Dialysis is a method for performing the filtration tasks of the kidneys artificially in patients with end stage renal failure or complications of renal failure. It involves removing excess fluid, solutes and waste products.
Indications for Acute Dialysis
The mnemonic is AEIOU can be used to remember the indications for acute dialysis in patients with a severe AKI:
- A – Acidosis (severe and not responding to treatment)
- E – Electrolyte abnormalities (severe and unresponsive hyperkalaemia)
- I – Intoxication (overdose of certain medications)
- O – Oedema (severe and unresponsive pulmonary oedema)
- U – Uraemia symptoms such as seizures or reduced consciousness
Indications for Long Term Dialysis
- End stage renal failure (CKD stage 5)
- Any of the acute indications continuing long term
Options for Maintenance Dialysis
There are three main options for dialysis in patients requiring it long term:
- Continuous Ambulatory Peritoneal Dialysis
- Automated Peritoneal Dialysis
The decision about which form to use is based on:
- Patient preference
- Lifestyle factors
- Individual differences regarding risks
Peritoneal dialysis uses the peritoneal membrane as the filtration membrane. A special dialysis solution containing dextrose is added to peritoneal cavity. Ultrafiltration occurs from the blood, across the peritoneal membrane, in to the dialysis solution. The dialysis solution is then replaced, taking away the waste products that have filtered out of the blood into the solution.
Peritoneal dialysis involves a Tenckhoff catheter. This is a plastic tube that is inserted into the peritoneal cavity with one end on the outside. It allows access to peritoneal cavity. This is used for inserting and removing the dialysis solution.
Continuous Ambulatory Peritoneal Dialysis
This is where the dialysis solution is in the peritoneum at all times. There are various regimes for changing the solution. One example is where 2 litres of fluid is inserted into the peritoneum and changed four times a day.
This involves peritoneal dialysis occurring overnight. A machine continuously replaces dialysis fluid in the abdomen overnight to optimise ultrafiltration. It takes 8-10 hours.
Complications of Peritoneal Dialysis
Bacterial peritonitis. Infusions of glucose solution make the peritoneum a great place for bacterial growth. Bacterial infection is a common and potentially serious complication of peritoneal dialysis.
Peritoneal sclerosis involves thickening and scarring of the peritoneal membrane.
Ultrafiltration failure can develop. This occurs when the patient starts to absorb the dextrose in the filtration solution. This reduces the filtration gradient making ultrafiltration less effective. This becomes more prominent over time.
Weight gain can occur as they absorb the carbohydrates in the dextrose solution.
Psychosocial effects. There are huge social and psychological effects of having to change dialysis solution and sleep with a machine every night.
With haemodialysis, patients have their blood filtered by a haemodialysis machine. Regimes can vary but a typical regime might be 4 hours a day for 3 days a week.
They need good access to an abundant blood supply. The options for this are:
- Tunnelled cuffed catheter
- Arterio-venous fistula
Tunnelled Cuffed Catheter
A tunnelled cuffed catheter is a tube inserted into the subclavian or jugular vein with a tip that sits in the superior vena cava or right atrium. It has two lumens, one where blood exits the body (red) and one where blood enters the body (blue).
There is a ring called a “Dacron cuff” that surrounds of the catheter. It promotes healing and adhesion of tissue to the cuff, making the catheter more permanent and providing a barrier to bacterial infection. These can stay in long term and be used for regular haemodialysis.
The main complications are infection and blood clots within the catheter.
An A-V fistula is an artificial connection between an artery to a vein. It bypasses the capillary system and allows blood to flow under high pressure from the artery directly into the vein. This provides a permanent, large, easy access blood vessel with high pressure arterial blood flow. Creating an A-V fistula requires a surgical operation and a 4 week to 4 month maturation period without use.
They are typically formed between an artery and vein in the patient’s forearm:
- Brachio-basilic (less common and more complex operation)
Examining an A-V fistula is a common exam question. Look for:
- Skin integrity
- Palpable thrill (a fine vibration felt over the anastomosis)
- Stereotypical “machinery murmur” on auscultation
A-V Fistula Complications
- STEAL syndrome
- High output heart failure
STEAL syndrome is where there is inadequate blood flow to the limb distal to the AV fistula. The AV fistula “steals” blood from the distal limb. The blood is diverted away from where is was supposed to supply and flows straight into the venous system. This causes distal ischaemia.
High output heart failure
Where there is an A-V fistula blood is flowing very quickly from the arterial to the venous system through the fistula. This means there is rapid return of blood to the heart. This increases the pre-load in the heart (how full the heart is before it pumps). This leads to hypertrophy of the heart muscle and heart failure.
TOM TIP: NEVER take blood from a fistula! This is a lifeline for the patient to allow them access to dialysis. If it gets damaged it will set them back and you will be in big trouble.
Last updated April 2019