Artificial kidneys; Hemodialysis; Peritoneal dialysis; Dialysis;
Dialysis is a method of removing toxic substances (impurities or wastes) from the blood when the kidneys are unable to do so. Dialysis is most frequently used for patients who have kidney failure, but may also be used to quickly remove drugs or poisons in acute situations. This technique can be life saving in people with acute or chronic kidney failure.
How the test is performed
Dialysis can be performed using several different methods.
Peritoneal dialysis works by using the body’s peritoneal membrane, which is inside the abdomen, as a semi-permeable membrane. Special solutions that help remove toxins are infused in, remain in the abdomen for a time, and then are drained out. This form of dialysis can be performed at home, but must be done on a continuous, everyday basis.
Hemodialysis works by circulating the blood through special filters. The blood flows across a semi-permeable membrane (the dialyzer or filter), along with solutions that help remove toxins. Hemodialysis requires a blood flow of 400 to 500 milliliters per minute (ml/min). A normal IV tube in an arm or leg will not support that volume of blood flow. Special forms of accessing your circulatory system are therefore required.
The access can be temporary or permanent. Temporary access takes the form of dialysis catheters. These are large-bore catheters placed in large veins that can support acceptable blood flows. Most catheters are used in emergency situations, for short periods of time. However, catheters called tunneled catheters can be used for prolonged periods of time, often weeks to months.
Permanent access is created by surgically joining an artery to a vein. This allows the vein to receive blood at high pressure, leading to thickening of the vein’s wall. Now this “arterialized vein” can sustain repeated puncture and also provides excellent blood flow rates. The connection between an artery and a vein can be made using blood vessels (an arteriovenous fistula, or AVF) or a synthetic bridge (arteriovenous graft, or AVG).
The AVF is more desirable, because rates of infection are very low and it is quite durable. It may take many months for the AVF to mature, so careful planning is required.
The AVG can be accessed a few weeks after creation. It provides good flows but has a high complication rate. It should be attempted only if the AVF is not feasible.
Blood is diverted from the access to a dialysis machine. Here, the blood flows counter-current to a special solution called the dialysate. The chemical imbalances and impurities of the blood are corrected and the blood is then returned to the body. Typically, most patients undergo hemodialysis for three sessions every week. Each session lasts 3-4 hours.
How to prepare for the test
It is important to adhere to the diet and medicines prescribed by the dialysis staff and your nephrologist.
Just before your health care provider begins the hemodialysis procedure, the following assessments will be made:
- Blood pressure
- Heart rate
- Breathing rate
- Chest assessment
- Examination of venous access
How the test will feel
Since dialysis takes several hours, it may become tedious. With children, it is especially important to have games, something to read, or other distractions.
Why the test is performed
This procedure removes contaminants from the blood that could, and eventually would, result in death if the kidney is not functioning.
The kidneys function as filters for the blood, removing products of amino acid breakdown. More than that, they serve to reclaim and regulate body water, maintain electrolyte balance, and ensure that the blood pH remains between 7.35 and 7.45. Without the function of the kidney, life is not possible.
Dialysis serves to replace some of the functions of the kidney. Since dialysis is not a constant ongoing process, it cannot serve as a constant monitor as do normal functioning kidneys, but it can eliminate waste products and restore electrolyte and pH levels on an as-needed basis.
What the risks are
The immediate risks include:
- Electrolyte imbalance
- Bleeding from the access site.
- Nausea and vomiting
- Dialyzer reaction
- Air embolism
- Cardiac ischemia or arrhythmia
Long-term risks include:
- Dialysis-associated amyloidosis
- Dialysis dementia (uncommon now that aluminium levels are closely monitored)
- Cardiovascular disease
- Autonomic Neuropathy
- Blood loss leading to iron deficiency (requiring regular iron replacement)
Take the following precautions if you using an AVF or AVG:
- When you sleep, avoid placing pressure on an arm with the access.
- Do not allow anyone to take a blood pressure reading on an arm with the access.
- Observe the access site after dialysis, watching for swelling, infection, or bleeding.
- Do not wear tight clothing around the access site.
- Routinely check the access site for the “thrill”, indicating that the AV site is still functioning. (If the thrill disappears, call your health care provider immediately.)
- Do not use creams or lotions over the access site.
If you have an external access, take additional precautions:
- Avoid physical activity that might dislodge the access, which could result in excessive bleeding and air entering the circulatory system. (If this happens, call 911 and get immediate medical attention.)
- If the color in the tubes changes color and becomes a dark red, call your health care provider immediately. (The blood may be clotting.)
- Call your health care provider immediately if your have a fever or other sign of infection.
by Sharon M. Smith, M.D.