Nutritional support therapy refers to dietary nutritional interventions guided by nutritional principles, aimed at treating and alleviating diseases while enhancing clinical outcomes. It can be classified into enteral nutrition (EN) and parenteral nutrition (PN). Appropriate nutritional support has the potential to reduce the incidence of complications, shorten hospital stays, and lower hospitalization costs.
Enteral Nutrition (EN)
EN involves providing the body with the necessary nutrients through the gastrointestinal (GI) tract. Compared to PN, EN offers advantages such as maintaining physiological function, preserving the gut barrier, and reducing metabolic complications. For this reason, EN is typically prioritized when the gastrointestinal function is intact.
Indications
Reduced Oral Intake Capacity:
- Neurological disorders, such as coma, severe intellectual disabilities, or cerebral palsy affecting orofacial motor functions.
- Anatomical abnormalities, such as head and neck tumors or severe deformities.
Insufficient Oral Intake:
- Increased energy requirements, such as in cases of severe burns or multiple traumas.
- Decreased appetite, such as with tumors, endocrine disorders, or anorexia nervosa.
Absorption Disorders or Metabolic Abnormalities:
- Absorption issues, such as chronic diarrhea, short bowel syndrome, or inflammatory bowel diseases.
- Metabolic conditions, such as phenylketonuria or glycogen storage diseases.
- Other diseases, including food allergies, pancreatitis, or celiac disease.
Contraindications
Absolute Contraindications
These include untreated acute abdomen, mechanical bowel obstruction, high-output fistulas, severe intra-abdominal infection, unremitting severe abdominal distension, abdominal compartment syndrome, significant gastrointestinal bleeding, shock, or during the acute resuscitation phase when high-dose vasopressors are required.
Relative Contraindications
These include severe short bowel syndrome or the acute phase of severe intestinal inflammation. For patients with relative contraindications, EN can often be initiated once gastrointestinal function improves after short-term treatment. For conditions classified as absolute contraindications, regular reassessment is necessary, and EN should commence as soon as these conditions resolve.
Nutritional Pathways and Feeding Methods
EN Pathways
EN can be administered orally or through feeding tubes.
Oral Feeding
Dietary formulations for oral feeding need not be isotonic and can be adjusted based on the patient’s condition. For infants, formula milk is a primary choice.
Tube Feeding
Options include nasogastric tubes (NGT), nasojejunal tubes (NJT), gastrostomy tubes (GT), gastrojejunostomy tubes (GJT), and jejunostomy tubes (JT). The choice of pathway depends on the patient's condition and the anticipated duration of nutritional support. For support lasting less than six weeks, NGT is the most commonly used method. In cases of gastroesophageal reflux, aspiration, vomiting, or delayed gastric emptying, NJT may be more suitable. For nutritional support exceeding six weeks, GT is preferred, while GJT or JT is recommended if gastric issues such as reflux or delayed emptying are present.
Feeding Methods
Feeding methods include bolus feeding, intermittent feeding, and continuous feeding.
Bolus feeding involves delivering the total required daily nutrition in divided portions over 30–60 minutes via the feeding tube.
Intermittent feeding provides nutrition six to eight times daily, with each session lasting more than an hour, allowing the GI tract to rest for 8–16 hours.
Continuous feeding delivers nutrition evenly over a 24-hour period via the tube. Continuous feeding may be the preferred option for premature infants, patients with short bowel syndrome, or those suffering from severe malnutrition accompanied by chronic diarrhea.
Enteral Nutrition Formulas
Enteral nutrition formulas should be selected based on factors such as the patient’s age, nutrient requirements, gastrointestinal function, eating status, and any food allergies.
Energy Requirements
The energy distribution of macronutrients within enteral nutrition solutions, as well as the daily fluid needs, must be adjusted according to the patient's nutritional status, activity level, and gastrointestinal absorption capacity. Energy demands typically increase under disease and stress conditions.
Osmolality
Most infant formulas are designed with an optimal osmolality of 300 mOsm/L. Specialized formulas may have higher osmolality due to added glucose and amino acids. GI tolerance is usually acceptable at an osmolality of 400 mOsm/L but is significantly compromised when exceeding 500 mOsm/L, necessitating feeding through the jejunum in these cases.
Complications
Mechanical Complications
These include improper placement or blockage of nasogastric or gastrostomy tubes, nasal, esophageal, or gastric injuries, sinusitis, otitis media, aspiration, or aspiration pneumonia.
Physical Complications
Common issues include nausea, vomiting, abdominal distension, or diarrhea; rare complications include intestinal necrosis or mucosal atrophy.
Metabolic Complications
These are less common than with PN but may occur, including hyperglycemia, hypoglycemia, electrolyte imbalances, or refeeding syndrome.
Parenteral Nutrition (PN)
Parenteral nutrition refers to the provision of essential energy, fluids, and nutrients via non-gastrointestinal routes, specifically through intravenous administration, to meet the body's metabolic and growth needs. Depending on whether a patient is capable of undergoing enteral nutrition (EN) treatment, PN is categorized into total parenteral nutrition (TPN) and supplementary parenteral nutrition (SPN).
Indications
Patients at nutritional risk or experiencing malnutrition, who are unable to meet at least 60% of their target nutritional needs via the gastrointestinal route for more than one week, are candidates for PN therapy.
Gastrointestinal Disorders
PN support is required in conditions where the gastrointestinal tract needs prolonged rest or when significant digestive and absorptive dysfunctions are evident. Common indications include intestinal obstruction, gastrointestinal fistula, acute flare-ups of inflammatory bowel disease, early postoperative stages of short bowel syndrome, severe acute pancreatitis intolerant to EN, severe malnutrition with gastrointestinal dysfunction, chronic refractory nausea and vomiting, and severe diarrhea.
Non-Gastrointestinal Conditions
Severe stress conditions such as extensive burns, severe multiple traumas, or intense therapeutic interventions like high-dose radiotherapy or chemotherapy, which suppress digestive functions, require PN support.
Advanced liver or kidney failure often results in edema and malnutrition, preventing adequate nutrient intake via the gastrointestinal route, necessitating combined PN therapy.
Adverse gastrointestinal reactions or mucosal ulcers caused by medications, as well as conditions like anorexia nervosa, are also indications for PN.
Special Circumstances
Premature infants, low birth weight infants, and cases of extrauterine growth restriction may require PN support.
Contraindications
While PN does not have absolute contraindications, there are conditions under which it may be inappropriate or should be used with caution.
Parenteral Nutrition Formulations
PN formulations typically include water, glucose, amino acids, lipid emulsions, electrolytes, trace elements, and vitamins. Energy distribution among the three macronutrients is approximately 15% from proteins, 35% from fats, and 50% from carbohydrates. To ensure sufficient nutrient provision while controlling fluid intake and the concentration of intravenous solutions, PN dosages are usually increased gradually. Amino acids are initiated at 0.5 g/kg per day and gradually increased to 2–3 g/kg per day. Lipid emulsions start at 0.5–1 g/kg per day and are eventually increased to 2–3 g/kg per day. Glucose concentration is generally maintained below 12.5%.
Delivery Routes
PN can be administered through two primary routes:
Central Venous Route
Common methods include the subclavian vein, internal jugular vein, femoral vein, and peripherally inserted central venous catheter (PICC). This route is suitable for long-term PN or for patients requiring hyperosmolar nutritional solutions.
Peripheral Venous Route
This is generally used for patients requiring PN therapy for no more than two weeks.
Complications
Catheter-Related Complications:
- Injuries from catheter insertion.
- Thrombosis.
- Catheter-related infections.
Metabolic Complications:
- Abnormal blood glucose levels: Including hyperglycemia, which may lead to hyperosmolar non-ketotic coma, and hypoglycemia.
- Hyperlipidemia and fat overload syndrome.
- Hyperammonemia.
- Cholestatic jaundice and liver dysfunction.
- Electrolyte and acid-base imbalances.
- Deficiencies or excesses of trace elements and vitamins.
- Prolonged TPN may lead to complications such as intestinal mucosal atrophy and reduced secretions from intestinal glands.
Transitioning from Parenteral Nutrition to Enteral Nutrition
Long-term TPN use may lead to gastrointestinal functional decline. Transitioning from TPN to EN is a gradual process where enteral nutrition is incrementally increased, and parenteral nutrition is correspondingly reduced until EN meets at least 60% of the required nutritional needs. At this point, TPN is discontinued entirely, and normal dietary intake is resumed.