Dialysis is a renal replacement therapy, a procedure during which the wastes and water are filtered and the blood is purified, namely, the kidney function is replaced by the machine. Dialysis has prolonged the lives of thousands and millions of people worldwide. There are two types of dialysis: hemodialysis and peritoneal dialysis. Hemodialysis is more common, although peritoneal dialysis is considered more convenient.
Renal replacement therapy is necessary for people with acute kidney injury or end-stage chronic kidney disease when their own kidneys fail to perform their main function – filter blood and excrete waste products and excessive amounts of water with urine and thus maintain the blood composition. Dialysis is the only treatment option except for kidney transplantation and should be considered when glomerular filtration rate is of less than 10 ml/min/1.73 m2. Dialysis may also be used to treat poisoning or overdose to eliminate the drugs from the blood.
- Low blood pH (metabolic acidosis);
- Severe hyperkalemia (high blood potassium levels) resistant to drugs;
- Fluid overload;
- Acute poisoning (with salicylic acid, ethanol, methanol, barbiturates, lithium, isopropanol, magnesium-containing laxatives, and ethylene glycol);
- Serositis (pericarditis, pleuritis) or encephalopathy due to uremia;
- Chronic kidney disease with GFR of less than 10-15 ml/min/1.73 m2;
Principles and mechanism
The procedure of dialysis is based on the diffusion of solutes and fluid filtration across a semi-permeable membrane – on one side of the membranes there is blood flowing, on the other side – a special solution known as the dialysate. Thus, the solutes move from the blood where their concentration is higher to the dialysate with low concentrations of the dissolved substances. A semi-permeable membrane ensures that larger substances such as red blood cells and proteins do not pass through the barrier and remain in the blood. In some way this process resembles the ultrafiltarion which naturally occurs in the kidneys.
During hemodialysis, the blood is filtered extracorporally – outside of the body. The blood is delivered to the machine which has a semi-permeable membrane via the vascular access – an intravenous catheter, an intravenous fistula or a synthetic graft may be used. When the blood passes through the machine, dialysis occurs and filtered, purified blood returns to the body.
- Conventional hemodialysis
One procedure lasts for about 3-5 hours (average 4 hours). Usually, a person needs dialysis three times a week.
- Daily hemodialysis
Daily hemodialysis is performed by a person at home for 2 hours 6 days a week.
- Nocturnal hemodialysis
Nocturnal hemodialysis is much more convenient for a person as it happens during the night when a person is sleeping. The procedure lasts from 6 to 10 hours and is performed from 3 to 6 times a week.
In the case of peritoneal dialysis, the dialysate is run by the catheter into the peritoneal cavity where the lining of the abdomen – peritoneum acts as the semi-permeable membrane and filter for the blood. After some time the dialysate with solutes is drained from the abdomen.
- Continuous ambulatory peritoneal dialysis
This type of peritoneal dialysis does not require any machine. A person can insert the dialysate by himself/herself and 4-6 hours later remove it and replace it with a fresh solution.
- Continuous cyclic peritoneal dialysis
A machine automatically drains and replaces the fluid during the night. The whole procedure lasts from 10 to 12 hours.
- Intermittent peritoneal dialysis
This type of peritoneal dialysis is performed in the hospital several times a week and lasts from 12 to 24 hours.
Despite the fact that peritoneal dialysis is less efficient than hemodialysis, peritoneal dialysis is preferred in infants and children, taking into consideration that vascular access in kids may be difficult and peritoneal dialysis is much more flexible and comfortable for young and active people as it is performed outside of a clinic.
Risks associated with dialysis
- Cramps, nausea, vomiting, a headache may bother some people who are on dialysis. These symptoms may vary and depend on the dialysate and the type of machine;
- Those who receive dialysis are always at risk of developing hypotension. Some medications may be given to maintain blood pressure;
- Hemodialysis involves blood exposure, therefore, there is always a risk of acquiring blood-borne infectious diseases such as hepatitis B and C. All people who undergo dialysis should have the hepatitis B vaccination. There were also few cases of HIV infection reported;
- Peritonitis may develop as a complication of peritoneal dialysis when the infection gets into the abdominal cavity and the peritoneum becomes inflamed. Peritonitis disrupts the dialysis.