Definition

In cases of severe or complete kidney failure (often with an eGFR between 5 and 10 ml/min/1.73 m²), renal replacement therapy (e.g., hemodialysis [HD], peritoneal dialysis [PD]) replaces the lost kidney function ¹. All types of renal replacement therapies (intermittent, continuous, PD) fundamentally impact metabolism and nutrient balance, often triggering inflammatory reactions and exacerbating underlying disease inflammation ². Nutritional therapeutic measures should be tailored based on laboratory values and the type of renal replacement therapy used.

Impact on Nutritional Status

A meta-analysis by Carrero et al. revealed that, on average, 42% of dialysis-dependent individuals globally suffer from protein-energy malnutrition ³. Between 5% and 10% have severe malnutrition. The causes are diverse, including anorexia, nutrient losses during dialysis, and specific metabolic changes, such as metabolic acidosis, hypercatabolism due to inflammation, and concurrent insulin resistance, all of which can lead to inadequate protein and energy intake ^{4, 5}.

Hemodialysis (HD)

Protein catabolism, low food intake, and nutrient losses are key concerns during HD treatments (approximately 7 g of amino acids are lost per dialysis session; 2 kg of lean mass lost per year). In addition to protein and amino acid losses, there is often a loss of water-soluble vitamins, L-carnitine, and electrolyte imbalances. The prevalence of Type 2 Diabetes is high among HD patients, leading to further reductions in protein stores ⁶.

Peritoneal Dialysis (PD)

Patients undergoing PD tend to have a body composition characterized by fluid overload and low lean mass. Additionally, low serum levels of albumin and prealbumin are common (with a daily loss of approximately 2-4 g of amino acids and 5-15 g of protein) ^{6, 7}. The loss of water-soluble vitamins is lower in PD than in HD, but the loss of protein-bound substances, such as various micronutrients like calcium and iron, is higher ⁸. Glucose absorption from the peritoneal dialysis fluid, up to 125 g/day, should be considered in daily energy intake ⁵.

Nutrient needs for dialysis patients. Adjustments are necessary for malnourished patients, physical activity, and patient age. The weight used is Adjusted Body Weight (ADJ) if BMI is ≥28; otherwise, pre-hospitalization body weight is used ³. BW = Body Weight; d = Day

Goals of Nutritional Therapy

• Maintain or improve nutritional status.
• Prevent malnutrition and nutrient deficiencies.
• Reduce accumulation of fluids, phosphate, and potassium.
• Prevent uremic complications.

To detect malnutrition early, a screening using Nutritional Risk Screening should be performed within the first 90 days after starting dialysis and then at least twice a year.

Energy and protein needs should, whenever possible, be met through oral nutrition. If less than 75% of requirements are covered with fortified foods, snacks, or oral supplements, enteral nutrition should be introduced as a supplement after 5 days. Complementary parenteral nutrition is indicated if less than 75% of needs are met through oral and/or enteral nutrition.

Oral Nutrition

The use of protein-rich foods and oral supplements one hour after meals and/or during dialysis has proven very effective in meeting the increased protein needs, thereby counteracting muscle loss and weight decline ¹⁶. Dialysis-specific oral supplements are indicated for electrolyte imbalances and contain a higher protein content with reduced levels of phosphorus and potassium ¹⁶.

Other therapeutic options for malnourished CKD patients include:

• Intake of specific nutrients to reduce protein breakdown: essential/branched-chain amino acids, keto acids.
• Anti-inflammatory supplementation: e.g., fish oil (Ω-3 fatty acids), antioxidants ⁵.

Practical Tips for Restrictions and Meeting Increased Protein Needs

• Protein: Include a protein source in each main meal (e.g., cottage cheese, lean quark, eggs, meat, poultry, fish, tofu, lentils), add protein-rich snacks and/or oral supplements.
• Phosphate: Avoid foods with artificial phosphate additives and high phosphate content, particularly processed foods with the following phosphate additives: [E 338, E 339, E 340, E 341, E 343, E 442, E 450, E 451, E 452, E 541, E 1410, E 1413, E 1414, E 1442]. Note: Organic meat products do not contain phosphate additives.
• Potassium: Reduce potassium-rich foods in favor of lower-potassium alternatives (e.g., limit potatoes to 120 g a maximum of three times per week, replace whole-grain products like pasta, bread, rice with white flour products and white rice, avoid dried products such as fruits, beans, mushrooms). Pay attention to preparation methods, portion size, and consumption frequency.
• Salt: Use salt moderately during preparation and avoid additional salting at the table. Use herbs, garlic, and onions for seasoning. Note: Spice mixes, bouillon, liquid seasonings, soy sauce, and ready-made sauces often have a high salt content. Favor cooking methods like steaming or braising instead of boiling in salted water. Consume salty foods like processed foods, canned goods, salty snacks, and charcuterie in moderation. Caution: Some diet and herbal salts contain potassium chloride instead of sodium chloride. These are suitable for patients with high blood pressure but not for those with kidney disease.

Enteral Nutrition

For short-term enteral nutrition up to 5 days, standard products can be used. A disease-specific composition is indicated if electrolyte concentrations in serum/urine are outside the normal range when enteral nutrition exceeds 5 days, or if standard products are poorly tolerated (e.g., nausea, diarrhea, bloating).

Parenteral Nutrition

If oral and/or enteral nutrition is insufficient or contraindicated, parenteral nutrition is used. However, this increases the risk of infections and glucose and electrolyte imbalances. Subcutaneous administration of a short-acting insulin can prevent post-dialysis hyperglycemia ¹¹.

Caution: Parenteral nutrition should never be administered through the dialysis catheter.

Monitoring

• Stimulating appetite through herbal bitters and spices, such as wormwood and ginger, as well as physical activity.
• Preventing malnutrition caused by dialysis losses: Monitor the normalized Protein Catabolic Rate (nPCR) in dialysis patients as a snapshot of protein intake under steady-state conditions (estimated protein intake in g/kg BW/24h). nPCR values below 1 indicate protein malnutrition.
• Measuring urine volume to determine fluid requirements.
• Monitoring and avoiding pathologically high levels of:
  • Potassium (track trends over the past weeks).
  • Phosphate (track trends over the past months).
  • Calcium (track trends over the past months).
• Check the following parameters and supplement as needed if levels are pathologically low:
  • Water-soluble vitamins: Vitamin C, folic acid, thiamine.
  • Fat-soluble vitamins: A, D, E.
  • Micronutrients: Selenium, zinc, and copper.
  • Administer oral phosphate binders, usually indicated for most hemodialysis patients ⁵.
  • Caution: Prevent accumulation of vitamins A and C after supplementation through proper administration ¹⁷.

Adapted from ¹⁸

Products/Medications

• Phosphate Binders: Examples include calcium carbonate, calcium acetate, Alucol®, Phosphonorm®, Renagel®, Renvela®, Fosrenol®, Velphoro®. Timing and dosage should align with the phosphate intake of meals.
• Potassium Ion Exchangers: Examples include Resonium®, Veltassa®, Sorbisterit®. Regular intake as per medical prescription is crucial and does not need to be taken with meals.
• Vitamin D Analogues: ViDe Drops, Rocaltrol®, Zemplar®.
• Calcimimetics: Cinacalcet (Mimpara®), Etelcalcetid (Parsabiv®).
• Other Vitamin Supplements: Dialvit®.