Chronic maintenance hemodialysis: Making sense of the terminology

Chronic maintenance hemodialysis: Makingsense of the terminology

John W. M. AGAR,1 Mark S. MACGREGOR,2 Christopher R. BLAGG3

1Renal Unit, Geelong Hospital, Geelong, Victoria, Australia; 2The John Stevenson Lynch Renal Unit,Crosshouse Hospital, Kilmarnock, U.K.; 3Northwest Kidney Centers, Seattle, Washington, U.S.A.

AbstractDuring the early decades, the hemodialysis (HD) terminology for modality, technique and function

altered little as the widely accepted regime of thrice-weekly, 4-hourly dialysis varied little. In the last

decade, however, a wide range of new options have emerged in all facets of HD therapy. This has led

to a sudden expansion in terminology, some duplicating, some contradictory, some superfluous. The

definitions used in 1 geographical region may mean something entirely different elsewhere, in-

creasing cross-continental misunderstanding and misinterpretation and raising the often-asked

question: ‘‘What exactly did the authors mean by that?’’ Although clearly the definitions used in this

paper are also only the authors’ opinion, we have sought to explore the use and sometimes con-

fusing application of many commonly used terms, and we propose a number of possible deletions.

Finally, we offer a descriptive data set that we believe should be used for all HD-related papers. Our

conclusions will not always be welcomed—particularly by those who use terms we have rejected.

Despite this, we believe it pertinent to fully review the dialysis terminology we use. Primarily, we

hope to stimulate debate about which terms should be globally adopted and what those terms

should mean when used. Although not all will agree with our conclusions, we hope this paper may

provide a framework for a more streamlined, efficient, and globally acceptable nomenclature.

Key words: Review, hemodialysis, terminology, definitions, nomenclature, international

INTRODUCTION

The terminology used to describe chronic maintenance he-

modialysis (HD) used to be simple, constrained as it was by

a universal regimen of 3 HD sessions per week, each of 3-

to 5-hr duration, based on the early experience in Seattle.1

However, the recent explosion in maintenance HD options

has generated a rapid growth in terminology as authors

seek to describe a range of new and emerging variants.The growth of options for location of dialysis such as

in-center, center, outpatient, facility, hospital, satellite,

and home and for dialysis modality such as HD, hemodia-

filtration (HDF), slow, low-efficiency daily dialysis

(SLEDD), continuous veno-venous high-flux HDF, con-

tinuous ambulatory peritoneal dialysis (CAPD), continu-

ous cycling peritoneal dialysis (CCPD), automated

peritoneal dialysis (APD), and tidal CAPD, CCPD, or

APD have bred a host of new descriptive terms. Conven-

tional, 3 times weekly, more frequent, quotidian, daily,

nightly, alternate daily, alternate nightly, second daily—all

have been variously introduced to describe new choicesin dialysis frequency while treatment timing and duration

have spawned terms like nocturnal, overnight, hemeral,

and daytime and options like continuous, intermittent,

long, short, and extended-hour therapy. Operational de-

scriptions include slow, fast, high flux, low flux, dialyzer

reuse, or nonreuse, while terms such as regular, mainte-

nance, periodic, and recurrent have also been applied to

renal replacement therapies.The increasingly popular term chronic kidney disease-

stage 5 (CKD5) was once better known as end-stage renal

Correspondence to: J. W. M. Agar, Renal Unit, GeelongHospital, Barwon Health, Geelong, Vic. 3220, Australia.E-mail: [email protected], [email protected]

Hemodialysis International 2007; 11:252–262

r 2007 The Authors. Journal compilation r 2007 International Society for Hemodialysis252

disease (ESRD or ESKD) following the establishment ofthe U.S. Medicare End-Stage Renal Disease Program in

1973,2 although kidney diseases outcomes quality initi-

atives (KDOQI) still uses both terms, CKD5 and ESRD, as

synonyms. Before 1973, the terms chronic renal failure

(CRF), renal dialysis, and chronic maintenance dialysis

were more commonly used. Although language changes

along with practice and preference, old terms can die

hard, while adding the new without replacing of the oldserves only to clutter and complicate.

In addition, each author and geographical region has

invariably added either personal or regional language

‘‘flavors’’ to the increasingly confusing mix, often com-

bining several terms together while attempting to describe

a particular variant. The same term may have different

implications, depending on the target audience or region-

al group. This inevitably increases the difficulty of achiev-ing any reliable international understanding.

Dialysis terminology has become sufficiently confused

and confusing that we felt that an attempt to define both

the meaning and pairing of the descriptive terms used in

HD was overdue. This paper, although clearly the au-

thors’ opinion, seeks to rationalize the newer HD nomen-

clature. At the end, it synthesizes a suggested, simplified,

and streamlined dialysis terminology. Although this maydisappoint, we have focused on chronic maintenance HD

alone; peritoneal dialysis and modalities specific to the

treatment of acute renal failure are not covered.

Literature references to the origins of HD terminology

have been intentionally avoided. It is rarely possible to

pinpoint the first literature use of any one specific term:

attempting to do so only invites an avalanche of protest

and dispute. The terms we have attempted to define,however, have all been variously used in the dialysis

literature.

DEFINITIONS

Chronic kidney disease-stage 5

Chronic kidney disease-stage 5 was, until recently, better

known as end-stage renal/kidney disease/failure (ESRD,

ESKD, ESRF, and ESKF). Even CKD5 is not universallyembraced as, in the United Kingdom, there is a prefer-

ence for the term established renal failure (ERF).3 Al-

though CKD5, defined as a glomerular filtration rate

(GFR) o15 mL/min/1.73 m2, has been proposed to in-

corporate all these terms, ESRD remains an administrative

term in the United States based on the conditions for

payment for health care by the Medicare ESRD Pro-

gram—a use unlikely to alter soon. In addition, ESRD

includes patients treated by dialysis or transplantation,irrespective of GFR and is a term mandated by govern-

ment, regardless of other terms we may choose to use.

Despite this, CKD was introduced in part because the

word failure was perceived to imply connotations of guilt

or inadequacy—either in medical treatment or patient

response—while some believed end-stage to be an ‘‘in-

sensitive’’ term to use with patients.

Even CKD5 is ‘‘imperfect’’ as it is not necessarily syn-onymous with maintenance dialysis.4 Although the ma-

jority of patients with CKD5 will have a GFR significantly

o15 mL/min/1.73 m2, many will not yet have com-

menced maintenance dialysis while a handful of CKD4

patients with a GFR � 15 mL/min/1.73 m2 may yet start

dialysis. Some have suggested that the suffix ‘‘D’’ be added

to CKD5 to denote patients receiving dialysis5—an ap-

proach also proposed more widely by the internationalrenal community.6 Although clinical consensus is favor-

ing the CKD (1–5) classification, these issues remain

thorns in the side of a watertight nomenclature.

Maintenance dialysis

Originating in the 1960s to describe clinical HD, it is now

less commonly associated with clinical programs but stillfrequently used, at least in Australia and New Zealand, by

administrative/funding bodies to differentiate the recur-

rent HD of CKD5 from shorter-term HD variants used in

acute renal failure.7

Center, in-center, satellite, andfacility-based dialysis8

In Australia and New Zealand, the terms center or in-cen-ter commonly refer to inpatients or outpatients who are

medically unstable or precarious and who are thus re-

ceiving maintenance HD where on-site nephrology care is

available. In the United States, center dialysis can refer to

dialysis delivered either in a hospital-based outpatient

dialysis unit or, more commonly, in a freestanding dialysis

unit that is usually, but not always, a for-profit unit.

United States dialysis inpatients are rarely dialyzed in ahospital outpatient dialysis unit but are more likely treat-

ed either in a hospital room or an intensive care unit. In

the United Kingdom, the terms center or in-center are

rarely used, ‘‘hospital’’ dialysis covering main unit and

satellites being the more common term. This is perhaps

because, unlike in Australia and New Zealand, most

satellites are hospital-based and freestanding dialysis

facilities are rare.

Hemodialysis: Reviewing the terminology

Hemodialysis International 2007; 11:252–262 253

The term satellite also has regional meanings. For ex-ample in the United Kingdom, although satellites are

commonly hospital-based, they are primarily situated in

hospitals without a formal renal unit, although an arrest

team, ICU, and/or a general medical team may be avail-

able. On the other hand, in Australia and New Zealand,

satellite dialysis initially referred to low-acuity, self-care,

community-based dialysis where cost efficiencies accrued

from machine sharing and staff minimization.Facility-based dialysis is a useful term used primarily to

differentiate home care from any other dialysis location.

The definition of a facility is, however, wide and may

range from low to high-acuity care locations. These may

include such sites as: nursing homes, general practitioner

practices (United Kingdom), stand-alone, not-for-profit

or for-profit ‘‘satellite’’ centers, ‘‘bush nursing centers’’

(Australasia), community health centers, or hospitals.Hospital facilities may range from general hospitals

through to tertiary referral centers and quaternary uni-

versity teaching hospitals. Although the use of all of these

sites (and others) has been reported and depends upon

regional practices and logistical considerations, the key

qualification is the level of support services that the

chosen or available facility provides. Facility may desig-

nate any inpatient or outpatient care locality wheretrained health professional care—although not necessari-

ly medical care—is available.

Home

This term clearly indicates dialysis performed in the pa-

tient’s own home without medical supervision. Although

the importance of self-care is central, a trained helper is

usually regarded as essential—commonly a spouse or

family member. With modern equipment and newer regi-mens, lone or unaccompanied dialysis has become an

option in some regions, with or without modem or In-

ternet real-time monitoring systems.

Although the definition of home seems self-evident, it

does not fully encompass patients who undertake un-

supervised HD in a GP office or in a nursing home en-

vironment, as sometimes encountered in the United

Kingdom. In the United States, classified home HD canbe performed in nursing homes. New Zealand permits a

locally successful model where several patients share the

facilities of an unsupervised community dialysis house.

The United Kingdom uses the term community HD to

distinguish these HD variants from home and facility-

based care. In some regions, for example Seattle, paid lay-

helper schemes cover nonhome, nonfacility-based care.

Helpers are trained where a spouse or family member is

lacking—although some helpers may already be dialysis-trained technicians.

Hemodialysis vs. HDF

Hemodialysis may be ‘‘pure’’ (a process of unequal diffu-

sion) or may be ‘‘augmented’’ (by the addition of convec-

tive force—HDF). Although HD techniques for managing

CKD5 are fully accepted and require no additional quali-

fication, the use of hemofiltration (HF) and HDF tech-niques for CKD5 is increasing—particularly in Europe

and especially in Italy—while hemadsorption (HA) tech-

nology is also expanding. The increasing popularity of

HF—and of HDF in particular—clearly introduces a

major definitional question: should HD remain the dom-

inant term or is it time and pertinent to introduce a new,

overarching term—hemopurification—to incorporate all

the combinations of extracorporeal blood purificationused in the management of CKD5? We believe that this

term may better serve holistic dialysis terminology as we

move forward into the 21st century, its major subsets

being currently HD, HF, HDF, and potentially, HA.

Conventional (or standard) dialysis

In most services, dialysis is a near variant of a standard,conventional regime of 3 sessions/week ranging from 3 to

5 hr/session. Although dialysis hours shortened in the

United States to as little as 90 min/session during the

1980s, more recently, sessional time has lengthened again

to between 3.5 and 3.75 hr, while in Europe, Australia

and New Zealand, and Japan, 5-hr sessions are common

and 4.5-hr sessions are the mean. Thus, conventional or

standard implies different regimes to different regionalgroups. Their use should, thus, be discouraged. It is pref-

erable to describe the actual dialysis duration and/or

frequency.

Daily, nightly, nocturnal, quotidian,hemeral, alternate

All have been applied in often confusing ways to describe

both dialysis frequency and timing—both within the con-

fines of a weekly schedule and a 24-hr clock. Most havebeen applied unsatisfactorily. The difficulty has been with

the description, in simple, acceptable, one-syllable words,

of frequency, duration, and day/night timing for multiple

scheduling options within a calendar week.

Daily dialysis implies treatment that occurs within a

24-hr period. Although it is commonly interpreted as

‘‘every day,’’ services promoting a daily program—for ex-

ample short daily HD (SDHD)—commonly permit 1 or 2

Agar et al.


days ‘‘off’’ each week, thus implying at least 1 ‘‘long break’’in each weekly cycle. Daily dialysis as currently used in-

dicates dialysis at least 5 or more days/week, not 7 days/

week as might be expected. Thus, daily as presently used

does not imply a specific time of day.

Nightly has implications of frequency and time of day. It

has commonly been used when dialysis takes place at

least 5 or more nights/week—and, clearly, at night-time.

Most schedules designated nightly permit 1 or 2 nightsoff each week—thus are not truly dialysis every night.

Nightly dialysis may also imply duration—in particular,

long-hour, overnight dialysis (note that shift workers

might possibly dialyze at night but may use a short-hour

regimen). However, although nightly is strictly a subset of

daily, the potential resultant combination daily nightly is

clearly utterly confusing.

Nocturnal refers to dialysis while asleep. Whether thepatient is awake or asleep during dialysis is a key issue

and cuts to the core of whether the patient can be re-

garded as ‘‘in control of’’ the machine. Although it is well

known that many day patients doze during treatment,

these patients are correctly regarded as undergoing day-

time dialysis. Daytime, ‘‘waking-hour,’’ or ‘‘aware’’ dialysis

is clearly—by intent—dialysis performed while awake.

Conversely, nocturnal or ‘‘overnight’’ dialysis is clearly—by intent—dialysis performed while asleep. By implica-

tion, this is also while recumbent. The term nocturnal has

come to imply ‘‘long-hour’’ or ‘‘extended hour’’ dialysis

while daytime dialysis carries no implications of duration.

Daytime dialysis may be of either short or long duration

although, in practice, it rarely exceeds a 6-hr span due to

lifestyle limitations. Although the term nocturnal dialysis

has been interchangeable with nightly dialysis, arguablythis is unhelpful. Nocturnal should not imply fre-

quency—simply ‘‘sleep-time’’ dialysis. It may be 3 nights

weekly, as practiced early by Shaldon9 and later by Char-

ra10 or to 6 nights weekly as advocated by Pierratos11 and

Agar.12 The use of nocturnal is fine, provided it is linked

with an expression denoting frequency: daily nocturnal

for � 5 nights/week: alternate nocturnal for alternate

night treatment: thrice-weekly nocturnal for 3 nights/week.

Quotidian (from the Latin quotidianus: for ‘‘daily’’), al-

though somewhat pretentious, has recently been applied

to dialysis ‘‘within any 24 hr period,’’ although one Inter-

net source defines quotidian as ‘‘everyday.’’13 In dialysis

usage, like daily, quotidian can refer to either a daytime or

night-time dialysis schedule—provided it is within any

given 24-hr cycle. The literature describes both quotidianshort daily and quotidian nocturnal. However, as with

daily and nightly, quotidian (everyday) is rarely every day:

quotidian schedules are for 5 or more days but not 7 daysin any given week.

Hemeral (from the Greek hemera: for ‘‘daytime’’) is also

a pretentious term not found in most dictionaries and,

although intended to define a daytime schedule, is iden-

tical in its dialysis application to ‘‘daytime’’ and is in less

common usage.

Alternate is commonly used to indicate a regime that

omits the ‘‘long-break’’—1 day on, 1 day off, ongoing, andrecurring. Some European regions still use the term Lecce

dialysis14 for this variant, named for an Italian unit where

it has been practiced. Lecce as a synonym for alternate is,

however, imprecise as some of the bigger patients at Lecce

underwent 4 treatments per week, not the ‘‘rolling 3.5

session per week’’ schedule of true one-on, one-off alter-

nating dialysis. Alternate night nocturnal dialysis with

long-hour overnight treatment is being used increasinglyin North America and Australasia, usually at home al-

though occasionally in-center. By definition, alternate

schedules offer 7 treatments per 2 weeks—sometimes

described as 3.5 treatments a week—to differentiate it

from conventional thrice-weekly regimens.

How can these terms be resolved into an acceptable

global nomenclature? First, there should be terminology

describing frequency (day/night timing not implied): besthere are daily (� 5 treatments/week), alternate (every

other day), and thrice (or 3 times) weekly. Second, there

must be terminology describing timing—especially the

key issue of whether the patient is awake or asleep: here

may best be aware or nocturnal. Finally, there should be a

bland statement of the mean hours/session.

It may be wisest to avoid the term nightly as it serves

more to confuse than solve. Quotidian, too, although acurrently used generic term for increased frequency (� 5

days/week) regardless of sessional duration, is difficult to

support even though the International Quotidian Dialysis

Registry15 may at first resist a change to its name. Com-

mon sense, however, dictates that these terms should go.

Hemeral, too, is little used and is best avoided.

Hybrid dialysis

Although uncommon, there have been occasions where

patients have undertaken unusual combinations of either

schedule or modality. For example, several reports in the

1970s to 1980s described mixed HD and peritoneal dia-

lysis regimens.16,17 Further, mixed day and night sched-

ules or mixed short and long daytime schedules have

occasionally been used by patients—particularly those

trained for home—to accommodate shift work and other



lifestyle commitments. Such regimes have been describedas hybrid.

Short-hour, short daily, and long-hour(extended-hour) dialysis

Short-hour (so-called, high-efficiency dialysis) was popu-

larized in the late 1970s and the 1980s, particularly in the

United States, when a Kt/V of 1.0 was thought to repre-

sent ‘‘adequate’’ dialysis. As larger surface area dialyzers

were developed, dialysis session duration for convention-al thrice-weekly dialysis trended sharply downward to

shorter-hour treatment durations as the same effective

Kt/V could be attained by combining more efficient mem-

brane technology with higher dialysate and blood flow

rates. This occurred at the expense of dialysis duration—a

trend initially welcomed by both patients and dialysis

services. Ninety-minute dialysis treatments became com-

monplace. However, as data linking short-hour conven-tional dialysis to higher patient morbidity and mortality

emerged,18 this trend has reversed. Conventional dialysis

sessions, especially in Europe, Japan, and Australasia,

have lengthened as the importance of dialysis time has

been fully appreciated. Importantly though, short-hour

dialysis should not be confused with short daily dialysis.

The 2 are very different.

As short-hour, conventional, thrice-weekly dialysis haswaned, the word short has been linked to an emergent

modality, SDHD. Here, although the dialysis duration is

short, the treatment frequency is commonly doubled. In

the United States, SDHD is most frequently encouraged at

home although it may also be supported in a facility-

based setting.19 By definition, it is ‘‘aware’’ dialysis, each

session lasting 90 to 180 min and given 5, 6, or occa-

sionally, 7 days each week. Short daily dialysis is, how-ever, a problematic term. It combines elements of time

and frequency. Note that regional interpretations of the

word short are of enormous importance. What some may

regard as ‘‘normal hour’’ dialysis would clearly be far too

‘‘short’’ for others. A 3-hr treatment in the United King-

dom, Europe, Australasia, or Japan would be regarded as

remarkably ‘‘short’’ while, for many centers in the United

States, a 3-hr dialysis would still be considered a normaltreatment duration.

The terms long-hour or extended-hour dialysis have

been primarily associated with nocturnal dialysis. The

standout program practicing extended-hour dialysis has

been that of Charra et al. in Tassin.11,20 Continuing to

practice the long, slow extended-hour treatments estab-

lished through the early years of the 1960s and 1970s

by Shaldon and Scribner, Charra has regularly reported

patient outcomes far beyond the reach of most otherprograms. Unfortunately, neither long-hour nor extend-

ed-hour truly satisfies as neither nominates treatment

duration.

Continuous and intermittent dialysis

The term continuous is commonly applied to renal re-

placement regimes for acute renal failure in intensive care

and not to chronic maintenance dialysis programs—al-

though this may change with the eventual development of

wearable artificial kidneys. Renal replacement therapies

in acute renal failure are most commonly continuous

24-hr variants of HDF although even then, continuous

therapy is rarely that—often being interrupted at leastonce a day.

While intermittent dialysis has been occasionally used

to describe chronic maintenance HD, more recently, it has

been applied to acute renal replacement schedules if dia-

lysis is for � 12 hr daily or alternate daily.

Long break

Few dialysis services run truly ‘‘rhythmic’’ dialysis sched-

ules, most arbitrarily avoiding dialysis on Sundays and

thereby enforcing an interdialytic ‘‘long break’’ at week-

ends. Although unphysiologic and unsupportable from

cardiovascular and volume perspectives, the long break is

(sadly) enshrined in dialysis lore and rolling alternate-day

schedules remain rare, other than in the home setting.Even the term long break is open to interpretation.

In conventional thrice-weekly programs, it references

the B68 hr hiatus at weekends but in 6-day/week mod-

els, the ‘‘long break’’ is shortened to the gap spanning the

single nondialysis day. Even the duration of this can vary,

depending on sessional hours. The term long break sim-

ply signifies the longest dialysis-free sequence in any roll-

ing schedule but, as its potential cardiovascular impact ismajor, it requires a clear statement of its duration.

Fast and slow dialysis

The term fast dialysis been used to indicate the up-regu-

lation of the blood and/or dialysate flow (‘‘pump speeds’’)and has been occasionally applied to either standard or

SDHD regimes to convey increased efficiency through

flow-mediated augmentation of Kt/V and/or other meas-

ures of dialysis ‘‘adequacy.’’ However, higher flows do not

extensively increase middle molecular clearances—only

duration allows this.

Slow, low-flow dialysis has been the province of noc-

turnal regimens where the increase in dialysis duration so

Agar et al.


increases Kt/V efficiency that blood and dialysate flow andultra-filtration rates can all be correspondingly reduced.

This, it has been argued, provides a gentler, more sub-

liminal, background dialysis framework. The term slow

has also been applied to an emergent treatment in acute

renal failure—SLEDD.

Membrane flux

This refers to the permeability (or ultra-filtration capacity)

of a dialysis membrane. Higher flux membranes permitthe increased clearance of ‘‘middle molecular weight’’

substances like b2 microglobulin and diminish the effects

of their long-term accumulation. Increasing flux also en-

hances membrane permeability to water. This, in turn,

increases the convective transport of small solutes like

urea. Although lower flux membranes are cheaper and

less prone to the back-filtration from dialysate of pyro-

gens and other impurities, improvements in water filtra-tion and reverse osmosis systems now more readily

provide ultra-pure water. As a result, higher flux mem-

branes are becoming the accepted standard in the West-

ern world. The coincidental advent of volumetric

machines that ensure the better regulation of intradialyt-

ic volume has made higher flux dialysis a safer and better

option. But what exactly is meant by low flux and high

flux and, at what point does ‘‘low’’ become ‘‘high?’’When the HEMO study was conceived in the early

1990s, membranes then regarded as high flux would not

be high flux now. Flux in the HEMO study was stratified

into low and high according to the clearance of b2

microglobulin: o10 mL/min equated low flux and

420 mL/min equated high flux.21 Most centers would

now consider the high-flux membranes of the HEMO

study as, at best, mid-flux. Furthermore, other studieshave used the clearance of other middle molecules (e.g.,

homocysteine) to ‘‘gauge’’ efficiency. An alternative to flux

as a measure of clearance is the ultra-filtration coefficient

(Quf)—as in Europe, or (Kuf)—as in the United States.

Ultra-filtration coefficient Quf is a measure of water per-

meability expressed in mL/h/mmHg.22 The Quf of the

high-flux dialyzers in the HEMO study23 was a mere

B20 mL/h/mmHg while many centers now use high-fluxmembranes with a Quf of 60 to 75 mL/h/mmHg.

One current industry definition of dialyzer flux used in

Europe now uses a combination of Quf and membrane

pore size rather than the Quf alone.24 Under this defin-

ition, membrane characteristics can be divided as follows:

low flux=Quf 2 to 10 mL/h/mmHg and pore size 1.8 nm

clearing toxins of a molecular weight o300 Da through

small pores; and mid flux=Quf 11 to 20 mL/h/mmHg and

pore size 2.4 nm clearing toxins of a molecular weight300 to 12,000 Da through a mixture of small and large

pores; high flux=Quf 21 to 60 mL/h/mmHg and pore

size 3.3 nm clearing toxins of a molecular weight 12,000

to 60,000 Da through large pores and super

flux=Quf470 mL/h/mmHg with the same pore sizes as

high-flux membranes but adding a larger surface area and

thus an increased number of pores. Further, it may be-

come important to consider surface area-adjusted Quf ra-ther than Quf alone. This expansion in flux ‘‘capability’’

shows that even flux is in a state of flux!

An alternative to Quf favored by some is the b2 sieving

coefficient and both terms are currently acceptable. Until

a consensus is reached, either is preferable to descriptive

terms like low, mid, or high. What might be high flux in

the United States is only mid-flux in Europe. If not de-

lineated by the Quf or b2 sieving coefficient, what will bethe next flux descriptor—megaflux, hyperflux?

Reuse

Dialyzer reprocessing (reuse) is aimed primarily at cost

reduction although whether reuse saves much—after fac-

toring in reprocessing costs—is debatable. Many regions,

including Australasia, have long ago discontinued reuse,

particularly as dialyzers are now cheaper and nagging

doubts remain about safety. Fresenius reports a decrease

in survival with reuse when compared with single use,

but this has been contradicted by data from the U.S. Re-nal Data System, which supports the view that reuse

‘‘conditions’’ the dialysis membrane, enhancing biocom-

patibility.

Even if reuse is practiced, there are differing methods

of dialyzer resterilization. Although chemical reprocess-

ing with agents such as peracetic acid remains the most

common way, the Aksys PHDs System25 has introduced

online hot water reprocessing for both blood lines anddialyzer, thus extending the potential options beyond

chemical resterilization.

Ultra-pure water

Ultra-pure water is water that is effectively endotoxin and

bacteria-free (o0.03 EU/mL and o0.1 CFU/mL)26 and is

prepared from standard-quality dialysis fluid by an addi-

tional step of controlled ultrafiltration. Current water

quality has vastly improved from the almost unaltered

feed water of the early 1970s to the particle-filtered and

reverse osmosis prepared water of the 1980s and 1990s.

Even now, however, standards vary with significant



differences still between the 2 main standards: theEuropean and the American.

As with changing perceptions of flux, the concept of

ultra-pure water was also nonexistent at the design phase

of the HEMO study, although now, in 2007, it is a process

standard for high-flux dialysis. The use of pejorative ter-

minology to describe water quality mirror those that con-

fuse the differentiation between low and high flux—when

do we introduce the next hyperbole for water—hyper-pure water? Although perhaps the better choice may be a

simple statement of the maximum allowed EU/m for en-

dotoxin and CFU/mL for the bacterial count, even then

problems emerge. The temperature at which dialysate is

cultured to yield a CFU/mL result matters. And, too, the

medium used and the duration of culture. Specification of

these criteria is essential for accurate cross-comparison of

dialysis literature.

Adequacy

Adequacy has been purposefully left until last as the

characteristics of dialysis adequacy depend considerably

upon all preceding definitions. In the authors’ view, ‘‘dia-

lysis adequacy’’ as it is currently defined is conceptually

narrow and unsatisfactory, is governed by the wrong cri-

teria, and is an inappropriate way to view the complex-ities of dialysis. It demeans the wider goals of dialysis

and should be abandoned. If aiming for ‘‘a measure,’’

we should reach for optimum and not simply settle for

adequate.

Optimum dialysis is a composite outcome goal—prob-

ably never attainable—which is a compilation of quanti-

tative and qualitative measures that achieve the very best

potential possible for any individual. This certainly in-cludes small solute clearance—the current sole measure

of adequacy—but should also embrace a range of out-

come measures excluded from the narrow Kt/V-driven

definition. Some of these include: middle molecular and

protein-bound solute clearances, blood pressure and vol-

ume control, the stability of the intravascular volume,

membrane-contact time (MCT)—dialysis frequency and

duration—medication minimization, nutritional meas-ures, liberalization of dietary, and fluid intake and out-

come measures such as rehabilitation, waking-hour

freedoms, lifestyle and/or quality of life, and the poten-

tial to return to employment, to name but a few.

Clinicians should stop using the terms adequate and

inadequate. They are misleading. If small solute clearance

is suboptimal, then this should be made clear but good

dialysis is far more—and it is time we said so. A more

rational definition of good, optimal dialysis is a majorchallenge for the next phase of dialysis medicine.

RECOMMENDED TERMINOLOGY

It is important to redefine the terminology we use in any

field of medicine as our knowledge, understanding, and

practice patterns change with time. This particularly ap-

plies to dialysis where the dialysis process and its asso-

ciated clinical practices have been subject to rapid

technological change. Imprecise and/or judgmental ter-minologies—small, bigger, biggest—are best avoided. If

the dialysis milieu is more precisely scripted, the inter-

pretation of comparisons, study with study or region with

region, will be more effective. We therefore propose a re-

classification of dialysis terminology.

To achieve this, 4 key dialysis factors must be defined:

the dialysis modality; the dialysis site where that modality

is supported; the clinical program or treatment scheduleused; and the technical processes by which that program

or schedule is delivered.

Modality

The issue of modality seems, at first glance, relatively

straightforward. Although there are 2 major current mo-

dalities—HD and peritoneal dialysis—this review dealsonly with direct hemopurification processes. Within

hemopurification, HD remains the dominant therapy al-

though, as alternative methods such as HDF and HA ad-

vance over the next decade, these may need to be more

actively included in any classification. For now, unless

specifically describing HDF techniques, HD suffices.

Site

Both the location of care and the level of care delivered

must be described with clarity when reporting any dia-

lysis program. Broadly, patients will either receive home

care or facility-based care. When care is delivered in a

facility with all nephrology services available—both med-

ical and nursing—these patients should be further de-

fined as receiving full specialty care. If only trainednephrology nursing is available, renal nurse care should

be stated. If the carer team is untrained in nephrology but

has any form of general medical or nursing training, then

those patients should be described as receiving general

care. If the patient is receiving medically untrained helper

care in either a facility or in the home, the designation

should be helper care with a further subclassification de-

pending on whether the helper is paid or unpaid. Finally,

Agar et al.


the home patient may provide self-care and may be underthe umbrella of a remotely monitored program—as is

most common in North America—or in an unmonitored

program—as is commonly the practice in Australasia.

Clinical dialysis schedule

When defining clinical dialysis, there is a need to stream-

line the burgeoning terminology. Clinical dialysis is either,

by intention, dialysis while awake or while asleep. For thepurposes of clear understanding, these could be simpli-

fied to daytime and nocturnal dialysis—although the use

of aware as the descriptor for awake dialysis has some

attraction.

Dialysis duration depends upon the MCT, which, in

turn, may differ depending on whether it is prescribed or

achieved, the difference being a surrogate measure of pa-

tient compliance or program reliability. Membrane contacttime can be expressed either as a sessional duration or a

weekly aggregate. It is preferable that MCTrefers to the total

prescribed weekly MCTwith a different measure being used

for dialysis frequency (vide infra). The prescribed MCT

should be known for any individual patient or group and

should be stated. The achieved MCT may or may not be

known or documented, although a carefully run program

should provide both by using machine operation data withcompliance as the ratio of achieved to prescribed MCT.

Dialysis frequency is now far less restricted to a thrice-

weekly pattern than previously. Imaginative programs

blending greater frequency with both longer and shorter

sessional MCT are now commonplace. The weekly treat-

ment frequency should thus be clearly stated.

A key cardiovascular and hemodynamic ‘‘risk factor’’ of

most current dialysis regimes is the hour duration of thelongest weekly interdialytic period—the longest interdi-

alytic gap. This is where the patient is at maximal risk of

circulatory overload, left ventricular stretch, and stress

and hyperkalemic arrhythmia. Stating the maximal inter-

dialytic period may generate a surrogate measure of the

maximal circulatory risk—although this potential tool is

yet to be tested in the clinical setting.

Technical process

In any dialysis program, the dialysis process must also be

defined. Although the following section primarily details

well-embedded terminology, these terms are essential to

include in any standardization process.

The blood flow rate (Qb), the dialysate flow rate (Qd),

and the substitution flow rate (Qs) in hemofiltration or

HDF should all be stated. Further, in convective thera-

pies, it is important to state the point of administration ofthe substitution fluid—predilution, middilution, or post-

dilution.

The dialyzer membrane type and dialyzer surface area

should be stated. Although many membrane characteris-

tics might be chosen, we believe that at least 2 membrane

parameters should be included: membrane flux as ex-

pressed by the ultrafiltration coefficient (Quf) as mL/h/

mmHg: for example, Quf59 or Quf18 and membrane poresize expressed in kilo Dalton (kD).

The dialysate composition should be stated—for ex-

ample: [Na1] 138; K1=3.0 mmol/L; Ca11=1.50 mmol/

L; and Glucose=5.0 mmol/L. If sodium profiling is under-

taken—a practice not recommended by KDOQI—then

state the [Na1] range as the Na1 profile falls across the

treatment (e.g., 140–136). To complete the description,

Mg11 and bicarbonate concentrations should be given.In longer dialysis schedules, the added efficiency of phos-

phate removal may require the addition of phosphate to

the dialysate to avoid hypophosphatemia. In this case, the

level of dialysate phosphate supplementation or, prefer-

ably, the required dialysate phosphate concentration

should be given. Finally, the dialysate temperature pro-

file should be included.

The method of and dosing regimen for extracorporealanticoagulation is important. This may range from stand-

ard sodium heparin regimens—loading and maintenance

dosing—through to low–molecular-weight heparin

protocols, the use of citrate and where/if agents

such as aspirin, clopidogrel, warfarin, hirudin, and dir-

ect thrombin inhibitors like megalatran. Anticoagulation

protocols are an integral part of the dialysis prescription

and should be recorded.Although the authors do not believe that the current

commonly used expressions of dialysis ‘‘adequacy’’—Kt/

Vurea or urea reduction ratio (URR)—are either ideal or

sufficient measures of this complex, multifaceted process,

dialysis dose as measured by Kt/V and/or URR must be

stated unless better measures emerge in time. A marker of

middle molecule clearance might also be of value, al-

though a consensus has yet to be established. As predi-alysis b2 microglobulin levels have been shown to

correlate with mortality,27 b2 microglobulin clearance

may be a reasonable starting point. Markers of protein-

bound solutes such as p-cresol may be of future value but

are not currently readily available to clinicians, and

improving their clearance remains challenging.

The practice of reuse, if applicable, must be clearly

documented. If membrane and/or line reuse is practiced,the sterilizing agent must be stated—for example:

peracetic acid or hot water.



Table 1 Proposed standardization of terminology for chronic maintenance hemodialysis (example schedules only)

Dialysis descriptor Example 1 Example 2 Example 3 Example 4

Modality HD HD HDF HDLocation of care Home Facility Facility GP OfficeFrequency Daily Thrice-weekly Alternate day DailyPrescribed dialysis regimen 6/week � 8.5 hr 3/week � 4 hr 3.5/week � 4.5 hr 6/week � 2 hrLevel of care

Full specialty care — — Yes —Renal nurse care — Yes — —General care — — — —Helper care No — — —Helper paid/unpaid – — — PaidSelf-care Yes — — NoMonitored No Yes Yes No

Clinical HD scheduleDaytime or Nocturnal Nocturnal Daytime Daytime DaytimePrescribed weekly MCT (hr) 52 12 14.875 12Actual weekly MCT (hr) 47 12 14.3 12Compliance (actual/weekly)(%)

90.4 100 96.1 100

Frequency (sessions/week) 6 3 3.5 6Prescribed longest gap (hr) 39.5 68.5 43.75 46

Dialysis processQb (mL/min) 225 450 300 450Qd (mL/min) 300 600 800 500Qs (mL/min) (predialysis,middialysis, postdialysis)

N/A N/A 75 (post) N/A

Membrane type Fres HF80 Fres F6 Fres FX 80 Fres FX60Membrane surface area (m2) 1.8 1.3 1.8 1.4Quf (mL/h/mmHg) 55 40 59 46D Na1 ( � range) (mmol/L) 136 134 135–140 138D K1 (mmol/L) 3.0 1.0 3.0 2.0D Ca11 (mmol/L) 1.75 1.3 1.75 1.3D Mg11 (mmol/L) 0.8 0.8 0.5 0.8D HCO3

� (mmol/L) 32 28 35 32D glucose (mmol/L) 5 10 5 5D phosphate (mmol/L) 12.92 — — —D temperature ( 1C) 36.0 35.5 37.0 36.5Mean UFR (mL/hr) 195 725 520 820Anticoagulation method Na1 Hepn LMW Hepn LMW Hepn Na1Hepn

Total anticoagulant dose 10,000 U Na1 heparin 40 mg enoxaparin 60 mg enoxaparin 4,000 U Na1 heparinSessional Kt/V (or URR) 0.9 1.3 1.5 0.55Reuse/nonreuse No Yes No NoWater — No — —Peracetic acid — Yes — —

D=dialysate; enoxaparin=enoxaparin sodium; Aventis Pharma P/L, Macquarie Park, NSW, Australia; Fres=FreseniusTM; HCO3� =bicarbonate

concentration; HD=hemodialysis; HF=High Flux; hr=duration of treatment in hours; K1=potassium concentration; MCT=membrane con-tact time; Mg11=magnesium concentration; N/A=not applicable; Na1=sodium concentration; Q/daily=quotidian daily; Q/nightly=quo-tidian nightly; Qb=blood flow rate; Qd=dialysate flow rate; Qs=substitution flow rate (if applicable); Quf=ultrafiltration coefficient;UFR=ultra-filtration rate; URR=urea reduction ratio; /week=sessions per week; —=not applicable to this schedule.

Agar et al.


Although arterio-venous (AV) access is a key influencein any dialysis program—whether the prescription or the

expected outcome—access is patient-specific rather than

program or process specific. It is appropriate, however, to

include base data on access type and efficacy including

access type(s), access site(s), and, if available, flow and/or

functional data. For the purposes of this review, however,

details of dialysis access are excluded from further defin-

ition.

DESCRIBING THE PROCESS

Table 1 shows 4 example profiles where location, level

and delivery of care, clinical schedule, and dialysate pre-

scription vary. These examples are but 4 possible protocol

variants and are not recommendations for protocol pre-

scription but examples of how a standardized language

might be applied.

CONCLUSION

The purpose of language is communication. Technical

and scientific language, although sometimes pejoratively

labeled ‘‘jargon,’’ requires precision of use if it is to serve

its purpose. To optimize cross-regional and international

clarity of expression and understanding, it is important

that (a) accepted descriptive terminology and (b) an es-tablished mechanism for defining the dialysis prescrip-

tion are agreed upon.

Additional words and phrases inevitably emerge as

newer and more varied options expand the restrictive

confines of past conventional dialysis practice. The def-

initions we provide are neither all-inclusive of current

terminology nor seek to restrict future changes. The con-

struct we propose is only one suggested expression forthe dialysis milieu—at both organizational and practical

levels.

Primarily, this paper seeks to stimulate discussion

about the best way to define and standardize current

and emerging dialysis practice. Any such standard must

include all key elements of dialysis therapy and yet must

allow comparison of both practice and process. Defin-

itions and practices will inevitably change and grow asdialysis emerges into a more flexible, exciting future. It is

appropriate and healthy that they should. It is timely,

however, that regular revisions of dialysis ‘‘lore’’ be at-

tempted.

We have sought to solidify the essential characteristics

of clinical dialysis through a standardized description of

the modality, the location of care, the level of care, and the

caring personnel.

We have defined the clinical dialysis schedule throughits timing, the prescribed weekly MCT, the frequency of

treatment, and the longest interdialytic period per week.

Finally, we have attempted a rational method for de-

scribing the dialysis prescription by stating its key elem-

ents: blood and dialysate flow rates; the dialyzer surface

area; the flux characteristics of the membrane; the dial-

ysate characteristics; the method of anticoagulation; an

expression of dialysis dose through either Kt/V or URR;and lastly, any reuse policy.

Although clearly this can never be an exhaustive list,

we believe that these key elements are, in 2007, essential

information to include in any peer review clinical dialysis

manuscript.

Finally, we hope that if nothing else, this manuscript

will generate vigorous debate. Not all will agree with our

view, perhaps particularly those that apply to dialysis‘‘timing’’—but we believe that this is a debate that must be

encouraged. We welcome comment and opinion.

ACKNOWLEDGMENTS

My thanks (J. W. M. A.) are extended to Dr Carolyn Clark,

Renal Registrar, the Geelong Hospital, for her valuable

assistance in the preparation of this manuscript.

Manuscript received July 2006; revised December 2006.

REFERENCES

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Blackwell Publishing has graciously permitted us to

trial a new interactive concept through the Internet site‘wikikidney’. To contribute to a living terminology

debate and to the modification of this paper’s

suggested dialysis nomenclature, please go to http://

wikikidney.org/index.php/Main_Page and click on

‘‘Hemodialysis’’ in the issues in Nephrology box. There

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the capacity to edit and/or discuss the article. Regi-stration is available to any bona fide nephorologist

or dialysis professional, and simply requires an

e-mail request to [email protected].



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Chronic maintenance hemodialysis: Making sense of the terminology

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