handbook of dialysis therapy || nutritional management in peritoneal dialysis

C H A P T E R 5 2

Nutritional Managementin Peritoneal Dialysis

Robert McGregor Lindsay, MD, FRCPC, FRCP (Edin), FACP, FRCP (Glasg), and Evelyn Spanner, MSc,R

Patients with progressive loss of kidney function often suffer a decline in their nutritional status. This was especially evident during the early days of dialysis, when predialysis therapy consisted of maintaining patients for prolonged periods of time with very-low-protein diets and allowing them to have advanced uremia before dialysis was instituted.

Current recommendations emphasize the need for earlier dialysis initiation to maintain a better nutritional state. The commencement of dialysis should lead to an improvement in nutritional status following correction of the uremic state. How-ever, dialysis therapy—whether by hemodialysis or peritoneal dialysis (PD)—imposes its own set of nutritional problems. Thus, despite major improvements in dialytic techniques malnutrition continues to be a concern in patients on dialysis. This chapter specifi cally addresses those aspects that pertain to PD.

Nutritional Requirements in Peritoneal DialysisThe daily nutrition requirements for PD are listed in Table 52.1, which highlights the attention that must be paid to daily energy intake (DEI) and protein, mineral, and vitamin intake.

Daily Energy IntakeFor these patients, energy requirements are greatly facilitated by the signifi cant quantity of glucose absorbed from the dialysate. However, in some patients oral energy intake may need to be decreased to prevent excess weight gain and obesity. The recom-mended level of energy intake is 145 kJ/kg/day. Total DEI should be the sum of the kilojoules from absorbed dialysate glucose plus the kilojoules that accrue from the diet. Because older age may be associated with reduced physical activity, it is recommended that DEI be reduced to 125 to 145 kJ/kg/day for older patients with

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Nutritional Management in Peritoneal Dialysis704

sedentary lifestyles. Absorption of glucose from the dialysate constitutes approximately 20 to 30% of a patient’s required energy intake. The following formula can be used to predict the grams of glucose absorbed.

(1 – D/D0)xi

Here, D/D0 is the ratio of remaining dialysate dextrose at 4 hours to the initial dextrose in the dialysate at zero hours, and xi is the

Daily Dietary Requirements for PD Patients

Protein Ideal: 1.2–1.3 g/kg standard body wt (50% high biological value) Minimum: 0.8 g/kgEnergy 145 kJ/kg ideal body wta (35 kcal/kg) if <60 years; 125–145 (oral + dialysate) kJ/kg if ≥60 yearsCarbohydrate Remainder of energy supplyFat 30% of total energy supplyCalcium ≤2000 mg/d inclusive of calcium from calcium- based phosphate bindersPhosphorus ≤1000 mg/d (50% of dietary phosphorus is absorbed, so phosphate binders are usually necessary to control serum phosphorus)Magnesium 200–300 mgPotassium Individualize level for maintenance of normal serum levelsSodium/water Individualize prescription for volume/blood pressure status; usually 130–175 mmol/d

Vitamin Supplements:Thiamin 1.5 mgRiboflavin 1.8 mgPantothenic acid 5 mgNiacin 20 mgPyridoxine HCl 10 mgBitamin B12 3 μgVitamin C 60 mgFolic acid 1 mgVitamin A No additionVitamin D IndividualizeVitamin E 15 IUVitamin K Noneb

a. Ideal body weight for normal persons of same age, sex, and height (not “dry” weight for the patient).b. Addition may be needed for patients who are not eating and who receive antibiotics.

Table 52–1

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Nutritional Management in Peritoneal Dialysis 705

initial grams of glucose instilled. Alternatively, glucose absorption from dialysate can be measured (rather than estimated)—when the 24-hour collection is being done—by subtracting the quantity of glucose in the daily dialysate effl uent from the total quantity of glucose instilled that day. This large glucose uptake may, in a negative sense, suppress the patient’s overall intake—particu-larly as the patient may experience abdominal discomfort and fullness.

ProteinThe attainment of energy needs affects protein requirements because energy has a protein-sparing effect. The primary concern, however, rests with the ability of a chronic PD patient to main-tain an adequate protein intake. A daily protein intake of 1.2 to 1.3 g/kg/day is recommended for stable PD patients. This fi gure has been derived from nitrogen balance studies in patients undergoing continuous ambulatory peritoneal dialysis (CAPD). Some experts suggest that the observations so made defi ne the lower limit of protein required to maintain positive nitrogen balance and that many PD patients could be in nitrogen equi-librium with lower protein intakes. Protein needs may vary depending on stress or metabolic needs. In our opinion, the minimum dietary protein intake for the PD population should be 0.8 g/kg/day. Any patient with a protein intake ≤0.8 should be reassessed by the registered dietitian to decrease the risk of protein malnutrition.

Allowing for essential amino acid requirements, at least 50% of the daily protein intake should be of high biologic value. As the amount of protein secreted into the peritoneal fl uid ranges from 5 to 15 g/day (60–80% as albumin), with occasional patients secreting <5 or as much as 20 g/day, the diet should be suffi cient in protein to compensate for these losses. Several factors make maintaining an adequate level of protein nutriture diffi cult: inter-current illnesses and peritonitis by causing increased protein requirement, early satiety related to glucose infl ux, altered taste sensation, and a particular loss of appetite for high-protein food sources.

Some general suggestions to assist patients in increasing their protein intake include ingestion of protein foods before others, frequent meals with high protein sources, and educating patients as to the use of oral enteral supplements (especially those high in protein and/or energy). Adequacy of protein intake can be assessed by evaluating the normalized protein equivalent of nitrogen

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appearance (nPNA, previously normalized protein catabolic rate or nPCR) by utilizing the following equations (Bergstrom formula).

nPNA = 13 + 0.204 UNA (mmol/day) + dialysate protein losses (g/day)

nPNA = 19 + 0.213 UNA (mmol/day)

UNA (urea nitrogen appearance) is the total urea in the daily dialysate plus urine measured in mmol/day. The results are then corrected to standard body weight.

MineralsThe balance between limiting phosphorus and achieving adequate protein intake is a major nutritional concern in PD. These patients are limited to ≤1000 mg/day from their food intake, of which 50% is absorbed. A lower ratio of phosphorus-to-protein intake should be emphasized. Phosphate binders are also required to control serum phosphate levels. Patients should be advised to redistribute their binders concomitantly with their food intake, particularly if these patients are consuming more frequent meals to boost their protein intake. Calcium intake should be ≤2000 mg/day from both food sources and calcium-based phosphate binders. In light of the evidence that aluminum toxicity is a major cause of osteomalacia and other low-turnover bone abnormalities, in addition to its adversely affecting red blood cells and the brain the use of aluminum-based phosphorus binders poses a risk. They may be prescribed for short time periods in cases of hypercalcemia.

Other non calcium-based phosphate binders may be needed in PD patients with hypercalcemia or a high calcium phosphate product that limits calcium-based binders, concerns with low serum parathroid hormone, or with severe vascular or soft tissue calcifi cation. It will be recalled that when the use of aluminum-based phosphate binders was widespread the recommended dialysate calcium concentration was 3.25 mEq/L (1.62 mmol/L). The advent of calcium-based binders led to the reduction of the dialysate calcium concentration to prevent non-aluminum low-turnover bone disease. A change back to non–calcium-based binders may require a reevaluation of the dialysate calcium concentration.

Sodium intake should be individualized based on blood pressure and weights, with the suggested sodium intake being approximately 130 to 175 mmol/day. If fl uid retention problems occur, sodium and fl uid intake should be altered to control any

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undesirable weight gain and to alleviate the need for higher glucose concentration exchanges. Recent studies have shown that subclinical volume expansion is common in PD patients, particularly once residual renal function is lost. Controlling daily sodium ingestion may therefore be important with declining residual function. This is also important in APD patients, in whom sodium removal has been shown to be signifi cantly lower than in CAPD patients. Potassium intake is generally unrestricted with PD unless the serum level is increased or decreased. Patients receiving PD may be at risk for hypokalemia, especially when their nutritional intake is poor. Some patients may require potassium supplementation.

VitaminsReduced serum and tissue vitamin levels may occur in PD patients with anorexia and poor nutritional intake or with altered metabolism and dialysate losses of water-soluble vitamins. Therefore, it is prudent to routinely supplement their oral intake (Table 52.1).

Nutritional Problems in Peritoneal DialysisThe major problem in the PD population is that of protein malnutrition. Recent investigations have assessed the incidence of protein-energy malnutrition and have found that approximately 40% of PD patients were at least mild to moderately malnourished, and that 4 to 8% were severely malnourished. Further studies have shown that 25 to 60% of PD patients were ingesting <0.8 g of protein/kg/day when this is assessed by either a 3-day food intake record or by calculation of the nPNA. The nPNA is a reliable tool for estimating the dietary protein intake when it is routinely assessed by qualifi ed registered dieticians.

Although plasma albumin can undoubtedly be infl uenced by factors other than nutrition (e.g., volume expansion due to decreased ultrafi ltration, increased transperitoneal protein loss, infl ammation, and co-morbidity), it is clear that a serum albumin will change with protein malnutrition. High peritoneal membrane transport among PD patients may result in lower serum albumin concentrations, particularly from higher protein losses without increased protein intakes. PD patients may also show a decrease in anthropometric values and nitrogen balance during frequently recurring episodes of peritonitis. Conversely, following aggressive treatment of peri-tonitis protein intake will increase, nitrogen balance will become

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positive, and anthropometric values will improve. In such patients, there is a direct linear correlation between nitrogen intake and nitrogen balance. In addition, serum albumin is a good marker of such changes.

Infl uence of Protein Malnutrition on OutcomeThe National Cooperative Dialysis Study (NCDS) indicates that for hemodialysis patients outcome is dependent on the dose of dialysis as modeled by the removal of urea. The more recent HEMO Study defi ned the upper limits of that dependency. The ADEMEX trial showed that mortality was not improved by increasing peritoneal small-solute clearance. However, signifi cant increases in death due to uremia and fl uid overload occurred in the control group. In the NCDS, nutrition was also shown to be important in outcomes because patients with a low nPNA (g/kg/day) had a high morbidity rate.

In the ADEMEX trial, patients with nPNA values greater than 0.8 g/kg/day had a signifi cantly better survival compared with patients whose nPNA values were less than 0.8 g/kg/day. More recent studies confi rm the importance of nutrition. Patients with a low plasma urea, low cholesterol, and low albumin have an increased risk of death compared to “standard” hemodialysis patients. Likewise, there is defi nite evidence that a low serum albumin in the PD population is associated with increased morbidity and mortality. In the CANUSA study of the adequacy of PD, the relative risk of either technique failure or death decreased by 3% for each 1 g/L increase in serum albumin—and 21% for each 1 unit increase in the subjective global assessment (SGA) score (see material following for an explanation).

The ADEMEX trial also showed a signifi cant survival effect with higher serum albumin levels. There is enough data to support the contention that many PD patients do not ingest the daily protein requirement to maintain nitrogen balance and that malnutrition is a common outcome. Dietary protein and energy intake (as well as other non-nutritional factors) can infl uence plasma albumin, and a falling albumin will infl uence outcome.

Relationships among Malnutrition, Infl ammation, and AtherosclerosisRecent evidence suggests that infl ammation alone or in combi-nation with a low protein intake and transperitoneal albumin

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losses plays a signifi cant role in the resulting hypoalbuminemia in PD patients. Serum albumin and C-reactive protein (CRP) participate reciprocally in the acute-phase process. In nonrenal subjects, elevated CRP levels predict cardiovascular morbidity. Similarly, increased CRP is a strong risk factor for both total and cardiovascular mortality in hemodialysis and PD patients.

It is suggested that there is a syndrome of malnutrition, infl am-mation, and atherosclerosis (MIA) that carries a high mortality rate in dialysis patients. The malnutrition associated with MIA is now referred to as type 2 malnutrition. Type 1 malnutrition, on the other hand, is associated with the uremic syndrome per se or with factors related to uremia and its treatment (e.g., under-dialysis, physical inactivity, food intake, and depression). The spectrum of altered nutritional status seen in dialysis patients may, however, entail a continuous overlap between both types of malnutrition and hence may evolve into a mixed type of malnutrition.

Infl uence of Adequacy of Dialysis on Nutritional StatusInadequate dialysis is a potentially reversible cause of protein malnutrition in dialysis patients, whether on PD or hemodialysis. The current NKF-K/DOQI guidelines recommend a minimum weekly peritoneal Kt/V urea of at least 1.7. The ADEMEX trial results indicated no improvement in 2-year survival when peri-toneal clearance of small solutes was increased to a weekly Kt/V = 2.27. A trial of increasing Kt/V should, however, be considered in patients with evidence of uremic symptoms that could be resulting in anorexia, nausea, and poor nutritional status. It may even be justifi ed considering a change to hemodialysis in some patients. Likely, manipulations of dialysis dose will only infl uence those patients with type 1 protein malnutrition.

Assessment of Nutritional StatusOptimal measures for comprehensively assessing nutritional status are not well established in the PD population. In nonuremic individuals, muscle mass is usually estimated from measurements of mid–upper-arm circumference and is felt to be representative of total body protein. The standard values in renal failure patients and in the PD population have not been established. Likewise, the same criticism can be applied to the use of anthropometric measurements—including skin-fold thickness to assess body fat

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and hence to calculate lean body mass. These measurements are useful but must be obtained serially by a trained individual to be of any value.

Energy intake is best estimated by a food intake record and from changes in the physical examination (actual weight, percentage of usual post-drain weight, percentage of standard body weight, muscle weakness, volume status, and so on). In addition, we have found regular measurement of dietary energy and protein intake, nPNA, serum albumin, and serum creatinine levels particularly useful. These should be performed at least every 3 months on all PD patients. SGA should also be done every 6 months. SGA was initially developed to determine the nutritional status of patients undergoing surgery and has subsequently been validated in the PD patient population. This technique, which combines medical history (weight loss, anorexia, and GI symptoms) and physical examination (loss of subcutaneous fat and muscle mass), is a potent predictor of survival. The CANUSA study showed that a higher SGA score was associated with a lower relative risk of death and fewer hospitalized days per year.

Management of Nutritional Problems

Protein MalnutritionThe most common problem in the PD population is that of protein malnutrition. A scheme for the assessment and management of this is shown in Figure 52.1. This scheme shows that early on the physician must determine whether dialysis is adequate. Thus, we have found it very useful to perform regular assessment of creatinine clearance and urea kinetics (Kt/Vurea and nPNA, and where necessary a peritoneal equilibration test). Details of how to perform these assessments and tests, as well as target values, are provided elsewhere in this book.

If dialysis is inadequate, clearly it has to be made adequate. Usually, this can be done by a change in the PD prescription. A few patients, however, simply cannot receive adequate treatment by any form of PD (very large size, limited residual function, inadequate peritoneal transport)—and these patients should be considered for hemodialysis. A change to hemodialysis may even be considered as a temporary measure in the occasionally very malnourished PD patient while either enteral or parenteral nutrition is given. Once a new, good steady state of nutrition is obtained a return to PD can be made.

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ASSESSMENT OF PROTEINNUTRITIONAL STATUS

DPI, nPNA, albumin, mid-arm circumferenceideal body weight (gain or loss), etc

Not adequateAdequate

Recent problem, ? coincidental illness (e.g.peptic ulcer, diabetic gastropathy, carcinoma,

infection, recurrent or severe/prolongedperitonitis, cardiac failure – MIA syndrome)

No

Is dialysis adequate?(PET, urea kinetics, etc)

No

Yes

Yes

Treat

Fail

Fail

Fail

Change tohemodialysis

Oral enteralsupplements

Nasogastric feed, aminoacid-containing dialysate orIV total parenteral nutrition? anabolic hormones? anticytokine therapy

Fail

Fail

Dietician to evaluate(protein + energy +

vitamins)

Success

Success

Ø Kt/V (urea) (Øvolume,Ø cycle number, change

to APD

Ø oral intake(protein ± energy)

Success

SuccessSuccess

Assessment and management of protein/energy malnutrition in PD patients (DPI = dietary protein intake, PET = protein equilibration test).

Figure 52–1

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A positive response to an increased dialytic dose is likely only in type 1 malnourished patients who may also show some benefi t from anabolic hormones. Small short-term studies in PD patients on the use of agents such as recombinant insulin-like growth factor (rh IGF-1) and growth hormone (rh GH) have shown them to improve nitrogen balance. However, high costs and potential side effects have limited their clinical use. The effectiveness of rh IGF-1 and rh GH in hemodialysis patients is blunted if infl ammation is present.

In the PD patient with type 2 malnutrition, the approach must be to identify and treat (if possible) the co-morbidity causing the infl ammatory response. It may be of benefi t to obtain a C-reactive protein level to distinguish these patients. In the future, it is possible that anticytokine therapy (e.g., 1L-1 receptor antagonists, anti-TNFa antibodies, thalidomide, and so on) may have a role.

A nephrology RD is important in any dialysis unit. This profes-sional is best able to assess the patient’s overall nutritional state (inclusive of protein, energy, and vitamin status) and individual requirements, and to advise the patient how best to manage his or her nutrition plan. If a patient cannot ingest the necessary protein plus energy requirement, oral enteral supplements should be tried fi rst—using the commercially available preparations that will give protein with or without energy. Should the use of oral enteral supplements not meet with success, either nasogastric tube feed-ing or the use of amino–acid–containing dialysis solutions must be considered. Intraperitoneal amino acids (IPAAs) appear to increase protein balance in type 1 malnourished PD patients who have low protein intakes. However, a limiting factor is that adequate quantities of energy and vitamins cannot be provided by IPAA. As a last resort, total intravenous parenteral nutrition may be used.

Glucose MalabsorptionEnergy intake may need to be modifi ed for PD patients because of their absorption of glucose from dialysate. Higher levels of glucose absorption have been associated with increased transport rates. As mentioned previously, the dialysate glucose may provide as much as 30% of the patient’s total daily energy intake. Unfor-tunately, considerable variability is seen in glucose absorption.

Nutrition-related problems may be created or worsened by absorption of glucose from dialysate: weight gain with increase in abdominal fat, high triacylglycerol levels, and increased risk of hyperglycemia. If weight gain is a major problem, the only

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options are to limit dietary calories, decrease sugars and fats, and increase exercise. The patient should also be instructed to limit sodium and fl uid intake suffi ciently to permit a decrease in the glucose concentration of dialysate as necessary for adequate ultrafi ltration. IPAA can be utilized to reduce the number of glucose-containing exchanges and to increase protein balance. These solutions can result in approximately 80% peritoneal uptake of amino acids, depending on dwell time. A polyglucose-based solution (such as icodextrin) can also be considered—to increase ultrafi ltration volumes in the longer-duration dwells, leading to reduced extracellular fl uid volumes without increasing the use of hypertonic glucose solutions. In the PD population, hypertriglyceridemia occurs because of conversion of excess glucose to triacylglycerols by the liver. Its management should be the same as that for weight gain. Some patients may benefi t from supplementation with omega-3 fatty acids or lipid-lowering agents. The excess glucose load presents an additional problem for the diabetic, who may have to adjust their diet, oral hypo-glycemic drugs, and insulin dose—or who may require insulin for the fi rst time to achieve optimal glycemic control.

SummaryPD is an excellent form of renal replacement therapy, but it does impose a set of unique and challenging nutritional requirements for the patient. Adequate protein and oral calories adjusted for those absorbed from the dialysate, and levels of mineral and vitamins, have to be considered in achieving the nutritional needs of the individual PD patient. Malnutrition, especially protein malnutrition, is a major cause of morbidity and mortality in this population. Hence, regular monitoring of nutritional status by an experienced nephrology RD is essential.

Recommended ReadingNutritional Management in Peritoneal Dialysis

Heimburger O, Stenvinkel P, Lindholm B. Nutritional effects and nutritional management of chronic peritoneal dialysis. In Kopple JD, Massry SG (eds.), Nutritional Management of Renal Disease. Philadelphia: Lippincott, Williams & Wilkins 2004:477–512.

Kopple JD, Hirschberg R. Nutritional and peritoneal dialysis. In WE Mitch, S Klahr (eds.), Nutrition and the Kidney. Boston: Little, Brown 1993:290–313.

National Kidney Foundation. NKF-K/DOQI Clinical Practice Guidelines and Clinical Practice. Recommendations for 2006 Updates: Hemodialysis Adequacy, Peritoneal Dialysis Adequacy, Vasular Access. Am J Kidney Dis, 48:S1–S322, 2006 (Suppl 1).

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General Review

Jones MR, Burkart JM, Hamburger RJ, et al. Replacement of amino acid and protein losses with 1.1% amino acid peritoneal dialysis solution. Perit Dial Int 1998;18:210–16.

Jones MR, Hagen T, Algrim-Boyle C, et al. Treatment of malnutrition with 1.1% amino acid peritoneal dialysis solution: Results of a multicenter outpatient study. Am J Kidney Dis 1998;32:761–69.

Kopple JD, Bernard D, Messana J, et al. Treatment of malnourished CAPD patients with an amino acid-based dialysate. Kidney Int 1995;47:1148–57.

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handbook of dialysis therapy || nutritional management in peritoneal dialysis

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