Dialysis

Definition

Dialysis is a process whereby solute composition of a solution (blood) is altered by exposing to it to a second solution (dialysate) through a semipermeable membrane ( peritoneum, dialyzer membrane).

Need for dialysis

When kidneys fail, the waste products and excess water, that are supposed to be thrown out by a normally functioning kidney, are not thrown out and hence an artificial means to do this is required.

A query that is often asked is, why not give more pills, so that “kidney functions are taken care of” and a dialysis avoided. To understand why pills may not be effective at an advanced stage, one has to understand what functions kidneys carry out. Click here for a brief overview.

Having understood kidney functions, one would realize that, after a certain stage, the excretory functions of the kidney ‘go down’ to such an extent, that no amount of medicines or any ‘magic pill’, would be able to replace those kidney functions. The toxins accumulate in the blood to dangerous levels and only artificial means of purification of blood will be able to remove these toxins. This is exactly what dialysis does to a patient !

Indications for starting Dialysis

As an elective decision, dialysis is initiated in one of the following situations:

Situations that demand urgent initiation of dialysis include:

  • Severe Breathlessness due to fluid congestion in lungs
  • Very high levels of potassium
  • Bleeding tendencies
  • Pericarditis ( inflammation of covering around heart)
  • Encephalopathy ( clouding of brain due to high levels of toxins)

Getting Ready for Dialysis

Since initiation of dialysis is commonly elective, it is prudent to be prepared for the situation. Preparation includes

  • getting educated for dialysis options
  • deciding on the modality of dialysis ( hemodialysis vs. peritoneal dialysis)
  • getting a small surgery called AV fistula construction
  • Getting vaccinated against certain infections

“Renal Replacement Therapy (RRT)” is a term that encompasses various options that can partly or completely ‘replace’ ‘renal’ (kidney) functions. The options include Hemodialysis, Peritoneal dialysis and kidney transplantation.

Arterio venous fistula ( AV Fistula)

AVFOne should get this small surgery done once the estimated GFR drops below 30 mL/min, i.e. at the beginning of stage IV. Before one understands how this surgery is done, let us briefly dwell on why this surgery is needed.

Blood flows in the arteries at high pressures and in the veins at low pressures. Commonly, it is the veins that are punctured for collection of blood samples etc.

Similarly, it is the veins that are punctured for doing hemodialysis. However, the veins as they are in a normal person, are too thin and fragile to be used for this purpose.

Besides, a high velocity blood flow to the tune of 300 to 500 mL/min is required for effective dialysis. Such a flow and pressure is present in the arteries. However, it is too unsafe to puncture arteries on a regular basis for obvious reasons !

Therefore, the artery and the vein are surgically joined together, so that the pressure and high velocity flows of the artery are transmitted to the vein. The vein now swells up and has big enough lumen for a big dialysis needle and blood flowing at the required pressure and velocity.

The commonest site for this surgery is at the wrist, followed by the elbow. Left wrist ( Right in case of left-handers) is preferred, but the other side can be used if surgery fails on one side.

Veins from an AV Fistula are ready for use only after a minimum of 4 weeks.

Next: Hemodialysis

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