Peritoneal dialysis

The use of peritoneal dialysis for several advantages over hemodialysis: better preservation of residual kidney function, fewer volume shifts, and more flexibility.

Successful peritoneal dialysis requires that patients be motivated and cognitively able and must have a preserved peritoneal anatomy.

The peritoneum histologically consists of a single layer of mesothelial cells resting on a submesothelial interstitial tissue, a gel like matrix containing fibroblasts, adipocytes, collagen fibers, nerves, lymphatic vessels, and capillaries.

The endothelium of the peritoneum‘s capillaries functions is the filter that regulates peritoneal transport.

Peritoneal dialysis involves diffusion and osmosis through a peritoneal membrane, measuring 1 m², that is highly vascularized with the flow rate of 100 to 150 mL per minute and has a total available capillary surface area of approximately 2 m².

The peritoneum therefore provides a suitable membrane for the performance of dialysis.

The peritoneum approximates body surface area in size.

Clean dialysate is placed in the patient’s abdominal cavity via a surgically placed catheter, it contans favorable fluid and electrolyte concentrations and remains in the abdomen for a number of hours, and is then drained removing metabolic wastes and other toxins that have diffused out of the blood into the fluid.

Water moves from the blood into the dialysate via osmosis and the osmotic pressure gradient is generated by a high concentration of glucose in the dialysate, drawing water into the abdominal compartment.

In individuals with less peritoneal vascularity solutes diffuse slowly in both directions:waste products accumulate in the dialysate slowly in the glucose gradient favoring ultrafiltration dissipates slowly.

Glucose has been used as the prototypical crystalloid osmotic agent to drive water removal in peritoneal dialysis.

Glucose is a small osmotic agent with a molecular weight of 180 g per mole that is prone to crystallization but easily diffuses across semi permeable membranes, hence it is known as a crystalloid substance.

In contrast choloid and non-crystalloid substances are retained by membranes because they are large.

Glucose is absorbed from the peritoneal cavity during the dwell time, and has unwanted metabolic effects and is associated with a decline in the osmotic gradient, with a decrease in net ultrafiltration of drained fluid volume.

The endothelial lining of capillaries and venules allows for water and solute exchanges through a three pore model.

ultra small pores are aquaporin-1 water channels which facilitates the transfer of water but not of solutes and is responsible for half the water removal that occurs through glucose crystalloid osmosis.

Peritoneal dialysis uses the peritoneum as a biological membrane for solute and fluid removal.

The process exchanges solute and volume between the extracellular fluid in the peritoneal dialysis solution across the peritoneal membrane.

Sodium transfer is across the peritoneal capillaries bidirectionally.

To prevent pericatheter leakage, peritoneal dialysis is started after a few weeks after tube placement.

An electrolyte in glucose containing solution fills the peritoneal cavity and is allowed to dwell there.

Typically there are four manual exchanges using 2 L of dialysate per day.

Constituents of dialysate are divided into three categories: osmotic agents, buffers, and electrolytes.

Glucose is divided in three concentrations 1.5%, 2.3%, and 4.25% and is the principal osmotic agent use for peritoneal ultrafiltration.

Other asthmatic agents including amino acids and icodextrin  are available.

Icodextrin Is a colloid osmotic agent that does

not diffuse across the peritoneum, and it affects ultrafiltration, that is sustained 12 to 16 hours.

A bedside cycler can perform exchanges while the patient is sleeping, as an automated peritoneal dialysis.

When dwell times increase, there is often an increase in retained fluid.

Fluid may accumulate in the retroperitoneum, the pleural cavity, or inguinal regions.

Hydrothorax may appear in the right chest cavity via a diaphragmatic defect.

Risk of infection is extremely low and the international Society of Peritonal Dialysis recommends the monitoring of peritoneal dialysis programs to achieve rates of infection lower them one case per 18 patient months.

It is associated with treatment specific complications including infection-related and mechanical.

Infections and cardiovascular complications are the most frequent causes of hospitalizations in peritoneal dialysis patients.

Associated with 2 hospitalizations/year.

Fluid exchanges can be done several times a day via continuous ambulatory peritoneal dialysis.

Efficacy can be limited by recurrent peritonitis and loss of peritoneal clearance or residual renal function.

Infection can occur with a breach in  aseptic technique that introduces infectious organisms into the peritoneal dialysis catheter, the catheter exit site or tunnel infection with skin organisms that might migrate into the peritoneal cavity, translocation of organisms from the G.I. or GU tract, or, in less than 1% of cases hematogenous spread to the peritoneal cavity.

When bacterial organisms enter the peritoneal cavity, polymorphonuclear leukocytes induce an  inflammatory reaction that causes abdominal pain and a cloudy dialysate.

Residual renal function is better preserved with peritoneal dialysis than with hemodialysis.

30-45% of patients will develop acquired cystic disease and of those 5-30% may develop renal cancer.

7% of patients on dialysis are on peritoneal dialysis.

Peritoneal dialysis is cheaper than hemodialysis by approximately $20,000 per patient per year.

There is great variability in water and solute transport across the peritoneal membrane among patients, which influences dialysis prescriptions and outcomes.

The peritoneal small-solute transport rate is associated with a polygenic risk score with a 17% heritability.

Aquasporin-1 is a family of water channels that facilitates water transport across membranes: A common variant is associated with decreased ultrafiltration and increased risk of death among patients treated with peritoneal dialysis.

Patients to start on PD are usually younger, healthier, more likely to be employed than are patients starting hemodialysis.

It is suggested than older patients with diabetes and congestive heart failure do not do as well on PD.

Over the last 8 years there has been experiencing reduction in mortality rate for new patients starting PD in the US.

In the most recent studies patients starting on PD compared to patients hemodialysis have similar outcomes (Mehrotra R et al).

Peritonitis in patients with peritoneal dialysis manifests with abdominal pain, fever, nausea, vomiting, diarrhea, tenderness, and rebound tenderness on clinical exam.

Peritoneal dialysis associated peritonitis is diagnosed with the clinical features noted above and or with a cloudy peritoneal fluid, a fluid with white blood cell count greater than equal to 100 cells per microliter with greater than or 50% of neutrophils in the dialysate.

Peritoneal dialysis associated peritonitis occurs in approximately 30 to 40% of patients during the treatment course and develops when infectious organism gains access to the peritoneal cavity.

Peritoneal dialysis programs should strive to achieve infection rates lower than one case per 18 patient months.

Infections and cardiovascular complications are the most frequent causes of hospitalization in patients on peritoneal dialysis.

Corraborating tests for peritonitis on PD include an elevated white blood cell evaluation on peripheral blood and peritoneal fluid analysis.

Abdominal pain may be absent in peritoneal dialysis associated peritonitis.

Manipulation of the open Catheter must be done on the aseptic technique.

Catheter malfunction is common in peritoneal dialysis and can be divided into failure in dialysate inflow or outflow.

Inflow failure can be due to intraluminal or extraluminal obstruction by fibrin strands, or omental wrapping, respectively.

Outflow failure is more common and describes an incomplete recovery of previously insilled dialysate within 45 minutes of a drain start.

Constipation is a frequent cause of outflow failure.

Malposition or migration of the catheter tip is an important differential diagnosis for this problem.

The catheter tip is located between the bladder bladder and rectum or uterus and rectum and can be identified by their radioopaque stripe.

Cloudy peritoneal fluid maybe seen with active peritonitis or chemical peritonitis, malignant processes or chylous fluid.

With suspicion of the presence of peritoneal infection antibiotics should be started empirically.

Antibiotics can be delivered intraperitoneally or intravenously and should cover both gram-positive and gram-negative organisms.

Peritoneal fluid within elevated white count of greater than 100 cells per high-powered field is consistent with the diagnosis of peritonitis.

Empirical antibiotic coverage should include gram-positive andvgram-negative coverage: agents should either be first-generation cephalosporins or vancomycin and third-generation cephalosporins, quinolone or gentamicin..

Iatrogenic hypoglycemia may occur with icodextrin, a peritoneal dialysis solution, when inappropriate glucose meters are used.

Icodextrin osmotic agent inducesna slower, sustained ultrafiltration than glucose.

Generally, a single lumen silicone rubber catheter traverses the anterior abdominal wall and accesses the peritoneal cavity.

The catheter is usually positioned with its tip in the true pelvis.

The exit site is oriented so the catheter is directed either inferiorly or laterally, but not superiorly, to reduce infection.

Dialysate is instilled into thr peritoneal cavity and allowed to dwell for a define period, after which it is drained and fresh fluid is instilled.

All exchanges are performed in a sterile fashion.

They volume of fluid installed is 2 L in most adults.

Periennial dialysis may be performed manually three or four times daily, with the dialysate dwelling in the abdominal cavity between exchanges, and this is termed continuous ambulatory peritoneal dialysis.

 Mechanically peritoneal dialysis can be performed over several hours in the procedure called automated peritoneal dialysis.

Automated peritoneal dialysis is performed, usually impatient with residual kidney function, who have sufficient solute removal and ultrafiltration to warrant dialysis only at night which is termed nocturnal intermittent peritoneal dialysis.

Absolute contraindications to peritoneal dialysis include: an insufficiently clean environment, inadequate cognitive or physical abilities on the part of the patient or assistant, and lack of act suitable peritoneal cavity due to scarring or adhesions.

Studies show that hemodialysis and peritoneal dialysis are associated with similar survival among patients with end-stage kidney disease: similarly health related quality of life is equivalent.

Complications of PD are divided into infectious and non-infectious types.

The most common infectious complication is bacterial pneumonitis with a grand positive organism predominant of a gram-negative agents.

Mycobacterial infection is rare, but is more common in under developed countries.

Fungal peritonitis is the most serious peritoneal dialysis related infection and requires catheter removal.

Peritoneal infection rate should not exceed 0.5 episodes per patient year.

Many peritoneal dialysis related peritonitis infections can be treated as an outpatient, but approximately 50% require hospitalization.

Mortality with peritoneal dialysis peritonitis ranges from 3 to 10%.

Intraperitoneal administration of antibiotics is preferred as it delivers higher concentrations of drugs directly to the infected site.

Non-infectious complications of peritoneal dialysis include: catheter malfunction, increased intra-abdominal pressure, and metabolic consequences of glucose rich dialysate.

Complications related to mechanical processes include: flow dysfunction, fluid leaks, and pain on infusion or draining of dialysate.

Constipation can commonly lead to poor outflow when distended bowel loops impinge on the catheter.

Metabolic complications of peritoneal dialysis include the development of metabolic syndrome, and hypokalemia.

Peritoneal dialysis contains no potassium, therefore patients on peritoneal dialysis are more likely to develop hypokalemia than hyperkalemia, which is more common with hemodialysis.

Patients receiving peritoneal dialysis are permitted to consume a more potassium rich diet than patients receiving hemodialysis.

Patients receiving long-term PD may develop encapsulating peritoneal sclerosis with peritoneal fibrosis and resulting bowel obstruction in malnutrition.

Patients with features consistent with peritoneal dialysis associated peritonitis should receive empirical broad-spectrum intraperitoneal antibiotics after peritoneal dialysis fluid samples are collected for Gram stain and culture.

Intraperitoneal  antibiotics are  the preferred route of administration, although intravenous or oral route can be used if necessary.

Approximately 80% of peritoneal dialysis associated peritonitis episodes resolved with intra-peritoneal antibiotics.

50% of such patients can be treated as an outpatient.

The peritoneal dialysis catheter can be removed for refractory and complicated infections.

The mortality rate for peritonitis related deaths is less than 5% of episodes of dialysis associated peritonitis.