**2. Medical nutrition therapy in different renal replacement therapy modalities**

This section discusses the different nutrient requirements for the different RRT modalities.

#### **2.1 Nutrition therapy in maintenance hemodialysis**

The goal of nutrition intervention in MHD patients is to optimize their nutritional status, control blood glucose and blood pressure and fluid overload, keep renal biochemistry within safe limits, and make dietary advice as practical as possible to assist in compliance. For this reason, all renal patients must have adequate renal-specific dietetic or nutritional support [9].

#### *2.1.1 Energy requirements*

Chronic Kidney Disease (CKD) impairs energy metabolism; therefore, it is prudent to maintain adequate energy intake, which is necessary to prevent PEW. To maintain a neutral nitrogen balance and nutrition status, studies suggest that energy intake should range between 30 and 35 kcal/kg/day [3].

#### *2.1.2 Protein requirements*

For metabolically stable patients, guidelines recommend a dietary protein intake of 1.0–1.2 g/kg body weight per day to maintain a stable nutritional status. However, higher dietary protein levels may need to be considered for patients at risk of hyperglycemia and/or hypoglycemia to maintain glycemic control. Dietary fat should not be restricted because they may be important sources of calories [10].

#### *2.1.3 Potassium*

Renal dieticians should focus on individualization, consistent checks on serum potassium levels, and clinical judgment, which would provoke the utilization of other interventions other than dietary restrictions to attain normal serum levels of potassium when appropriate. Studies suggest that dietary potassium restriction may limit heart-healthy diets and lead to the intake of more atherogenic diets [10].

It is important to note that there have not been any clinical trials done on how modifying diet can influence serum potassium levels in patients with CKD [3]. Several factors could influence the shift in serum potassium levels, including [11]: medications such as angiotensin-converting enzyme (ACE) inhibitors, thiazides, and loop diuretics; gastrointestinal problems (vomiting, diarrhea, constipation); acid– base balance; glycemic control; and catabolic state.

Individualized potassium recommendations can improve patient outcomes and quality of life. Moreover, pinpointing the root cause of hyperkalemia would be ideal to help with appropriate interventions. Lindsey suggests the following reflections to help in finding the root cause of hyperkalemia [12]: If the potassium level is consistent with the current trend; if it could be a laboratory error; if there are medications that would affect potassium levels/recent dose change; if there is constipation; the patient's carbon dioxide and blood sugar trend; recent muscle mass loss, reduced appetite, and recent food intake. The author further clarifies that restricting fruits and vegetable may not have a positive impact since most potassium in diets come from coffee, tea, savory foods, beer, animal protein, and dairy.

#### *2.1.4 Phosphorous*

Recent studies point out that restrictions on dietary phosphorous may lead to worse survival and poorer nutrition status [10]. The KDQOI guidelines

recommend that to reach the decision of restricting dietary phosphorus, there needs to be the presence of progressively or persistently high serum phosphate levels, taking into consideration the trends rather than a single laboratory value and after paying attention to concomitant calcium and parathyroid hormone (PTH) levels [3].

In MHD patients, if the nutrition requirements cannot be met through the oral and enteral intake, intradialytic parenteral nutrition is recommended to improve and maintain nutritional status [3].

#### **2.2 Nutrition therapy in peritoneal dialysis**

Guidelines recommend comprehensive and regular nutrition assessment for patients with PD, including body measurements, patient appetite, nutrition-related laboratory markers, clinical status, and dietary intake. However, different factors influence dietary recommendations, and as such, dietary recommendations are not yet universal [13]. Energy requirements range from 30 to 35 kcal/kg/day, with patients below 60 years of age proposed to get 35 kcal/kg/day and those older than 60 years to get 30 kcal/kg/day incorporating the calories from the dialysate into the calculations, which are usually mostly the dextrose because absorption occurs into the patient's body [3].

Patients undergoing PD do quite a number of exchanges in a day; thus, they experience losses of essential elements and nutrients, including amino acids, peptides, vitamins, and trace elements. Dietary restrictions are, therefore, minimal compared to MHD patients. Guidelines suggest that dietary protein should range from 1.0 to 1.3 g/kg/day and even be higher up to 1.5 g/kg/day during peritonitis [3, 13]. Dietary potassium is generally not restricted, while sodium recommendation is <4 g based on serum levels. Phosphorous allowable is between 800 and 1000 mg/day, and phosphate binders with meals are recommended if serum levels are high. The fluid is adjusted based on the dextrose concentration of the dialysate.

#### **2.3 Nutrition therapy in continuous renal replacement therapy**

Continuous Renal Replacement Therapy (CRRT) is the modality of choice for critically ill patients. While it permits better control of fluids and is hemodynamically tolerated better than intermittent hemodialysis in critically ill patients, it has greater effects on nutrition [14–16]. The clearance of CCRT is not only specific to uremic toxins; it also clears low molecular substances, which are essential. Macronutrients and micronutrients are also cleared from the patient's blood into the waste [17–20]. Studies are limited on nutrition requirements, and as such, it is impossible to generalize given the different CCRT performance modalities, types of fluids, and different prescriptions [21]. However, some studies suggest that energy requirements range from 20 to 35 kcal/kg/day with a proportion of 60–70% being carbohydrates and 30–40 being lipids, respectively, considering the anabolic and catabolic phases while considering non-nutritional calories and being cautious about overfeeding [6, 19, 22]. Protein requirements range from 1.5 to 2.5 g/kg/IBW/day [23, 24]. There is no standard recommendation for the electrolytes, vitamins, and trace elements, but the medical team should continue monitoring the critically ill patients, checking the serum levels, and correcting/or adjusting the fluids/feeds as appropriate. The medical team should monitor serum levels of phosphorous, potassium, and calcium and adjust as appropriate.
