54 ENTERAL AND PARENTERAL NUTRITION
Harrison’s Manual of Medicine
ENTERAL AND PARENTERAL NUTRITION
Specific Micronutrient Deficiency
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, or trauma). An approach for deciding when to use various types of specialized nutrition support (SNS) is summarized in Fig. 54-1.
Enteral therapy refers to feeding via the gut, using oral supplements or infusion of formulas via various feeding tubes (nasogastric, nasojejeunal, 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. Where feasible, enteral nutrition is the preferred route because it sustains the digestive, absorptive, and immunologic functions of the GI tract, at about one-tenth the cost of parenteral feeding. Parenteral nutrition is often indicated in severe pancreatitis, necrotizing enterocolitis, prolonged ileus, and distal bowel obstruction.
The components of a standard enteral formula are shown in Table 54-1; however, modification of the enteral formula may be required based on various clinical indications and/or associated disease states (Table 54-2). After elevation of the head of the bed, 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.
Table 54-1 Composition Characteristics
Table 54-2 Modified Enteral Formulas
The components of parenteral nutrition include adequate fluid (35 mL/kg body weight for adults, plus any abnormal loss); energy from glucose, protein, and lipid solutions; nutrients essential in severely ill pts, such as glutamine, nucleotides, and products of methionine metabolism; 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 patients 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, WBC (baseline, then 2× per week)
INR (baseline, then weekly)
Micronutrient tests as indicated
SPECIFIC MICRONUTRIENT DEFICIENCY
Appropriate therapies for micronutrient deficiencies are outlined in Table 54-3.
Table 54-3 Therapy for Common Vitamin and Mineral Deficiencies
For a more detailed discussion, see Russell RM: Vitamin and Trace Mineral Deficiency and Excess, Chap. 75, p. 461, and Howard L: Enteral and Parenteral Nutrition Therapy, Chap. 76, p. 470, HPIM-15.