Harrison's Internal Medicine Part 4. Nutrition Chapter 73. Enteral and Parenteral Nutrition Therapy
Enteral and Parenteral Nutrition Therapy: Introduction
The ability to provide specialized nutritional support (SNS) represents a major advance in medical therapy.
Decision-making for the implementation of specialized nutrition support (SNS). CVC, central venous catheter; PICC, peripherally inserted central catheter. (Adapted from previous chapter by Lyn Howard, MD.)
The first step in deciding to administer SNS is to consider the nutritional implications of the disease process. Is the condition or its treatment likely to impair food intake and absorption for a prolonged period of time? For example, a well-nourished individual can tolerate approximately 7 days of starvation while experiencing a systemic response to inflammation (SRI).
Disease-Specific Nutritional Support
SNS is basically a support therapy and is primary therapy only for the treatment or prevention of malnutrition. Certain conditions require modification of nutritional support because of organ or system impairment. For instance, in nitrogen accumulation disorders, protein intake may need to be reduced. However, in renal disease, except for brief periods of several days, protein intakes should approach requirement levels of at least 0.8 g/kg or higher up to 1.2 g/kg as long as the blood urea nitrogen does not exceed 100 mg/dL.
Protein or Amino Acid Requirements
Although the recommended dietary allowance for protein is 0.8 g/kg per d, maximal rates of repletion occur with 1.5 g/kg in the malnourished. In the severely catabolic patient, this higher level minimizes protein loss. In patients requiring SNS in the acute care setting, at least 1 g/kg is recommended, with greater amounts up to 1.5 g/kg as volume, renal, and hepatic tolerances allow. The standard parenteral and enteral formulas contain protein of high biologic value and meet the requirements for the eight essential amino acids.
(BQ) Part 2 book "Nutrition support for the critically ill" presents the following contents: Access and complications of parenteral nutrition, surgical intensive care considerations, major infections and sepsis, organ failure and specialized enteral formulas, management of the obese patient
Intravenous nutrition (IVN), also known as parenteral nutrition (PN),
involves the administration of nutrients, electrolytes, minerals and fluid
directly into patients’ veins. It is used in patients whose gastrointestinal
absorption of food and/or fluids is inadequate, unsafe or inaccessible.
Infusing a mixture of nutrients and fluid, however, is not without risk.
Efficacy of SNS in Different Disease States
Efficacy studies have shown that malnourished patients undergoing major thoracoabdominal surgery benefit from SNS. Critical illness requiring ICU care including major burns, major trauma, severe sepsis, closed head injury, and severe pancreatitis [positive CT scan and Acute Physiology and Chronic Health Evaluation II (APACHE II) 10] all benefit by early SNS, as indicated by reduced mortality and morbidity. In critical illness, initiation of SNS within 24 h of injury or ICU admission is associated with a ~50% reduction in mortality.
Table 73-10 Enteral Formulas
STANDARD ENTERAL FORMULA
1. Complete dietary products (+)a
requiring tube feeding; some can be a. Caloric density 1 kcal/mL used orally b. Protein ~14% cals, caseinates,
c. CHO ~60% cals, hydrolyzed corn starch, maltodextrin, sucrose
d. Fat ~30% cals, corn, soy, safflower oils
e. Recommended daily intake of all minerals and vitamins in 1500 kcal/d
f. Osmolality (mosmol/kg): ~300
MODIFIED ENTERAL FORMULAS
1. Caloric density 1.
Although PN was initially relatively expensive, its components are often less expensive than specialty enteral formulas. Percutaneous placement of a central venous catheter into the subclavian or internal jugular vein with advancement into the superior vena cava can be accomplished at the bedside by trained personnel using sterile techniques. Peripherally inserted central catheters can also be placed within the lumen in the central vein, but this technique is usually more appropriate for non-ICU patients.
Total energy expenditure comprises resting energy expenditure (two-thirds) plus activity energy expenditure (one-third) (Chap. 72). Resting energy expenditure includes the calories necessary for basal metabolism at bed rest. Activity energy expenditure represents one-fourth to one-third of the total, and the thermal effect of feeding is about 10% of the total energy expenditure. For normally nourished healthy individuals, the total energy expenditure is about 30– 35 kcal/kg.
Mechanical The insertion of a central venous catheter should be performed by trained and experienced personnel using aseptic techniques to limit the major common complications of pneumothorax and inadvertent arterial puncture or injury. Catheter position should be radiographically confirmed to be in the superior vena cava distal to the junction with the jugular or subclavian vein and not directly against the vessel wall. Thrombosis related to the catheter may occur at the site of entry into the vein and extend to encase the catheter.
Table 73-8 Selected Metabolic Disturbances and Their Correction
Corrective Action with PN
water or decreased total body water sodium sodium
Occurs commonly with
or water to produce net
hypertonic fluid followed by positive fluid balance diuretic administration with maintaining sodium
free water clearance; can also and chloride balance occur with dehydration and normal total body sodium
Inadequate relative to need
Infections of the central access catheter rarely occur in the first 72 h. Fever during this period is usually from infection elsewhere or another cause. Fever that develops during PN can be addressed by checking the catheter site and, if the site looks clean, exchanging the catheter over a wire with cultures taken through the catheter and at the catheter tip. If these cultures are negative, as they are most of the time, the new catheter can continue to be used.
Enteral feeding often leads to diarrhea, especially if bowel function is compromised by disease or drugs, particularly broad-spectrum antibiotics. Diarrhea may be controlled by the use of a continuous drip, with a fiber-containing formula, or by adding an antidiarrheal agent to the formula. However, Clostridium difficile, which is a common cause of diarrhea in patients being tube fed, should be ruled out before using antidiarrheal agents. H2 blockers may also assist in reducing the net fluid presented to the colon.
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