The Production of Dialysis Fluid

Historically the production of dialysis fluid was by the manual mixing of concentrated electrolyte solution with water in a large tank, which was then heated and pumped to the dialyser [1]. With the advent of single-patient proportioning systems in the late 1960s, the production of the dialysis fluid moved to the patients bedside and whilst this approach remains the most widely used, alternatives such as a central delivery system or systems that incorporate pre-mixed dialysis fluid continue to be used [2].

KAI\G Ed

© 2007 S. Karger AG, Basel 0253-5068/07/0251-0062$23.50/0

Nicholas A. Hoenich, PhD

School of Clinical Medical Sciences, Faculty of Medical Sciences Newcastle University, Framlington Place Newcastle upon Tyne, NE2 4HH (UK)

Tel. +44 191 222 6998, Fax +44 191 222 0723, E-Mail [email protected]

Fig. 1. Two different approaches to bicarbonate concentrate used in haemodialysis. a The Bi Bag (Fresenius Medical Care). b BiCart cartridge (Gambro Renal Products).

Early single-patient proportioning systems used sodium bicarbonate for buffering, but problems arising from the formation of calcium carbonate meant that this approach was abandoned in favour of acetate [3]. Acetate remained the buffer of choice until the early 1980s when, with the increased use of high-efficiency dialysis treatments and the availability of new technology to minimise calcium carbonate formation, bicarbonate re-emerged as the preferred buffer.

The preparation of bicarbonate-buffered dialysis fluid requires the use of two separate concentrates, an acid concentrate containing sodium chloride, calcium chloride, magnesium chloride, potassium chloride, glucose monohydrate and a small amount of organic acid generally in the form of glacial acetic acid, although other acids may also be used (sodium di-acetate, lactic acid or citric acid), and bicarbonate or base concentrate containing powdered or liquid bicarbonate (fig. 1). Systems in current clinical use proportion these at different ratios with the more commonly used ratios being 1:1.225:32.775,

1:1.83:34, and 1:1.72:42.28 (acid concentrate:base con-centrate:water). The different proportioning ratios are a consequence of the presence of varying amounts of sodium chloride in the bicarbonate solution, necessitating a corresponding adjustment in the acid concentrate to achieve the final electrolyte concentration.

The dialysis fluid thus produced is heated and degassed before passing to the dialyser. Safety circuits monitor the ionic composition to ensure patient safety and comfort. At the normally used temperatures (36.5-38°C) dialysis produces a marked increase in body temperature and considerable heat accumulation arising from peripheral, and cutaneous vasoconstriction arising from the body's compensation for the ultrafiltration induced decrease in blood volume. This thermal accumulation contributes to treatment-related vascular instability and has led to the development of temperature or thermal balance monitoring and control systems to minimise hypotension [4, 5].

Table 1. Water contaminants known to pose problems to the dialysis patient

Symptom

Related water contaminants

Anaemia

Al, chloramine, nitrate, Pb, Cu, Zn, Si

Bone disease

Al, fluoride, Si

Hypertension

Ca, Mg, Na

Hypotension

Bacteria, endotoxin, nitrate

Acidosis

Low pH, sulphate

Muscle weakness

Ca, Mg

Nausea/vomiting

Bacteria, endotoxin, chloramine, low pH, nitrate,

sulphate, Ca, Mg, Cu, Zn

Neurological disturbances

Al, Pb, Ca, Mg

FDA 89-4234 manual on water treatment for hemodialysis.

FDA 89-4234 manual on water treatment for hemodialysis.

Table 2. Water and dialysis fluid microbiological contaminant levels in US and European standards

Water

Dialysate

bacteria

endotoxin

bacteria

endotoxin

CFU/ml

EU/ml

CFU/ml

EU/ml

AAMI, proposed

200a

2b

NS

NS

AAMI, current

NS

NS

200

2

EBPG

100

0.25

100

0.25

NS = Not specified. EBPG = ERA-EDTA best practice guidelines. a Action level 50 CFU/ml. b Action level 1 EU/ml.

NS = Not specified. EBPG = ERA-EDTA best practice guidelines. a Action level 50 CFU/ml. b Action level 1 EU/ml.

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