Hemodialysis

From Wiki.Nephron.org

Terminology recommendations for hemodialysis

This page is based on the final section of a published article, with the gracious permission of the publishers Blackwell and the International Society of Hemodialysis (Agar JWM, MacGregor MS, Blagg CR. Chronic maintenance hemodialysis: making sense of the terminology. Hemodialysis International 2007;11(2):252-262. [1]). It is an attempt to facilitate ongoing discussion and evolution of the terminology, by merging old and new media. Please do not edit this paragraph, as the link to the article is a requirement of the publisher. The remainder of the article is open for comment or editing – indeed we hope you will!

It is important to redefine terminology as knowledge, understanding and practice patterns change with time. This particularly applies to dialysis where dialysis processes and clinical practices have undergone rapid technological change. Imprecise and/or judgmental terminologies – ‘small’, ‘bigger’, ‘biggest’ – are best avoided. Using precise definitions ensures a more effective interpretation of comparisons, study with study or region with region. We have therefore proposed a reclassification of dialysis terminology.

Four key dialysis factors must be defined: the dialysis modality; the dialysis site where that modality is supported; the clinical program or treatment schedule used and the technical processes by which that program or schedule is delivered.

Dialysis Modality

The issue of modality seems, at first glance, relatively straightforward. Although there are two major current modalities – hemodialysis and peritoneal dialysis – the review deals only with direct hemopurification processes. Within hemopurification, hemodialysis remains the dominant therapy although, as alternative methods such as hemodiafiltration and hemadsorption advance over the next decade, these may need to be more actively included in any classification. For now, unless specifically describing hemodialfiltration techniques, hemodialysis suffices.

Dialysis Site

Both the location of care and the level of care delivered must be described with clarity when reporting any dialysis 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 medical and nursing – these patients should be further defined as receiving ‘full specialty care’. If only trained nephrology 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 sub-classification depending on whether the helper is paid or unpaid. Finally, the home patient may provide self-care and may be under the umbrella of a remotely monitored program – as is common in North America – or in an unmonitored program – as is commonly the practice in Australasia.

Treatment schedule

Clinical dialysis is either, by intention, dialysis while awake or while asleep. For the purposes of clear understanding, these could be simplified to ‘day-time’ and ‘nocturnal’ dialysis.

Dialysis duration depends upon membrane-contact-time (MCT), which, in turn, may differ depending on whether it is prescribed or achieved, the difference being a surrogate measure of patient compliance or program reliability. MCT can be expressed either as a sessional duration or a weekly aggregate. It is preferable that MCT refers to the total prescribed weekly MCT with 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 weekly MCT may or may not be known or documented, though a carefully run program should provide both by using machine operation data with compliance 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 treatment frequency should thus be clearly stated.

A key cardiovascular and hemodynamic ‘risk factor’ of most current dialysis regimes is the hour duration of the longest weekly interdialytic period – the longest interdialytic gap. This is where the patient is at maximal risk of circulatory overload, left ventricular stretch and stress and hyperkalemic arrhythmia. Stating the maximal interdialytic period may generate a surrogate measure of the maximal circulatory risk – though as a potential tool this is yet to be tested in the clinical setting.

Technical Processes

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 hemodiafiltrationshould all be stated. Further, in convective therapies, it is important to state the point of administration of the substitution fluid – pre-, mid- or post-dilution.

The dialyser membrane type and dialyser surface area should be stated. Although many membrane characteristics might be chosen, we believe at least two membrane parameters should be included: membrane flux as expressed by the ultrafiltration coefficient (Quf) as ml/h/mmHg: for example, Quf59 or Quf18 and membrane pore size expressed in kilo Dalton (kD).

The dialysate composition should be stated – for example: [Na+] 138; K+= 3.0mmol/l; Ca++= 1.50mmol/l; Glucose= 5.0mmol/l. If sodium profiling is undertaken – a practice not recommended by KDOQI – then state the [Na+] range as the Na+ profile falls across the treatment (eg: 140-136). To complete the description, Mg++ and bicarbonate concentrations should be given. In longer dialysis schedules, the added efficiency of phosphate removal may require the addition of phosphate to the dialysate to avoid hypophosphatemia. In this case, the level of dialysate phosphate supplementation or, preferably, the required dialysate phosphate concentration should be given. Finally, the dialysate temperature profile should be included.

The method of and dosing regimen for extracorporeal anticoagulation dose is important. This may range from standard 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 direct thrombin inhibitors like megalatran. Anticoagulation protocols are an integral part of the dialysis prescription and should be recorded.

Though the authors do not believe 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 though a consensus has yet to be established. As pre-dialysis β2 microglobulin levels have been shown to correlate with mortality 27, β2 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 re-use, if applicable must be clearly documented. If membrane and/or line re-use is practiced, the sterilizing agent must be stated – for example: peracetic acid or hot water.

Though arterio-venous (AV) access is a key influence in 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 definition.

Table of Examples

HD = hemodialysis; HDF = hemodiafiltration; MCT = membrane contact time; Qb = blood flow; Qd = dialysis fluid flow; Qs = substitution fluid flow; Quf = ultrafiltration co-efficient; D = dialysate; Na+ = sodium; K+ = potassium; Ca2+ = calcium; Mg2+ = magnesium; HCO3- = bicarbonate; UFR = net ultrafiltration rate

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