Overview of Total Parenteral Nutrition (TPN)

Most people receive the energy and nutrients they need through their diets, but sometimes this is not possible for medical reasons. Parenteral nutrition gives a person the nutrients and calories they need through a vein instead of through eating.

With total parenteral nutrition (usually called TPN), a person gets 100% of the nutrition they need each day through a vein.

Parenteral nutrition can be given temporarily or for a longer time. In the United States, around 30,000 people rely completely on feedings given directly through their veins to get the nutrition they need.

What Is TPN?

A person who is on total parenteral nutrition receives all the nutrients and energy they need through an intravenous (IV) line. The nutrients enter through the veins and travel through the blood vessels to the entire body. 

Normally, the organs of the gastrointestinal tract (especially the small intestine) absorb the calories and nutrients the body needs. Parenteral nutrition completely bypasses the stomach and intestines. Instead, the nutrients are made available directly to the veins, from which they can be pumped all over the body.

You might also hear the term “partial parenteral nutrition.” This refers to someone who is receiving some, but not all, of their total nutrition through their veins. A doctor may prefer this method if a person's gut is impaired but can still perform some digestion. 

Parenteral Nutrition vs. Enteral Nutrition

Another option is “enteral” nutrition. Even though “enteral” sounds a lot like “parenteral,” they are not the same. “Enteral” comes from the Greek word meaning “intestine.” The suffix “para” means, roughly, “beyond.”

Technically speaking, normal eating is a type of enteral nutrition. However, the term is more often used to describe medical interventions that allow someone to get nutrition into their gastrointestinal tract in other ways (“tube feeding”). 

For example, enteral nutrition includes nasal or oral tubes that run down to the stomach or intestines from the nose or mouth. Other examples are gastrostomy and jejunostomy tubes (G-tubes and J-tubes), which are medically inserted into the stomach or part of the small intestine, respectively, to allow food to be administered there.  

Why Enteral Is Preferred

When an alternative method of feeding is needed, doctors prefer to use enteral feeding methods instead of parenteral whenever possible. One reason is that enteral nutrition does not disrupt the body’s normal physiological processes the way parenteral nutrition does. 

The body is specifically adapted to absorb and process nutrients through the lining of the intestines. Because of these physiological differences and some other factors, enteral feeding has less risk of serious complications compared with parenteral feedings. 

For example, parenteral nutrition causes more inflammation than enteral nutrition, and it’s harder for the body to regulate its blood sugar levels with parenteral nutrition. Parenteral nutrition is also more complicated and expensive than enteral feeding. 

An enteral method might be recommended for someone who was having difficulty swallowing after having a stroke but who has a normally functioning gastrointestinal tract. In contrast, parenteral feeding might be necessary if a person is having trouble absorbing calories and nutrients through their gastrointestinal tract.

Who Might Need TPN?

Any person who is unable to get enough calories through their gastrointestinal tract might need to receive TPN. Some medical situations that might require TPN include:

• Cancer (particularly of the digestive tract) or complications from cancer treatment
• Ischemic bowel disease
• Obstruction of the digestive tract
• Inflammatory bowel disease (such as Crohn’s disease)
• Complications from previous bowel surgery

Some premature infants also need to receive TPN temporarily because their digestive tracts are not mature enough to absorb all the nutrients they need. 

Some hospitalized people need TPN if they are unable to eat for an extended period and enteral methods are not possible.

How Is TPN Given?

If you need to receive TPN, your medical team will need to have access to your veins. A catheter—a long thin tube—will be put in some part of the venous system. The careful placement of a catheter is done in the hospital while a person is under heavy sedation or anesthesia.

Some catheter and TPN delivery methods are better suited for temporary use and others for more long-term use.

Tunneled Catheter

Depending on your situation and personal preferences, you might opt to get a tunneled catheter, which has a segment of the tube outside the skin and another portion under the skin.

Port-a-Cath

Another option is an implanted catheter (sometimes called a “port-a-cath,” or just a “port”). In this case, the catheter itself is completely beneath the skin and is accessed with a needle to infuse the parenteral nutrition.

To administer TPN, a health professional can use either type of catheter to connect to an external bed of fluids containing the necessary nutrients and calories. This can be done in different places, such as one of the main veins in the neck or upper chest.

PICC Line

A PICC line (peripherally inserted central catheter) is another choice, particularly when a person will need to use TPN for a longer time.

With a PICC line, the entry point that is used to deliver the TPN is a vein in the arms or legs, but the catheter itself threads all the way to a larger vein deeper inside the body.

Setting

TPN is started in a hospital setting. A person will often be hooked up to TPN to receive the infusion steadily over 24 hours.

Some people will need to continue to receive TPN even after they go home from the hospital. They may get nutrition over eight- to 12-hour blocks.

What Does TPN Contain? 

TPN is designed to replace all the important nutrients that a person would normally be getting through their diet.

These components include:

• Proteins
• Carbohydrates
• Fats
• Vitamins (e.g., vitamin A)
• Electrolytes (e.g., sodium)
• Trace elements (e.g., zinc)
• Water

There are many specific formulations available for TPN. Not everyone gets the same components in the same amounts. The TPN that you need will depend on several factors, such as your age and any medical conditions that you have.

Your nutritional team will also determine how many calories you need each day. For example, a person with obesity might be given a slightly smaller number of calories and may even lose a little weight on TPN.

In contrast, nutritionists would likely give a solution that is much higher in calories to someone who is significantly underweight.

Your medical team will carefully tailor your TPN to you based on your specific circumstances, and they will modify the formulation as needed. This helps reduce the risk of complications from TPN. 

A person receiving parenteral nutrition—but not total parenteral nutrition—might only get some of these elements, such as carbohydrates and water. 

Laboratory Assessment and Monitoring for TPN

Before starting TPN, your medical team will assess whether TPN is safe and necessary for you. They’ll also need to do some blood tests to help them decide on the ideal formulation. 

You’ll need to get certain blood tests at regular intervals after you start TPN to help your medical team monitor for and prevent medical complications.

Blood tests that you might need include:

• Complete blood count (CBC)
• Electrolytes
• Blood urea nitrogen (to monitor kidney function)
• Blood sugar (glucose) levels
• Liver tests

The blood tests generally need to be done more often at first (sometimes multiple times a day). As a person’s medical situation stabilizes, testing is not needed as frequently. The specific tests that you need will depend on your medical situation. 

What Are the Side Effects and Risks of TPN?

Some people still get hungry while they are on TPN. The brain is not getting the signals that it normally does to trigger a feeling of fullness. The sensation tends to diminish with time.

Other people experience nausea from TPN, which is more likely when they have an intestinal blockage.

Catheter Issues

The placement of the catheter can cause problems, although they are rare.

Some possible complications of catheter placement include:

• Air embolism
• Pneumothorax
• Hitting an artery instead of a vein
• Nerve damage from incorrect insertion
• Catheter fragment embolism
• Cardiac tamponade (very rare but life-threatening)

Other Catheter-Related Problems

Catheters can also cause problems after they have been placed, including infections and, less commonly, blood clotting issues.

Catheter Infections

Catheter infections are also a serious problem and one that clinicians try very hard to prevent. One of the first steps to prevent catheter infections is to ensure that the person accessing the line uses good hand hygiene and cleans the area properly before accessing the line.

An infected catheter often requires antibiotic treatment and rehospitalization if a person is already at home. A person might also need to have a new procedure to replace their catheter, which carries its own risk for complications and is also expensive.

Blood Clots

Blood clots in the vessels near the catheter are another serious risk. These clots can sometimes cause symptoms like swelling of the arm or neck.

Catheter-related blood clots can also lead to complications such as pulmonary embolism and infection, as well as post-thrombotic syndrome. This complication can cause long-term swelling and pain in the affected area.

Problems From TPN Infusions

Being on TPN even for a short time comes with risks related to the different levels of some compounds in the body, such as electrolytes and vitamins.

Electrolyte and Fluid Imbalances

Electrolyte and fluid imbalances can be a problem for people receiving TPN. The body has several important electrolytes (minerals that are dissolved in fluids) that are critical for many of the body's basic physiological processes.

Important electrolytes in the body include sodium, potassium, and calcium, as well as some that are present in smaller amounts, such as iron and zinc. If the concentration of these electrolytes in the blood is too high or too low, it can cause serious health problems (such as heart rhythm issues).

The body may have more difficulty regulating the amount of these substances in the body because of how TPN is delivered. People on TPN also often have serious medical issues that make it difficult to predict exactly how much of these substances to deliver as part of the TPN.

Your medical team will carefully monitor the amount of these substances in your blood and adjust your TPN formula as necessary. That’s part of why frequent blood tests are needed for people on TPN, especially when it is first started.

Vitamins and Blood Sugar

The amounts of certain vitamins in the body (such as vitamin A) can also be harder to control when a person is on TPN. Another concern is the level of sugar in the person's blood (blood glucose levels).

A person on TPN can develop high blood glucose levels (hyperglycemia). One reason a person on TPN might be more likely to develop high blood sugar is that their body is under stress.

Sometimes a person can develop high blood sugar levels because the TPN formulation is delivering too much glucose or carbohydrates. However, doctors monitor a person for this carefully as part of regular blood tests.

Hyperglycemia can be addressed by altering the TPN formulation and/or potentially giving a person insulin, if needed.

Liver Function

Liver problems can also happen, especially in people who are using TPN for a long time. Some of these problems are not serious and go away when the TPN is stopped or adjusted.

However, in more serious cases, liver scarring (cirrhosis) or even liver failure can happen. A person's medical team will monitor their liver function carefully while they are on TPN.

Mental Health and Lifestyle Changes

People on TPN often experience diminished quality of life and may develop depression. It’s natural to miss the enjoyment of eating a good meal and the shared social connection with others that eating brings. It’s important to get the psychological support you need in whatever way feels right for you, such as through professional counseling.

If your medical situation has stabilized, you might be able to leave the hospital even if you are still on TPN. While many people feel better at home, it still presents challenges. For example, if you are hooked up to TPN overnight, you may need to wake several times to urinate.

If you opt to do your TPN during the day, it can interrupt your planned activities (although you can get it while working at your desk, for example). Still, getting TPN at home instead of in the hospital will usually improve a person's quality of life.

How Long Will I Need to Stay on TPN?

How long you need to have TPN depends on your underlying medical condition. Some hospitalized people need TPN for a relatively short time—such as a week to 10 days.

Other people may need TPN for months (e.g., for problems related to surgical complications), but they are eventually able to come off TPN. You may also eventually be able to reduce the amount of parenteral nutrition that you need.

If the medical issue requiring TPN cannot be resolved, a person might need to remain on TPN for the rest of their life.