Parenteral Nutrition (PN)

Parenteral nutrition (PN) is the process of nourishing a person or animal intravenously when a patient is not able to eat for a variety of reasons that can range from being comatose to a blockage or absorption issue in the stomach and small intestines. Prior to the 1960s, patients that were not able to eat often did not thrive. Since adequate nutrition is paramount to aiding the body in healing, not being able to eat and absorb nutrients led to serious effects in the patient.

Broad strides were made in the seventeenth century after it was discovered that blood circulated in the body. However, before the optimal route for delivering solutions to patients who could not eat was discovered, much needed to be learned about what essential nutrients were required to live and maintain health. These discoveries were made in tandem with basic science that characterized fat (lipid), carbohydrates, and protein in the laboratory, and was subsequently translated into medicine that could be used to treat malnutrition in patients who were unable to eat.

Brief History

The history of total parenteral nutrition (TPN) began with William Harvey’s discovery of general blood circulation in 1628, which provided the basis for the idea that solutions could be given intravenously that could help with disease processes. Following Harvey’s discovery, many experiments using electrolytes and glucose were performed. Over time, enough information about the safety of this route of drug or fluid delivery had been amassed to develop protocols for treating diseases, such as dehydration and nutritional deficiencies. In the late 1930s, Robert Elman, a nutritional biochemist, had demonstrated that amino acids could be safely administered in humans. This was the first step toward the development of TPN. The main issue with this route of administration was preparing high energy solutions with low osmotic pressure.

Initially, the idea was to infuse solutions that had a soluble form of fat, since it was the most challenging of the nutrients. Most of the solutions created at the time caused severe adverse events, even death. In the 1960s, the first safe fat emulsion was created. After this hurdle was passed, adding in vitamins, electrolytes, and other elements necessary for adequate nutrition was a much easier task. A few years later, it was demonstrated that these nutrient solutions could be delivered by a central venous catheter (a large IV).

Stanley J. Dudrick, a surgical resident at the University of Pennsylvania, was the first person to successfully nourish a Beagle puppy that was born with a gastrointestinal malignancy, using an intravenous solution.

Overview

Parenteral nutrition (PN) is the process of nourishing a person or animal intravenously, in the event that it is neither advisable to eat by mouth (e.g., after a stroke) or because of a gastrointestinal malignancy or malabsorption. TPN is called total nutrient admixture when it is the only means of obtaining nutrition, such as when a patient can take nothing by mouth. When the mixture is administered through a vein in a normal intravenous site, it is called peripheral parenteral nutrition.

TPN is used in patients who have cancer, a poorly functioning gastrointestinal (GI) tract, or other disorders of the GI tract (bowel obstruction, prolonged diarrhea, or Crohn’s disease). It may be used short-term in patients whose GI tract has slowed down and are underweight. TPN is used long-term in patients who are recovering from accidents, GI surgery, and digestive disorders.

A typical TPN solution is made of distilled water, electrolytes (sodium and potassium), glucose, amino acids, lipids, and essential vitamins and minerals. However, the mixtures can be customized to fit the nutritional and health needs of the patient. Before prescribing a nutrient mixture, a team of the patient’s physician, pharmacists, registered dietitians, and nurses evaluate the patient’s needs and devise a comprehensive TPN plan. The solution is administered as prescribed, sometimes changing as the patient’s needs change.

Receiving TPN long-term can bring about many challenges, both mentally and physically. When children and teens receive TPN, it can be very difficult for them to lead normal lives. Not only do they have to restrict their activities to protect their IV access site, but they also must contend with the mental toll that can result from not being able to participate in sports (contact sports) or other social events. TPN therapy can result in body image issues due to being underweight (or overweight, in some cases).

Complications from TPN therapy can range from mild to very severe. These complications are infection, blood clots, liver failure and fatty liver, intense hunger pains, and pregnancy complications. Since long-term TPN therapy requires a permanent catheter, infection is the most common complication, which can result in sepsis and death in some patients. The permanent catheter can cause a blood clot simply because a foreign body can stimulate clotting. Often a blood clot is released from its site of origin and causes an obstruction in the lungs, called pulmonary embolism. A physician will often prescribe a drug called heparin, which will help to dissolve an existing clot or prevent any from forming. Liver disease resulting from long-term TPN therapy affects nearly half of patients, and half of those will die from complications.

Interestingly, even though a patient might be adequately nourished, they will still experience intense feelings of hunger. This is due to the fact that the hunger drive is a complex process that involves olfactory (smell), taste, and the need to feel full (which involves a protein that is only released when eating by mouth). Pregnancy complications arise from the fetus and mother not being adequately nourished. Despite these complications, when the therapy is properly administered and the patient is compliant (follows physician’s orders), these individuals can lead long lives with minimal complications.

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