Parenteral Nutrition Support for Adults
Manual of Clinical Nutrition Management B- 52 Copyright © 2013 Compass Group, Inc.
excess, hyperglycemia, hepatic steatosis, and increased CO 2 production can occur. Maintaining glucose in the
range of 80 to 110 mg/dL has been associated with decreased morbidity and mortality in cardiac surgical
intensive care patients (16-18). However, recent studies have suggested that moderate glucose control (140 to
180 mg/dL) reduces the risk of hypoglycemia and hypoglycemia-associated mortality as compared to stricter
glucose control (80 to 110 mg/dL) (6). Considering this evidence, ASPEN guidelines recommend targeting a
more moderate range of 100 to 150 mg/dL when providing nutrition support therapy to critically ill patients
(6). The Standards of Medical Care in Diabetes, updated annually by the American Diabetes Association,
recommends a target glucose level of 140 to 180 mg/dL in critically ill patients with existing diabetes mellitus
(19). The Academy of Nutrition and Dietetics (AND) recommends glucose levels targeting 140 to 180 mg/dL
for all critically ill patients (18). Dietitians should collaborate with the medical team to identify protocols for
optimal glucose control based on clinical management guidelines (6).
For patients with hyperglycemia, the parenteral-nutrition dextrose should be started conservatively and
gradually increased to the patient’s individualized goal rate. It is suggested PN be initiated at half the patients
estimated energy needs or 150 to 200 grams dextrose in the first 24 hours, or approximately 100 grams
dextrose if patient is already hyperglycemic or requiring insulin therapy. (20). It is recommended that the goal
CHO rate should not exceed 4 to 5 mg/kg per minute or 20 to 25 kcal/kg per day from CHO (20). Capillary
blood glucose should be measured at least every 6 hours and more frequently in hyperglycemic patients (19).
Regular insulin can be provided subcutaneously, intravenously via insulin infusion, or added directly to the
parenteral solution (18,20). An insulin drip provides more consistent and safe glucose control (19). Blood
glucose concentrations can be controlled by an initial insulin regimen of 0.05 to 0.1 U/g of dextrose in the
parenteral solution or by 0.15 to 0.2 U/g of dextrose in hyperglycemic patients (20). When added to the
solution, it is recommended that two thirds of the total amount of sliding-scale insulin required over 24 hours
be added to the next day’s parenteral formula (20). A proportional increase in fat may be necessary to increase
the energy provided to patients whose blood glucose levels are difficult to control (20). Rarely, hyperglycemia
is caused by a chromium deficiency. If insulin is ineffective or a chromium deficiency is confirmed, increasing
the chromium contained in the parenteral formula may be appropriate (21). Refer to Section III: Metabolic
Complications of Central Parenteral Nutrition and Section IC: Medical Nutrition Therapy for Diabetes Mellitus
for specific glycemic goals in managing hospitalized patients with diabetes mellitus.
Patients at risk of developing refeeding syndrome should be monitored closely. Refeeding syndrome refers
to metabolic and physiologic shifts of electrolytes and minerals (eg, phosphorus, magnesium, and potassium)
caused by aggressive nutrition support (1,22). Carbohydrate delivery stimulates insulin secretion, which
causes an intracellular shift of these electrolytes and minerals with the potential for severe
hypophosphatemia, hypomagnesemia, and hypokalemia (19,22). Symptoms of refeeding syndrome include
fatigue, lethargy, muscle weakness, edema, cardiac arrhythmia, and hemolysis (19,22). Patients who have
marginal nutrient stores secondary to a disease or medical therapy are at the greatest risk for refeeding
syndrome; these patients should initially receive 15 to 20 kcal/kg of formula, 100 – 200 grams CHO or no
more than 2 mg/kg/min per day, and then the amount of parenteral formula should be slowly increased
(20,22). (Refer to Section III: Metabolic Complications of Central Parenteral Nutrition.)
Protein sources: Crystalline amino acids, which provide 4 kcal/g, are the most common source of protein in
parenteral formulas. Standard or balanced amino acid products are mixtures of essential and nonessential
amino acids ranging in concentrations from 3% to 20%, although 8.5% and 10% are most frequently used for
parenteral nutrition compounding (11). Most commercially available amino acid formulations also contain
electrolytes, buffers, or both. Modified or special amino acid products have been formulated for certain
disease states and conditions in which conventional amino acid solutions may not be well tolerated (eg, renal
failure and hepatic failure) (11). The contribution of these formulas to an improvement in overall clinical
outcome is debatable. These formulas usually cost much more than conventional amino acid solutions.
Therefore, the clinician should evaluate the cost in light of the potential benefit to the patient.
ASPEN guidelines for nutrition support are the basis for the following discussion of specialized amino acid
formulas (1,6):
Formulations for liver disease: Standard formulations should be used in ICU patients with acute and
chronic liver disease (6). Protein restriction should be avoided in patients with liver failure (6). Formulas
that contain high levels of branched-chain amino acids (BCAA) and low levels of aromatic amino acids are
designed to correct abnormal amino acid profiles associated with hepatic encephalopathy, as BCAA are
metabolized independently of liver function. ASPEN guidelines recommend that BCAA formulas only be