What is dialysis?
Dialysis is a scientific term for the movement of substances across a membrane by a process called diffusion. If a great deal of a substance is in one place, some of that substance will tend to move out to where the substance is not present. If we gently add a teaspoon of mile to a cup of tea, the milk will diffuse out with time to all areas of the cup.
In dialysis, we add a barrier or membrane between two liquids. On one side of the membrane is liquid with a high concentration of a substance. On the other side of the membrane is a liquid without that substance. If the membrane has small holes or pores, the substance on one side of the membrane will travel or diffuse across the membrane to the other side until the amount on each side is equal. Dialysis membrane are said to be semi-permeable. They allow some small substances to pass through while large substances cannot fit through the holes.
In medical dialysis treatments, one liquid is a patient’s blood. One the other side of the semi-permeable membrane is another liquid called dialysate. Substances in the blood, if they are small enough, will move through the membrane into the dialysate. If the dialysate is then discarded and new dialysate is added, more of the substance can be removed. Removal of substances depends on the size of the substance, the electrical charge of the substance, and also the difference in the amount of the substance on one side of the membrane compared to the other.
If we change the amount of substances in the dialysate, we can remove more or less of a substance. We can even add more of a substance to the dialysate than is in the blood. In this instance, the substance will move from the dialysate into the patient’s blood. This can be done with substances that can pass through the semi-permeable membrane. If we put a high concentration of the sugar glucose in the dialysate, it will move or diffuse across the membrane into the blood and raise the level of glucose in the blood.
Dialysis sounds complicated, but it all boils down to the process of diffusion. Large things such as red blood cells, large proteins, and other large substances are trapped on one side of the membrane in the blood. Small things including slats such as sodium and potassium, water, and small proteins can freely move across the membrane from areas where large amount are present to areas where they are not present.
How often and for how long must a person dialyse?
Most people dialyse for between three and five hours, two or three times a week. The length of time depends on how much waste is in your blood, and how big you are. The amount of waste (creatinine and urea) you produce depends on the amount of muscle that you have, as well as the amount of protein in your diet.
Indications for dialysis
- Acute renal failure (ARF). Indications of dialysis in ARF are hyperkalaemia, acidosis, encephalopathy, myoclonus, seizures and severe azotaemia and prolonged ARF.
- Chronic renal failure: Short term indications are the same as those for acute renal failure. In patients with end stage renal failure who are unfit for renal trans-plantation, dialysis is necessary to sustain life. Occasionally, dialysis is needed for graft dysfunction following renal trans-plantation.
- Poisoning: Barbiturates, ethylene glycol, lithium, and methyl alcohol are some of the important poisons removed effectively by dialysis.
In addition, hypercalcaemia, hyperuricaemia, hypothermia and Reye’s syndrome are treated with variable success by dialytic support.
Dialysis- Related Complications
- Hypotension: hypotension can be minimized with an accurate assessment of target weight, judicious use of antihypertensive medications, sodium restriction, increasing treatment duration, and careful choice of dialysis modality, e. g., hemo-diafiltration in the cardiovascularly unstable patient.
- Anaphylaxis: Anaphylaxis can occur by complement activation with the use of a bio-incompatible membrane and normally occurs within the first 20 minutes of treatment.
- Catheter related-sepsis: Catheter related sepsis requires aggressive antibiotic treatment and catheter removal. If temporary catheters are being used, once weekly catheter changes are recommended.
- Pyrogenic reactions: Uncommon if ultrapure water is used.
- Dialysis equilibrium syndrome: Rare in established dialysis patients. It can occur from overaggressive dialysis causing a rapid reduction in serum osmolarlity and resulting in cerebral edema.
- Modern fail: safe machines minimize other complications such as air embolism and accidental circuit disconnection.
Lawrence E. Stam- 100 Question & Answers about Kidney Dialysis; 2009; 20
Andy Stein, Janet Wild- Kidney Dialysis and transplants: the ‘at your fingertips’ guide; 2002; 120
Sainani- Medical Therapeutics; 1998; 379
Sara Blakeley- Renal Failure and Replacement Therapies; 2007; 67