HAEMODIALYSIS EQUIPMENT

HIGHTLIGHTS The essential components for HD include the : Dialyser (artificial kidney) Dialysis solution (dialysis water and concentrates) Dialysis tubing HD machines

Dialyser The dialyser (the artificial kidney) is the apparatus in which the dialysate fluid and blood are in contact across a semipermeable membrane. Ports Dialysis membrane Membrane composition Dialyser specifications

Ports There are four ports attached : Two for the dialysate Two for the blood. Blood flowing from the patient to the dialysis machine is carried along the ‘arterial’ limb of the circuit. Conversely the ‘venous’ limb carries purified blood from the dialysis machine back to the patient.

Dialyser Dialysate Inflow Bundle of Capillaries in the Housing Blood Outflow Dialysate Outflow Solute Transfer across the Capillary Walls Blood Inflow The dialysate flows outside of the capillaries, blood within the capillaries countercurrently.

Dialysis Membrane The semipermeable membranes is suspended within the dialyser. These can be arranged in two different configurations : Hollow fibre (capillary) configuration: contains thousands of hollow fibres through which the blood flows, while the dialysate flows outside the fibres within the dialyser; most dialysers used in adults are of this type. Parallel plate configuration : contains flat sheets of membrane material stacked on top of each other arranged so that blood and dialysate fluid flow in alternate spaces; there is low flow resistance, making them particularly useful for ‘single needle’ dialysis in children.

Membrane Composition Cellulose (cuprophan or cuprophane) - made from cotton (cellulose polymer). Less ‘biocompatible’ than other membrane types due to activation of inflammatory pathways. Substituted cellulose – cellulose polymer in which the free hydroxyl groups are substituted. Cellulosynthethic – synthetic material added to liquified cellulose. Examples included Cellosyn and Haemophan. Synthetic – not cellulose based. Examples include polysulfone, polyacrylonitrile and polyamide

Dialyser Specifications Surface area – usually 0.7-2.4 m². The larger, the higher the clearance (and priming volume). Dialyser efficiency – measured by the mass transfer coefficient (KoA). The KoA is a function of the permeability of the membrane and its surface area. A high-efficiency dialyser is one with a KoA of greater than 600-700 mL/min (usually achieved by a larger membrane surface area). Ultrafiltration coefficient (Kuf) – this determines the degree of convective transport (flux) achieved by a particular dialyser. High-flux membrane have large pore sizes and allow greater removal of high-MW solutes

Dialyser Solution (dialysate) Dialysate is made by mixing treated water with preprepared ionic concentrates using a proportioning device within the HD machine. Typical composition of a bicarbonate-based dialysate: pH 7.1-7.3, sodium 135-145 mM, Potasium 2-4 mM, Chloride 90-120 mM, Calcium 0.9-1.7 mM, Magnesium 0.3-0.8 mM, Bicarbonate 27-40 mM, Dextrose 5-10mM.

Water for haemodialysis In dialysis centres, water for dialysis is genmerated in a central water treatment plant ( a scaled-down versions used for patients on home HD) Dialysis water is purified in a number of steps, including softening ( removing impurities such as chloramine), removal of small-MW solutes (either by reverse osmosis or deionisers) and sterilization (by passage through a bacterial filter).

Water for haemodialysis Impurities that should be removed include : * aluminium – may cause ‘dialysis dementia’, bone disease and anaemia. * chloramine – may cause haemolysis * bacteria * endotoxin – usually filtered out by the dialyser membrane, but not by the high-flux membranes; may cause pyrogenic reactions on dialysis. * Copper-may cause haemolysis * Fluoride-may cause bone disease (chronic) or death (acute)

Water for haemodialysis Recommendations exit for the minimum levels of these contaminants in water for dialysis ( refer to the AAMI guidelines in the reference list for more information). Regular testing of water quality is recommended

Dialysate concentrates In bicarbonate-buffered dialysis, two separate concentrates are mixed with the treated water. The acid concentrate contains most of the important ionic constituents of blood (i.e. sodium, potassium, chloride, calcium, magnesium and dextrose). Bicarbonate is added from a separate concentrate reservoir-it would form insoluble carbonate if stored in the same concentrate.

Dialysis tubing Disposable tubing connects the dialyser to the paitient. Low-priming volume lines used for dialysing children in the paediatric setting.

Toros Kapoian, Jeffrey L. Kaufman, John Nosher & Richard A. Sherman

Haemodialysis Machine Standard Components : Roller pumps for dialysate and blood paths. An infusion pump for heparin. Pressure monitors on the ‘arterial’ and ‘venous’ limbs of the blood circuit. Air trap/air detector and blood leak detector. Dialysate heater and dialysate temperature monitor. Conductivity monitor (to monitor dialysate sodium)

Haemodialysis Machine Optional device : Dialysate urea sensor (allows the continuous calculation of urea removal as an index of dialysis dose). Blood volume sensor ( monitors change in haematocrit and volume status during dialysis )

Vascular access Dilated Vein - Shunt - Twinlumen Catheter Jugular Vein (V. jugularis interna) Connection: Vein and Artery Closure of the Distal End of the Vein Aorta The vascular access using peri-pheral veins of the forearm has the big advantage of long usage, but it needs some weeks waiting time after the operation before the first use. The access by a catheter inserted in a central vein can be immediately used, but its lifetime is limited to a few weeks.

Flow Scheme Hemodialysis Anti-Coagulation Blood Pump Dialyzer Blood to the Patient Fresh Dialysate Blood from the Patient Used Dialysate

Flow Scheme Hemofiltration Dialyzer Anti-Coagulation Blood Pump Sterile Infusion Solution Blood from the Patient Ultrafiltrate An exact balancing of infused and ultrafiltrated volumes is mandatory when using Hemofiltration ! Blood to the Patient