Continuous ambulatory peritoneal dialysis

Contents:

CAPD schedule:

Indications and contraindications:

Clearances of CAPD in comparison to other dialysis forms:

Sterile technique

Transfer sets

Connectors for CAPD

Dialysis solutions

Advantages and disadvantages

he basic principle of continuous ambulatory peritoneal dialysis (CAPD) is a continuous presence of dialysate in the peritoneal cavity. The dialysis fluid is left in place for 6-8 hours and slowly equilibrates with plasma solutes in the peritoneal cavity. The fluid is then discharged in a plastic bag ,connected to the catheter, and the contents of new bag are introduced through the catheter. Increasing the osmolality of dialysis fluid by adding concentrated glucose (hypertonic) will increase the fluid loss.. It has a lower cost than HD and with better hemodynamic stability.

CAPD schedule:

The basic technique of CAPD is extremely simple. Three or four exchanges are required every day [every 4-8 hours]. The patient can undertake this treatment alone without machine. Usually 2 L of dialysate are used by most of the patients i.e.56 liters per week. The total outflow ~ 10 L including ultrafiltrate. Some of the patients can tolerate 2.5-3 L of dialysate per exchange

Indications and contraindications:

  Review the previous Tips-Principles

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Clearances [liters/week] of CAPD in comparison to other dialysis forms:

CAPD provides a continuous urea clearance of about 57 L/week. The weekly plasma urea clearance for the forms of chronic peritoneal dialysis are comparable but less than that achieved by hemodialysis.

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Sterile technique:

 Rigid adherence to aseptic technique is required when performing bag exchanges in order to prevent peritonitis. The following guidelines to be considered:

1- Follow specified techniques carefully without deviation.

    -Perform bag exchanges in  a clean area and wear a mask.

    -Exclude animals from the working area.

    -Restrict any activities during a bag exchange

    -Close off the area if possible.

2- Good personal hygiene is obligatory.

    -Wash the hands scrupulously for 3-5 minutes with soap or bacteriostatic agents (see the

        training module)

    -shower (see the training module)

3- Observe and inspect supplies and dialysate outflow regularly.

    -Examine the new bag, ports, line etc., for possible defects or leaks.

    -Examine the outflow bag for cloudy appearance, fibrin, or blood.

    -Examine the catheter exit site and palpate the tunnel tract for signs if infection.

4-Accidental contamination of the spike during the procedure must be reported to dialysis

     staff.

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Transfer sets

1-Straight transfer set

 It is a simple plastic tube ; one end connected to the peritoneal catheter and the other to the dialysate bag.. Bag exchanges are performed by breaking the connection between the transfer set and the dialysate bag. The dialysate is instilled by gravity and the empty bag with the transfer  set are rolled and stored in a pouch carried by the patient. The bag is used as drainage bag for the following exchange after 4-8 hours dwell time. The bag is then disconnected from the transfer set and discarded then a new bag is attached and fresh solution is instilled.

2-The Y transfer set

This set is a Y-shaped tube ; the stem is connected to the peritoneal catheter via a short adapter. The two limbs of the Y are attached to dialysis solution bags , one empty and one  filled with fresh solution. The used dialysate is drained into the empty bag and the peritoneum is filed with from the containing fresh solution. The Y set is disconnected when not performing a solution exchanges. The use of Y set permit flushing the tubing with 15-30 ml of fresh solution before draining the spent dialysate and refilling. The bacteria that may be introduced during connection and washed out rather than washed into the patient.

The Y sets are designed in two forms [1] Reusable: Disinfectant is injected into the set and kept safely with the two limbs connected to each other. The two limbs are rinsed free antiseptic at the time of next exchange using fresh dialysis solution. [2] Disposable: The set is preattached to the dialysis solution bag and empty bag. It is discarded after each use.

Positives of the Y set: [1]Unlike straight set the patient is free from the set and the bag between exchanges with less mechanical stress to the exit and the tunnel. [2]Low peritonitis rate than that of straight set due to less mechanical stress to the exit and the tunnel and to the flush before fill.

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Connectors for CAPD

1-Catheter-to-transfer set connectors

A luer-lok made of titanium or durable plastic are designed to reduce the possibility of bacterial contamination. A sterile connections at the catheter-to-transfer set joint are also available for the removable Y sets.

2-Transfer set- to- container connectors

Over several years a number of transfer set-to-container connections have been developed. The spike and port design is the standard. It is operated by pushing a spike located at the end of transfer set into a port on diaysate container. Other transfer set-to-container connections includes; Inpersol system, Easy lock, and Delflex system.. Recently some systems have eliminated the transfer set-to-container connection, and are known as double bag systems.

3-Special connectors:

It is more complex and sophisticated devices such as ; in-line filters , ultraviolet light sterilization device ; heat sterilization ,thermic splicing of transfer line ,tube cutter and mechanical aids

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Dialysis solutions (Dialysate):

Dialysate is available in premixed clear flexible bags. Dialysate volumes ranging from 250 to 750 for pediatric and 1 to 3 L for adult patients. The standard volume is 2 L.

The composition of dialysate varies somewhat by manufacturers but the standard dialysate as follows:

·      Dextrose chemically signifies the D-isomer of glucose. The molecular weight of D-glucose monohydrate is 10% greater than that of anhydrous glucose. For this reason the dextrose solution bottle are 10% greater than the true glucose concentrations.(e.g. 1.36% glucose is listed as 1.5% dextrose and 3.86% glucose is listed as 4.25% dextrose.

·      Icodextrin (Extraneal), glucose polymer, has recently been introduced. This is a very large (20 –≥500 glucose molecule) polymeric gluco-pyranose molecule produced by hydrolysis of starch. It allows ultrfiltration to occur over log period of time by dragging water molecule through the membrane. It provides ultrafiltation similar to 3.86% after 8-12 hours. It is used once daily.

·      Lactate is used as bicarbonate generating base. Metabolism of lactate in the liver will result in generation of bicarbonate. Hence the bicarbonate loss during peritoneal dialysis is compensated.

·      Preparations with low calcium and magnesium concentration are used for patients with hypercalcaemia or hypermagnesemia.

·      Preparations with amino acids are also used for malnourished patients.

·      Additives like heparin, insulin, potassium and antibiotics are added to dialysate according to the patient requirements.

·      Heparin (500/L) is added in the following situations:

          Fibrin in the dialysate outflow

          Peritonitis to maintain the patency

          After placement of a dialysis catheter to maintain the patency

          Hemoperitonium

NB:Heparin is not absorbed in amount sufficient to result in anticoagulation of the patient

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Advantages and disadvantages

Advantages:

1-Ease of performance

2-Safe - fewer dialysis related symptoms and with better hemodynamic stability.

3-It has a lower cost than HD.

3-Portability

4-Hemoglobin concentration generally increase during the first few months and remain stable thereafter. The proposed reasons include the possibility of extrarenal erythropoietin by peritoneal macrophages and the better removal of uremic inhibitors of erythropoietin.

5-Excellent blood pressure control.

6-Adequate control of electrolyte and acid base balance.

7-Stable control of nitrogenous waste products.

8-No routine anticoagulation

9-Control of parathyroid hormone

10-Libral diet

Disadvantages: "review the tip of complication of peritoneal dialysis"

1-Potential for infection [peritonitis-exit site and tunnel infection]

2-Low efficiency than hemodialysis

3-Weight gain and hyperlipidaemia particularly during the first year.

4-Body image problem

5-Potential protein loss ; nutritional supplementation is recommended when serum albumin tend to decrease.

6-Patient dropout is higher than with hemodialysis[ peritonitis-malnutrition-inadequate dialysis]

7-Potential pulmonary compromise

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