By Phil Niles, Clinical Nurse Manager, Medical Solutions
As healthcare providers, many of you have cared for a patient that is dependent on dialysis. Yet, even you may have wondered, what the heck is dialysis? Well, let’s talk about that! A friendly dialysis RN shows up on their dialysis day, takes up your sink, clogs your room with machines, and, in the end, leaves you with a healthy smell of bleach lingering in the air. What happened? You know the basics of the process: The blood is “cleaned” and fluid is removed from the patient over three-four hours. The patient has
First, we start with water. A single dialysis treatment uses over 150 liters of water. Water from the faucet cannot be used because there are impurities, trace heavy metals, and chlorine in standard faucet water. This is all fine and dandy for us to drink, but during dialysis this water will come into contact with the patient’s blood, so it must be as pure as possible. One of the machines that a Dialysis RN brings into the room is a reverse osmosis machine or RO. This machine moves solutes from a concentration to a higher concentration producing high-concentrated water (waste water) and very low concentration water (RO water). The RO water is used for the treatment and delivered to the hemodialysis machine by a product hose. Tap water generally has total dissolved solutes level of 100-200 parts per million. Dialysis water is 10-15 parts per million — a much lower concentration. Before the water can be used the Dialysis RN must conduct a series of quality control tests to be sure the water is good to use. The main test is a chloramine test. Chloramine is a derivative of ammonia that’s used to treat drinking water. It cannot be in the product water because regular levels of chloramine would cause seizures and potentially death in your dialysis patients. After all the tests are complete, the water is considered good and the hemodialysis machine can now be set up.
The dialysis machine is then put through its own tests and it is “strung.” Stringing the machine means installing the blood tubing and dialysis filter, and priming out all of the air in the system. During this process “acid” and “bicarb” are added to the water being delivered by the RO. Acid is acetic acid or vinegar with electrolytes added specific to the patient’s needs. The bicarb is just sodium bicarb. The machine mixes dialysate at a ratio of one part acid, two parts bicarb, to 40 parts water. The pH is blended to the pH of normal blood. Dialysis patients are usually in early metabolic acidosis before treatment. The dialysis treatment normalizes this, while also balancing electrolytes and removing excess body fluid.
Once the machine is set up and has passed all quality control tests, the patient can be accessed and bled on to the dialysis tubing, which is called the circuit. Patient access is either an externalized catheter or internalized fistula or graft. The catheter is commonly surgically placed in the right or left jugular vein then tunneled under the skin four-six inches to where it comes out into two limbs, the arterial and venous access. The blood being accessed is venous blood. The arterial limb is called arterial only because it is moving away from the body. The “venous” limb returns cleaned blood back to the patient. A fistula is an access created by a passthrough or “fistula” between an artery and a vein that was not there before. This causes higher pressure arterial blood to flow through a lower pressure larger vein. Over time, usually two-three months, the vein enlarges due to the increased pressure and the walls of the vessel thicken. At this point the newly developed fistula vessel can be accessed by larger fistula needles. New fistulas are accessed by 16-17-gauge needles until the vessel becomes accustomed to the needlestick. Standard dialysis treatments are run with 15-14-gauge needles. Two needles are required — an arterial needle to pull blood to the dialysis machine and a venous needle to return the newly cleaned blood. Needles are placed at least an inch apart from each other to prevent recirculation, or recleaning of freshly cleaned blood. A graft access is a synthetic tube that is placed under the skin connecting a vein to an artery. The optimal access for a dialysis patient is a fistula. However, not all patients are candidates to receive one.
The biggest rule to follow is to never allow the extremity with the fistula or graft to be occluded, including and especially taking blood pressures. All lab draws and blood pressures must be done on the non-fistula extremity. Occluding the vessels or the fistula itself can lead to it clotting off and potentially losing that access. Many long-term dialysis patients do not have many options for accesses, so it is so important to protect your dialysis patient’s access while in your care. This is their lifeline!
The dialysis process itself is a fairly simple one that works on two principles — a concentration gradient and a pressure gradient. Diffusion, as most of you are very aware, is the movement of solute from a high concentration to a lower concentration. This is the entire science of electrolyte balance in a dialysis treatment. Potassium is usually high in a dialysis patient needing treatment. The dialysate mixed by the machine has a specific potassium prescription based on a sliding scale. This prescription will bring the patient’s potassium to a normal level after dialysis. The dialysis treatment does this with all electrolytes. It is important to note that the dialysis treatment only balances electrolytes in the blood. Higher levels may exist in the tissue and as dialysis progresses these higher levels continue to shift to the blood stream throughout treatment. Lab values are not accurate until at least an hour after dialysis treatment. It is highly discouraged to order labs before this so that inaccurate results are not given.
The other half of the dialysis treatment is fluid removal. This is accomplished by the dialysis machine exerting a specific negative pressure on the dialysis filter that causes fluid to move from the blood stream to the dialysate side of the filter and be disposed of. Generally speaking two-four liters of patient fluid is removed from the patient during a four-hour treatment. Fluid removal is the component of the dialysis treatment that can lead to episodes of low blood pressure in the patient. This occurs when fluid is being “pulled” faster than the patient’s vasculature can tolerate. The ability to tolerate fluid removal varies greatly from patient to patient. Blood pressure and other vitals are watched and recorded at least every 15 minutes during treatment. Fluid removal also requires work from the body to shift that fluid. Patients are often very tired after treatment due to this.
And there you have it! I hope this sheds a little light on the often-mysterious ways of dialysis and gives you more knowledge to better care for you patients. I also hope it makes you more aware of what your kidneys do for you! Uncontrolled diabetes and high blood pressure are the top causes of kidney failure. Love, protect, and care for your kidneys!