Dialysis Basics


Published: 23 March 2022

The kidneys are responsible for filtering waste from the blood and excreting it via urine. However, when the kidneys become damaged, such as in the case of renal failure, they are unable to filter waste properly, causing it to accumulate in the blood (Healthdirect 2020). This is a potentially life-threatening complication (NHS 2021).

What is Dialysis?

Dialysis is a treatment used to artificially filter waste from the blood if the kidneys are no longer able to do so on their own (Healthdirect 2020). While dialysis isn’t a cure for renal failure, it’s a type of supportive care that can sustain the patient until they can receive a kidney transplant, or for the rest of their life if a transplant is contraindicated (NHS 2021).

In the case of acute renal failure, dialysis can be used until the kidneys recover (NHS 2021).

Specifically, the role of dialysis is to:

  • Remove waste, salt and excess water from the blood
  • Maintain a safe level of electrolytes such as potassium, sodium and bicarbonate in the blood
  • Regulate blood pressure.

(NKF 2022)

Dialysis is typically required once a patient enters end-stage renal failure: that is, when 85 to 90% of kidney function has been lost and their glomerular filtration rate (GFR) is under 15 (NKF 2022).

Types of Dialysis

There are two types of dialysis:

  1. Haemodialysis
  2. Peritoneal dialysis.

(Healthdirect 2020)


haemodialysis diagram

Haemodialysis, which is the most common type of dialysis, involves filtering blood through an external device known as a dialyser (NIDDK 2018).

The procedure involves gaining vascular access to the patient’s arm or leg (either via a fistula, graft or catheter) and drawing blood into a tube connected to the dialyser. The blood is then filtered through the dialyser before being circuited back into the patient’s bloodstream. Only a small amount of blood is outside of the patient’s body at one time (Better Health Channel 2019).

The process takes about four to five hours and needs to be performed at least three times per week (Better Health Channel 2019).

Haemodialysis can be performed at a haemodialysis unit or satellite centre, or in the patient’s home, providing they have the appropriate equipment (Better Health Channel 2019).

Home haemodialysis is generally preferred as it allows the patient to tailor their treatment schedule to their needs (e.g. while they are sleeping) and receive dialysis more frequently, which will improve their health (Better Health Channel 2019).

Peritoneal Dialysis

peritoneal dialysis diagram

Rather than employing an external device, peritoneal dialysis involves using the peritoneal membrane - the lining of the abdominal cavity - as an internal filter (Better Health Channel 2019).

In order to perform peritoneal dialysis, a catheter needs to be inserted into the peritoneal cavity, where it will stay in situ as long as the patent requires dialysis (Better Health Channel 2019).

A cleansing solution (dialysate) is pumped into the body via the catheter, where it absorbs the waste products that have been filtered out of the blood by the peritoneal membrane. The dialysate, now containing the waste, is then drained back out of the body and into a bag and replaced with fresh dialysate (Mayo Clinic 2021; NHS 2021).

Each cycle of filling, draining and replacing the peritoneal membrane with dialysate is known as an exchange. There are two different schedules of exchange that may be used:

  1. Continuous ambulatory peritoneal dialysis (CAPD), where four manual exchanges are performed each day. Each exchange takes about 30 minutes. The process uses gravity - placing the drainage back on the floor drains the fluid out of the body, and raising it above the shoulder allows the new dialysate to flow into the body.
  2. Automated peritoneal dialysis (APD), where a machine known as a cycler performs several exchanges overnight, while the patient is asleep. The entire process takes 8 to 10 hours and dialysate is typically left inside the body during the day to continue the dialysis.

(Better Health Channel 2019)

Which Type of Dialysis is Better?

In most cases, both types of dialysis are equally effective and the chosen method will depend on the patient’s preference and lifestyle (NHS 2021).

However, there are certain circumstances where a particular type of dialysis might be preferred:

Haemodialysis may be preferred for: Peritoneal dialysis may be preferred for:
  • Patients who would be unable to perform peritoneal dialysis independently due to factors such as vision impairment, dementia or poor health
  • Children under two
  • Patients who still have limited kidney function
  • Patients without comorbidities (e.g. heart disease, cancer)

(NHS 2021)

There are also a variety of pros and cons to consider for each type of dialysis:

Haemodialysis Peritoneal dialysis
  • The patient is able to have up to four days per week without treatment
  • If performed at home, the patient has flexibility to work around their routine
  • If performed in a dialysis unit:
    • The procedure is performed by trained staff
    • The patient may develop friendship and camaraderie with others undergoing treatment at the same time
  • Dialysis can be performed at home
  • Fewer dietary and fluid restrictions are required
  • More flexibility
  • Continuous dialysis will improve the patient’s wellbeing
  • It’s easier for the patient to travel
  • No injections are required
  • Takes less time overall than attending a dialysis unit
  • The patient will need to plan their life around treatment sessions if receiving dialysis in a unit
  • Diet and fluids requirements (e.g. reduced sodium, increased protein)
  • Less privacy if receiving treatment at a dialysis unit
  • Needs to be performed every day, which may be disruptive to the patient’s daily life
  • The patient needs to have a permanent abdominal catheter in situ, which may be distressing or adversely affect body image
  • Greater risk of peritonitis infection
  • Potential for peritoneum scarring
  • Dialysate may reduce protein levels, leading to reduced energy or malnutrition
  • Potential for weight gain
  • Swimming and bathing may be limited

(NHS 2021; NKF 2021; NIDDK 2018)

Side Effects of Dialysis

Both types of dialysis can cause side effects. These may include:

Haemodialysis Side Effects

  • Fatigue
  • Hypotension caused by decreased fluid levels during dialysis
  • Nausea or dizziness due to hypotension
  • Infection of the vascular access site
  • Poor perfusion or obstruction at the vascular access site caused by a blood clot or scar
  • Increased risk of sepsis
  • Muscle cramps, often in the lower leg - this is believed to be caused by the muscle reaction to fluid loss
  • Itchy skin caused by an accumulation of minerals in the body between sessions
  • Headache
  • Chest or back pain
  • Restless legs syndrome
  • Sleeping difficulties
  • Bone and joint pain
  • Reduced libido
  • Erectile dysfunction
  • Dry mouth
  • Anxiety.

Peritoneal Dialysis Side Effects

  • Fatigue
  • Risk of peritonitis (bacterial infection of the peritoneal membrane), which can occur if the equipment used during dialysis isn’t clean
  • Increased risk of hernia
  • Weight gain
  • Skin infection around the catheter
  • Abdominal bloating or discomfort during exchanges.

(NHS 2021; Cleveland Clinic 2021; NIDDK 2018)

Caring For Patients Undergoing Dialysis


haemodialysis site care
The haemodialysis vascular access site should also be monitored and cared for in order to prevent complications.

Patients who are undergoing haemodialysis should undergo blood testing once per month to ensure that any required adjustments to their dialysis prescription can be made. Furthermore, they should be weighed before and after each treatment, and monitor their own weight at home, to ensure there is no accumulation of fluid between dialysis sessions (Berns 2021).

The vascular access site should also be monitored and cared for in order to prevent complications. Site care should include:

  • Washing the site with warm water and soap every day and before dialysis
  • Checking for signs of infection daily (e.g. warmth, redness)
  • Checking for perfusion in the site daily
  • Discouraging the patient from wearing tight clothes or jewellery, carrying heavy items or sleeping on the affected arm, in order to prevent site trauma
  • Avoiding taking blood pressure on the affected arm
  • Rotating needle sites on the area and applying gentle pressure to manage any bleeding after injection.

(Berns 2021)

Peritoneal Dialysis

Infection is one of the most serious potential complications of peritoneal dialysis. It’s crucial to know when to escalate care. Signs to look out for include:

  • Catheter site infection signs
    • Redness, firmness, or tenderness
    • Pus-like drainage
  • Peritonitis signs
    • Mild to severe abdominal pain
    • Used dialysate fluid with a cloudy appearance
    • Fever
    • Nausea or diarrhoea.

(Burkart 2021)


Test Your Knowledge

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Overall, which type of dialysis is most effective?


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