- Clinical science
Specialized nutrition support (SNS) is required when oral intake is either limited or not possible for a prolonged period of time. Common indications for SNS include patients in critical care, those with dysphagia, unconscious patients who cannot be fed, severely malnourished patients, and those with intestinal malabsorption. The two forms of SNS are enteral nutrition and parenteral nutrition. Enteral feeding is always preferred whenever possible, but parenteral feeding may be instituted if the patient has a nonfunctional GI tract (e.g., gastroschisis, short bowel syndromes), and/or if enteral feeding is contraindicated. Patients who are on SNS may develop several complications related to feeding tubes or intravenous catheters, as well as additional metabolic complications such as electrolyte imbalances, hyperglycemia, refeeding syndrome, gallstone disease, and nonalcoholic fatty liver disease.
- Dysphagia; (e.g., post-stroke state; , multiple sclerosis, esophageal carcinoma)
- Patients with a low GCS who cannot be fed
- Difficulty with oral intake in the early postoperative state
- Severe anorexia (e.g., terminally ill cancer patients, anorexia nervosa)
- Severe malnutrition
- Critically-ill patients
- Intestinal malabsorption
First-line: enteral feeding
- Easier to perform
- Metabolic complications occur less often
- Intestinal motility is stimulated, preventing mucosal atrophy
- Lower risk of blood stream infection
- Second-line: parenteral feeding
The following principle applies in most situations: oral before enteral, enteral before parenteral!
- Definition: administration of nutrients directly into the stomach, duodenum, or jejunum with the help of feeding tubes
- Short-term: nasogastric, nasoduodenal, nasojejunal, orogastric, oroduodenal, or orojejunal tubes
- Long-term (> 2–3 weeks): gastrostomy (e.g., percutaneous endoscopic gastrostomy, percutaneous radiologic gastrostomy, surgically placed gastrostomy), or jejunostomy tubes (e.g., percutaneous endoscopic jejunostomy, percutaneous radiologic jejunostomy)
Composition of enteral feeding solutions
- Protein supply: amino acids/peptides / high-molecular-weight proteins
- Carbohydrate supply: mono-, oligo- or polysaccharides
- Fat supply: medium or long-chain fatty acids.
- Osmolality of enteral feeds: approximately 300 mOsmol/L
- Electrolytes, trace elements, and vitamins are added according to the recommended daily intake (see “Nutritional requirements during SNS” below).
- Definition: intravenous administration of nutrients that bypasses the gastrointestinal tract (from Greek “ para” = besides; “ enteron” = the inside)
- Parenteral nutrition is required for < 2 weeks: peripheral venous line, or peripherally inserted central catheter
- Parenteral nutrition is required for > 2 weeks: tunneled central venous catheter or a port
Continuous parenteral nutrition
- Most commonly used, especially in hospital settings
- Slower infusion rate
- Higher risk of fatty liver
- Cyclical parenteral nutrition
- Continuous parenteral nutrition
- Composition of parenteral feeding solutions
- Venous catheter-related:
- Catheter displacement
- Thrombosis and/or embolism
- Catheter-related blood stream infection
- Fluid overload
- Venous catheter-related:
Discontinuation of parenteral nutrition
- Indication: > 75% of the recommended calorie and protein intake can be achieved by oral or enteral feeding.
- PN is tapered off by halving the infusion rate hourly.
- Modular preparations: Modular preparations are more expensive but they allow individualized TPN solutions to be compounded.
- Standard preparations: These preparations are available as prepacked solutions and have fixed macronutrient compositions.
|Type of standard solution||Energy content||% of energy from proteins||% of energy from fats||% of energy from carbohydrates|
|Three-in-one preparations||High glucose solutions||0.6–1.2 kcal/mL||10–15%||30–35%||45–55%|
|Low glucose solutions||35–45%||35–45%|
- 20–25 kcal/kg/day
Critically ill patients
- Initial 10–14 days: a hypocaloric intake of approximately 10–15 kcal/kg/day
- After 2 weeks: The energy intake may be increased to meet the recommended daily intake of 25 kcal/kg/day.
- Initial 10–14 days: 0.8 g/kg/day.
After 2 weeks: the dose may be increased to 1.5 g/kg/day
- Patients with burns may require up to 2 g/kg/day until the wound heals.
- Protein preparations: Both modular and standard formulations contain a mixture of all 9 essential amino acids and some non-essential amino acids in varying proportions.
- Nitrogen balance measures the effectiveness of protein supplementation.
- Nitrogen balance = Nitrogenintake - Nitrogenloss = (Protein intake in grams/6.25) - (24 hour urine nitrogen + 4)
- 1 g of lost nitrogen → loss of 30 g of lean mody mass
- A negative nitrogen balance of -2 to -4 g/d may be allowed.
- The recommended dose of carbohydrates for TPN is 4 g/kg/day.
- Carbohydrate preparations: Both modular and standard formulations use D-glucose (dextrose).
- The recommended dose of fats for TPN is 1 g/kg/day.
- Fat preparations: In the US, lipid formulations consist of soybean oil stabilized in an emulsion of egg yolk lecithin.
Fluid, electrolytes, and micronutrient requirements
|Fluid and electrolytes|
A patient's nutritional requirements must be considered when choosing a PN solution. It is important to note that patients with life-threatening illnesses have higher energy requirements.
- Severe electrolyte imbalances (e.g., hypocalcemia, hypomagnesemia, hypophosphatemia)
- Acalculous cholecystitis
- Gallstone disease
- Non-alcoholic fatty liver disease
- Renal damage
- Bone demineralization
Metabolic complications are more common with parenteral nutrition than enteral nutrition!