Dialysis: Types, Indications and Complications

Dialysis is a renal replacement therapy or procedure that filters blood and removes metabolic wastes and excess fluid when kidneys have failed to function optimally. These are the cases when a patient has either an acute kidney injury or chronic kidney disease.

There are two types of dialysis;
1.    Hemodialysis
2.    Peritoneal dialysis

What are the indications for dialysis?

Dialysis is needed when a patient develops end-stage kidney failure. 85 to 90 percent loss of kidney function and a Glomerular Filtration Rate of < 15.

It is also needed when a patient develops a severe acute kidney injury and dialysis is considered as a life-saving procedure as the patient waits for recovery. Some of these patients, despite being put on dialysis therapy, their kidney function do not recover therefore, they require long-term renal replacement therapy.

Specific indications for dialysis are;

⦁    Pericarditis or pleuritis.
⦁    Progressive uremic encephalopathy or neuropathy (AMS, asterixis, myoclonus, seizures).
⦁    Bleeding diathesis.
⦁    Fluid volume overload that is unresponsive to diuretics
⦁    Metabolic disturbances that are refractory to medical therapy (hyperkalemia, metabolic acidosis, hyper- or hypocalcemia, hyperphosphatemia).
⦁    Persistent nausea/vomiting, weight loss, or malnutrition.
⦁    Toxic overdose of a dialyzable drug such as Lithium
⦁    Acute poisonings such as ethylene glycol.

Goals of Dialysis

The goals of dialysis are; Solute clearance and Fluid removal.

Solute clearance is achieved by:

Diffusive transport (based on counter-current flow of blood and dialysate) and convective transport (solvent drag with ultrafiltration).

Dialysis Modalities/Types of dialysis

There are three dialysis modalities. That is:

1. Peritoneal hemodialysis (PD),

Peritoneal dialysis works through diffusion. In this case, a sterile solution known as dialysate is run through a tube into the peritoneal cavity, the abdominal body cavity that surrounds the intestine.

It has a semi-permeable membrane, the peritoneal membrane.

Peritoneal dialysis uses the natural filtering ability of the peritoneum, the internal lining of the abdomen, to filter waste products from the blood. The dialysate is left in the peritoneal cavity for some time so that it can absorb waste products. Then drained out through a tube and discarded. The only fluid getting out of the patient is the dialysate.

With peritoneal dialysis, there is direct access into the peritoneal space by the use of a surgically inserted peritoneal catheter known as a PD catheter. This catheter is inserted through the patient's abdominal wall and it's usually ready for use 2 weeks after the surgery.

The dialysate used in peritoneal dialysis is very hypertonic to the patient's blood unlike the one used in hemodialysis. This helps in creating a concentration gradient for ultrafiltration to take place.

There are two main types or methods of peritoneal dialysis:

A) Continuous ambulatory peritoneal dialysis (CAPD).
B) Continuous cyclic peritoneal dialysis (CCPD)/automated peritoneal dialysis

Both of these methods use the same catheter for dialysis and generally have the same clinical outcomes, with selection dependent on patient preference.

The difference between these two methods is the use of a machine known as a cycler in continuous cyclic peritoneal dialysis to automatically pump the dialysis fluid into and out of the body.

A. Continuous ambulatory peritoneal dialysis (CAPD).

Unlike automated peritoneal dialysis, continuous ambulatory peritoneal dialysis does not use a machine, instead, it utilizes gravity to allow the dialysate to flow into and out of intraperitoneal space. This implies that the drainage bag needs to be below the patient.

In this method,  the patient uses sterile a technique to connect the PD catheter tubing to the dialysate bag and about 2 liters of dialysate are infused into the abdomen.
Then the patient is required to use a sterile technique to disconnect from the dialysate bag.

During the dialysis process, the patient can ambulate while the fluid acts.

After some hours later, the patient uses a sterile technique to connect to the drainage bag and dialysate bag and then drains the spent dialysate from the abdomen into the drainage bag.

After draining, they are required to do an exchange, this refers to the filling of fresh dialysate into the abdomen.

B. Continuous cyclic peritoneal dialysis (CCPD)/automated peritoneal dialysis

In this method, there is the use of a machine known as a cycler that pumps fluid into and out of the peritoneal space. This kind of modality is preferably done in night as the patient turns the cycler machine on and goes to sleep.

The cycler then pumps 2 liters of dialysate fluid into the peritoneum that then lasts for several hours and the cycler then pumps the fluid out and performs the exchange automatically

2. Intermittent hemodialysis (IHD), 

Intermittent hemodialysis (IHD is a renal replacement procedure by which metabolic waste products and excess fluids are removed from a patient’s blood. This is achieved by directly removing blood from the patient’s circulatory system to a machine outside the body, through a dialysis filter, and then redirecting the blood back into the patient's circulation.

Intermittent hemodialysis (IHD), is usually delivered 3 to 6 times a week, 3 to 4 hours per session, with blood flowing at a rate of over 250 mL per minute and a dialysate flowing at a rate of 500 to 800 mL/min. In this mode, solute clearance occurs by the process of diffusion, whereas volume is removed by ultrafiltration.

The advantage of applying IHD is that there is a rapid solute and volume removal. This results in rapid correction of electrolyte disturbances, such as hyperkalemia, and rapid removal of drugs or other substances in fatal intoxications in a matter of hours.

This modality also has a decreased need for anticoagulation as compared with other types of RRT because of the faster blood flow rate and shorter duration of therapy

The main disadvantage of IHD is the risk of systemic hypotension caused by rapid electrolyte and fluid removal.

Rapid solute removal from the intravascular space can cause cerebral edema and increased intracranial pressure, limiting this therapy in patients with head trauma or hepatic encephalopathy.

3. Continuous renal replacement therapy (CRRT).

The decision of a modality is determined by catabolic rate, hemodynamic stability, and whether the primary goal is fluid or solute removal.

To start with let us look at the apparatus used in hemodialysis basics.

Hemodialysis Apparatus

1. Dialyzer or a dialysis filter - This is cellulose, substituted cellulose, or synthetic noncellulose membranes.
2. Dialysis solution (Dialysate) - This solution must remain free of Aluminium, Copper, chloramine, bacteria, and bacterial endotoxins.
3. Tubing for the transport of blood and dialysis solution.
4. Machine to power and mechanically monitor the procedure (includes air monitor, proportioning.
5. Hemodialysis system and correct settings.

Hemodialysis Access

For hemodialysis to take place effectively, there must be adequately functioning direct access to the patient’s circulatory system via the large central veins.

There are two basic types of hemodialysis access: 

1. Central venous catheters 

2. Permanent access points

Central Venous Catheters

Central venous access catheters are usually of large bore French gauge 11-13 so as to allow faster blood flow rates. These catheters are inserted into the internal jugular vein or femoral vein

These catheters can either be tunneled catheters or non-tunneled catheters.

Nontunneled dialysis catheters are referred to as “Quinton catheters” or “temporary dialysis catheters” and are most commonly used in patients who have acute kidney injury and require dialysis for just a short duration of time. This type of catheter is then secured with a suture and a surgical dressing.

However, the use of non-tunneled catheters is associated with a higher risk of infection over time and a significant bleeding risk if accidentally dislodged. Therefore a patient with this type of catheter may not really be not be discharged with the catheter from the hospital.

Tunneled dialysis catheters (TDC) are also known as “Hickman catheters” or “permacaths”

These kinds of catheters are used for patients who need longer times for dialysis that is to be started urgently but do not yet have permanent vascular access. These catheters are inserted into the internal jugular vein and tunneled subcutaneously to exit the skin underneath the clavicle where it is secured to the patient via a “cuff” around the part of the catheter resting underneath the skin near the exit site of the catheter.