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Parenteral nutrition (PN) is feeding a person intravenously, bypassing the usual process of eating and digestion. The person receives nutritional formulae that contain nutrients such as glucose, amino acids, lipids and added vitamins and dietary minerals. It is called total parenteral nutrition (TPN) or total nutrient admixture (TNA) when no significant nutrition is obtained by other routes. It may be called peripheral parenteral nutrition (PPN) when administered through vein access in a limb, rather than through a central vein.
|This section relies on references to primary sources. (April 2014)|
Developed in the 1960s by Dr Stanley J. Dudrick, who as a surgical resident in the University of Pennsylvania, working in the basic science laboratory of Dr Jonathan Rhoads, was the first to successfully nourish initially Beagle puppies and subsequently newborn babies with catastrophic gastrointestinal malignancies. Dr Dudrick collaborated with Dr WIllmore and Dr Vars to complete the work necessary to make this nutritional technique safe and successful.
|This section does not cite any references or sources. (May 2013)|
A mechanical pump under computer control is used to dispense the TPN fluid. Pumps are available that allow TPN administration at home, usually with the preparation and attachment by a family member. These pumps operate on an external dispensing line, part of a single-use dispensing cassette. Connection of the dispensing line to the patient is via a valve on a semi-permanent attached venous port whose closure is displaced by a connection on the dispensing line. Preparation, attachment, and valve replacement require care in sanitation and sterile techniques at specific locations. The use of a rechargeable battery and a portable component pack allows a convenient household mobility for many patients during administration periods, these being typically from twelve to sixteen hours a day.
Total parenteral nutrition (TPN) is provided when the gastrointestinal tract is nonfunctional because of an interruption in its continuity (it is blocked, or has a leak - a fistula) or because its absorptive capacity is impaired. It has been used for comatose patients, although enteral feeding is usually preferable, and less prone to complications. Parenteral nutrition is used to prevent malnutrition in patients who are unable to obtain adequate nutrients by oral or enteral routes.
TPN may be the only feasible option for providing nutrition to patients who do not have a functioning gastrointestinal tract or who have disorders requiring complete bowel rest, including bowel obstruction, short bowel syndrome, Gastroschisis, prolonged diarrhea regardless of its cause, high-output fistula, very severe Crohn's disease or ulcerative colitis, and certain pediatric GI disorders including congenital GI anomalies and necrotizing enterocolitis.
The benefit of TPN to cancer patients is largely debated, and studies to date have generally showed minimal long term benefit. There is no evidence to support the idea that intravenous nutrition 'feeds the cancer, not the patient'.
Short-term PN may be used if a person's digestive system has shut down (for instance by peritonitis), and they are at a low enough weight to cause concerns about nutrition during an extended hospital stay. Long-term PN is occasionally used to treat people suffering the extended consequences of an accident, surgery, or digestive disorder. PN has extended the life of children born with nonexistent or severely deformed organs.
Approximately 40,000 people use TPN at home in the United States, and because TPN requires anywhere from 10–16 hours to be administered, daily life can be affected. Although daily lifestyle can be changed, most patients agree that these changes are better than staying at the hospital. Many different types of pumps exist to limit the time the patient is “hooked-up”. Usually a backpack pump is used, allowing for mobility. The time required to be connected to the IV is dependent on the situation of each patient; some require once a day, or five days a week.
It is important for patients to avoid as much TPN related change as possible in their lifestyles. This allows for the best possible mental health situation; constantly being held down can lead to resentment and depression. Physical activity is also highly encouraged, but patients must avoid contact sports (equipment damage) and swimming (infection). Many teens find it difficult to live with TPN due to issues regarding body image and not being able to participate in activities and events.
TPN fully by-passes the GI tract and normal methods of nutrient absorption. Possible complications, which may be significant, are listed below.
TPN requires a chronic IV access for the solution to run through, and the most common complication is infection of this catheter. Infection is a common cause of death in these patients, with a mortality rate of approximately 15% per infection, and death usually results from septic shock.
Chronic IV access leaves a foreign body in the vascular system, and blood clots on this IV line are common. Death can result from pulmonary embolism wherein a clot that starts on the IV line but breaks off goes into the lungs.
Patients under long-term TPN will typically receive a periodic heparin flush to dissolve such clots before they become dangerous.
Fatty liver is usually a more long term complication of TPN, though over a long enough course it is fairly common. The pathogenesis is due to using linoleic acid (an omega-6 fatty acid component of soybean oil) as a major source of calories. 
Because patients are being fed intravenously, the subject does not physically eat, resulting in intense hunger pangs. The brain uses signals from the mouth (taste and smell), the stomach/G.I. Tract (fullness) and blood (nutrient levels) to determine conscious feelings of hunger. In cases of TPN, the taste, smell and physical fullness requirements are not met, and so the patient experiences hunger, despite the fact that the body is being fully nourished. In cases where the patient eats food despite the inability, they can experience a wide range of complications.
Pregnancy can cause major complications when trying to properly dose the nutrient mixture. Because all of the baby’s nourishment comes from the mother’s blood stream, the doctor must properly calculate the dosage of nutrients to meet both recipient’s needs and have them in usable forms. Incorrect dosage can lead to many adverse, hard-to-guess effects, such as death, and varying degrees of deformation or other developmental problems.
It is recommended that parenteral nutrition administration begin after a period of natural nutrition so doctors can properly calculate the nutritional needs of the fetus. Otherwise, it should only be administered by a team of highly skilled doctors who can accurately guess the fetus’ needs.
Total parenteral nutrition increases the risk of acute cholecystitis due to complete disuse of gastrointestinal tract, which may result in bile stasis in the gallbladder. Other potential hepatobiliary dysfunctions include steatosis, steatohepatitis, cholestasis, and cholelithiasis. Six percent of patients on TPN longer than 3 weeks and 100% of patients on TPN longer than 13 weeks develop biliary sludge. The formation of sludge is the result of stasis due to lack of enteric stimulation and is not due to changes in bile composition. Gallbladder sludge disappears after 4 weeks of normal oral diet. Administration of exogenous cholecystokinin (CCK) or stimulation of endogenous CCK by periodic pulse of large amounts of amino acids have been shown to help prevent sludge formation. These therapies are not routinely recommended. Such complications are suggested to be the main reason for mortality in people requiring long-term total parenteral nutrition, such as in short bowel syndrome. In newborn infants with short bowel syndrome with less than 10% of expected intestinal length, thereby being dependent upon total parenteral nutrition, 5 year survival is approximately 20%.
Complications are either related to catheter insertion, or metabolic, including refeeding syndrome. Catheter complications include pneumothorax, accidental arterial puncture, and catheter-related sepsis. The complication rate at the time of insertion should be less than 5%. Catheter-related infections may be minimised by appropriate choice of catheter and insertion technique. Metabolic complications include the refeeding syndrome characterised by hypokalemia, hypophosphatemia and hypomagnesemia. Hyperglycemia is common at the start of therapy, but can be treated with insulin added to the TPN solution. Hypoglycaemia is likely to occur with abrupt cessation of TPN. Liver dysfunction can be limited to a reversible cholestatic jaundice and to fatty infiltration (demonstrated by elevated transaminases). Severe hepatic dysfunction is a rare complication. Overall, patients receiving TPN have a higher rate of infectious complications. This can be related to hyperglycemia.
The nutrient solution consists of water and electrolytes; glucose, amino acids, and lipids; essential vitamins, minerals and trace elements are added or given separately. Previously lipid emulsions were given separately but it is becoming more common for a "three-in-one" solution of glucose, proteins, and lipids to be administered.
Only a limited number of emulsifiers are commonly regarded as safe to use for parenteral administration, of which the most important is lecithin.[medical citation needed] Lecithin can be biodegraded and metabolized, since it is an integral part of biological membranes, making it virtually non-toxic. Other emulsifiers can only be excreted via the kidneys, creating a toxic load. The emulsifier of choice for most fat emulsions used for parenteral nutrition is a highly purified egg lecithin, due to its low toxicity and complete integration with cell membranes. Use of egg-derived emulsifiers is not recommended for people with an egg allergy due to the risk of reaction. In situations where there is no suitable emulsifying agent for a person at risk of developing essential fatty acid deficiency, cooking oils may be spread upon large portions of available skin for supplementation by transdermal absorption.
Solutions for total parenteral nutrition may be customized to individual patient requirements, or standardized solutions may be used. The use of standardized parenteral nutrition solutions is cost effective and may provide better control of serum electrolytes. Ideally each patient is assessed individually before commencing on parenteral nutrition, and a team consisting of specialised doctors, nurses, clinical pharmacists and Registered Dietitians evaluate the patient's individual data and decide what PN formula to use and at what infusion rate.
For energy only, intravenous sugar solutions with dextrose or glucose are generally used. This is not considered to be parenteral nutrition as it does not prevent malnutrition when used on its own. Standardized solutions may also differ between developers. Following are some examples of what compositions they may have. The solution for normal patients may be given both centrally and peripherally.
|Examples of total parenteral nutrition solutions|
|Substance||Normal patient||High stress||Fluid-restricted|
|Amino acids||85 g||128 g||75 g|
|Dextrose||250 g||350 g||250 g|
|Lipids||100 g||100 g||50 g|
|Na+||150 mEq||155 mEq||80 mEq|
|K+||80 mEq||80 mEq||40 mEq|
|Ca2+||360 mg||360 mg||180 mg|
|Mg2+||240 mg||240 mg||120 mg|
|Acetate||72 mEq||226 mEq||134 mEq|
|Cl-||143 mEq||145 mEq||70 mEq|
|P||310 mg||465 mg||233 mg|
|MVI-12||10 mL||10 mL||10 mL|
|Trace elements||5 mL||5 mL||5 mL|
Individual nutrient components may be added to more precisely adjust the body contents of it. That individual nutrient may, if possible, be infused individually, or it may be injected into a bag of nutrient solution or intravenous fluids (volume expander solution) that is given to the patient.
Administration of individual components may be more hazardous than administration of pre-mixed solutions such as those used in total parenteral nutrition, because the latter are generally already balanced in regard to e.g. osmolarity and ability to infuse peripherally. Incorrect IV administration of concentrated potassium can be lethal, but this is not a danger if the potassium is mixed in TPN solution and diluted.
Vitamins may be added to a bulk premixed nutrient immediately before administration, typically in two doses, one fat soluble, the other water soluble, this since the additional vitamins can promote spoilage of stored product.