The losses of protein into dialysate have been considered a major limitation of maintenance peritoneal dialysis. We, therefore, undertook a comprehensive evaluation of protein losses in 30 patients undergoing maintenance intermittent peritoneal dialysis (IPD), 12 patients undergoing acute IPD, and 8 patients undergoing continuous ambulatory peritoneal dialysis (CAPD). The weekly loss of protein based upon the usual treatments per week was relatively similar with the three modes of dialysis. Protein losses during repeated dialyses were similar for a given patient, but there was repeated dialyses were similar for a given patient, but there was marked interpatient variation. During maintenance IPD, protein loss was 12.9 +/- (SD) 4.4 g per 10 hours of dialysis; albumin loss was 8.5 g, and IgG loss was 1.3 g. Approximately 50% of the protein loss was from the ascitic fluid accumulated during the interdialytic interval, and concentrations of most proteins in the ascitic fluid correlated with their serum levels. Serum protein concentrations were in the low, normal range and did not change during dialysis. The development of peritonitis markedly increased protein losses. During acute IPD, 23.3 +/- 16.5 g of protein were lost per 36 hours of dialysis, lower losses than those previously reported. With CAPD, 8.8 +/- 1.7 g of protein were removed per 24 hours; also immunoglobulin losses correlated with their serum concentrations. The results of these studies suggest that, in the absence of peritonitis, dialysate protein losses do not appear to limit the usefulness of peritoneal dialysis.

Since wasting and malnutrition are common problems in patients with renal failure, it is important to develop techniques for the longitudinal assessment of nutritional status. This paper reviews available methods for assessing the nutritional status; their possible limitations when applied to uremic patients are discussed. If carefully done, dietary intake can be estimated by recall interviews augmented with dietary diaries. Also, in a stable patient with chronic renal failure, the serum urea nitrogen (N)/creatinine ratio and the rate of urea N appearance reflect dietary protein intake. A comparison of N intake and urea N appearance will give an estimate of N balance. Anthropometric parameters such as the relationship between height and weight, thickness of subcutaneous skinfolds, and midarm muscle circumference are simple methods for evaluating body composition. Other methods for assessing body composition, such as densitometry and total body potassium, may not be readily applicable in patients with renal failure. More traditional biochemical estimates of nutritional status such as serum protein, albumin, transferrin, and selected serum complement determinations show that abnormalities are common among uremic patients. Certain anthropometric and biochemical measurements of nutritional status are abnormal in chronically uremic patients who appear to be particularly robust; thus, factors other than altered nutritional intake may lead to abnormal parameters in such patients. Serial monitoring of selected nutritional parameters in the same individual may improve the sensitivity of these measurements to detect changes. Standards for measuring nutritional status are needed for patients with renal failure so that realistic goals can be established optimal body nutriture.

Patients undergoing continuous ambulatory peritoneal dialysis (CAPD) are exposed to a continuous infusion of glucose via their peritoneal cavity. We performed studies to quantitate the amount of energy derived from dialysate glucose. Net glucose absorption averaged 182 +/- (SD) 61 g/day in 19 studies with a dialysate dextrose concentration of 1.5 or 4.25 g/dl. The amount of glucose absorbed per liter of dialysate (y) varied with the concentration of glucose in dialysate (x), (y = 11.3x - 10.9, r = 0.96). The amount of glucose absorbed per day during a given dialysis regimen was constant. Energy intake from dialysate glucose was 8.4 +/- 2.8 kcal/kg of body wt per day, or 12 to 34% of total energy intake. This additional energy may contribute to the anabolic effect reported during CAPD. The ability to vary glucose absorption by altering the dialysate glucose concentration may prove a useful tool to modify energy intake.

Balance studies for nitrogen, potassium, magnesium, phosphorus, and calcium were carried out in eight men undergoing continuous ambulatory peritoneal dialysis (CAPD) to determine dietary protein requirements and mineral balances. Patients were fed high energy diets for 14 to 33 days which provided either 0.98 (seven studies) or 1.44 g (six studies) of primarily high biological value protein/kg body wt/day. Mean nitrogen balance was neutral with the lower protein diet (+0.35 +/- 0.83 SEM g/day) and strongly positive with the higher protein diet (+2.94 +/- 0.54 g/day). With the higher protein diet the balances for potassium, magnesium, and phosphorus were strikingly positive, there was an increase in body weight in all patients, and a rise in mid-arm muscle circumference in five of the six patients. The relation between protein intake and nitrogen balance suggests that the daily protein requirement for clinically stable CAPD patients should be at least 1.1 g/kg/day; to account for variability among subjects 1.2 to 1.3 g protein/kg/day is probably preferable. Potassium balance correlated directly with nitrogen balance (r = 0.81). High fecal potassium losses (19 +/- 1.2 mEq/day) in all patients probably helped maintain normal serum potassium concentrations. Mean serum magnesium was increased (3.1 +/- 0.1 mg/dl), and magnesium balances were positive suggesting that the dialysate magnesium of 1.85 mg/dl is excessive. The net gain of calcium from dialysate was 84 +/- 18 mg/day; this correlated inversely with serum calcium levels (r = -0.90).

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