24×7 has been running this certification column (formerly known as ICC Prep) for many years, so it’s always a challenge to bring new information to certification seekers. One of the areas that has been written about very little is dialysis units.

Many hospital BMETs may not work on these units, as most are located in dialysis centers and not within the hospital. Also, these dialysis centers usually employ their own technicians to perform maintenance on this equipment, limiting exposure to this technology for many HTM professionals seeking to become certified.

That said, realize there will likely be questions about this technology on your exam. With that in mind, let’s take a look at some dialysis information you may need to know.

Types of Dialysis

Dialysis is used by patients who have lost the ability to filter waste salts and fluids from the blood because their kidneys are no longer functioning properly. There are two forms of dialysis which may be asked about on the exam: peritoneal dialysis and hemodialysis. You should know about both these types, but questions on the exam will most likely focus on hemodialysis and the dialyzer, a machine that accomplishes this filtering task by pumping the patient’s blood through an artificial kidney.

Peritoneal dialysis is the first, but less common, form of dialysis. Peritoneal dialysis gets its name because the cleansing solution, called dialysate, is administered into the lining of the abdominal cavity, known as the peritoneum. This solution of pure water, electrolytes, and salts (such as bicarbonate and sodium) will pull toxins from the blood into the dialysate during a process called diffusion. Peritoneal dialysis is often performed in the ambulatory setting, and consists of two categories.

There is continuous ambulatory peritoneal dialysis, known as CAPD, and automated peritoneal dialysis, or APD. CAPD and APD are referred to as “exchanges,” since the patient exchanges the dialysate through catheters into the peritoneal cavity. CAPD exchanges usually take place about 4 to 6 times per day, while CCPD exchanges can take 10 to 12 hours and are usually done at night while the patient is sleeping.

Hemodialysis is the other, and most common, type of dialysis treatment. It is usually performed in some type of outpatient clinic, such as a kidney dialysis center. Hemodialysis machines will create the dialysate by mixing an acidified solution of electrolytes and minerals, which is commonly referred to as the acid. This acid is mixed with bicarbonate, which is basically baking soda and reverse osmosis-purified water, or RO water.

Hemodialysis Preparation

RO water is the result of a water purification technology that uses a semipermeable membrane to remove larger particles from standard public water systems. The basic components of an RO water system include a prefilter, pump, and separator. The separator is a spiral wound membrane that filters the water. The RO water used in hemodialysis should be an isotonic solution with an optimal pH range of 6.8 – 7.8. Normal RO water has a pH of around 5.0, so base must be added to the RO water system used in dialysis treatments.

Proper mixture of the dialysate is verified by checking the conductivity of the solution. Conductivity is measured in siemens, a unit which is the reciprocal of the ohm and is also known as a mho. The conductivity measurements must be in a range of 12-16 mS/cm. The dialysate solution is particularly well-suited for this type of measurement, as it’s basically a salt mixture in water.

The conductivity behavior of the dialysate is very complicated, as it is a nonlinear function with temperature and salt/glucose playing heavily into the measurement. The chemistry and conductivity of the dialysate is far beyond the scope of the exam, but basic knowledge concerning the proper mixture of the dialysate and the conductivity of the solution could definitely be on the test.

The Dialysis Process

Once the dialysate solution is mixed, it is pumped through a device called a dialyzer, along with the patient’s blood. Because of the system’s construction, the two solutions never actually touch. The dialyzer is a special two-compartment filter with very small pores that allow tiny particles or toxins such as urea, creatinine, and potassium to pass through to the dialysate. However, these pores are sufficiently small to keep larger particles such as blood cells and proteins from diffusing through the filter. The filtered blood is then returned to the patient through a fistula, a surgically implanted connection pathway to an artery and vein of the circulatory system. The dialysate is then disposed of by washing it down a drain. Since dialysis treatments usually take several hours, the dialysis machine must continue to supply fresh dialysate for the entire process, keeping it at the required temperature of 37°C.

During patient treatments, the machine must continually monitor several parameters such as blood flow, blood pressure in the dialyzer, and blood tubing, as well as the patient’s blood pressure and the temperature, proper mixture, and flow of the dialysate. If any of these parameters vary beyond tolerance levels, the machine will go into an alarm mode. Depending on the alarm, the filtering process may be terminated.

This is by no means a thorough look into the technology of dialysis, but the information here should get you through many of the questions you might find during your exam. I hope you find this information useful in your quest to become certified.

John Noblitt, MAEd, CBET, is the BMET program director at Caldwell Community College and Technical Institute, Hudson, NC. For more information, contact chief editor Jenny Lower at [email protected].

Photo credit: © Dario Lo Presti | Dreamstime.com

Quick Study:

1) RO water stands for:
a) Removed Oxygen
b) Released Oxygen
c) Reverse Oxygen
d) Reverse Osmosis

2) Proper dialysate mixtures are checked with this type of test:
a) Conductivity
b) Weight
c) Spectrophotometry
d) Resistance

3) RO water should have a pH of:
a) 5.1­–6.4
b) 6.0–7.0
c) 5.5–7.5
d) 6.8–7.8

4) Dialysate temperature should be kept at what degree?
a) Room temperature
b) 99°F
c) 37°C
d) 42°C









Answers: 1—D, 2—A, 3—D, 4—C