Peritoneal Dialysis

This process involves instilling dialysis fluid into the peritoneal cavity via a dialysis catheter, so that dialysis takes place by diffusion of uraemic toxins through the patient's peritoneal capillaries, down a concentration gradient into the dialysis fluid. Water is removed from the circulation by varying the concentration of osmotic agents (normally glucose) in the dialysis fluid to draw water through the capillary membranes. The fluid is repeatedly removed and replaced with fresh solution.

A catheter is implanted into the abdomen by a minor surgical procedure. Peritoneal dialysis (PD) may be performed manually or by using a machine to perform the dialysis at night. About 2 to 3 litres of dialysis fluid are infused into the abdominal cavity through this catheter. The fluid is allowed to dwell for two to several hours before being drained, taking these unwanted wastes and water with it. The process of draining and filling is called an exchange and takes about 30 to 40 minutes. The period the dialysis solution is in the abdomen is called the dwell time. A typical schedule calls for four exchanges a day, each with a dwell time of 4 to 6 hours. Different types of PD have different schedules of daily exchanges.¹

• PD offers much more freedom compared to haemodialysis, as patients do not need to go to a dialysis centre for their treatment.
• Many normal activities can be performed whilst undergoing treatment. It may be the preferable therapy for children.
• Most patients are candidates for both haemodialysis and peritoneal dialysis.
• There are little differences in outcomes between the two procedures.²

15-20% of all patients on chronic dialysis worldwide receive peritoneal dialysis.
500-600 per million population on renal replacement therapy.³

Dialysis solutions

Contain glucose as osmotic agent together with balanced electrolyte solutions and lactate to correct acidosis. However, because of their low pH and hyperosmolality they may cause long term damage to the membrane with mesothelial cell loss and glycation of the membrane. Newer solutions contain bicarbonate/lactate as buffer, glucose polymer and amino acids to help correct hypoalbuminaemia and malnutrition.

Catheters

• There are a variety of designs that exist, with no clear advantages for any of them.
• The catheter is left in place on a semi-permanent basis, with the subcutaneous portion providing anchorage and a barrier to infection.
• The catheter can be inserted either percutaneously with a trochar and cannula, or via a laparoscope or with a mini-laparotomy.⁴
• The wound needs time to heal before starting dialysis.

The patient's peritoneal capillary membrane has varying permeability to both uraemic toxins and glucose. This needs to be assessed using the Peritoneal Equilibration Test; 2.27% glucose-based dialysis solution is instilled into the peritoneal cavity and membrane transport characteristics are classified as low, average or high by measuring glucose and creatinine concentrations in both blood and dialysate. Those with high transporter status will allow rapid removal of uraemic toxins, but will not be able to maintain the glucose gradient essential for adequate fluid removal. Similarly, those with low transporter status will have adequate fluid removal but may not be able to remove the solute load resulting in underdialysis. In this way, the proper prescription for peritoneal dialysis can be made

• In this technique patients manually drain and replace the fluid content of their peritoneal cavity several times a day using bags of solution supplied to them. It doesn't require a machine.
• Standard prescription is 4 x 1.5-2.0ltr exchanges per day. However, this takes no account of body weight, membrane function or residual renal function. Standard prescription may be adequate in early stages of dialysis when there is some degree of residual renal function that may eliminate 25-30% of solutes.
• After 2-3 years very important to individualise patient's prescription with those with a low transporter function requiring higher volume exchanges, those with high transporter membranes needing short frequent exchanges if they are to remain oedema-free.
• If adequate dialysis is not achievable, then transfer to haemodialysis may be required.

CCPD uses an automated cycler to perform three to five exchanges during the night while the patient is asleep. In the morning one exchange begins with a dwell time that lasts the entire day. It is also sometimes called automated peritoneal dialysis (APD). May be particularly suitable for the young still at work or school. Initially, when there is still residual renal function, it may use relatively low, small volumes of dialysis fluid, but as this declines larger fill volumes and longer over night dwells are needed.

• Need to monitor urea and creatinine clearance at least yearly.
• Change dialysis prescription if inadequate.
• Patients commonly suffer from malnutrition due to appetite suppression and peritoneal protein loss. They may need specialist dietary advice.⁴ Studies have shown that treatment with 1.1% amino - acid based dialysis solution is safe and may improve protein malnutrition in CAPD patients with low protein intake. ⁵
• Cardiovascular status; up to half of all deaths from peritoneal dialysis are from this cause and particular attention should be given to controlling risk factors e.g. smoking, exercise, hypertension, hyperlipidaemia.
• Anaemia; treated with recombinant human Erythropoietin (EPO) and oral/IV iron.

Patients can be transplanted in safety with evidence of lower incidences of delayed graft function and early rejection. If necessary, the catheter may be used after transplantation providing the peritoneum has not been breached. The catheter can be removed 2-3 months later when the risk of graft failure has reduced.

• The catheter exit site frequently becomes infected and may cause peritonitis and/or necessitate catheter removal unless properly treated.
• Commonest organisms are Staph. aureus or Strep. epidermidis and occasionally Gram-negative bacteria.
• Needs meticulous care of site with regular cleaning with antiseptics and local application of mupirocin to eradicate Staph. aureus.
• If infection develops needs broad spectrum antibiotics and if necessary removal and replacement.

Peritonitis

• This is a major complication and may require transfer to haemodialysis.
• Infecting organisms are similar to those at the catheter wound site.
• Diagnosis on presence of cloudy dialysate fluid ± abdominal pain.
• Treat on clinical suspicion using intraperitoneal cefazoline or vancomycin plus an intraperitoneal aminoglycoside or oral quinolone e.g. ciprofloxacin. Change therapy to match culture results. It should be possible to achieve 1 episode of peritonitis every 2 years with >85% cure rate, without catheter removal.