Principles of Peritoneal Dialysis Flashcards
How does the peritoneal membrane work in dialyzing the patient?
The Peritoneal Membrane is a semi-permeable membrane that lines the abdominal walls and covers the abdominal organs.
The peritoneum derives its blood supply from the arteries in the abdominal wall. This blood drains into the systemic circulation.
The visceral peritoneum is supplied by blood from the mesenteric and celiac arteries, which drain into the portal vein.
Sub-diaphragmatic lymphatics are responsible for 80% of the drainage from the peritoneal cavity.
The drainage is then absorbed into the venous circulation through the right lymph duct and the left thoracic lymph duct.
The semi-permeable membrane allows solutes and water to be transported from the vascular system to the peritoneal cavity and vice versa through diffusion.
Is the peritoneal membrane closed in men or women?
The membrane is a closed sac in males.
Is the peritoneal membrane open in men or women?
The fallopian tubes and ovaries open into the peritoneal cavity in females.
Describe how diffusion removes wastes in peritoneal dialysis (PD)?
Diffusion is the passage of solutes through a semi-permeable membrane from an area of greater concentration to an area of lesser concentration, until equilibrium is reached.
Solute transport is influenced by the membrane permeability and size, characteristics of the solute, the volume of dialysate instilled, and blood flow to the membrane.
Solute transport can be increased by maximizing the contact of dialysis solution with the membrane by placing the patient in a supine position (laying down) or increasing the exchange volume.
How does osmosis remove fluid in PD?
Osmosis is the passage of water through a semi-permeable membrane from an area of lower solute concentration (more water) to an area of higher solute concentration (less water).
The peritoneal solution contains dextrose.
Dextrose acts as an osmotic agent by drawing fluid from the blood into the peritoneal space where the solution is stored.
The solute dextrose is the osmotic agent. The effectiveness of the solute depends on the resistance the membrane exerts to keep the solute from passing through and the concentration of solute present in the solution.
The more solutes the more fluid is removed.
How does ultrafiltration work in PD?
Ultrafiltration is the removal of plasma water by means of a pressure gradient.
Net ultrafiltration is the amount of fluid removed by PD.
Two things determine net ultrafiltration: how much water is transferred from the capillaries to the peritoneum and how much water is reabsorbed into the capillaries and lymphatic system.
What 2 things determine net ultrafiltration?
Two things determine net ultrafiltration:
- how much water is transferred from the capillaries to the peritoneum
and
- how much water is reabsorbed into the capillaries and lymphatic system.
What impacts net ultrafiltration?
There are several factors that impact net ultrafiltration.
The physiochemical nature of the peritoneal membrane affects UF, and is influenced by individual patient variations, pathological changes, and pharmacological influences.
Some patients have a membrane that is more “porous” than others do.
There are variations in the thickness of the membrane as well.
Inflammation and or adhesions may change the nature of the membrane.
Certain hormones and many medications also alter the characteristics of the membrane.
How does the vascular surface area impact ultrafiltration?
An important point to consider is that it is not only the anatomical surface area, but also the vascular surface area that impacts ultrafiltration.
Together, they make up the effective surface area.
The number and size of perfused capillaries determine the vascular surface area.
The vascular surface area is variable and plays a larger role in osmosis and thus ultrafiltration.
In other words, the more capillaries the more surface area for osmosis and ultrafiltration to occur.
What affects the osmotic gradient?
Increasing the dextrose concentration of the dialysis solution enhances fluid removal by increasing the osmotic gradient between the plasma and the peritoneal fluid.
Generally, the higher the dextrose concentration, the larger the volume of fluid removal.
The osmotic gradient is always greatest at the beginning of the dialysis exchange.
As osmotic equilibration is achieved, the gradient decreases.
Some re-absorption of fluid occurs when dialysate dwells beyond the point of equilibration.
Fluid crosses the membrane faster than solutes; therefore, longer dwell times are needed for solute transfer.
What is the significance of protein loss in PD patients and why does it occur?
Loss of protein leads to poor health and increases the risk of infection, morbidity and mortality and poor wound healing.
There is a significant amount of protein lost in dialysate.
The amount lost varies from patient to patient, but averages between 5-15 g/day.
Protein loss stabilizes and remains relatively constant unless the patient experiences peritonitis, then the protein loss increases during the infection.
It is important the protein intake be adequate in the PD patients and may need to be increased.
Work with the dietitian to improve protein intake.
Some patients may require nutritional supplements.
What other substances besides protein are lost to PD?
Amino acids, water-soluble vitamins, hormones and some medications are other substances lost to the PD fluid.
Are there substances absorbed into the blood stream during PD?
Some substances are absorbed from the dialysis solution into the systemic circulation.
Examples are dextrose and calcium.
The increased concentration of dextrose in the dialysis solution will also cause dextrose to move into the systemic circulation.
Dextrose may suppress appetite and increase blood glucose levels.
Calcium uptake may increase serum levels.
What is ultrafiltration failure (UFF)?
Ultrafiltration Failure (UFF) occurs when fluid is not adequately removed.
The degree of UF loss varies from patient to patient.
Studies suggest there is an increased risk of change or loss of UF capacity in PD patients related to length of time on PD.
If ultrafiltration failure is suspected, patient should be evaluated for membrane effectiveness.
A thorough history and physical is recommended. Check for residual renal function (RRF), noncompliance with diet or exchanges, inappropriate fluid choices, inadequate drain or dwell times and hyperglycemia.
How is ultrafiltration failure (UFF) determined?
A transient change in permeability due to peritonitis can also lead to decreased fluid removal.
If the cause of UF loss has not been determined after completing a history and physical, a 2 liter flush can be performed.
Observe and document the length of drain and fill times, drain volume, presence of fibrin and position needed for draining.
X-Ray can also determine catheter placement and presence of kinking or leaks.
Many factors contribute to changes in the performance and function of the peritoneal membrane.
In order to provide quality patient care, a thorough assessment, evaluation, diagnosis and treatment plan must be formulated for every patient who presents with signs/symptoms of UFF.
Although some patients will need a permanent modality change to hemodialysis, others will be able to maintain their chosen dialysis modality (peritoneal) with proper management of these complications.
