Peritoneal Transport during Dialysis with Amino Acid-Based Solutions

Objective

To evaluate the potential clinical role of amino acids as an osmotic agent.

Design

The peritoneal transport of fluid, amino acids, and other solutes was investigated during a 6–hour single-cycle peritoneal dialysis with PDA 1% versus 1.36% glucose (n=6) or PDA 2.7% versus 3.86% glucose solution (n=9).

Patients

Fifteen stable nondiabetic continuous ambulatory peritoneal dialysis (CAPD) patients.

Results

The fractional absorption of the osmotic agents at 6 hours was higher with PDA 2.7% versus glucose 3.86% (p<0.005). The diffusive mass transport coefficient, KeD’ calculated for a period of dialysate isovolemia was higher with PDA 2.7% versus PDA 1% for essential, nonessential (p<0.005), and total (p<0.05) amino acids. The intraperitoneal volume-over-time curves and KqD values for urea, creatinine, glucose, albumin, β2microglobulin, and total protein did not differ between the amino acid solutions and the corresponding glucose solutions. KeD for urea was significantly higher during the dwell with PDA 2.7% versus PDA 1% (p<0.05). Plasma amino acid concentrations increased substantially during the first 1– 2 hours and then decreased gradually. Valine and methionine rose to 792% and 1119% of baseline values, respectively.

Conclusions

We conclude that the peritoneal transport of fluid and investigated solutes, except amino acids, was not different with the amino acid solutions compared with the corresponding equimolar glucose solutions. However, ultrafiltration tended to be lower with amino acid solutions. Furthermore, the fractional absorption of amino acids and KeD values for amino acids was higher with PDA 2.7% versus PDA 1 %, suggesting an effect of the hypertonic amino acid solution on the peritoneal membrane transport properties. Also, the hypertonic PDA2.7% solution yielded nonphysiologically high plasma levels of several amino acids. We therefore consider this solution not to be safe enough for long term clinical use.”

Effects of Amino Acid Dialysis Solution on the Nutrition of Continuous Ambulatory Peritoneal Dialysis Patients

Objective

To evaluate the influence of 1.1% amino acid dialysis solution (AADS) on parameters of nutrition in continuous ambulatory peritoneal dialysis (CAPD) patients.

Study Design

Studies were performed in 8 men, using AADS for the overnight exchange. Before starting AADS, food intake, nutritional status, and laboratory indices were evaluated and compared to the respective parameters obtained after 3 and 6 months of treatment with AADS, as well as after 3 months of AADS withdrawal. With the start of AADS, doses of antacids were increased and modified during AADS administration; the modified doses were continued through 3 months after cessation of AADS. Another group of CAPD patients using standard dialysis solutions served as controls. In these patients the same parameters were evaluated four times at 3-month intervals.

Results

Administration of AADS resulted in: (1) 91% absorption of amino acids and improvement of serum amino acid pattern; (2) no change in nutritional intake during the treatment, but after the 3 months of AADS therapy, levels of nutrient intake were lower than those 3 months after withdrawal of AADS with correction of metabolic acidosis; (3) no change in indices of nutritional status, but 3 months after AADS discontinuation, total body weight, lean body mass, and body mass index were significantly higher than those shown after 3 months of treatment; (4) an increase in hemoglobin concentration, hematocrit, BUN, and blood H+. The examined parameters were not significantly changed in patients treated for 9 months with standard dialysis solutions exclusively. The values of nitrogen balance obtained during AADS administration and after 3 months of AADS withdrawal were significantly higher than those obtained in the respective periods in the control group. The blood pH, pCO2, and HCO3– in the last period of the study were higher in the AADS group than in the control group.

Conclusion

In relatively well-nourished CAPD patients, overnight AADS administration results in increased serum concentration of amino acids without changes in other nutritional parameters. The use of AADS should be associated with increased doses of antacid medication, which abolishes the metabolic effects of acidosis that develop during AADS administration and facilitates positive nitrogen balance.

Albumin and Amino Acid Levels as Markers of Adequacy in Continuous Ambulatory Peritoneal Dialysis

Similar to previous findings in HD patients, a markedly decreased serum albumin level has been found to be a strong predictor of morbidity and mortality in CAPD patients. However, a slight decrease in serum albumin levels (to about 30 g/L if measured with nephelometry or the bromcresol purple method) does not always seem to reflect impaired nutritional status or to be associated with an increased morbidity or mortality in CAPD patients. A low serum albumin level among CAPD patients is related to dialysate albumin loss, comorbidity, age, and a low dietary protein intake. The possible relation between the dialysis dose (as assessed by small solute clearances) and serum albumin levels among CAPD patients is much less established and needs further study, although serum albumin tends to increase in prospective studies of increased peritoneal dialysis dose.

Although the plasma levels of amino acids seem to be lower in CAPD patients compared to HD patients, this does not reflect the intracellular amino acid pattern in muscle which is less abnormal in CAPD patients, possibly because of the sustained hyperinsulinemia during CAPD, resulting in an in creased intracellular to extracellular gradient. It is at present not established to what extent the amino acid abnormalities are related to the dialysis dose.

Malnourished and hypoalbuminemic CAPD patients should be recommended to increase the protein intake, and if this is not effective, the dialysis dose should be increased. Furthermore, the use of amino acid-based peritoneal dialysis solutions is a promising new tool for the treatment of malnourished CAPD patients and may become an important component of CAPD therapy in the future. On the other hand, if the nutritional status deteriorates in spite of these efforts, the patient should be transferred to hemodialysis if possible.

Biocompatibility of a Peritoneal Dialysis Solution with Amino Acids: Histological Evaluation in the Rabbit

Objective

To determine the biocompatibility of a peritoneal dialysis (PD) solution containing amino acids compared to PD solutions containing glucose.

Design

The biocompatibility of three dialysis solutions containing 1.1% amino acids, 1.36% glucose, and 3.86% glucose, respectively, was evaluated in vivo in rabbits.

Methods

After 60 days of PD, peritoneal histological changes in rabbits were investigated by light and transmission electron microscopy. The parameters investigated were: (1) mesothelial damage; (2) submesothelial edema; (3) submesothelial cell infiltration; (4) submesothelial fibrosis; and (5) vascular alterations. Semiquantitative evaluations were performed for all the above alterations; quantitative morphometric evaluation was performed for mesothelial damage (cubic transformation of the mesothelium, areas devoid of mesothelium, submesothelial edema) and thickness of peritoneal arteriole walls.

Results

(1) Mesothelial damage was practically nonexistent in rabbits dialyzed with the solution containing amino acids, and intermediate and severe with low glucose and high-glucose solutions, respectively. Both controls and rabbits dialyzed with amino acid solution showed flat continuous mesothelium; rabbits dialyzed with low-glucose solution showed cubic continuous mesothelium; and rabbits dialyzed with high-glucose solution showed cubic discontinuous mesothelium. Cytopathic mesothelial effects were slight with the solution containing amino acids and severe with both the low and high-glucose solutions. Duplication and thickening of mesothelial basement membrane were never observed. (2) Submesothelial edema showed a worsening trend from controls to rabbits dialyzed with solution containing amino acids, low glucose, and high glucose. (3) No difference in submesothelial infiltration was found between groups. (4) Submesothelial fibrosis was never observed. (5) Vascular alterations were never observed.

Conclusion

These results are evidence that PD solution with amino acids is more biocompatible than high and also low-glucose solutions.

Nutrition in patients on peritoneal dialysis

Protein-energy wasting (PEW) is prevalent among patients on dialysis and has emerged as an important risk factor for morbidity and mortality in these patients. Numerous factors, including inflammation, inadequate dialysis, insufficient nutrient intake, loss of protein during dialysis, chronic acidosis, hypercatabolic illness and comorbid conditions, are involved in the development of PEW. The causes and clinical features of PEW in patients on peritoneal dialysis and hemodialysis are comparable; assessment of the factors that lead to PEW in patients receiving peritoneal dialysis is important to ensure that PEW is managed correctly in these patients. For the past 20 years, much progress has been made in the prevention and treatment of PEW. However, the results of most nutritional intervention studies are inconclusive. In addition, the multifactorial and complicated pathogenesis of PEW makes it difficult to assess and treat. This Review summarizes the nutritional issues regarding the causes, assessment and treatment of PEW, with a focus on patients receiving peritoneal dialysis. In addition, an in-depth overview of the results of nutritional intervention studies is provided.

Glucoregulatory hormones and choice of osmotic agent in peritoneal dialysis

OBJECTIVE

The present study was performed to explore the range of effects of amino acid-based peritoneal dialysis (PD) solutions on glucoregulatory hormones in comparison with an osmotically equivalent glucose-based solution. ♢

METHODS

13 adult nondiabetic patients on PD underwent 2 peritoneal dwells of 2 hours' duration with either 1.5% dextrose solution or 1.1% amino acid solution. Serial sampling for glucoregulatory hormones was done throughout the duration of the dwell. ♢

RESULTS

Instillation of the 1.5% dextrose solution resulted in a modest change in plasma glucose, paralleled by a small increase in plasma insulin levels and plasma insulin-like growth factor (IGF-1). Plasma glucagon was not changed and plasma growth hormone level declined. Instillation of the 1.1% amino acid solution resulted in an increase in plasma glucose, plasma insulin, plasma glucagon, and plasma IGF-1. Plasma growth hormone level declined. Both solutions led to an increase in plasma norepinephrine but no changes were observed in epinephrine or dopamine. ♢

CONCLUSIONS

Our observations suggest that the mere replacement of glucose by amino acids in PD solutions does not necessarily imply "glucose sparing" from the perspective of induction of a glucoregulatory hormonal response because of the aminogenic stimulation of secretion of multiple hormones.

Effect of Peritoneal Dialysis Solution Type on Serum Lipid Levels in End-Stage Renal Disease

Among the different cardiovascular risk factors, lipid abnormalities dominate the high mortality in chronic ambulatory peritoneal dialysis patients. So far, no data comparing the effect of standard glucose-containing, amino acid-containing, and icodextrin-containing peritoneal dialysis solutions on serum lipid concentrations in a chronic ambulatory peritoneal dialysis population are available. To determine the effect of peritoneal dialysis solutions on parameters of lipid metabolism, 67 subjects who had continued their usual dialysis for the last six months were enrolled in the study. Group A consisted of 18 patients who were receiving only glucose-based peritoneal dialysis solutions, group B consisted of 18 patients who were receiving glucose and amino acid-based peritoneal dialysis solutions, and group C consisted of 31 patients who were receiving glucose and icodextrin-based peritoneal dialysis solutions. Serum lipid parameters including total cholesterol, low-density lipoprotein, high-density lipoprotein, triglyceride, and lipoprotein (a) were determined in all groups. No significant difference in serum lipid parameters was found between groups A, B, and C. These results demonstrate the lack of the effect of amino acid or icodextrin-based peritoneal solutions on dyslipidemia of CAPD patients.