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TPN: Administration & Calculations

Instructor: Scott Keane

Scott has a Bachelor's degree in Nursing, a Master's degree in Christian Studies, and has taught college level nursing.

Find out how to get all your nutritional requirements when you cannot eat due to illness or disease. This lesson describes many adjustments that go into calculating a total nutritional solution.

What is TPN?

You are going to make your secret recipe Razzle Dazzle Chocolate Cake for your friend's birthday. You mix the four main ingredients: flour, sugar, eggs, and milk. Then you add some chocolate, a pinch of cinnamon, and the rest of the 12 spices and flavorings that make this cake one-of-a-kind.

In the same way, a healthy diet calls for a 'recipe'. Carbohydrate, fat, protein, and water are the four main ingredients. Also necessary are twelve vitamins and minerals with electrolytes and trace elements. Healthcare providers can duplicate this recipe in liquid form. This is handy when you cannot eat because of digestive tract problems.

Liquid nutrition given outside your digestive tract, into your veins, is called parenteral nutrition. If you are unable to eat for more than 4-7 days, you can receive all your energy and nutritional needs intravenously. Total parenteral nutrition, or TPN provides all your necessary carbohydrate, protein, fat, water, vitamins, minerals, electrolytes and trace elements from a solution going directly into the largest vein in your body.

How Do You Administer TPN?

To receive total parenteral nutrition (TPN), a doctor inserts a long, thin tube (catheter) through your skin, into a vein in your chest, neck, or arm. This catheter travels inside the vein and ends up in a large vein near your heart, the Superior Vena Cava. The catheter is now called a central venous line (CVL). Since TPN is given for long term illness, you may have the same catheter in place for up to one year. The most common problem you have from a central venous line is infection. Providers can prevent serious infections by using sterile technique to care for your catheter. Nurses also use sterile technique when plugging the TPN solution into the central venous line.

Recipe Calculations for Total Parenteral Nutrition

Water

A standard TPN recipe calls for sterile water, carbohydrates (dextrose), protein (amino acids), fat (lipids), vitamins, minerals, electrolytes, and trace elements. One liter (about one quart) of water holds all these ingredients in solution in a soft plastic bag. The amount of each ingredient is calculated according to your age, illness, and nutritional requirements. Normally, you will receive about two liters of TPN each day. If you have severe heart or kidney conditions, you will get less fluid. Children and infants also require less fluid.

Less fluid means a more concentrated solution of nutrients. Healthcare providers can adjust the concentration of nutrients by looking at daily weight measurements and fluid intake versus fluid output (urine). If you gain more than two pounds in a day, you need less fluid. If you are losing weight and have signs of dehydration you need more fluid.

Carbohydrate

The second ingredient in a TPN solution is dextrose. Dextrose, a carbohydrate, provides most of your energy needs from total parenteral nutrition. You will need, on average, 2,000 calories per day. Providers achieve this by varying the dextrose concentration. Normal intravenous solutions contain 5% dextrose in water (D5W). Total parenteral nutrition IV solutions contain ten times as much dextrose, or 50% dextrose in water (D50W). TPN solutions may go as high as 75% dextrose in water (D75W) if you are fluid sensitive. New born babies use a concentration of around 17% dextrose.

Your blood sugar will rise dramatically with this much dextrose going directly into your veins. Insulin is a hormone medication that controls blood sugar. While you are on TPN you will have insulin in your TPN solution and possibly insulin shots. You would get insulin shots based on blood sugar testing done from a poke in your finger.

Another way to control blood sugar is to place the TPN bag in a pump that controls the infusion rate. This helps prevent excessively high or low blood sugar, and too rapid or too slow movement of fluid into your body.

Fat

Lipids (fat) will supply about one quarter of your total caloric needs from a TPN solution. In a 2,000 calorie solution this is about the same amount of fat contained in one small milkshake. This fat comes in lipid emulsions of 10%, 20%, or 30%. The concentration of lipid emulsion is calculated according to your weight and body fat reserves.

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