2 Principles of PD Dialysis fluid is introduced to the peritoneal cavity through a catheter placed in the lower part of the abdomen. A thin membrane, called the peritoneum, lines the walls of the peritoneal cavity and covers all the organs contained in it. In PD the peritoneum serves as the dialysis membrane. The peritoneal cavity can often hold more then 3 litres, but in clinical practice only 1.5 – 2.5L of fluid are used. This is an intra-corporeal blood purification as no blood ever leaves the body of the patient.
3 Principles of PD The abdominal cavity, hold the large organs of the digestive system, is lined by the peritoneum. In PD, special fluid is instilled through a permanent catheter in the lower abdomen.
4 Principles of PD An osmotic pressure gradient is applied by the addition to the dialysis fluid of an osmotic agent which will “suck” fluid from the blood. The concentration of this osmotic agent is chosen to give just the fluid removal needed. In most cases glucose is used to create the osmotic pressure. Fluid is removed by ultrafiltration driven by an osmotic pressure gradient. (Eg. Yellow/Green/Red Bags)
5 Principles of PD Solutes are transported across the membrane by diffusion. The driving force is the concentration gradient between the PD fluid and the blood. Waste products present in the blood per fusing the peritoneum will diffuse from the blood vessels into the “cleaner” dialysis fluid.
6 Principles of PD The dialysis fluid should be instilled for 4 to 6 hours. When the dialysis fluid is drained from the abdominal cavity, it contains waste products and excess fluid extracted from the blood. PD is most often applied and effective as a continuous therapy. In this way it is a more physiological treatment then Haemodialysis (HD)
9 The abdominal cavity and all the organs contained in it are lined by a thin smooth membrane, the peritoneum. It is a loose connective tissue containing blood vessels and nerves. If put under the microscope, three layers can be identified between the peritoneal cavity and the blood stream. The capillary wall / the interstitium / the mesothelium Each of these is a barrier to the transport of fluid and solutes.
10 Fluid Removal To understand how fluid removal is achieved, we need to understand how osmosis works. Osmosis is the process in which water moves through a semi permeable membrane from an area of high water concentration (ie; low solute concentration) to an area of low water concentration (ie; higher solute concentration).
11 Fluid Removal The osmotic agent normally used in PD fluid is glucose. Not an ideal osmotic agent, as it is readily transported across the peritoneum. Large concentration glucose creates a temporary osmotic gradient before being adsorbed into the blood. The higher the glucose concentration, the larger the osmotic pressure, resulting in a larger fluid removal. If PD exchanges are missed or dwell more than 6-8 hours, fluid may be gained by the patient rather then lost. The Volume of dialysis solution administered is also important for the total fluid removal, as it will take longer for the concentration gradient to decline in a large volume of fluid.
12 Fluid Removal Transport capacity for the fluid across the Peritoneal membrane varies greatly between patients. Mainly the pore area and the capacity to reabsorb fluid which affect fluid removal
13 Solute Removal The most important principle for solute removal in PD is diffusion, for which the driving force is the concentration gradient between the blood and the dialysis fluid. Small solutes move quickly through the membrane creating an equilibrium during the dwell period. Larger solutes move slowly across the peritoneum, reaching equilibrium point takes a long time.
14 Fluid Removal So……………………………………………………………… Both solute and fluid removal in PD is controlled by 1) glucose concentration 2) dwell time 3) volume 4) peritoneal membrane characteristics
15 PD Fluid Components of PD fluid can be divided in into electrolytes, buffer and osmotic agents. The most abundant electrolyte in PD fluid is sodium. It’s hyponatremic, so it has a concentration lower than blood to ensure sufficient removal of sodium. Standard PD fluid contains no potassium. Today, there is a tendency to use normcalcemic PD fluid as many patients receive extra calcium from phosphate- binding drugs. The buffer normally used in PD is lactate. Lactate is metabolised to form bicarbonate, the most important buffer in the blood.
16 PD Fluid The major osmotic agent used today is glucose. As the rate of fluid transport is related to the osmotic strength of the PD solution, the ultrafiltration can be controlled by an appropriate glucose concentration. Normal range of concentrations include 1.5%, 2.3% & 4.25%. Glucose is not ideal, as it is rapidly absorbed from the PD fluid. This may lead to problems with fluid removal, patient gains calories and can lose there appetite. Resulting in overweight and malnourishment. Disturbances of the carbohydrate and lipid metabolism may also occur. Research to find alternative osmotic agents has resulted in new products which are still not widely used. Amino acids are an interesting alternative as they provide nutritional supplement. High molecular weight glucose polymer (extraneal/icodextrin) provide sustained ultrafiltration for long overnight dwells.
17 Treatment Modes CAPD/APD Whatever method is used it is of the highest importance that the treatment is performed with great hygienic care as the introduction of bacteria in to the abdomen can lead to peritonitis. Continuous Ambulatory Peritoneal Dialysis, CAPD is most widely used; know as the manual method where each exchange is taken care of by the patient. Typically regime 4 bags x 2L/day. This means that the patient performs 4 bags during the day.
18 Treatment Modes CAPD/APD To increase the efficiency of PD and help the patient with the exchanges, a machine can be used, known as Automated Peritoneal Dialysis of APD. Advantages of APD v CAPD are 1) higher clearance of solutes, as higher volumes can be used 2) better fluid removal, as shorter dwell time can be used 3) more freedom during the daytime as no exchanges need to be made. Drawbacks of APD are that of a higher cost and portability.
19 Complications The most common in PD and also one of the major problem with the therapy in general, is PERITONITIS. The normal cause of inflammation is bacterial infection. Bacteria from the patients skin, equipment or from an unclean environment can be flushed into the abdominal cavity by the instilled PD fluid. The exit site of the catheter is also an infection route. In rare cases bacteria may enter from the intestines.
20 Complications D uring an episode of peritonitis many events take place in the affected tissue which may change the transport characteristics of the peritoneum (eg formation clots or adhesions) Repeated episodes eventually damage the peritoneum and force the patient to choose another treatment (HD). PD leaks, Hernia’s are another complications; partly a result of the increased abdominal pressure. APD can be a suitable option (lying down) as these patients are not CAPD candidates with the added abdominal pressure. Patient technique survival is better for HD; ie, patients can usually be treated with HD for a longer period of time. Reoccurring episodes of peritonitis together with loss of residual function are the major causes for patients transferred from PD to HD.
21 Treatment Strategy Many factors are considered and assessed to ascertain the best effective treatment for each individual patient………………………………………… Personal needs and preferences are of great importance, to suit lifestyle. Some prefer nightly treatments and are comfortable operating a machine PD is often chosen as a temporary treatment of transplant candidates, waiting for a suitable kidney. PD is often the best choice for pediatric patients; as the continued blood purification is probably the reason why children grow better than HD. Cardiovascular problems and blood access problems can be impossible to treat on HD; PD is an alternative. The peritoneal membrane characteristics, ie. The transport properties of the peritoneum can vary widely among patients. A small person may have a large peritoneal surface area with many pores available for transport. However, a large person who needs much more dialysis, may have only a small peritoneum.
22 Ged PD Coordinator Thanks for your time this morning and have a great day!!!!!
23 Peritoneal Dialysis Information and pictures in this presentation has been collaborated in conjunction with; Gambro BASICS Fresenius Medical Care Baxter Health Care
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