INTRODUCTION — Moderate to severe malnutrition (also called protein-energy wasting) is associated with an increased risk of death in patients on both hemodialysis and peritoneal dialysis. The early identification and treatment of malnutrition may improve nutritional status and patient outcome.
This topic reviews malnutrition among patients treated with peritoneal dialysis. Malnutrition among hemodialysis patients and among patients with chronic kidney disease who are not on dialysis is discussed elsewhere:
●(See "Patient survival and maintenance dialysis", section on 'Malnutrition' and "Overview of the management of chronic kidney disease in adults", section on 'Malnutrition'.)
●(See "Overview of the management of chronic kidney disease in adults", section on 'Malnutrition'.)
Malnutrition among older patients in the general population is discussed elsewhere. (See "Hospital management of older adults", section on 'Malnutrition'.)
CRITERIA FOR DIAGNOSIS — The diagnosis of malnutrition (protein-energy wasting) is based upon biochemical measures, anthropometric parameters, and history of dietary intake. In 2008, the International Society for Renal Nutrition and Metabolism (ISRNM) published standardized criteria for the diagnosis [1].
Four categories of criteria are recognized:
●Biochemical parameters – Biochemical surrogates for malnutrition such as serum albumin concentration of <3.8 g/dL, serum prealbumin <30 mg/100 mL, serum cholesterol <100 mg/100 mL
●Body mass – Body mass index (BMI) <23, unintentional weight loss of >5 percent weight over three months or >10 percent over six months, total fat percentage <10 percent
●Muscle mass – Reduction in muscle mass >5 percent in three months or >10 percent in six months, reduced mid-arm muscle circumference area, low serum creatinine
●Dietary intake – Unintentionally low dietary protein intake (DPI) <0.8 g/kg/day for at least two months, unintentionally low energy intake <25 kcal/kg/day for at least two months
The use of biochemical parameters alone may be less specific for the diagnosis of malnutrition in individuals who start peritoneal dialysis with nephrotic-range proteinuria and significant urine output. Such individuals may have a low serum albumin but have no other evidence of malnutrition. It has been shown that the normal rate of albumin synthesis is approximately 12 g/day, corresponding to a fractional albumin catabolic rate of approximately 4 percent/day (assuming total body albumin is approximately 270 grams in a normal individual), one-half of which is extravascular [2]. In peritoneal dialysis patients with chronic inflammation, there tends to be a decrease in overall albumin synthesis [3]. Finally, volume expansion may be associated with hypoalbuminemia. Hence, it is not clear that all individuals with biochemical abnormalities such as a low serum albumin are truly malnourished.
EPIDEMIOLOGY — Early publications estimated that 40 to 66 percent of peritoneal dialysis patients in the United States are malnourished [4-10]. In a subsequent study that defined protein-energy wasting by a serum albumin of <3.8 g/dL, 63 percent of peritoneal dialysis patients were classified as malnourished [11].
Many patients are malnourished when they begin dialysis. As an example, in one study, approximately 75 percent of patients initiating peritoneal dialysis were malnourished [12]. Nutritional parameters tended to improve after the initiation of dialysis in this study.
ETIOLOGY — Factors that contribute to the development of malnutrition among peritoneal dialysis patients include:
●Inadequate dialysis – As in nondialysis patients, solute clearance may influence appetite. At times, the amount of solute clearance by dialysis may be inadequate, which decreases appetite. Dialysis may be inadequate because the initial prescription was suboptimal, the dialysis dose was not increased in the setting of loss of residual kidney function, or because there was a change in the rate of solute clearance across the peritoneal membrane. (See "Inadequate solute clearance in peritoneal dialysis", section on 'Routine monitoring for adequate clearance'.)
●Protein loss into the peritoneal dialysate – Protein losses into dialysate contribute to malnutrition. Protein losses are often as high as 8 g/day and tend to be highest in patients who are rapid transporters [13-15]. (See "Rapid transporters on maintenance peritoneal dialysis".)
Protein losses into dialysate increase during episodes of peritonitis. As a result, peritoneal dialysis patients who have peritonitis tend to have biochemical evidence of malnutrition, such as a low serum albumin level. (See "Rapid transporters on maintenance peritoneal dialysis", section on 'Relationship between transport type and plasma albumin'.)
●Dialysate in the abdomen – Dialysate in the abdomen may impart a feeling of fullness that dulls the appetite. The mechanism by which this occurs appears to be independent of intragastric pressure increases [16]. In one study, intragastric pressures were no different when patients had a dialysis dwell and when they were dry [16].
●Slow gastric emptying – Slow gastric emptying may cause a feeling of fullness, which diminishes appetite. This is especially common among diabetic patients.
●Hyperglycemia-induced anorexia – Hyperglycemia induced by the absorption of glucose from the dialysate may suppress appetite [17,18]. This problem may be exacerbated by the frequent use of hypertonic exchanges to achieve adequate ultrafiltration [17,18].
●Continuous glucose absorption from the peritoneum – Continuous glucose absorption may suppress appetite, even in the absence of hyperglycemia [17].
●Protein loss into the urine – Many patients starting peritoneal dialysis still have significant residual kidney function and nephrotic-range proteinuria. Such patients may have a low serum albumin resulting from loss of albumin into the urine. In a retrospective review of 388 peritoneal dialysis patients in Hong Kong, among patients with significant proteinuria (>3500 mg/day) at the start of dialysis, a decline in residual kidney function was associated with an improvement in serum albumin concentration (baseline 3.05 + 0.61 versus 3.59 + 0.48 mg/dL at the end of follow-up) [19]. However, for all of the reasons reviewed above, among such patients, it is not clear that the low albumin is an accurate marker of malnutrition. (See 'Criteria for diagnosis' above.)
PREVENTION — It is important to prevent malnutrition because it is associated with increased mortality (see 'Prognosis' below). Optimal dietary protein intake for peritoneal dialysis patients is not known. Thus, recommendations are based upon indirect evidence and opinion. We generally instruct patients to eat 1.2 to 1.3 g of protein/kg per day. This is consistent with the recommendations from the 2005 European Best Practice Guidelines (EBPG) for peritoneal dialysis [20].
Early balance studies have suggested that a minimal protein intake of 1.2 g/kg per day is required to prevent malnutrition [21,22]. However, some patients ingest 0.9 to 1.0 g/kg per day without any obvious signs of malnutrition [23,24].
Dietary instructions should be reviewed at least quarterly. The initially recommended protein intake may be reduced during subsequent visits if the patient has high potassium, phosphate, or urea nitrogen concentrations, despite performing an adequate amount of dialysis. Protein intake should only be reduced if the patient has no evidence of malnutrition.
In addition to monitoring dietary intake to prevent malnutrition, an adequate amount of dialysis should be performed and comorbid conditions should be addressed since both contribute to malnutrition. (See "Prescribing peritoneal dialysis", section on 'Optimal amount of dialysis (target Kt/Vurea)'.)
MONITORING — We monitor weight, serum albumin, blood urea nitrogen (BUN), and serum creatinine monthly. (See "Assessment of nutritional status in patients on hemodialysis".)
The goal is to maintain a normal plasma albumin concentration (greater than 4.0 g/dL or 40 g/L).
However, it is recognized that most peritoneal dialysis patients do not have a normal serum albumin level. Serum albumin levels tend to be 0.2 to 0.3 g/dL lower in peritoneal dialysis patients compared with hemodialysis patients [25,26]. Because the baseline albumin value is often low, it is important to follow trends: Declining values for albumin, BUN, and creatinine suggest malnutrition.
Other methods that may be used to monitor nutritional status include following trends in lean body mass (LBM), maintaining logs of dietary protein intake, and estimating the protein catabolic rate (PCR) using urea kinetic modeling techniques.
The LBM is no longer routinely determined, since it requires an accurate measure of the total body water, which is difficult to determine. In addition, in the absence of an established baseline, a single determination of LBM is not likely to be clinically useful. However, if trends are followed over time, a decrease in LBM suggests worsening nutritional status.
Logs of daily dietary protein intake can provide an estimate of the patient's underlying nutritional status. However, it is difficult to determine protein intake using dietary logs because it requires extensive food record keeping by the patient and requires a dietitian specifically trained in evaluating food-intake histories.
Urea kinetic modeling techniques can also be utilized to calculate the PCR, which reflects the dietary protein intake. The PCR is also called the protein equivalent of nitrogen appearance (PNA). (See "Measurement of solute clearance in continuous peritoneal dialysis: Kt/V and creatinine clearance", section on 'Definitions and calculation'.)
The PCR may be estimated from the total amount of urea that is lost in dialysate and urine over a defined time. This is referred to as "the urea appearance." The urea appearance is presumed to reflect protein intake in a noncatabolic patient.
Since most dialysis units routinely use a kinetic modeling tool to measure dialysis adequacy (Kt/V), which also utilizes 24-hour collections of urine and dialysate urea, the data needed to calculate the urea appearance are readily available. However, in clinical practice, PCR is seldom used. The PCR may be falsely elevated due to catabolism.
EVALUATION — Any patient with a low plasma albumin concentration should be further evaluated for malnutrition, especially if other signs of malnutrition are present. (See 'Criteria for diagnosis' above.)
Patients should be interviewed by a nutritionist regarding dietary intake.
The patient should be questioned regarding compliance with the dialysis regimen, even if the Kt/V is at target. This is because the patient may be compliant with the regimen during the 24 hours of testing but not at other times. Among patients on automated peritoneal dialysis (APD), the device used for dialysis (ie, cycler) may have built-in software that records the treatments that are actually performed; these data should be reviewed, if available.
It is important to determine the reasons for noncompliance since the dialysis regimen may be changed to encourage compliance. (See 'Treatment' below.)
It is important to exclude or treat any overt or occult comorbid disease that might be impairing nutritional status. The evaluation should include a complete history and physical examination and directed laboratory and radiologic tests. (See "Failure to thrive in older adults: Evaluation", section on 'General evaluation'.)
A chronic inflammatory state should be excluded. Patients may have a low albumin as part of a chronic inflammatory state. Such patients typically have a low serum albumin, elevated ferritin level, and increases in other markers of chronic inflammation, such as C-reactive protein (CRP) and sedimentation rate. The approach to and treatment of this condition is discussed separately. (See "Inflammation in patients with kidney function impairment".)
Rapid peritoneal transport with associated peritoneal albumin losses should be excluded as a cause of an isolated low serum albumin. Rapid transporters can be identified by performing a standardized peritoneal equilibration test (PET). These patients may need even higher dietary protein intake to prevent negative nitrogen balance. (See "Peritoneal equilibration test".)
TREATMENT — Among all peritoneal dialysis patients who have evidence of malnutrition, no evidence of a comorbid condition that explains the malnutrition, and no evidence of rapid transport by peritoneal equilibration test (PET), we do one or more of the following:
●Increase the dialysis dose or change the regimen to one that increases appetite or encourages adherence.
●Prescribe dietary supplements.
●If malnutrition is severe enough and increasing or changing the dialysis dose is not feasible, a transfer to center hemodialysis may be indicated.
Interventions are discussed individually below.
Increase the dialysis dose — Among patients who have no evidence of comorbid disease or chronic inflammation and no evidence of rapid transport on PET and are compliant with the current dialysis prescription, the dialysis dose should be increased. This is most easily achieved by increasing the dwell volume per exchange (eg, from 2 to 2.5 L) or by increasing the number of exchanges per day. (See "Prescribing peritoneal dialysis", section on 'Adjustment in prescription'.)
The effect of increased dialysis dose on protein intake has been demonstrated. This relationship was first demonstrated in a randomized study of hemodialysis patients in whom the intensity of dialysis was increased by enhancing dialysis time, blood flow, and/or membrane surface area [27]. As the Kt/V rose from 0.82 to 1.32 over a three-month period, there was a concurrent elevation in protein catabolic rate (PCR) from 0.81 to 1.02 g/kg per day. A second group in which the dialysis regimen was unchanged had no increase in either Kt/V or PCR.
The relationship between nutritional intake and dialysis dose among peritoneal dialysis patients was examined in the Canada-United States (CANUSA) peritoneal dialysis study group trial, in which 680 patients were followed for approximately two years [28]. The correlation between changes in peritoneal dialysis adequacy and alterations in nutritional intake was evaluated using numerous parameters of intake, including serum albumin, subjective global assessment (SGA), lean body mass (LBM), PCR, and normalized protein catabolic rate (nPCR). For the first six months, a direct correlation was observed between increased peritoneal dialysis and improvement in all parameters of nutrition except for the serum albumin concentration. In addition, at 6 to 18 months of follow-up, a decrease in total clearance due to the loss of residual kidney function was associated with a nonsignificant trend toward reduced LBM and SGA and significant declines in PCR and nPCR.
In another study, improved body weight was observed with more frequent, daily hemodialysis [29].
Change the dialysis prescription — The dialysis prescription may be changed to increase appetite or encourage adherence:
●In order to increase appetite, the usual glucose-containing dialysate may be substituted with an amino acid-containing dialysis solution for one exchange per day. We believe that, if used only once a day, such solutions are safe. However, these solutions are not available in the United States.
In 2005, the European Best Practice Guidelines (EBPG) on peritoneal dialysis recommended considering the use of one amino acid exchange per day in malnourished patients [20].
There are potential problems with amino acid solutions. Although the use of a single 1.1 percent amino acid solution has approximately the same ultrafiltration profile as a 1.5 percent dextrose dwell, in one study of diabetic peritoneal dialysis patients, the use of an amino acid solution as part of a glucose-sparing prescription was associated with an increase in mortality [30]. The increased mortality appeared to be due, at least in part, to volume overload, possibly related to decreased ultrafiltration.
●The dialysis regimen may be changed to encourage adherence. As an example, among continuous ambulatory peritoneal dialysis (CAPD) patients performing five 2-liter exchanges per day, a change to four 2.5-liter exchanges per day or a change to automated peritoneal dialysis (APD) may encourage adherence. (See "Evaluating patients for chronic peritoneal dialysis and selection of modality", section on 'Initial modality'.)
Dietary supplements — Dietary supplements may be required in patients with persistent malnutrition, despite a seemingly adequate dialysis dose. Use of oral protein supplements is one option. (See "Pathogenesis and treatment of malnutrition in maintenance hemodialysis patients", section on 'Oral supplements'.)
PROGNOSIS — In the peritoneal dialysis population, when surrogate markers of malnutrition (serum albumin or creatinine concentrations) are used as predictors of mortality risk, mortality is increased in a dose-dependent fashion, with either hypoalbuminemia or a low plasma creatinine concentration predicting an increased relative risk of death (figure 1).
In the prospective, multicenter Canada-United States (CANUSA) study of peritoneal dialysis patients, each 1 g/dL increase in the plasma albumin concentration was associated with a decrease in the relative risk of death by 6 percent [31].
A related issue is the nutritional status upon initiation of peritoneal dialysis. Increasing evidence suggests that survival is lower and nutritional status remains poor if dialysis is initiated late in the course of chronic kidney disease, particularly among those who are malnourished and have minimal kidney function [32].
The importance of nutrition was illustrated in a study that compared serum creatinine and albumin in patients who survived one year on continuous ambulatory peritoneal dialysis (CAPD) with those who did not [7]. Compared with nonsurvivors, survivors had a higher plasma albumin concentration (3.4 versus 3.7 g/dL [34 versus 37 g/L], respectively) and a higher plasma creatinine concentration (9.8 versus 10.7 mg/dL [866 versus 946 micromol/L], respectively).
However, as noted above, hypoalbuminemia may result from multiple causes, including chronic inflammation [33]. As an example, a possible mechanism for the increased mortality associated with hypoalbuminemia may be via accelerated atherosclerosis. A strong relationship has been demonstrated between malnutrition, elevated C-reactive protein (CRP) levels, hypoalbuminemia, and atherosclerosis, which is referred to as the malnutrition, inflammation, and atherosclerosis (MIA) syndrome [34,35]. (See "Inflammation in patients with kidney function impairment", section on 'Malnutrition may lead to inflammation'.)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Dialysis and diet (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Moderate to severe malnutrition is common in patients undergoing continuous peritoneal dialysis. Many patients are malnourished when they begin dialysis. (See 'Introduction' above and 'Epidemiology' above.)
●Factors that may contribute to the development of malnutrition among peritoneal dialysis patients include inadequate dialysis, loss of protein and amino acids into dialysate, loss of proteins into the urine, anorexia due to feeling full because of the dialysis dwell or slow gastric emptying, or anorexia due to glucose absorption from the peritoneum. (See 'Etiology' above.)
●The optimal protein intake to prevent malnutrition among peritoneal dialysis patients is not known. For all peritoneal dialysis patients, we target 1.2 to 1.3 g of protein/kg per day. Dietary instructions should be reviewed at least quarterly. (See 'Prevention' above.)
●Among all patients on peritoneal dialysis, we monitor nutritional status monthly. We monitor weight, serum albumin, blood urea nitrogen (BUN). and serum creatinine. The goal is to maintain a normal plasma albumin concentration (greater than 4.0 g/dL or 40 g/L). One could also follow trends in BUN, creatinine, lean body mass (LBM), and protein catabolic rate (PCR) over time. Estimations of daily dietary protein intake provide an estimate of the patient's underlying nutritional status. (See 'Monitoring' above.)
●Patients with a low plasma albumin concentration should be further evaluated for malnutrition, particularly if the albumin level has declined over time. We perform the following evaluation prior to treating malnutrition (see 'Evaluation' above):
•A nutritionist interviews patients regarding dietary intake.
•We question patients regarding compliance with the dialysis regimen, even if the Kt/V is at target.
•We exclude or treat any overt or occult comorbid disease that might be impairing nutritional status.
•We exclude chronic inflammatory states.
•We exclude rapid transport with peritoneal equilibration test (PET) test.
●Malnutrition may be treated by increasing the target Kt/V or by changing the dialysis prescription to increase appetite or encourage compliance. Dietary supplements may also be used. (See 'Treatment' above.)
