24th June 2023

Peritoneal dialysis

Mechanism

• Peritoneal dialysis (PD) utilises the patient’s peritoneum as the semi-permeable membrane. Dialysate fluid is introduced into the peritoneal cavity via a catheter where it can then be in contact with the membrane and its blood supply.
• Fluid moves from the blood through the peritoneum to the higher osmolality dialysate fluid via osmosis, other molecules either diffuse down their concentration gradients or move via convection alongside fluid.
• The qualities of each patient’s membrane varies:
  • ‘High transporters’ will remove solutes quickly and will also absorb glucose from fluid quickly.
  • ‘Low transporters’ have a slower rate of solute removal.
  • Membrane qualities will change over time and will generally move towards high transporter status.

Requirements and process

• Access – peritoneal dialysis requires the presence of an indwelling peritoneal catheter.
• Types of fluid – dextrose is commonly used to create high osmolality dialysate fluid, the concentration can be varied to affect the degree of fluid removal. However, glucose from the fluid can be absorbed and metabolised, abolishing the gradient – this is not a risk with alternatives such as glucose polymers (e.g. icodextrin).
• Regimes:
  • Continuous Ambulatory Peritoneal Dialysis – usually four exchanges of dialysate fluid per 24-hour period, performed manually by the patient. Relatively long dwell periods are, therefore, generally more suitable for low transporters.
  • Automated Peritoneal Dialysis (APD) – multiple exchanges of dialysate fluid performed by a machine overnight with shorter dwell periods. Patients may have fluid left in the abdomen during the day or perform an additional manual exchange during the day. Generally more suitable for high transporters.
  • Tidal APD – the machine is set to leave a small amount of fluid in the abdomen when draining. This avoids discomfort associated with the removal of the full volume, however, it means dialysis is less efficacious.

Contraindications

• Anatomical – hernias (inguinal, umbilical, diaphragmatic), abdominal wall defect (e.g. a stoma).
• Infection – intra-abdominal or of the abdominal wall.
  Technical/practical – patient/carer needs adequate dexterity and skill to perform safe exchanges, and the home environment needs to be suitable for the required equipment.
• Cautions:
  • Multiple previous abdominal surgeries causing adhesions
  • Severe obesity
  • Severe respiratory disease (increased intra-abdominal pressure can cause diaphragmatic splinting)
  • Very large polycystic kidneys

Complications

• Infection
  • Superficial catheter exit site infection.
  • Peritonitis – repeated infections will affect the quality of the membrane and may reduce the patient’s time on peritoneal dialysis.
• Encapsulating peritoneal sclerosis – rare but serious. Fibrous scar tissue surrounds the peritoneum and bowel – leading to poor dialysis quality and the development of symptoms of bowel obstruction.
• Catheter issues – the PD catheter can become occluded or wrongly positioned. This can be due to constipation and it is therefore important that patients have regular bowel movements.
• Hyperglycaemia – due to glucose absorption from dialysate fluid.
• Longevity – the quality of peritoneal dialysis generally decreases over time, necessitating a switch to another modality like haemodialysis for ongoing renal replacement.