An Update on Peritoneal Dialysis
Peritoneal dialysis (PD) is the main form of renal replacement therapy (RRT) performed in the home environment. The number of patients treated with PD in the United States continues to rise as a result of multiple factors, including economic incentives and improved patient and provider education. The outcomes on PD were recently explored in an article in AJKD.
When evaluating the two PD modalities, survival amongst CAPD (continuous ambulatory PD) versus APD (automated PD) is similar. It remains uncertain if a survival advantage exists between PD versus in-center hemodialysis (iHD). Access type does indeed impact mortality as shown by a Canadian study of over 38,000 patients initiating dialysis. The study demonstrated that the risk of death was 20% higher in patients who started HD with a central venous catheter (CVC), compared to the PD group in the first five years of dialysis. In addition, those starting HD with an AV access had similar survival to the PD group.
Congestive heart failure with preserved ejection fraction is a common co-morbidity among PD patients, and has been noted to lead to poor outcomes. Diabetic patients on CAPD are noted to have worse survival and technique success than their age matched non-diabetic controls. The role of residual renal function (RRF) continues to be of importance with respect to survival. The use of ACE inhibitors or ARBs has been shown to preserve this function.
Multiple PD catheter options exist, and to date, no one catheter design has proven to be superior. Although numerous PD catheter insertion techniques exist, it is important to note that laparoscopic placement is associated with longer operative times, higher costs, and the need for general anesthesia, but can proactively address problems that may adversely affect catheter outcomes. The laparoscopic approach is associated excellent long term outcomes. The role of an embedded PD catheter should also be considered as it may allow for an urgent initiation of RRT while avoiding a CVC.
Conventional PD solutions use dextrose as the osmotic agent with 3 main concentrations: 1.5%, 2.5%, and 4.25%. These solutions have been associated with both local and systemic toxicities, which are a result of exposure to the low pH, lactate buffer, hyperosmolality, glucose as the osmotic agent, and glucose degradation product (GDP) levels. The main glucose-sparing agent used in PD is icodextran, which has been associated with improved glycemic control, glucose-induced lipid abnormalities, and ultrafiltration.
The concept of PD adequacy has multiple components. Factors such as nutrition, anemia management, mineral and bone disorders, and acid-base balance are critical. Total solute clearance as expressed by weekly Kt/Vurea is the main clinical factor used to assess adequacy. A delivered weekly clearance should be a minimum Kt/Vurea of 1.7, combining both peritoneal and renal clearances.
Adequacy can be achieved using three modalities of PD. CAPD, continuous cyclic peritoneal dialysis (CCPD), and nocturnal intermittent peritoneal dialysis (NIPD). Adjustments to the prescription can be based on achieved adequacy and the peritoneal equilibration test (PET).
In addition to adequacy, maintaining euvolemia is essential in PD. This can be achieved by PD prescription alterations, maintaining sodium restriction guidelines, preserving RRF (ACEi/ARB therapy, avoiding nephrotoxins/hypovolemia/peritonitis), and the use of diuretics. In line with these maneuvers, understanding the role of transport characteristics and PD prescription management is key.
Infectious complications of PD can be devastating, and are associated with significant morbidity and mortality. 15-18% of patients treated with PD die as a result of peritonitis. One of the key strategies used to reduce the rate of peritonitis is prevention of exit site infections. This can be achieved via exit site care and topical gentamicin applied to the exit site. Empiric treatment should exit site infections occur should include a penicillinase-resistant or first generation cephalosporin.
Patients presenting with cloudy effluent should be presumed to have peritonitis. This is confirmed by a cell count and culture of the peritoneal fluid. An effluent white blood cell count of 100 per microliter after a 2 hour dwell with at least 50% neutrophils indicates inflammation, with peritonitis as the most likely cause. Empiric treatment to cover both gram-negative and gram-positive organisms should be initiated until final culture results are reported. It is important to note that the most frequent cause of peritonitis is gram-positive in origin. Intraperitoneal administration is recommended unless the patient is hospitalized and acutely ill, in which case IV antibiotics may be appropriate.
The three major non-infectious complications related to PD include peritoneal membrane changes, ultrafiltration failure (UFF), and encapsulating peritoneal sclerosis (EPS). Long-term use of PD may result in morphological changes. There are three types of membrane failures with Type 1 (high transporter) being the most common followed by Type 3 (aquaporin deficit and excessive lymphatic reabsorption). Type 2 (low transporter) membrane failure is the least common. EPS continues to be a devastating complication of PD, carrying a significant morbidity and mortality. The management of EPS can be supportive (nutritional), medical, or surgical.
Both urgent start PD and PD for AKI initiatives offer alternatives to the current treatment paradigms. In both cases the avoidance of vascular access and the complications associated with this may lead to possible overall better patient outcomes.
Dr. Sean Kalloo
AJKD Blog Contributor
To view the article full-text or PDF (freely available), please visit AJKD.org.
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