The kidneys are one of the most important organs present in our body, as they are responsible for the continuous filtration of our blood from unnecessary and potentially harmful substances, which are subsequently excreted in the urine. Blood passes from the kidneys through the renal artery. This large blood vessel branches into gradually smaller blood vessels until the blood reaches the kidneys, where it is filtered by tiny blood vessels called glomeruli.
This process takes place several times a day and it is estimated that every day, the kidneys filter about 150 litres of blood. The useful substances are returned to the blood, and about 1 to 2 litres of fluids are excreted in the urine.
In particular, the kidneys eliminate waste substances and excess fluids that accumulate in the body, maintaining a healthy balance of water, acid-base balance (pH) and electrolytes – such as sodium, calcium, phosphorus, and potassium – in the blood. Without this balance, the heart, nerves, muscles, and many other tissues in the body would not be able to function properly and our overall health would be at very serious risk.
Generally there are two methods of replacing kidney function: hemodialysis and peritoneal dialysis, which uses a network of capillaries in the abdomen (peritoneal cavity) as a “filter” in order to filter the blood instead of a dialysis machine. The choice of the appropriate method, however, depends on the patient’s overall health as well as on the instructions of the patient’s attending physician.
Hemodialysis is a revolutionary and life-saving method of replacing kidney function with the dialysis machine, which substitutes a very vital process of the body when the body itself is unable to do so. Hemodialysis is performed using the dialysis machine, filter, and a special fluid solution.
When functional, the kidneys filter the blood, removing harmful substances and excess fluids from food and liquids consumed during the day and converting these substances into urine to be excreted from the body. However, in cases where the patient’s kidneys or kidney (in cases where there is a single kidney) are very limited in function due to a serious kidney condition (failure), then hemodialysis is required in order to artificially carry out the process that the kidneys would normally perform.
If the kidneys are not working properly, for example if you suffer from advanced chronic kidney disease (kidney failure) – then the blood may not be filtered properly, and this can result in harmful substances and fluids building up in your blood to levels that are dangerous for your body. In fact, if kidney failure is left untreated for long enough, it can bring about a range of unpleasant symptoms – constant nausea, and vomiting, fatigue, edema (swelling), skin lesions – and can ultimately prove fatal.
The aim of hemodialysis is therefore to substitute for poor kidney function and filter unwanted substances and fluids from the blood, preventing your health from deteriorating. You will usually start dialysis when you first experience symptoms or if laboratory tests show toxic levels of waste products in your blood. When to start hemodialysis depends on many factors, including:
Your doctor will tell you when you should start treatment, as well as what type of hemodialysis or renal replacement therapy may be ideal for your individual case. Dialysis is the most common treatment for kidney failure patients worldwide. It is estimated that more than 1 million patients around the world are kept alive with hemodialysis and if it were not for this method they would have ended up with kidney failure within 2 weeks.
As mentioned above, there are two different methods of renal function replacement, even though they have a common goal and effect. The procedure to achieve blood dialysis differs slightly and depends on the overall health and condition of the patient.
Hemodialysis is the most common type of kidney function replacement and the one that most people are familiar with. During the procedure, an arteriovenous communication (fistula) is established between the artery and vein, either by placing a dialysis graft (AVG) or by placing a hemodialysis catheter (CVC) in a major vein of the body (jugular, subclavian, femoral).
The above vascular accesses allow connection via biocompatible synthetic tubes (“hemodialysis lines”) to the dialysis machine at two points, “artery” and “vein”. The blood is passed along the “artery” to the machine which has a special filter to purify it and then returns filtered through the “vein”.
In hemodialysis centers this procedure is usually carried out 3 days a week, and each session lasts about 4 hours.
Peritoneal dialysis uses the peritoneum (the inner lining of your abdomen) as a filter. Like the kidneys, the peritoneum contains thousands of tiny blood vessels, making it a useful filtering device. Before treatment begins, an incision is usually made laparoscopically near your navel (belly button) and a thin tube called a catheter is inserted through the incision into your abdomen (the peritoneal cavity) and stays there permanently. You will use the catheter to transfer the peritoneal dialysis solution from a bag located near your abdomen.
This special liquid is a medicated solution that contains an osmotic agent (dextrose or other) and other additives to absorb harmful substances and extra fluids from your body. The fluid is pumped into the peritoneal cavity through the catheter and as the blood passes through the blood vessels there, it is cleansed of harmful substances and excess fluids. The used fluid is then drained into the outflow bag and a few hours later replaced with fresh fluid, a process called “exchange”.
The fluid exchange takes about 30 to 40 minutes and usually needs to be repeated about 4 times a day. If you prefer and provided it is possible, this process can also be done with a machine during the night time, while you sleep.
To confirm that the procedure is effective, blood tests are performed before and after the dialysis in order to measure the amount of urea in the blood. The two key indicators that doctors emphasize to measure the effectiveness of dialysis are Kt/V and URR. Kt/V is the most accurate indicator of hemodialysis efficacy and is essentially a comparison of the amount of fluid “cleared” of urea at each session against the amount of fluids in the body, and takes into account other factors, such as weight loss during dialysis. The Kt/V ratio should be within 1,2.
URR is the calculation of the Urea Reduction Ratio and in order to calculate it, blood is drawn before and after dialysis and then the urea percentages in the two results are compared. The desired urea reduction rate after dialysis should be in the range of 65%. If the results of these tests show that the dialysis is not sufficient, then the doctor should check that everything is working properly with the machine and filter, review the patient’s treatment time or investigate any problems that may have arisen after the arteriovenous communication was placed.
In addition to the above clear indicators, the quality of the dialysis is also seen secondarily in the change in the patient’s blood pressure, but also in the results of laboratory tests that show us the potassium, creatinine, phosphorus, and albumin in the blood. If all the above mentioned element values are good, then hemodialysis works effectively.
Most people on hemodialysis generally have a good quality of life. In particular, provided your general health allows it, you will be able to:
Most people can remain on hemodialysis treatment for many years, although such treatment can only partially compensate for the loss of kidney function.
Having kidneys that do not function properly can put a significant strain on the body. This means that it is a temporary solution and that people with kidney failure will eventually have to undergo a kidney transplant. Age and comorbidities play an important role in survival, e.g. a person who starts dialysis at 25 with no comorbidities is expected to live 20 years or more, whereas adults over 75 with comorbidities may have a life expectancy of around 3 years.
All things considered, medical technology is constantly evolving and survival rates for people on dialysis have improved over the last decade and are expected to continue to improve in the future.