TPN Basics...there are times when a patient will not should not, cannot eat.

There are times when a patient can not eat, will not eat or should not eat.  There are also times when a patient is taking in an insufficient number of calories.  Examples of these situations are chronic illness, short term illness or post surgery.  Patients in these situations have to be fed because no matter what our physical state is, in order to sustain life, our bodies require a certain amount of calories each day.  We need these calories in order to maintain our weight and nourish our cells.

The abbreviation TPN actually stands for Total Parenteral Nutrition and depending on the practice setting, the term can be used to describe all IV feedings or it can be used specifically to say that only IV feedings that are administered through a central line are called TPN.  It depends on the institution.  Your institution may use terms such as PPN which tands for Partial or Peripheral Parenteral Nutrition.  Your institution may even use terms like 3 in 1 solution or Total Nutrient Admixture  abbreviated, TNA.

For purposes of this discussion, we are going to consider all of these to be fundamentally the same.  The difference between TPN and PPN are the concentration of dextrose and as a result the site of administration.  The difference between TPN and TNA is that the total nutrient admixture has an extra base solution, etc.  As far as the calculations are concerned, they are basically the same.  In other words, once you can do the calculations for one, you can do the calculations for the others.

So let’s break this topic down into its elemental parts.  There are two major components of these formulations.  They are Base solutions and then Additives.

The base solutions for TPN are Dextrose and Amino Acids.  The base solutions for TNA are Dextrose, Amino Acids and Lipids.  Think about it, in order to sustain life, our diets must have carbohydrates, fats and protein.  Dextrose is a crbohydrate; Amino acids are the building blocks of protein and Lipids are fats.  These base solutions are stated as percentages for the most part.  The only exception is the TNA where there is a percentage of Lipid Emulsion (either 10% or 20%) followed by a volume.

When we are calculating for the amount of base solution to add, we can use either quantity times strength or the alligation method.  So to calculate for each base solution, we would set up an independent quantity times strength problem or allegation problem to solve for the volume to be added.

Then there are the additives.  Examples of additives are as follows:

Electrolytes (ex: KCl, NaCl, KPO₄, etc)

Insulin (Regular only)

MVI (Multivitamins)

Trace minerals

H2 antagonist (ex: ranitidine, famotadine)

Vitamin K

Heparin