Nutritional support should be initiated in pts with malnutrition or in those at risk for malnutrition (e.g., conditions that preclude adequate oral feeding or pts in catabolic states, such as sepsis, burns, major surgery, or trauma). An approach for deciding when to use various types of specialized nutrition support (SNS) is summarized in Fig. 7-1.
Decision-making for the implementation of specialized nutrition support (SNS). CVC, central venous catheter; PCM, protein-calorie malnutrition; PICC, peripherally inserted central catheter. (Adapted from chapter in Harrison’s Principles of Internal Medicine, 16e, by Lyn Howard, MD.)
Enteral therapy refers to feeding via the gut, using oral supplements or infusion of formulas via various feeding tubes (nasogastric, nasoduodenal, gastrostomy, jejunostomy, or combined gastrojejunostomy). Parenteral therapy refers to the infusion of nutrient solutions into the bloodstream via a peripherally inserted central catheter (PICC), a centrally inserted externalized catheter, or a centrally inserted tunneled catheter or subcutaneous port. When feasible, enteral nutrition is the preferred route because it sustains the digestive, absorptive, and immunologic functions of the GI tract, and because it minimizes the risk of fluid and electrolyte imbalance. Parenteral nutrition is often indicated in severe pancreatitis, necrotizing enterocolitis, prolonged ileus, and distal bowel obstruction.
The components of a standard enteral formula are as follows:
Caloric density: 1 kcal/mL
Protein: ~14% cals; caseinates, soy, lactalbumin
Fat: ~30% cals; corn, soy, safflower oils
Carbohydrate: ~60% cals; hydrolyzed corn starch, maltodextrin, sucrose
Recommended daily intake of all minerals and vitamins in ≥1500 kcal/d
Osmolality (mosmol/kg): ~300
However, modification of the enteral formula may be required based on various clinical indications and/or associated disease states. After elevation of the head of the bed and confirmation of correct tube placement, continuous gastric infusion is initiated using a half-strength diet at a rate of 25–50 mL/h. This can be advanced to full strength as tolerated to meet the energy target. The major risks of enteral tube feeding are aspiration, diarrhea, electrolyte imbalance, warfarin resistance, sinusitis, and esophagitis.
The components of parenteral nutrition include adequate fluid (30-mL/kg body weight/24 h for adults, plus any abnormal loss); energy from glucose, amino acids, and lipid solutions; nutrients essential in severely ill pts, such as glutamine, nucleotides, and products of methionine metabolism; and electrolytes, vitamins, and minerals. The risks of parenteral therapy include mechanical complications from insertion of the infusion catheter, catheter sepsis, fluid overload, hyperglycemia, hypophosphatemia, hypokalemia, acid-base and electrolyte imbalance, cholestasis, metabolic bone disease, and micronutrient deficiencies.
The following parameters should be monitored in all pts receiving supplemental nutrition, whether enteral or parenteral:
Fluid balance (weight, intake vs. output)
Glucose, electrolytes, BUN (daily until stable, then 2× per week)
Serum creatinine, albumin, phosphorus, calcium, magnesium, Hb/Hct, ...