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TPN: Nutrition & Guidelines

Instructor: Nancy Kilmer

Nancy is a registered nurse with a bachelor of science in nursing degree.

During a serious illness or injury, one may not be able to take food orally temporarily. Full nutritional needs can be met intravenously with TPN, total parenteral nutrition. We will explore the nutritional content and guidelines for these IV feedings.

Normal Nutritional Requirements

Most of us are familiar with the Food Pyramid that was developed as a guide for basic nutritional needs for a healthy, well-balanced diet. You have probably seen the pyramid as part of health education in school, or if you were researching a specific type of diet that you were interested in following.

Food Pyramid
Food Pyramid

Though many different food pyramids have been developed to accommodate different beliefs in ratios of healthy nutrients, the basic nutritional components for a healthy human being remain essentially the same. These nutrients can be divided into a few main categories.

Macronutrients Micronutrients
Proteins Vitamins
Carbohydrates Minerals
Fats Trace Elements

Providing Normal Nutrition in TPN Formula

Your normal daily diet probably consists of the same type of nutrients that are used to make a total parenteral nutrition (TPN) formula.

  • Proteins/amino acids from meats, nuts, dairy
  • Carbohydrates from fruits, vegetables, grains
  • Fats/lipids from oils, nuts, meats, dairy
  • Vitamins and minerals from a variety of fruits and vegetables

All of these food ingredients are necessary for maintaining health and promoting healing during illness or injury. TPN is a way of providing all of the same nutrients when a patient is unable to take them by mouth.

In order to provide the right type and amount of nutrients required for an individual who needs TPN, there are many factors that are considered.

  • Age
  • Sex
  • Size
  • Current nutritional status
  • Type of illness or injury

Each daily TPN dose is calculated based upon these factors in order to make an intravenous 'food' that meets the specific needs of that patient that day. For example, a 200-pound male will need more calories than a 30-pound girl, and a 30-year old female will need more magnesium than a 3-year old boy. You can easily see that a standard solution is not likely to meet each patient's individual needs appropriately.

In order to determine the correct mixture of nutrients for each patient, a team of professionals is involved. The team usually consists of the following three professionals:

  • The physician who understands the physiologic needs of the patient based upon his injury or illness
  • The dietitian who understands the nutritional requirements of the patient based on age and development
  • The pharmacist who determines the right amount of each nutrient to add to the mixture taking into account fluid volume and infusion rate

Daily Formula Process

Let's take a closer look at how this is done on a daily basis. In order to know the appropriate amounts of both macronutrients and micronutrients, blood is drawn for a lab study each day. The amounts of protein, calcium, phosphorus, and other nutrients are measured. Then the proper amounts of each of the nutrients goes into the formula for that TPN for that day. In many patients, the formula changes on a daily basis as their needs change. This supports keeping the body in the proper balance in order to heal. Then the solution is mixed using amino acids (the nutrients found in proteins), dextrose (basic carbodydrate solution), lipids (fats that are necessary for the body to function), vitamins, minerals, and trace elements.

Potential Complications

The following precautions for the use of TPN are needed to avoid potential complications:

  • Monitoring the patient's blood glucose up to four times per day. Because the solution has a high concentration of dextrose (carbohydrate), the patient may be at risk for abnormally high blood glucose, requiring adding insulin to the solution to maintain normal levels.
  • Maintaining the appropriate rate of infusion. The fluids and nutrients in the TPN must be given at a slow, constant rate. Use of an IV pump is required to maintain the proper rate of infusion.
  • Avoiding vein irritation. TPN is a concentrated solution that can be irritating to veins. It is necessary for the solution to be given through a large central vein in the body, as smaller veins would become too irritated. The IV line is generally placed in the shoulder or upper chest area where there are larger veins.

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