20 TPN (Total Parenteral Nutrition) Calculations

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Sometimes a patient is not able to process food normally through their digestive tract or even through an og (orogastric) or ng (nasogastric) tube. This means we need an alternative way to provide them with macronutrients: carbohydrates, amino acids (protein), lipids (fat) and/or micronutrients: electrolytes, vitamins, minerals, sugars, as well as other additives. One reliable method of doing this is to administer the patient some or all of these substances through intravenous solutions, called TPN (total parenteral nutrition) solutions. TPN solutions are also referred to as “parenteral hyperalimentation solutions” or “hyperal solutions”.

TPN solutions normally contain 50% dextrose solution (for carbohydrate calories), 10% amino acid solution (for protein) & 20% lipid emulsion (fat). PPN or “peripheral parenteral nutrition” solutions normally contain 25% dextrose, 10% amino acids & 10% fat. Both come premixed from the manufacturer but the other additives are added at the pharmacy later. TPN & PPN are commonly administered either directly into the right atrium of the heart via a central IV line or infused via the subclavian vein under the collar bone over 8 to 24 hours, respectively.

A TPN solution containing a fat emulsion is called a TNA or “total nutrient admixture” & is commonly piggybacked into the administration set below the in-line filter, if the in-line filter has a pore size of less than 1.2 microns. It is important to prepare these IV admixtures with aseptic technique in order to prevent septic shock, contamination & infection.

TPN solutions are typically prepared in horizontal airflow hoods. Other types of IV admixtures such as chemotherapy (cytotoxic) medications are prepared in vertical airflow hoods or biological safety cabinets to protect the technician(s) preparing them. Lastly, TPN solutions are typically prepared using a TPN compounder — which is a machine that aids the technician(s) in pumping all the different components into empty sterile bags.

Common Diagnoses for TPN includes:

  • Conditions that severely limit intestinal function
  • Crohn’s disease
  • Cystic fibrosis
  • GI tract cancer
  • Inflammatory-bowel disease
  • Malabsorption syndrome
  • Massive bowel resection
  • Pancreatitis
  • Persistent intestinal fistulae
  • Short-bowel syndrome
  • Trauma-related GI complications
  • Ulcerative colitis

Now let us examine some simple TPN calculations! First, we present you with the “Volume/Concentration Available” of a vial, ampule, injection or syringe, along with the “Volume Needed” for the TPN. Can you use what you’ve learned so far to obtain the same values in the ANSWER KEY for the “Volume Used”? GIVE IT A TRY 😀 !

Volume / Concentration Available Volume Needed
A. 10 mL vial of multivitamins 7 mL of multivitamins
B. 10 mL of regular insulin vial
(100 units/mL)
50 units of regular insulin
C. 20 mL vial of sodium acetate
(2 mEq/mL)
50 mEq of sodium acetate
D. 10 mL vial of calcium gluconate
(4.65 mEq/vial)
2.8 mEq of calcium gluconate
E. 1 L of 8.5% amino acid injection 0.2 L of 8.5% amino acid injection
F. 10 mL vial of potassium chloride
(2 mEq/mL)
30 mEq of potassium chloride
G. 30 mL vial of sodium chloride
(4 mEq/mL)
40 mEq of sodium chloride
H. 2 mL of ranitidine syringe
(25 mg/mL)
300 mg of ranitidine
I. 0.5 mL of vitamin k ampule
(2 mg/mL)
2,000 mcg of vitamin k
J. 1,000 mL of 70% dextrose injection 0.3 L of 70% dextrose injection

ANSWER KEY: Volume Used
A. 0.7 of the vial F. 15 mL of the vial
B. 0.5 mL of the vial G. 10 mL of the vial
C. 1 vial (20 mL) + 5 mL of
another vial, for a total of 25 mL
H. 6 syringes, for a total of 12 mL
D. 6 mL of the vial I. 2 ampules, for a total of 1 mL
E. 200 mL of the injection J. 300 mL of the injection

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