Parenteral Nutrition Support for Adults
Manual of Clinical Nutrition Management B- 54 Copyright © 2013 Compass Group, Inc.
based, lipid-free parenteral nutrition regimen has been shown to be associated with a significant reduction in
infectious morbidity (pneumonia and catheter-related sepsis), a decreased length of hospitalization and ICU
stay, and a shorter duration of mechanical ventilation as compared to the use of lipid-containing parenteral
nutrition (6). ASPEN guidelines for critically ill ICU patients recommend that during the first week of
hospitalization when enteral nutrition is not feasible, a parenteral formulation without soy-based lipids
should be considered (6). Lipid sources are emulsified with egg yolk phospholipid; therefore, their use may
be contraindicated in patients with egg allergies. Lipid emulsions contain glycerol, so lipid emulsion does not
provide 9 kcal per gram as it would if it were pure fat. Lipid emulsions are available in 10% (1.1 kcal/mL),
20% (2 kcal/mL), and 30% (3 kcal/mL) concentrations (11). The 30% lipid formulation is approved only for
compounding of the total nutrient admixture, not for direct intravenous administration (11).
Investigational intravenous fat emulsion (IVFE) products include physical mixtures of medium-chain
triglycerides and long-chain triglycerides. These formulations may be useful for patients who are intolerant
to the long-chain triglyceride products during critical illness and metabolic stress and also for patients with
carnitine deficiency (11). Structured lipid formulas containing linoleic acid, medium-chain fatty acids, and very
long–chain omega-3 fatty acid are being investigated to determine if they produce less inflammatory and
nonthrombogenic prostaglandins than standard lipid emulsions (11). These formulas have been studied in
patients with sepsis, atopic dermatitis, or severe ulcerative colitis and patients undergoing elective surgery
(27,28). These formulas are under investigational study and are not available for intravenous use in the United
States (11).
Because of the enhanced microbial growth potential with the infusion of IVFE separately from dextrose and
amino acid formulations, the Centers for Disease Control and Prevention recommends a 12-hour hang-time
limit for IVFE (29). The United States Pharmacopeial has also endorsed the use of IVFE products within 12
hours of opening the original manufacturer’s container if the IVFE products are infused as separate
preparations from dextrose and amino acids (30). However, because of the lower pH (5.6 to 6.0) of a total
nutrient admixture that contains IVFE, dextrose, and amino acids in the same container, the fat emulsion may
be administered over 24 hours when infused in a total nutrient admixture (11). Whether infused separately or
as a total nutrient admixture, the infusion rate of IVFEs should not exceed 0.11 g/kg per hour to reduce side
effects, such as hypertriglyceridemia, and infectious complications (11,31).
Lipid requirements: When a patient is medically stable, lipids provide an important source of essential fatty
acids. A total of 2% to 4% of daily energy needs should be supplied as linoleic acid (1% to 2% of linoleic acid
and 0.25% to 0.5% of alpha-linolenic acid) (1) or 25 to 100 mg/kg of essential fatty acids (1,32,33). A minimum
of 500 mL of 10% lipid stock solution or 250 mL of 20% stock solution administered over 8 to 10 hours, two
to three times per week, is sufficient to prevent a deficiency of essential fatty acids. Alternately, 500 mL of a
20% fat emulsion can be given once a week (34). Excessive amounts of intravenous lipids or rapid infusion
rates can cause hyperlipidemia (20). Levels of serum triglycerides should be evaluated before the infusion of
intravenous lipids. Four hours after lipid infusion, acceptable serum triglycerides levels are less than 250
mg/dL for piggybacked lipids and less than 400 mg/dL for continuous lipid infusion (1). The infusion of
intravenous lipids has been associated with impaired immune responses and vascular integrity (19,32,35).
Infusion rates of greater than 110 mg/kg per hour may result in reduced lipid clearance and impaired
reticuloendothelial function and pulmonary exchange (32). It is recommended that fat intake be restricted to
less than 25% to 30% of total energy, or 1 g/kg per day, and provided slowly over 8 to 10 hours if
administered as an intravenous supplement (32,34). No more than 2.5 g/kg per 24 hours should be provided to
adult patients (1). The rapid infusion of fat emulsions, regardless of the total amount, should be avoided in
patients who have severe pulmonary failure (6).
The recommendations for lipids given to critically ill patients requiring parenteral nutrition are more
conservative; the data support the administration of less than 1.0 g/kg per day (1,34). ASPEN guidelines for
critically ill ICU patients suggests during the first week of hospitalization (when enteral nutrition is not
feasible), the use of a parenteral formulation without soy-based lipids should be considered in order to
reduce the risks associated with the proinflammatory effects previously discussed (6). These guidelines
acknowledge that parenteral nutrition without lipids might exacerbate stress-induced hyperglycemia;
therefore, the recommendation should be cautiously applied with consideration to the individual patient’s
nutritional needs and acute medical situation (6). Carnitine deficiency can lead to fat deposition in the liver
and muscle, impaired ketogenesis, and neurologic symptoms. Parenteral nutrition solutions do not contain
carnitine, and the supplemental use of carnitine in adults has not been studied. However, carnitine
supplementation has been suggested for neonates who receive parenteral nutrition for more than 2 weeks
(36).