Flashcards in Principles of Peritoneal Dialysis Deck (27):
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:
1. how much water is transferred from the capillaries to the peritoneum
2. 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.
What is Type I Membrane Failure?
There is an increase in solute transport and it is
responsible for 70-80% of all instances of UFF.
Type I Failure causes an increase in glucose absorption, which leads to a loss of the osmotic gradient.
The etiology of Type I failure is unknown.
Some studies suggest severe and multiple episodes of peritonitis and time on dialysis.
What is the treatment for Type I Failure?
Treatment includes resting the peritoneum for at least 4 to 16 weeks.
This temporary modality change has been associated with remesothelialization (tissue growth and healing) of the peritoneal membrane and an increase in ultrafiltration.
The continuation of hypertonic dialysate solutions should be discouraged, as it exposes the peritoneal membrane to further damage.
The dialysis prescription may need to be changed to cycling or IPD in order to improve UF and reduce absorption.
For some patients, a permanent modality change to hemodialysis may be the only option.
What is Type II Membrane Failure or sclerosing peritonitis?
This type of failure is characterized by low solute and water transport. It is relatively rare, occurring in less than 1% of PD patients.
Some amount of sclerosis occurs in most PD patients over time, but usually has a low clinical impact and rarely extends to the whole peritoneum.
What is Sclerosing peritonitis?
The formation of thick fibrous sheaths that cover, bond and constrict the viscera preventing normal motility or movement of the bowel.
Can extend into the abdominal organs and can be fatal to the patient.
What are signs and symptoms of type II membrane failure?
Fluid overload and uremia.
Sclerosing peritonitis can also include nausea, vomiting, diarrhea, anorexia, constipation, fever, weight loss, abdominal distention, abdominal pain, palpable abdominal mass, ascites, chronic bloody effluent and incomplete or complete bowel obstruction.
What is the treatment of type II membrane failure?
Treatment may include stopping PD and removing the catheter.
Surgery may be needed if intestinal obstruction or bowel necrosis is present.
Due to the high mortality rate associated with type II failure, preventive measures should be taken. Use biocompatible solutions, close monitoring of diet and medications along with treatment of peritonitis is indicated.
Avoid using excessive intraperitoneal medications to prevent further inflammation.
What is Type III Membrane Failure?
An increase in lymphatic absorption leading to a lower net ultrafiltration.
It is estimated that Type III membrane failure may be a contributing factor in approximately 60% of UFF.
May be due to an increase in intraperitoneal pressure. There is a strong negative correlation between intraperitoneal pressure and net ultrafiltration.
Diagnosis is often made by exclusion of other causes of UFF.
What is the treatment for Type III Membrane Failure?
Decrease the intraperitoneal pressure by changing to CCPD or decreasing volumes.
Utilizing shorter dwells and draining the patient at peak UF before extensive re-absorption occurs can maximize the net UF.
What is aquaporin failure (AQF)?
A malfunction in the ultra-small pores (called aquaporin channels) in the capillary wall.
These pores normally account for 40-50% of UF, and allow water, but not solutes to pass through.
The etiology is unknown but it is felt that exposure to high glucose dialysate leads to the formation of advanced glycosylation end products, which may impair aquaporins.
What is the treatment for aquaporin failure (AQF)?
Use of shorter, more frequent exchanges and use of higher glucose solutions.
If available, a colloid-type osmotic agent
(Icodextrin) may help sustain UF at the small and large pores.
However, these agents are not without some risks, and treatment may not be effective.
How do we optimize the PD dose?
To improve peritoneal dialysis dose take into consideration the patient’s body mass, residual renal function and peritoneal transport rates.