Total Parenteral Nutrition and Glucose Utilization Rate

Total parenteral nutrition (TPN) is a method of feeding which bypasses the gastrointestinal tract,
and is an integral part of medical treatment when normal physiological means of nourishment cannot be utilized. TPN is associated with inherent risk such as hyperglycemia, electrolyte imbalances, increased oxidative stress, hepatic dysfunction, and potential infectious morbidity. The most commonly reported hepatic abnormalities include fatty liver, cholelithiasis, and cholestasis.

The primary source of energy in TPN solutions is carbohydrate in the form of dextrose
monohydrate, which is oxidized at a maximum rate of 4-7 mg/kg/min in humans. Higher dextrose
infusion rates may contribute to excess carbon dioxide production, which is undesirable for patients
with respiratory problems. Additionally, excess glucose is used by the liver for repletion of glycogen
stores and lipid synthesis, contributing to abnormal liver function test (LFT) values secondary to fatty
liver.

According to the ASPEN Guidelines of Nutrition Support Care in the Adult Critically Ill Patient,
those patients who require TPN in the ICU setting may benefit from a hypocaloric feeding strategy which also provides adequate protein. Dextrose infusion rates of 5 mg/kg/min or less is generally
recommended to prevent hyperglycemia and hepatic dysfunction. Effort should be made to avoid
energy provision that exceeds estimated energy requirements, as carbon dioxide production increases significantly with lipogenesis and may be tolerated poorly in patients prone to CO 2 retention.
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In conclusion, avoiding excessive energy intake in the critically ill patient requiring TPN Support
may reduce the potential for infectious morbidity, duration of mechanical ventilation, and hospital
length-of- stay. At Saint Joseph Hospital, Registered Dietitian Nutritionists follow ASPEN guidelines and aim to provide dextrose infusions of 4 mg/kg/min or less when recommending TPN support for critically ill patients.