Dialysis plumbing requirements

By Timothy Allinson, P.E.

Murray Company, Long Beach, Calif.

Those of you who design hospitals probably know that dialysis plumbing requirements vary greatly from project to project and that this variance can leave the engineer wondering, "What's the right design solution?" To answer this question, it is helpful to have an understanding of how dialysis works.

By way of history, the dialyzer, or artificial kidney, was invented in 1943 by a brilliant doctor and biomedical engineer, Dr. Willem Kolff. It was first used in a remote Dutch hospital during World War II. After the war, Dr. Kolff generously donated five of his machines to hospitals around the world. They were received with mixed reviews; many considered them to be ridiculous machines.

Ultimately, Kolff gave the blueprints of his dialyzer to Brigham Hospital in Boston, where the design was refined, paving the way for the first kidney transplant in 1954. In 1962, the first outpatient dialysis was performed. Dr. Kolff went on to become the world's greatest biomedical engineer and was instrumental in the design of the heart-lung machine and the artificial heart. Today, in his late 90s, he continues to work on artificial eyes and ears.

The dialyzer is essentially a specialized osmosis machine, performing the work of the kidneys for people with kidney malfunction. It passes a person's blood across an artificial kidney, which is an osmotic membrane with a large surface area. The blood stays on one side of the membrane, while a carefully composed fluid called "dialysate" passes in reverse flow across the other side. Prior to the dialysis process, a doctor determines the needed composition of the dialysate, based on the patient's blood composition. Desirable minerals such as potassium will be kept in the blood by putting an equal amount of potassium in the dialysate. Unwanted waste products of high concentration will flow out of the blood across the kidney membrane into the dialysate where they are of non-existent low concentration. This is simple osmosis.

The dialysate eventually discharges into the drain on the dialysis box. Often it is diluted before discharge, but not always. When the process is complete, the machine is rinsed, sometimes with a solution of water and chlorine; this rinse water discharges to the dialysis box as well.

The plumbing requirements at the dialysis box will vary based on the function of the dialysis machine used by the hospital, the operational procedures of the hospital and the relevant plumbing code.

For many years, dialysis boxes were always provided with high purity (RO) water, because the dialyzer needed pure water to produce dialysate of controlled composition. This was such common practice that some Codes, such as the 2001 California Plumbing Code (CPC, based on the UPC), dictated RO system requirements for dialysis.

In more recent years, portable dialysis machines were designed with their own RO membranes to filter the water supplied for the dialysate. This meant that the dializer could function independently from the RO water supply. It also meant that the plumbing engineer no longer had to provide RO water for the dialysis boxes. Accordingly, the 2007 CPC no longer dictates RO system requirements for dialysis.

In order to determine whether there is a need for RO water at the dialysis boxes, the designer needs to coordinate with the hospital representative or medical equipment planner. Chances are it is not required; however, some dialysis centers with fixed equipment still might require RO water.

Backflow prevention is the next contentious issue of dialysis plumbing services. Some jurisdictions require strict RP type backflow prevention ahead of any dialysis box connection. Others are satisfied with just a vacuum breaker. The real need, or lack thereof, for backflow prevention again will depend on the dialyzer used in the process. Most modern equipment has inherent backflow prevention on the machine itself, making an upstream RP device unnecessary. Again, the engineer needs to coordinate backflow requirements with the type of dialysis machine used by the hospital and to check local codes. Note that when a vacuum breaker is provided it is sometimes located in an access panel above the box; however, a hose-connected vacuum breaker can often be provided inside the box, making the need for an additional access panel unnecessary.

Dialysis boxes are available in two standard configurations - one valve or two. The reason for having two valves has changed over time. When central RO water was used for dialysis, the box might have one valve for RO water and one for domestic rinse water. Since this is no longer the typical configuration, only one valve should be required. There is another practical reason, however, for the second valve position: Some jurisdictions require a trap primer for the drain on the dialysis box, because there is no way to determine its frequency of use. When this is the case, the second valve position is a convenient spot to place a trap primer, in lieu of the standard valve.

Another source of contention is the material of the P-trap serving the dialysis box. Some jurisdictions or hospitals have a requirement that the trap be made of corrosion resistant material, such as polypropylene, PVDF, glass or Duriron. The driver for this requirement is the fact that the dialyzer discharges RO water used for the dialysate, and this aggressive water sits in the trap where it can corrode traditional cast iron. As noted above, some dialysis machines will dilute the dialysate prior to discharge, making it less corrosive. Further, the rinse cycle would normally bypass the RO unit on the machine, so the last water to enter the trap is tap water, making the requirement for a corrosion resistant trap unnecessary. Again, the engineer must coordinate with the medical equipment planner, the hospital and the local authority.

Last, but not least, I once saw a design on a project that provided industrial hot and cold water to the dialysis boxes. I never determined whether this configuration was a mistake or whether it was a requirement of the hospital. My only guess is that the hospital might use hot water for the rinse cycle of the dialyzer. Although I haven't encountered this before or since, it is one more issue that the engineer might consider when coordinating the dialysis plumbing requirements.

Timothy Allinson is a Senior Professional Engineer with Murray Company, Mechanical Contractors, in Long Beach, Calif. Prior to entering the design-build industry he worked for Popov Engineers, Inc. in Irvine, Calif, and JB&B in New York City. Tim holds a BSME from Tufts University and an MBA from New York University. He is a professional engineer licensed in both mechanical and fire protection engineering in various states, and is a leed Accredited Professional. Tim is a past-president of ASPE, both the New York and Orange County Chapters, and sits on the board of the Society of American Military Engineers, Orange County Post.