Dialysis Modalities

Once the kidney fails, there are four options.  None of these options are a cure but a form of treatment. The four types of treatment will be discussed below. Kidney transplant, peritoneal dialysis (PD), hemodialysis (HD), and palliative care.

Kidney Transplant

Surgery that involves transplanting one healthy kidney from a living donor or a deceased donor.  Transplant is not a cure for kidney failure but another form of treatment.  As a candidate for kidney transplant a rigorous pre-transplant evaluation is done by a transplant center to determine your candidacy. There are three different ways to receive a kidney transplant 1. Living donor from family/friend/stranger; 2. Donor exchange program; 3. Deceased donor (free kidney).  To receive a kidney from a deceased donor, wait time depends on the state.  In California, the wait time for a deceased donor is approximately 5-7 years.  Talk to your transplant center to have a better understanding of the wait time.  The advantages of having a kidney transplant are no longer having to do dialysis, normal diet without out having to take phosphorus binders with each meal, regularly feeling normal/increased energy, most important a better quality of life. After having a kidney transplant, anti-rejection medications will be required for the life of the transplanted kidney to prevent the body from attacking the organ causing rejection.

Peritoneal Dialysis (PD)

 This is a type of dialysis which the patient’s peritoneum is used as the dialysis membrane.  The peritoneum is an anatomical structure which covers the abdominal organs.  This natural organ filters the toxins and excretes waste from the body.  The peritoneum has two layers which together forms a “pocket” called peritoneal cavity. Fluid is instilled into the peritoneal cavity using   peritoneal catheter (Peritoneal catheter is implanted by the surgeon into the abdominal wall.).  The dialysis fluid is instilled into the cavity by either gravity (CAPD) or a machine called cycler (CCPD).  The fluid is left in for several hours, during that time, waste materials and excess fluids pass through the membrane and are then drained from the cavity via the peritoneal catheter.  No needles are involved for this type of dialysis.  It is done primarily during the night when you are sleeping.  Once medical advantage is that is preserves your veins and arteries for future use.  Patient of this type of modality have better blood chemistries, flexible schedules, independence, and above all are able to travel to anywhere in the world.  It is also the self-esteem due to empowerment of the patient.  More liberal diet compared to other methods, better “feel-good feelings” compared to hemodialysis and research has shown that patient of this modality has better transplant outcome compared to hemodialysis.  The downside of this modality is that it requires home supplies and storage space, risk for infection, and requires dialyzing daily.

Hemodialysis

 Is a medical treatment in which an artificial filter outside the body is used to clean the blood.  An access is needed to remove blood from the body to the machine which is attached to an artificial filter.  Two needles are need for hemodialysis. One is to remove the blood through the access to the machine for filtering.  Another needle is needed to return the filter blood back to the body.  The blood is pumped passed a semipermeable artificial dialysis membrane called a dialyzer.  Poisons and toxins removed through this method are diffused into a liquid called dialysate.  The dialysate are then discarded along with the toxin; the purified blood is then return to the body.  Because the patient’s blood is outside the body, for this process, the dialysis machine has a warmer to keep the blood at body temperature.  Once the blood is outside the body in the tubing system, there is a tendency to form clots which can be fatal.  A blood thinner called heparin is given to prevent the clotting in the plastic tubing.  Hemodialysis can be done in three ways:

1. In-Center hemodialysis
2. Home hemodialysis
3. Nocturnal dialysis

In-center hemodialysis is usually done at a dialysis facility usually three to four times per week.  These sessions last three to four hours and are done during the day.  Nurses and technicians are involved in setting up and operating the dialysis machine.  The main advantage of in-center hemodialysis are patients are able to meet nurses three times per week and emergency are address immediately, social support from in-center, and patients are not directly involved in their care.  The disadvantage of in-center hemodialysis are the treatment schedules are strict, lack of independence,  are at high risk for nosocomial infection due to exposures to other patients, difficult traveling.  Overall, hemodialysis as a modality has several disadvantages.

Nocturnal hemodialysis is done at night in-center, sessions usually last six to eight hours during the night.  Nurses and technicians operate the dialysis machine.  The advantages and disadvantages for this modality are the same as in-center.

Home hemodialysis is done about five to six times per week.  Sessions are 2.5-3hrs during the day; a partner is required for this modality.  The partner could be a spouse, a family member, a caregiver, or a paid hemodialysis technicians or a nurse.  Training usually takes about one month for this method.  The advantages of home hemodialysis are being include independence and convenience of dialyzing at home..  It has a relatively flexible schedule compared to in-center hemodialysis.  Traveling is relatively possible compared to in-center hemodialysis.  The disadvantages for this modality are: treatments are done during the day, frequent needle sticks, and the need for having a partner.

The main disadvantage for hemodialysis is a permanent access such as a fistula or graft is required.  There are greater risk for clots and infections.  It can also cause steal syndrome.  The fistula can decrease the amount of blood flow to the hand, making it painful, cold, and pale.  It is called steal syndrome because the fistula steals blood from the distal part of the hand.  Doctor’s refer to this as ischemia.  Fistula and grafts remains permanent in the body and are difficult to remove.  Frequent clotting can lead to exhaustion of vascular access for future use.

The term used in the dialysis world to describe the various available treatment options is “modality”...but—especially in dialysis—“modality” is an increasingly dirty word. Not dirty as in smutty, but dirty as in confused, confusing, and unclear.

So, what does modality really mean in dialysis 2017? Vanishingly less, I fear, as the margins between options—and within options—become increasingly blurred.

Once upon a time, the term “treatment modality” described one of four relatively clear and well-demarcated choices:

• Peritoneal Dialysis (PD)
• Haemodialysis (HD)
• Transplantation (Tx)
• Conservative Care (CC)

But, then it started to get complicated. Indeed, by 2007, I felt it had become so complicated that I asked Mark Macgregor (UK) and Chris Blagg (USA) to co-author a paper(1) that focused on the developing difficulties (back then) with the burgeoning terminology of dialysis. Little did we know then that it would get worse, and not better, in the decade that followed! Here are just some of the changes since 2007...

First, Peritoneal Dialysis (PD)

I am purposefully glossing over the very early days when PD was done as an inpatient in hospital (commonly 3 days a week by intermittent “stick” catheter insertion) and was called intermittent PD (IPD). Though, it is important to acknowledge that early time of IPD if we are to understand why the term “continuous” was later introduced… The first broadly available PD “modality” was truly continuous, as it spanned a 24/7 delivery cycle. Continuous PD became possible through the technique advances made Popovich and Moncrief, and became known as continuous ambulatory peritoneal dialysis (CAPD).

CAPD ruled the peritoneal firmament for 10-15 years while (in particular) the Baxter conglomerate worked out how to automate the process. In that period, PD was relatively easy: four (or occasionally five) bags a day, using manual exchanges, and delivered almost exclusively by a surgically inserted straight Tenckhoff catheter (TC). Then stuff began to change. Automation slowly arrived, and improved. Odd octopus and gantry-style machines evolved to deliver PD fluid. Different versions of the abdominal TC emerged, some spiral-shaped, some with disc separators, the Toronto Western catheter…all attempting to improve on Henry Tenckhoffs’ original design. Catheters that exited through the skin above the sternum appeared. Soon, automation brought the option of a night-time-only version to PD.

Suddenly, PD split into two primary options: manual 24/7 CAPD, and an overnight 10-12/24 automated PD (APD) choice. But then, sometimes overnight-only APD proved to be not quite enough, so, the option of a single manual exchange during the day in addition to overnight APD seemed to suit some patients better. An array of fluid options emerged. TCs began to be implanted at the bedside, or in radiology, and not the operating theatre. PD was moving, changing, morphing into a smorgasbord of micro-choice.

Now, while PD is still PD, the wide array of differing options can create problems for studies, or for patient educators, when trying to compare one “modality” with another or to assist patients in choosing what might suit their needs best. Is APD really the same as CAPD? Is APD with Physioneal® and/or Icodextrin® the same as CAPD with Dianeal®?

• Well, yes, they are, at least in principle. They all use the peritoneal cavity.
• But, no, they aren’t, as the chosen option(s) may significantly impact efficacy, and alter the complication and infection rates.

In my view, APD is a different beast than CAPD…and it is sufficiently different to be (at the least) a different sub-modality. Studies should evaluate it in its own right vs CAPD, rather than lumping both together in both studies and registries. Too often, “PD” is referenced as an undifferentiated, amorphous modality when, in truth, the nuances matter.

Next, Haemodialysis (HD): a Proper Minefield

First, there is facility-based 3x week HD. Easy, right? No, wrong! Three times weekly HD delivered at a facility is not a uniform modality: it varies, jurisdiction-to-jurisdiction, country-by-country, around the world. US-style in-facility HD (= 3 x 3.0-3.5 hour) is not the same as Japanese or ANZ-style in-facility HD (= 3 x 4.5-5.0 hour). Note that this supposedly “one” modality actually tries to equate 9-11.5 hours HD/week with 13.5-15 hours HD/week …as if they are the same.

Are they comparable? Probably not, especially when it comes to the incomparable UFR commonly required by each. Yet, they are all-too-often compared and contrasted as if they are the same. They both likely do cut the mustard for a minimum Kt/V urea, though the US model more likely just gets there, while the Japanese/ANZ model more likely well exceeds. But they are chalk and cheese when it comes to comparable (or rather incomparable) rates of volume removal; a distinction that likely matters enormously when it comes to cardiovascular outcomes. Yet, both are often compared as if they are the same. After all, they are both facility-based, and that is often what seems to be taken to matter—and not the quality of the treatment provided.

Home HD is even more complex. While short daily HD (SDHD) can, of course, be offered in-facility—incidentally, a factor that complicates the interpretation of global in-facility dialysis data—it is a common option used (especially in the US) for the delivery of home HD via the NxStage System One. But, while SDHD (at home) is clearly different to long nightly HD (at home), both are often conflated as “home HD.” But, what do each of these really mean?

• SDHD can be short-short (5-6/week x 2-2.5 hours/treatment) or mid-short (5-6/week x 3-ish hours/treatment), yet both are called SDHD. This is despite the math that tells me that that one is as few as 10 hours/week (5 x 2) while the other offers as much as 18 hours/week (6 x 3) of membrane contact time (MCT) each week. One is nearly double the MCT of the other, yet both are often confused under the single banner of SDHD. Are they the same? I don’t think so.
• Meanwhile, nocturnal HD can be clinic-delivered, or delivered at home. If clinic-sited, it is never more than 3 x week. From my reading of US practices, it is offered in variants from 3 x 5-6 (15-18 hours/week) to 3 x 8 (24 hours/week), a likely highly significant difference in MCT. Yet even more importantly, the greatest threat—the “Killer gap” first emphasized by Kjellstrand—remains. (NB: clinic NHD is not an offered option for nocturnal HD in ANZ.)

How can these “modalities” be compared to the Canadian or ANZ 6 x 8 hours/week models of nocturnal home HD? The latter models deliver up to 48 hours of MCT/week with no extended inter-dialytic break. These regimens, often referred to as extended hour and frequency, or “intensive” nocturnal home dialysis cannot fairly or truly be compared with an NHD model (facility-based) that offers less than half the number of hours/week and with a long break as well! Although all are commonly conflated as one overarching therapy (or modality)...NHD…indeed, they are far from the same.

The most common NHD variant in ANZ is the alternate night model (3.5 x 8 hours/week) that offers 28 hours/week without a long break. This is an option that just might be the best compromise of all, though I still struggle (just a little) to put that in writing! But, again, the alternate night home NHD option, along with 3 x week in-facility NHD, and the Pierratos intensive home NHD modality, are all called NHD, and are too often compared, often quite undifferentiated, as if they were like options, or one modality.

Then, if incremental dialysis starts were to catch on, or if haemodiafiltration (HDF) should take root in the US (see this post as well), the modality mayhem would increase even further.

But…There is More

None of this scratches the surface of the smorgasbord of differences in blood flow rates, the vexed issue of blood to dialysate flow ratios, the differing dialysate flow rates in differing HD systems, the variations in dialyser surface area and/or membrane type, the dialysate temperature as a key factor in less symptomatic dialysis, the differences in access and access capacity, and all-important variables like ultrafiltration volume and its relevance to sessional duration through its key intercept: ultrafiltration rate.

All of these matter. All change the dynamics of HD significantly. Yet, rarely are they well delineated or standardised in studies that blithely compare modality “x” with modality “y.” As no two runs are the same, as no two sets of settings are the same, and as no two patients are the same, studies that compare modality “x” with modality “y” will ever remain confounded from the start.

So, yes, it is getting messy—very messy indeed. Well-intentioned literature comparisons all-too-often use labels like facility-based, in-centre, PD, SDHD, or NHD, indeed, sometimes just “home dialysis” without even attempting to make a distinction between home PD (CAPD or APD) or home HD (in its many forms and options). Even where the distinctions are made, few attempt to segregate regimens by MCT, flow rates, and/or a likely estimate of the exchangeable volume-past-the-post.

How, then, can our patients negotiate this tangled web to wisely choose their optimum modality when the most important variable of all—lifestyle—enters the fray?

Importantly, too, I have read many patient-to-patient comments and seen much heart-felt advice at social media sites, made without doubt in all good faith and with the best intent, that extoll the virtues and traps in option choice and describe the personal outcomes ascribed to modality “x” or modality “y”, all shared with great conviction—when it seems clear that the options being debated are quite different. Sadly, though, it often seems that these differences go unrecognised. This often adds to, rather than lessens, the confusion as, in response to a plea for help from a new-to-dialysis questioner, long multi-commented “advice” rollicks back and forth…some commenting PD, others describing variants of HD…to the complete confusion of the original question and questioner.

In my view, only four things end up counting:

1. The lifestyle aspirations of the patient (PD or HD).
2. The weekly membrane contact time (HD): the time allowable for solute and volume removal, and the shorter the total, the worse. 
3. The inter-dialytic interval (HD): where the key comparator cut-off ought be the inter-dialytic gap … one that never exceeds 43 hours (based on a 5 hour Rx) vs. any option with an interval that does. 

The site of delivery: whether facility (HD) or home (PD or HD).