WHAT IS DIALYSIS?

• A process for removing waste and excess water from the blood.

• Provides an artificial replacement for lost renal function in patients with renal failure.

• Dialysis can also be used for those with acute disturbance in kidney function and stage 5/end stage renal failure (Stage 5/end stage renal failure may develop over months/years and is not usually reversible)

• Dialysis used until a renal transplant can be performed (long term if treatment is inappropriate)

TYPES OF DIALYSIS

• There are 3 primary & 2 secondary types of dialysis:

     O Peritoneal dialysis (primary)

     O Haemodialysis (primary)

     O Haemofiltration (primary)

     O Haemodiafiltration (secondary)

     O Intestinal dialysis (secondary)

PERITONEAL DIALYSIS

INTRODUCTION

• Simple to perform

• Requires less complicated equipment than haemodialysis and is easier at home.

• It is useful in; children, the elderly, those with cardiovascular disease.

• PD fluid is introduced into the peritoneal cavity via a Tenchkoff catheter

• Uraemic solutes diffuse into it across the peritoneal membrane.

• Ultrafiltration is achieved by adding osmotic agents, eg glucose to the dialysis fluid.

• The dialysate contains

     o Sodium

     o Chloride

     o Lactate/bicarbonate

     o And a high percentage of glucose (to ensure hyperosmolarity)

PERITONEAL DIALYSIS



(ihacares.com) This image depicts the process of peritoneal dialysis, or more specifically CAPD (Continuous ambulatory peritoneal dialysis ). The dialysis solution (dialysate) is left in your abdomen for 3 to 5 hours. This is called the dwell time. After the dwell time, the dialysate is drained out through the catheter. Filling and emptying your abdomen with dialysate is called an exchange.

The last process is Drainage

(Wikipedia: Peritoneal Dialysis). This image portrays the steps carried out in peritoneal dialysis. The step named "Diffusion" indicates the period at which the dialysate is left in the abdomen (dwell time), allowing for waste products to enter the abdomen.

PROBLEMS WITH PD

• Peritonitis

     o 60% Staphylococci

     o 20% Gram -ve organisms

     o <5% fungi

• Exit-site infection

• Catheter malfunction

• Loss of membrane function

• Obesity due to glucose in dialysis fluid

• Hernias

• Back pain

CONTINUOUS AMBULATORY PERITONEAL DIALYSIS (CAPD)

• Uses the smallest daily volume of dialysate fluid to prevent uraemia.

• Dialysis occurs through regular exchanges throughout the day.

• ~4 fillings of PD fluid which remain in the peritoneal cavity for 4-8 hours at a time.

     o For maximum exchange of waste products.

     o The fluid is then removed and replaced with fresh fluid.

AUTOMATED PERITONEAL DIALYSIS

• Dialysis takes place at night whilst the patient is asleep using a cycler machine.

• The process cycles between 3 and 10 fillings of fluid per night.

HAEMODIALYSIS (HD)

INTRODUCTION

• Blood flows on one side of a semi-permeable membrane.

     o Dialysis fluid flows in the opposite direction on the other side.

• Solute transfer occurs by diffusion.

• Ultrafiltration is the removal of excess fluid by creating a negative transmembrane pressure.

     o This gradient causes water & dissolved solutes to move from blood to dialysate.

     o Allows the removal of several litres of excess fluid during a typical 3- to 5-hour treatment.

HOW IS HD CARRIED OUT?

• Before HD can be carried out, patients need an access to their blood supply.

• There are 3 different ways:

     o IV catheter

          § Inserted into a central vein 

          § Blood flow slower than other options.

          § Stenosis and infection are risks.

          § Used for urgent dialysis

     o Arteriovenous (AV) fistula

          § Made to prepare for dialysis.

          § Takes weeks to be able to be used

          § Artery and vein joined.

          § Less chance of infection

          § Increased risk of aneurysm 

     o Arteriovenous (AV) graft

          § Artificial vessel linking artery & vein.

          § Just like a fistula

          § Increased chance of infection



(Wkipedia: Cimino fistula). The above image is  a type of AV fistula known as a Cimino fistula. It is a type of vascular access for haemodialysis. It is a surgically created connection between an artery and a vein. This diagram shows the connection between the brachial artery and the cephalic vein.

HD PROCESS



(Scanned in from OCR Biology A2 textbook). This image depicts the process of haemodialysis. Blood from the vein is passed over a dialysis membrane in an external machine. Heparin is added to prevent clotting of the blood externally, and all bubbles are removed before the blood is returned to the body.

PROBLEMS WITH HD

• Disequilibration syndrome

• Arrhythmias

• Time consuming

• Access:

     o Fistula (Thrombosis, stenosis, aneurysm, steal syndrome, ischaemia

     o Temporary line (Infection, blockage)

HAEMOFILTRATION

  • Hemofiltration is a type of renal replacement therapy.
  • It is usually used in an intensive care unit following acute kidney injury (AKI) to remove waste products from the body until the functions of the kidney can be restored.
  • Hemofiltration is similar to haemodialysis, but no dialysis solution is used.
  • Instead the blood is passed to a semipermeable membrane where a positive hydrostatic pressure pushes water across.
  • As the water passes through the membrane large and small waste solutes are also drawn through.
  • Haemofiltration, unlike haemodialysis, provides solute clearance solely by convection and not diffusion, as solutes are dragged down a pressure gradient with water. 
  • Replacement fluid must be extremely pure as fluid is administered directly into the patient.


(http://renalbiomarkers.com/acute_kidney_injury.asp#treatment). This image clearly shows the difference between haemodialysis and haemofiltration. 

  • A illustrates haemodialysis and shows solutes being driven across a semipermeable membrane by diffusion.
  • B illustrates haemofiltration and shows fluid being driven across the semipermeable membrane by convection. The solute-containing plasma water is removed from the body and replaced with clean fluid.

HAEMODIAFILTRATION

  • Haemodiafiltration is a combination of haemodialysis and haemofiltration. 

- Haemodialysis is used to diffuse molecular solutes that are relatively small in weight and size.

- Haemofiltration is use to remove bigger molecular waste products and substances.

  • Hemodiafiltration can therefore be used to dispose, at a slower rate, all sizes of toxic molecules.

INTESTINAL DIALYSIS

  • Intestinal dialysis is a relatively new dialysis technology
  • Patients consume large quantities of soluble fibre (such as acacia fibre), which is consumed by colonic bacteria.
  • They then use the bacterial growth to help filter unwanted compounds and to keep them from being absorbed into the circulation.

GENERAL COMPLICATIONS OF DIALYSIS

• Cardiovascular disease

     o IHD

     o Heart failure

     o Stroke

     o Much more common in dialysis patients & a major cause of mortality.

     o Hypertension persists in 25-30% of patients on haemodialysis.

• Anaemia common and treated with erythropoietin

• Bleeding tendency is due to platelet dysfunction.

• Acute bleeding is treated with desmopressin and transfusion, as necessary.

• Renal bone disease is treated with dietary modification

     o Alfacalcidol

     o Ca2+ supplements

     o Phosphate binders

• Infection may be due to non-sterility in PD or intravascular lines in haemodialysis.

• β2 microglobulin amyloidosis

     o Due to amyloid

     o Accumulates in long-term dialysis patients

     o May cause carpal tunnel syndrome, arthralgia, fractures.

• Acquired renal cysts occur years after dialysis

     o May present with haematuria or malignant transformation.

• Malignancy is commoner in dialysis patients

     o This may be related to the cause, eg urothelial tumours in analgesic nephropathy

PERITONEAL DIALYSIS VS HAEMODIALYSIS

REFERENCES

- Kumar & Clark Clinical Medicine: 8th edition

- Wikipedia

- "Physiology of Peritoneal Dialysis". Handbook of dialysis. Lippincott Williams & Wilkins. p. 323.

- IHAcares.com

- Bellomo R, Ronco C. Continuous renal replacement therapy in the intensive care unit. Intensive Care Med 1999;25:781-789

- Oxford handbook of Dialysis

- http://renalbiomarkers.com/acute_kidney_injury.asp#treatment

- A2 Biology textbook by OCR

http://www.ehow.com/about_4566521_dialysis-technology.html

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