Parenteral Nutrition Support for AdultsManual of Clinical Nutrition Management B- 53 Copyright © 2013 Compass Group, Inc.
used in the rare case of a patient who has hepatic encephalopathy that is refractory to standard
treatment with luminal-acting antibiotics and lactulose (1,6).
Formulations for renal disease: Essential amino acids are the primary protein source in formulations
designed for patients with renal disease. This formula design is based on the theory that nonessential
amino acids can be physiologically recycled from urea, while the essential amino acids must be provided
by the diet (11). These formulas have no statistically significant advantages when compared to standard
amino acid formulas (1,23). The ASPEN guidelines suggest that ICU patients with acute renal failure
receive standard enteral or parenteral formulations and that the standard ICU recommendations for
protein and energy provision should be followed (6). A specialty formulation designed for renal failure
(with the appropriate electrolyte profile) may be considered for patients who have significant electrolyte
abnormalities (6). Patients receiving hemodialysis or continuous renal replacement therapy should
receive increased amounts of protein, up to a maximum of 2.5 g/kg per day (6). Protein should not be
restricted in patients with renal insufficiency as a means to avoid or delay the initiation of dialysis
therapy (6).
Concentrated amino acid formulations: Highly concentrated (15% to 20%) amino acid formulations
are available for use when fluid restriction is required. These formulations are similar in composition to
standard amino acid formulas, except that they may contain larger amounts of acetate (11). However,
chloride salts may be used to balance the chloride-to-acetate ratio in the final PN formulation to avoid
iatrogenic acid-base disturbances (11).
Pediatric formulations: Pediatric formulas have been designed to meet the unique amino acid
requirements of neonates, infants, and children in order to promote weight gain, nitrogen balance, and
growth and to avoid an excess of certain amino acids (eg, phenylalanine and methionine) (1). These
products generally contain taurine, tyrosine, histidine, arginine, and L-cysteine (semi-essential to
neonates) (1).
Glutamine: Glutamine is a conditionally essential amino acid during times of metabolic stress. There has
been considerable interest in the potential beneficial effects of glutamine, including systemic antioxidant
effects, maintenance of gut integrity, induction of heat shock proteins, and use as a fuel source for rapidly
replicating cells (6). The addition of parenteral glutamine at a dose of 0.5 g/kg per day to a parenteral
regimen reduces infectious complications, ICU length of stay, and mortality in critically ill ICU patients, as
compared to the same parenteral nutrition regimen without glutamine (6). Currently, crystalline amino
acid formulations in the United States and Canada do not contain glutamine (6). Due to stability and
compatibility issues, there is no intravenous form of glutamine that is commercially available for
admixture in parenteral solutions (6,11). Studies of glutamine-supplemented parenteral formulas have
used preparations of powdered L-glutamine sterilized by filtration (6,24,25). ASPEN and AND guidelines
currently recommend that supplementation with parenteral glutamine be considered when parenteral
nutrition is used in the critical care setting to reduce infectious complications (Grade 1)* (18); or for those
with demonstrated benefits eg, surgical patients with extensive abdominal surgery, burn patients, acute
pancreatitis (6,24). Providing PN glutamine supplementation early and in doses of > 0.5/kg/day is
currently suggested to be effective in critical ill patients (24).
Protein requirements: Protein requirements should be based on the patient’s individual needs and disease
process. Critical illness and hypermetabolism are associated with increased protein turnover, protein
catabolism, and negative nitrogen balance (6,26). During a critical illness, protein requirements can double
increasing to approximately 15% to 20% of total energy (26). Protein requirements for the critically ill patient
are at least 1.5 g/kg per day, and adequate energy should be provided to meet the estimated needs as
determined by indirect calorimetry or predictive equations (26). The protein requirements of critically ill
patients who are not obese (BMI <30 kg/m^2 ) are 1.2 to 2.0 g/kg actual body weight per day, although burn
patients or multiple-trauma patients may require greater amounts of protein (6). Protein sparing does not
typically improve with protein intakes greater than 1.5 g/kg per day, except in severely burned patients (26).
Critically ill patients with obesity may have higher protein needs. The ASPEN guidelines for critical care ICU
adult patients recommend a daily protein intake of more than 2.0 g/kg ideal body weight for class I and II
obese patients (BMI, 30 to 40 kg/m^2 ) and more than 2.5 g/kg ideal body weight for class III obese patients (BMI
40 kg/m^2 ) (6). For all patients, a 24-hour urine collection for urinary urea nitrogen may be collected and
used to subsequently adjust the prescription for protein delivery.
Lipid sources: Isotonic lipid emulsions provide energy and essential fatty acids. Lipid sources are derived
from soybean oil or a 50:50 mixture of soybean and safflower oils (11). In North America, the choice of
parenteral lipid emulsion is severely limited to a soy-based, 18-carbon omega-6 fatty acid preparation that
has proinflammatory characteristics in the ICU population (6). During the first 7 days in the ICU setting, a soy-