Whether you’re administering TPN (total parenteral nutrition) or a pharmacist compounding it you are going to ask or be asked about these 4 things at some point.
How we dose TPN is dependent on lots of factors like the level of care (ICU versus medical), organ dysfunction and body composition to name a few. But these 4 concepts concerning administration apply across the board.
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1. Central vs Peripheral Administration
With TPN we are administering the patient’s nutritional needs intravenously, completely bypassing the gastrointestinal tract. Intravenous administration can be either via a central line or a peripheral line.
Almost always, a patient requiring TPN will need a central line.
Simply put, a central line connects into large veins while peripheral lines terminate into smaller veins that are closer to the skin surface.
Osmolarity
The 3 main components of TPN are amino acids, dextrose and fats. TPN is prepared and administered in 1 of 2 ways:
- 3 in 1: amino acids, dextrose and fats are prepared in a single container and administered together
- 2 in 1: amino acids and dextrose are prepared in a single container and administered together. Fats are administered separately.
The deciding factor for central versus peripheral administration is osmolarity. Osmolarity is a measure of concentration. Most TPN will have a high osmolarity that exceed 900 mOsmol/L because of the dextrose and amino acids it contains.
Administering high osmolarity medication into a peripheral vein creates an osmotic gradient that pulls fluid from the tissues surrounding the vein. This causes inflammation (phlebitis) and extravasation (drug leaks out of damaged vein and into surrounding tissue). The immune response to tissue damage causes in influx of inflammatory mediators that can initiate clot formation in an attempt to limit damage to the vein. This increases the risk of clot formation (thrombophlebitis).
Administration hyperosmolar solutions like TPN via central rather than peripheral vein allows for dilution and a subsequent lower risk of vein irritation, phlebitis, extravasation and thrombophlebitis.
Types of Central Lines
The most common central line for TPN administration is a PICC (Peripherally Inserted Central Catheter) line. As the name implies, the point of entrance is a peripheral vein, but it terminates into a large central vein. PICC lines are appropriate for acute care and short to intermediate term administration of TPN.
Patients requiring more long term or permanent administration of TPN will require tunneled central venous access devices or implanted ports that have a lower risk of microbial migration and infection with long term use.
2. In Line Filters
All TPN will require a filter for administration. The filter and administration tubing should be changed every time you change the bag or every 24 hours (whichever comes first).
A filter is necessary to reduce the patient’s exposure to microprecipitation, microparticles, microorganisms, fungi and air emboli.
The current recommendation is for all parenteral nutrition be filtered with a 1.2-micron filter.
Placement of In-Line Filter
Where the filter is placed is very important.
It should be placed as close to the patient as possible not close to the bag.
When lipids are administered as a separate infusion, the filter should be placed below the Y site where the infusions meet.
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3. TPN Compatibilities
Ideally TPN should have a dedicated line for administration.
A catheter with multiple lumens, one dedicated to TPN with others available for other medications is ideal but not always possible.
In short, nothing should ever run together with TPN for 2 main reasons:
Risk of Infection
TPN has a high concentration of dextrose which is a favorable environment for bacterial growth. We want to minimize manipulation of the line and minimize access to the port as much as possible to reduce the risk of bacterial transfer.
Each time that line is accessed to change from TPN to another medication is an opportunity for central line associated blood stream infections (CLABIs).
Precipitation
TPN is a very sensitive formulation. It is light sensitive, pH sensitive, temperature sensitive. Every exposure matters.
We would never run other medications through the same line as TPN because the combination can result in pH changes that cause precipitation of electrolytes like calcium and phosphates. The changes in pH that can occur when medications are combined is not easily measured.
These precipitates can occlude vessels in the pulmonary system causing embolism or pneumonitis.
Always advocate for a dedicated line for TPN administration. Often, providers are simply unaware of the risk of line sharing with TPN.
4. Discontinuation of TPN
TPN introduces a high dextrose solution right into the blood stream. This is very different to how glucose is introduced into the bloodstream when we eat (via the gastrointestinal tract).
Eating a meal results in a gradual rise and decline in blood glucose with a corresponding response in insulin release from the pancreas in an attempt to maintain normoglycemia.
With intravenous administration of TPN, dextrose enters the blood stream at a fixed rate. There is no fluctuation. The body responds with a steady release of insulin. There is no period of fasting.
If we suddenly stop TPN infusion the influx of glucose immediately stops but insulin release will remain elevated for a short period of time. The ratio of insulin to dextrose is very high for a period of time. Some patients can tolerate the abrupt discontinuation but, in some patients, this can lead to rebound hypoglycemia.
Because of this, we recommend titrating patients off of TPN by decreasing the rate by half for 1-2 hours before discontinuation. This allows the pancreas time to decrease the levels of insulin circulating in the blood.
If there is a sudden unplanned interruption in the supply of TPN, 10% dextrose solution should be infused at a rate equal to the TPN infusion. This can occur if there is a delay in delivery from pharmacy, damage to the TPN bag, or if precipitation is noticed during infusion.
TPN preparation and administration can be complex and very patient specific but familiarity with these 4 pointers will improve patient safety across the board.
The American Society of Parenteral and Enteral Nutrition (ASPEN) provides clinical guidelines and standards for all aspects of nutrition.
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The information on this website is intended to be used solely for educational and informational purposes. While the content may be about specific medical and health care issues, it is not a substitute for or replacement of personalized medical advice and is not intended to be used as the sole basis for making individualized medical or health-related decisions.
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