Should Total Parenteral Nutrition Be Started and Stopped Gradually?

Karen Jensen, PharmD, BCPS

Disclosures

April 23, 2009

Question

Is it necessary to gradually increase the rate of total parenteral nutrition when initiating and gradually decrease the rate when discontinuing? What is the standard practice on this and what is the rationale for it?

Response from Karen M. Jensen, PharmD, BCPS
Clinical Pharmacist, Mason General Hospital, Shelton, Washington

This titrate-up and taper-down controversy stems from concerns regarding the potential for hyperglycemia upon initiation of total parenteral nutrition (TPN) and for hypoglycemia upon discontinuation. Volume tolerance is also a concern.

Hyperglycemia is a complication of TPN associated with excessive dextrose infusion. Patient conditions will often affect dextrose tolerance, and care must always be taken to avoid excessive carbohydrates. Acute care, stable patients are generally able to tolerate target carbohydrate rates as early as day 1. Critically ill patients, however, have a lower tolerance for dextrose due to stress-induced metabolic changes, as do patients with diabetes mellitus. These patients will likely benefit from achieving the target dextrose intake over 2-3 days.[1]

The initial maximum carbohydrate given in a stable adult is usually 150-200 g/day (15%-20% final dextrose concentration) with a target dextrose intake of ≤ 7 mg/kg/minute based on estimated dry weight or 120% of ideal body weight in obese patients. For adult patients with diabetes mellitus or hyperglycemia of stress, 100-150 g/day of dextrose (10%-15% final dextrose concentration) may be administered initially with a target dextrose intake of ≤ 4 mg/kg/minute based on estimated dry weight or 120% of ideal body weight in obese patients.[1]

The approach to limit initial dextrose intake will depend on the products and services available. With the availability of a clinician to perform the necessary calculations and the ability to provide customized products, the ideal approach is to compound a custom base formula that incorporates the daily nutritional requirements into the necessary volume to satisfy the daily fluid requirement. The dextrose content of the base formula can then be titrated up to meet the dextrose target. This base formula will unlikely need more than 1 adjustment before a maintenance base formula is obtained.

In an institution that must use premixed solutions with a limited variety of concentrations available, the infusion rate can be adjusted to limit initial dextrose administration and titrated up to the target dextrose intake over the next day or 2.

Protein is associated with minimal metabolic side effects, and while it is acceptable to administer the maximum amount (60-70 g/L) on day 1,[1] titrating up over a day or 2 to control dextrose content is without consequence. Limiting volume to control dextrose content, however, may require supplemental fluid administration to achieve daily fluid requirements.

Hypoglycemia upon abrupt discontinuation of TPN is a complication that may result from endogenous insulin levels not adjusting to the sudden reduction in dextrose. While some patients with underlying conditions affecting glucose regulation may be more susceptible, the risk in patients with stable glucose levels, especially those receiving another source of carbohydrate, is likely low. Although several studies have shown that tapering of TPN is generally not needed in patients maintaining stable glucose levels while receiving moderate amounts of dextrose,[2,3,4] eliminating risk by tapering TPN over 1-2 hours before discontinuation can easily be justified.

Tapering of TPN is a very common clinical practice, and while perhaps not always necessary, it is easy to accomplish and serves to provide an added measure of safety. Reducing the rate by 50% for an hour or 2 before discontinuation is an adequate strategy that also tends to be well tolerated by the nursing staff. Another proposed strategy is to decrease the infusion rate by 50% over the first hour and an additional 50% over the second hour.[4] Should the current TPN solution suddenly become unavailable, 10% dextrose solution may be used in its place for tapering.

While initiation and discontinuation guidelines can guide clinical practice and reduce the incidence of complications, it is important to remember that TPN requires close and careful monitoring by clinicians trained to recognize and respond to any complications that may arise.

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