sensible in home dialysis patients where the far simpler levers of variable duration and frequency are the stand-out best options.
Duration or frequency … frequency or duration?
The safest, most amenable, and most important variables in haemodialysis are dialysis duration and treatment frequency. Duration and frequency govern all else. While I do not intend to debate in this 101 which is the more important, it is suffice to say that both have their distinct benefits and advantages. Skimping on time and frequency will fool no-one but yourself.
Home haemodialysis patients possess the training, the ability, the where-with-all, and the right to do optimal dialysis like no other patients can. Duration and frequency – and ideally both – are the twin keys to a successful and fulfilling life with dialysis.
The role of the dialysis professional should be to make safe, well-taught, and flexible home care attainable for as many patients as possible.
Having patients understand the principles behind dialytic management is a major step towards that goal. I hope this 101 will help that effort.