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What is dialysis?

Flow Diagram of Dialysis
Dialysis is the process whereby waste products and excess water is removed from the body by circulating blood through an artificial filter and returned to the body.

What is the physiological basis for Hemodialysis?

Dialysis is the process whereby the solute composition of a solution A for instance is altered by exposing it to second solution B through a semi permeable membrane.

Water molecules and small molecular weight solutes in the two solution can pass through the membrane course and intermingle, but large molecules like proteins cannot pass through the semi permeable barrier. Diffusion and ultra filtration are the two mechanism by which dialysis occurs. Diffusion is the process of movement of solutes from a higher to a lower concentration across a semi–permeable membrane.

The rate of diffusion depends on:
  1. Concentration gradient.
  2. Size of the molecule.
  3. Membrane properties such as thickness and pore size.
Ultra filtration is the second mechanism of solute transport. The water molecule are extremely small and can pass through all semi permeable membrane. Ultra filtration occurs when water is driven by hydrostatic or osmotic force is across the membrane. Along with water, solutes are dragged across and process is called solvent drag.

Describe the dialysis filter.

Dialysis Filter Dialysis Filter
Hemodialysis apparatus consists of the dialyser. It consists of a tube with four parts The tube contains the membrane in the form of hollow fibers through which blood passes.
Filter Diagram
The fibers can be of different types:
Natural Fibers
Made from processed cotton like cellulose or cellulose acetate.
Polyacrylnitrile, polysulfone, polymethylmethacrylate etc.

Which membranes are better for Hemodialysis?

Synthetic membranes have been designed to achieve more efficient dialysis and also have lesser incidence of adverse reaction.

Can dialysis membranes be reused?

Yes. But only in the same patient. Reuse is a safe and effective practice that is used worldwide. The average number of times the dialyser is reused varies although many dialysis units average about anywhere between 5 to 10 reuses per dialyser. After use the dialyser should be chemically disinfected.

What agents are used to clean the dialyser?

The dialyser is cleaned either with bleach (sodium hydrochloride) or hydrogen peroxide. Once cleaned the dialyser must undergo a physical or chemical process that renders all living organism inactive. Germicides which are used are formaldehyde, gluteraldehyde, mixture of per acetic acid and hydrochloric acid acetic acid (Renalin).

What is the dialysis solution usually composed of?

Dialysis water is usually obtained from the municipal supply. This water is purified and additional electrolytes are added to achieve a composition of standard dialysis solution. The solution typically contains sodium, potassium, calcium, magnesium chloride, bicarbonate or acetate. The electrolytes can be pre–mixed and pumped through a central delivery system or the electrolytes are added individually to each machine.

How much water is used during each dialysis treatment?

Patients are exposed to 120 liters of water during each dialysis treatment.

Is it necessary to purify water before using it for dialysis?

Yes. It is necessary to purify the water before it is used for dialysis. Important contaminant of the water include aluminum, copper, Chloramine etc. Chloramine is a chemical frequently added to municipal water supplies to control bacterial contaminations.

Is it necessary for water to be free of bacteria?

Water for dialysis need not be completely sterile because the dialyser membrane is normally an effective barrier to both bacterial and endotoxins. However the bacterial counts should be kept below 200 colonies /ml in the water by periodically disinfecting the water treatment system.

What are the different methods of purifying water for dialysis?

Methods of purifying water for dialysis:
  1. The Reverse Osmosis (RO) process pushes water through the semi permeable membrane with pores small enough to restrict passage of even small molecular weights solutes. Reverse osmosis removes more than 90% of the impurities and frequently will produce water sufficiently pure for dialysis.
  2. Ion exchange resins remove all charged irons from water supply.
  3. Some dialysis machine incorporate an optional hollow fiber ultra filter in the dialysis solution line to remove bacteria and endotoxins.

How can one be sure of the concentration of the dialysis solution?

Blood Flow thro Catheter
To ensure that the dialysis solution is neither too dilute nor too concentrated the conductivity of the dialysis solution is checked by the machine itself prior to starting the dialysis statement. In addition, the dialysis solution temperature is also checked by the machine.

How is the blood taken out of the body for dialysis?

The process is enabled by gaining access into the blood circulation either by catheters, or by constructing a fistula or a graft. This is called as obtaining vascular access.

Where are the catheters usually inserted?

The catheters are usually inserted in the internal jugular vein in the neck or in the subclavian vein (located below the collar bone).

How long can the catheters be used?

Usually they can be used for a few weeks (max. 4 weeks) which gives some time to construct a more permanent access. The silicone catheters (Permacath) can be used for much longer periods, from 6–12 months.

Does the catheter require any general anesthesia?

The insertion of the catheter does not require any general anesthesia.

Are there any complications associated with the procedure?

Bleeding, injury to the lung or nerves can occur. These complications in experienced hands are rare. The catheters can get infected in which case they must be removed.

What is a fistula?

Fistula showing needle placement
The fistula is an anastomosis (joining) of an artery to a vein, which makes the vein bigger and thicker so that it can be used to insert needles for dialysis. The fistula is usually created in the non dominant arm to facilitate self dialysis and limit the consequence of any functional disability if it should occur.

How long can a fistula be used?

As long as it works. The AV fistula is the safest and longest lasting permanent access.

When should a fistula be placed?

The AV fistula ideally should be placed 2 to 6 months prior to initiation of hemodialysis. It is extremely important during the evaluation of the patient of chronic renal failure to preserve the arm which means that no needles should be placed into the vein at any time for drawing blood or giving medications.

Once the fistula is created how soon can it be used?

The fistula once it has been constructed should be given time to mature. The time period usually varies from 4 to 8 weeks. 4 weeks being usually the minimum time required. The perforation is with needles of either 15 or 16 gauge.

Are there any complications of fistula?

  1. Bleeding from fistula.
  2. Infection of the fistula is rare.
  3. Clotting of fistula is rare. More common in diabetics.
  4. Swelling of the hand.

What is a graft?

When a fistula cannot be created a synthetic material tube is used to connect the artery and vein. The graft usually are more prone to infections and clotting.

Some patients complain of giddiness after dialysis. What is it due to?

The giddiness is usually due to hypotension or low blood pressure after dialysis. Hypotension after dialysis is seen in 20–30% of patients. It is more commonly seen when the dialysis solution contains acetate. In addition, if the dialysis is too warm it can cause low blood pressure. It is important to remember that blood pressure lowering medicines can contribute to it. In some patients it may be due to underlying heart disease.

Is there any remedy for this giddiness?

It is usually treated by giving some saline and decreasing the amount of fluid removal and reassessing the weight of the patient in between dialysis.

What is the cause of nausea and vomiting after dialysis?

Nausea and vomiting, seen in about 5–15% of patients, is usually related to hypotensive episodes. May be seen when patient has skipped dialysis treatments and have high urea levels.

What are some of the other complications seen during dialysis?

Headache, chest pain, back pain, itching and fever may be seen during dialysis.

Can infections be transmitted by dialysis?

Yes. If adequate precautions and proper screening of patients for viruses are not taken. Patients should be screened for Hepatitis B, Hepatitis C and HIV. Dialysis nurses should wear gloves while handling patients or dialysis apparatus, appropriate methods of disinfecting the dialysis equipment should be done.

If a patient is Hepatitis B or HIV positive can that patient undergo dialysis?

If the patient is positive for HIV or Hepatitis B usually machines dedicated for these patients are used in order to minimize these transmission of these diseases.