Treating kidney failure by dialysis

Water and waste

The consequences of kidney damage or disease

The kidney is responsible for the removal of waste products from the blood. Damage from accidents or disease can lead to a build-up of poisonous wastes in the body. Humans can survive with one kidney, but for people who suffer from total kidney failure this would be fatal if not treated. Treatment is available for kidney failure and can be by organ transplant or by using kidney dialysis.

In this procedure, patients are connected to a dialysis machine which acts as an artificial kidney to remove most of the urea and restore/maintain the water and ion balance of the blood.

Patients with kidney failure can be kept alive by using kidney dialysis until a transplant becomes available, but they have several disadvantages:

  • they are expensive
  • the patient must have his or her blood connected to the machine for several hours every week
  • patients must follow a very rigid diet to avoid complications
  • they only work for a limited time for a patient

How dialysis works

Diagram of a dialysis machineHow dialysis works

Unfiltered blood that is high in urea is taken from a blood vessel in the arm, mixed with blood thinners or an anti-coagulant to prevent clotting, and pumped into the dialysis machine. Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a concentration gradient exists.

Dialysis fluid contains:

  • a glucose concentration similar to a normal level in the blood
  • a concentration of ions similar to that found in normal blood plasma
  • no urea

As the dialysis fluid has no urea in it, there is a large concentration gradient - meaning that urea moves across the partially permeable membrane, from the blood to the dialysis fluid, by diffusion. This is very important as it is essential that urea is removed from the patients' blood.

As the dialysis fluid contains a glucose concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists. This is very important as the patients' need to retain glucose for respiration.

And, as the dialysis fluid contains an ion concentration similar to the ideal blood plasma concentration, movement of ions across the membrane only occurs where there is an imbalance.

  • If the patient's blood is too low in ions, they will diffuse from the dialysis fluid into the blood, restoring the ideal level in the blood.
  • If the patient's blood is too high in ions, the excess ions will diffuse from the blood to the dialysis fluid.

Advantages of dialysis

Kidney dialysis allows a person with kidney failure to maintain their health.

The overall effect of this is that the blood leaving the machine and returning into the patient's arm will have:

  • greatly reduced levels of urea – it is 'cleaned blood'
  • no overall change in blood glucose levels
  • the correct water and ion balance maintained or restored (with only excess ions removed)

Disadvantages of dialysis

Kidney dialysis requires highly specialised and expensive machinery. The patient must be connected to this machinery 2-3 times a week for periods (on average) of between 4-6 hours at a time. This is time consuming and restrictive, as this mainly happens in hospital.

As the filtration only works when they are connected, kidney patients must monitor their diet carefully in between dialysis sessions. They need to avoid eating foods with a high salt content or a high protein content as excess amino acids are broken down into urea. This again can be difficult to control and monitor, but will help maintain the health of the patient.

Finally, dialysis will only work for a limited amount of time before a transplant is needed, and sadly many patients will die before a suitable one is found.