Hemodialysis

In the last 3 decades, hemodialysis has become a common method of treatment for patients with end-stage renal disease. During hemodialysis, blood from the patient flows through one compartment of an artificial kidney (dialyzer), while isotonic salt solution (dialysate) flows in a countercurrent manner through another compartment. A thin semipermeable membrane separates the two compartments, allowing metabolic waste products in the patient’s blood to diffuse across the membrane into the dialysate and to be discarded with the dialysate to drain. The cleansed blood is then returned to the patient.

Because the patients blood and dialysate are separated by only a thin semipermeable membrane, the microbiological quantity of dialysis water and dialysate is important. The primary microbial contaminants of the dialysis fluids are naturally occurring water bacteria consisting of a variety of micro organisms, including gram-negative bacteria and nontuberculous mycobacteria. Virtually all disinfection strategies for hemodialysis are targeted at these groups of bacteria.

In general, a hemodialysis system consists of a raw water supply, a water treatment system, a distribution system, a water and dialysate concentrate mixing system, and a dialysis machine to pump the dialysate through the dialyzer.

WATER TREATMENT SYSTEM:

WETICO supplies the water treatment and distributon systems (loop) for hemodialysis as a part of our wide range of water treatment.

The water treatment system is comprised of the following main parts: 1. Water Supply 2. Filteration station 3. Softening station 4. Reverse Osmosis station 5. Disinfection station (polishing station) 6. Loop supply system  7. Control system

1. Water supply The water supply system consists of a raw water break tank and filter feed pumps. The raw water is usually a community water source or another treated water source. Raw water is analysed and inspected as the first step towards the design of a hemodialysis water treatment system. The filter feed pumps are selected and installed depending on system feed flow, head, losses,pump’s NPSH,material of construction ,power supply, factor of saftey and other factors.

2. Filteration station The filteration station mainly consists of a carbon filter (for chlorine (chloramines) ,some organic substances and odor removal) and (if necessary) a birm or sand filter where the birm filter acts as an iron removal and filteration item while on the other hand the sand filter acts as a filteration item only.

The word filteration indicates the filteration of suspended solids sizing from 10 microns and larger. 1 micron and/or 0.2 micron filteration is also installed on the Reverse osmosis skid. Fig 2 shows the filter feed pumps and filteration station for a small hemodialyis unit( Fig 2A with automatic multiport valves, Fig 2B with manual multiport valves).

3. Softener Station  A water softener removes calcium and magnesium by ion exchange from the feed water before it reaches the Reverse osmosis system. The excess calcium and magnesium in “hard” water is removed to prevent patient injury, however the primary practical reason for removing these ions is to prevent them from “plating” on the Reverse osmosis membranes, resulting in performance deterioration.  The softener station is made up of a single or duplex softener. The single softener consists of a control head, a resin softener, and a brine tank, whereas the duplex softener consists of two resin vessels (one duty & 1 stand by) ,a common control head, and a brine tank. It should be nted that improper sizing and regeneration scheduling ,results in increased hardness late in cycle before regeneration.

4. Reverse Osmosis Station The Reverse osmosis system is responsible for water salt rejection and minimizing the total dissolved solids (TDS) content to the minimum (depending on raw water TDS). i.e. the target is to get product water composition to be lower but not higher than the AAMI standard (Assosiation for the Advancemen of Medical Instrumentation). Reffer to table 1.

A Hemodialysis Reverse osmosis system consists of : 1. Cartridge filter ( 1 micron ) 2. High pressure Pump 3. Pressure Vessels 4. membranes 5. piping ad electrical works 6. Instrumentation.

Items 1 to 5 are also reffered to as Brackish Water Treatment. As for the instrumentation, it consists of pressure guages,pressure switches, flow and TDS meters only as basic requirements due to the fact that there are no chemical additions for hemo dialysis Reverse osmosis. Other instrumentations are equipped in the system as options.

5. Disinfection station (polishing station) the disinfection or polishing station is a post treatment of RO product water for disinfection purposes. It uses an ultraviolet and / or heat exchange (steam sanitization) system for removal of all bacteria.

The ultraviolet system produces ultraviolet light at 254 microns, while the heat exchanger heats the water. Any or both of the above are installed after the loop supply pumps for recirculation of water and disnfecting the loop in adition to the water. Recirculation time is usually 10 – 15 minutes.

A 0.2 micron filter is installed after the disinfecting equipment as part of the station to capture all dead organics (bacteria). The pumps are designd to give the required flow and head (depending on the number of beds (patients)).

6. Loop Supply System The loop or supply system is generally constructed of plastic piping, such as polvinylchloride (PVC) or high grade Stainless steel (316L) piping. Galvanized or copper pipes and fittings cannot be used because they will contaminate the treated dialysis water with toxic concentrations of Zinc and Copper.

Oversized pipes and unnecessarly long runs decrease fluid flow rates and increase bacterial potential reservoirs for both treated water and dialysate. Rough joints, dead ends and unused ranches also act as bacterial reservoirs and should be elnminated. Outlet taps should be located at the lowest elevation to prevent loss of chemical germicide during disinfection and to prevent any stagnation of water.

Storage tanks can be significant reservoirs of bacteria there fore must be equiped with drainage, ultrafilter distal and be cleaned periodically . The loop outlet should have a control valve and pressure guage to have enough pressure in the loop during operation (Fig 6). The tank and loop are usually looped all together with the disinfection station as described earlier.

7. Control System The control system (main control panel ) consists of a programmable logic control and asociated instrumentation, cabling, breakers , contactors, lights , switches,…etc necessary for controlling the whole water treatment system.