PPN vs TPN: What is the Difference?
What Is Parenteral Nutrition (PN)?
PN is the medical abbreviation for parenteral nutrition, also known as intravenous nutrition. Nutrition is delivered directly to the body through the veins when a person is unable to obtain adequate nutrition through the digestive tract. When properly managed, this can be safely done at home. There are two subtypes of PN: total parenteral nutrition (TPN) and peripheral parenteral nutrition (PPN).
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Total Parenteral Nutrition (TPN)
Those who cannot obtain nutrition through oral consumption may be prescribed TPN. TPN is typically composed of some or all of the following ingredients: carbohydrates, proteins, lipids, electrolytes, trace elements, and insulin. Trace elements (copper, manganese, zinc, chromium, and selenium), as well as multivitamins, may be added for further nutritional supplementation.
Common conditions that TPN is used to treat are:
- Ischemic bowel disease
- Short bowel syndrome
- Inflammatory bowel disease
Generally, patients who have conditions that do not allow for a normally functioning digestive tract may benefit from TPN therapy. This includes those who have poor blood flow to their bowels as well. TPN is usually formulated to meet and replace complete daily nutritional needs. Because solutions can be very concentrated to deliver enough nutrients, a central line, which is an intravenous catheter that accesses one of the largest veins in the body, is typically needed for administration.
Peripheral Parenteral Nutrition (PPN)
PPN is PN that is administered through a peripheral intravenous line, also known as a hep-lock. Because it is administered into smaller veins, PPN solutions are formulated to be much more diluted than TPN solutions to prevent extravasation and vein thrombosis. As a result, PPN solutions generally provide significantly fewer calories than TPN solutions. PPN is prescribed for short-term nutritional support, usually 2 weeks or less.
PPN vs TPN
Both PPN and TPN serve the same general purpose, which is to provide nutrition to the body through alternative means. The key differences between the two are associated with calorie content and treatment duration.
PPN is reserved for the short-term when the expected duration of treatment is no greater than 2 weeks, usually during or after an acute event. Solutions are much more dilute and often meant to supplement nutritional needs rather than replace daily requirements.
TPN, on the other hand, is much more comprehensive. Each formula is calorie-dense and may replace the daily needs completely. It is often prescribed over PPN when the condition being treated is expected to be chronic with no definite timetable of recovery. When PPN treatment extends beyond 2 weeks, it is often converted to TPN.
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Total parenteral nutrition usually contains a combination of the following:
- Proteins / amino acids
- Carbohydrates / dextrose
- Lipid emulsions
- Trace elements
TPN nutrition composition should be personalized to meet the specific needs of each patient.
Lipid emulsions, amino acids, and dextrose are the three major macronutrients that provide the daily calorie needs.
- Dextrose content in a TPN solution may be anywhere from 10% to 25% (wt/vol). It is often the largest calorie contribution source.
- For most patients, the body’s maximum rate of glucose utilization is between 4 and 5 mg/kg/min. The dextrose infusion rate is best maintained less than or within this range, depending on the caloric need.
- Over-administration of carbohydrates can cause dangerous blood sugar and lipid imbalances.
- Long-term rapid administration of carbohydrates may lead to the development of fatty liver.
- A healthy adult usually requires between 0.8 and 1 gm of protein per kilogram of body weight per day.
- Patients with acute hepatic encephalopathy require a temporary protein restriction of 0.8 gm/kg/day.
- Patients with critical illnesses may sometimes require up to 2 gm/kg/day.
- Hemodialysis patients generally need 1.2-1.3 gm/kg/day.
- Lipids provide healthy calories and essential fatty acids. Without them, deficiencies can occur after three weeks of fat-free TPN nutrition.
- Cholesterol and lipids usually account for 20% to 30% of total calories consumed.
- Lipids can be infused by themselves or be added to the overall solution. When combined, the resulting product is known as a “total nutrient admixture (TNA)” or “3-in-1” TPN (versus “2-in-1” TPN, which contains only amino acids and dextrose). Lipids are what sometimes give these solutions the “milky” color.
Micronutrients: Electrolytes, Vitamins, and Trace Elements
- Essential vitamins are provided as an additive to TPN. They are commonly known as Infuvite, which is a multivitamin solution made for intravenous administration.
- Trace elements (zinc, copper, manganese, selenium, and sometimes chromium) are added based on daily needs.
- In most cases, each daily TPN bag will contain the following amounts of electrolytes per liter of solution:
- Sodium (Na): 1 – 2 mEq/kg/day
- Potassium (K): 1 – 2 mEq/kg/day
- Phosphorus (Phos): 15 – 30 mM/day
- Magnesium (Mg): 8 – 20 mEq/day
- Calcium (Ca): 5 – 15 mEq/day
Note: Exact amounts will vary from patient to patient based on laboratory response.
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Total parenteral nutrition is usually administered via a central venous catheter (CVC). Common types of CVC are peripherally inserted central catheter (PICC line), tunneled CVC, and implanted port. These are used to access the central circulatory system where more concentrated solutes can be infused.
PICC lines can be placed in the median cubital veins (brachial, cephalic, or basilic), depending on size and desired location. The catheter is inserted peripherally, guided by radiographic imaging until the tip is placed near the superior vena cava of the heart. PICC lines can be used for TPN infusion, for up to 6 months as long as the catheter and the site of insertion remain stable and infection-free. After 6 months, these catheters will need to be replaced with a new one. Upon completion of treatment, PICC lines can safely be removed by a trained nurse in almost any setting.
Tunneled CVCs are surgically placed to enter the central circulatory system via the internal jugular veins, subclavian, or femoral vein. These function the same way as PICC lines, except that they are sutured into the skin. For removal, the patient must be referred back to interventional radiology.
An implanted port, commonly known as medi-port or port-a-cath, is the most permanent type of central venous catheter. It is also surgically placed, but the entry point is placed under the skin. Each access will require a special type of needle called a Huber needle, which comes in various sizes and types depending on preference and how the port was placed. TPN has long been delivered via implantable ports, especially to patients who require chronic IV nutrition. Ports may stay placed indefinitely as long as the catheter remains stable and infection-free. Removing ports also requires a referral to interventional radiology.
TPN may not be administered via peripheral intravenous catheter due to high osmolarity. For peripheral administration (PPN), PN solutions must be formulated below 900 mOsm. This provides much less flexibility on how many calories to add into each bag, and therefore, PPN often will not provide enough to meet daily nutritional requirements. PPN is often reserved for nutritional support rather than nutritional replacement. It is given short-term when the expected need does not exceed 2 weeks. Also, because peripheral catheters access the circulatory system through smaller veins, these devices cannot remain stable for very long after access.
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TPN therapy is considered when a patient’s gastrointestinal function is inadequate and enteral nutrition is contraindicated. Enteral diets are preferable to parenteral diets because they are less expensive and have fewer potential complications. However, it is only possible if the patient has a functional gastrointestinal system. TPN indications include the following:
- Cancer of the digestive tract: Tumors can obstruct the bowels, which may compromise the consumption of sufficient calories. Chemotherapy and other cancer treatments may also cause your body to have difficulty absorbing nutrients.
- Food intolerance combined with pseudo-obstruction of the bowel.
- GI fistulas with high flow: TPN nutrition can be used to rest the bowel and replace fluids lost from drains.
- Pediatrics: Children and infants may have immature digestive tracts or congenital gastrointestinal malformation.
- A leak from a postoperative bowel anastomosis.
- Severe vomiting or diarrhea preventing adequate nutritional intake
- Small bowel obstruction.
- Hypercatabolic states such as sepsis, polytrauma, major fractures, and burns.
- Exacerbations of inflammatory bowel disease
- Critically ill patients
- Any other conditions with expected NPO (nothing by mouth) time longer than seven days.
Other Reasons for TPN
The following conditions may necessitate the use of TPN depending on their severity:
Crohn’s disease is an inflammatory bowel disease that may manifest as abdominal pain, bowel narrowing, and other symptoms that impair food intake, digestion, and absorption.
Short bowel syndrome
A person may be born with this condition or develop it due to any surgery removing a significant portion of the small intestine. A patient with short bowel syndrome does not have adequate bowels to absorb enough nutrients from oral consumption.
Ischemic bowel disease
In ischemic bowel disease, bowel dysmotility and malabsorption result from decreased blood flow to the intestines due to cardiovascular causes.
Other abnormal bowel function
Idiopathic abnormal bowel function can result from any disruptions in bowel motility due to an external factor. Some causes include surgical adhesions, radiation enteritis, and small fiber neuropathy.
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Parenteral Nutrition in Pregnancy
Nausea and vomiting are widespread side effects of pregnancy, and they can significantly impair activities of daily living, including nutrition. Approximately 85% of pregnant women will experience nausea and vomiting during the first three months of pregnancy. 20% may continue to have them for the remainder of the pregnancy.
Approximately 2% of pregnant women suffer from hyperemesis gravidarum, a severe form of nausea and vomiting that can last for several days and even sometimes weeks. This is a high-risk condition that may put both the mother and the fetus in danger. According to the American College of Obstetricians and Gynecologists (ACOG), parenteral nutrition may be considered in pregnant patients who have lost 10% or more of their pre-gestation body weight. Treatment may be continued until birth if the mother continues to have difficulty tolerating oral intake despite using antiemetics. Complications from hyperemesis gravidarum such as ketonuria, severe dehydration, and catabolism are considered emergencies and may necessitate hospitalization.
According to Maudar (1995), total parenteral nutrition is generally contraindicated in the following circumstances:
- Infants with a small bowel that is less than 8 cm in length.
- Patients who are irreversibly decerebrate.
- Patients who are suffering from severe cardiovascular instability or metabolic instabilities. Before initiating parenteral nutrition, it is necessary to correct any instabilities.
- Patient’s digestive tract is functional and usable.
- Patient’s nutritional status is favorable with only short-term expected benefit from TPN.
- Patient’s death is unavoidable regardless of nutritional status. Total parenteral nutrition should not be used to prolong life in such situations.
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The following parameters are routinely monitored during TPN therapy:
- Liver function
- Serum protein
- Blood urea nitrogen (BUN) and serum creatinine
- Serum electrolytes: sodium, potassium, chloride, bicarbonate, calcium, magnesium
- Urine sugar levels (usually in the hospital)
- Input and output charts (usually in the hospital)
At PN initiation, patients should be monitored closely for signs or symptoms of refeeding syndrome, which manifests as severe electrolyte instabilities, mainly with potassium, magnesium, and phosphate. The risk is greatest with severely malnourished and cachectic individuals. Patients experiencing refeeding syndrome may also present with respiratory distress, acute kidney injury, and even rhabdomyolysis. A slow initial TPN infusion and titration, especially with dextrose and lipids, will help prevent refeeding syndrome.
TPN therapy does not come without risks. Some possible major adverse events to consider are:
- Chemically-induced metabolic abnormalities
- Vascular injury
- Venous thrombosis
- Air embolism
- Liver dysfunction
Unfortunately, PN solutions also encourage the growth of other unwanted organisms such as bacteria and fungi. Patients on chronic TPN therapy are at higher risk of the following complications associated with intravenous catheters:
- Skin infection at the site of the catheter insertion
- Bloodstream infections, also known as bacteremia or sepsis
With proper aseptic and sterilization techniques, these risks can be significantly minimized. Consult your nurse on how to best care for intravenous catheters.
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Because nutrition and electrolytes are administered directly into the veins, TPN patients are more susceptible to metabolic fluctuations, especially when solutions are administered too quickly. Common metabolic complications with TPN therapy include:
- Refeeding syndrome: The greatest concern with this is at the beginning of TPN therapy, especially with patients with severe malnutrition. The risk is minimized with slow titration of calories to the desired goal.
- Hyperglycemia: This is most concerning in patients with diabetes.
- Hypoglycemia: This risk is increased with abrupt discontinuation of infusions. To minimize, PN infusions should be tapered up at the start and tapered down at the end.
- Electrolyte abnormalities: This is regularly evaluated via labs. It is important to have blood draws done at least once weekly while on TPN therapy to prevent imbalances.
- Cholestasis: This is a consequence of prolonged bowel rest. If the patient has somewhat of a functional GI tract, he or she should be encouraged to have some oral intake, no matter how small. If “NPO,” the patient should be regularly evaluated for this possibility.
Metabolic Bone Disease
Some patients who have been on TPN nutrition for more than three months develop metabolic bone disease, also known as bone demineralization (osteoporosis or osteomalacia). The cause of this is not well defined. Advanced forms of this disease can cause severe back, lower-extremity, and periarticular pain as well as swelling and inflammation.
TPN-Induced Liver Toxicity
Excess caloric intake with glucose and lipids can lead to hepatic steatosis. For most patients, a glucose infusion rate of more than 5 mg/kg/min is the most common cause of this. High blood glucose and insulin levels trigger hepatic lipogenesis. To avoid this, the dextrose dose should be reduced to less than 5 g/kg per day with an infusion rate of less than 5 mg/kg min.
Liver dysfunction may occur without regard to caloric intake. The risk becomes greater the longer a patient is on TPN therapy. Liver function tests, including transaminases, bilirubin, and alkaline phosphatase, are monitored to help detect signs of liver dysfunction.
Patients who require a large number of calories often also require a large volume of fluids. In these cases, they are at risk of volume overload, which is indicated by a weight gain of more than 1 kg/day. Symptoms include edema, shortness of breath, and frequent urination.
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TPN Healthcare Team
A well-coordinated health care team using an interprofessional approach is required to manage TPN therapy.
Teams usually include:
- Infusion nurse (RN)
- Prescriber (MD, DO, NP, or PA)
- Dietician (RD)
- Pharmacist (PharmD/RPh)
The prescriber decides on the appropriate course of treatment and the type of nutrition. Collaborating with the patient’s primary health care team, the clinician ensures that care is coordinated appropriately.
The pharmacist provides sterile parenteral nutrition. Consult a pharmacist about the compound’s stability and any possible drug/nutrient interactions. Under the direction of the prescriber, pharmacists may also make reasonable adjustments to the TPN formula based on clinical assessments and laboratory results.
The dietician assesses the patient’s nutritional status, calculates the daily requirements, and designs an appropriate feeding regimen.
The TPN nursing specialist oversees catheter and TPN tube care. They educate and train the patient and the caregiver on adequately managing the TPN tubes in their homes.
The extended team of professionals may also include wound management nurses, occupational therapists, and social workers.
What is the Prognosis for Those on PN?
According to ASPEN’s Parenteral Nutrition Fact Sheet, children and adults can thrive on parenteral nutrition when no complications arise. Generally, the goal of PN is to continue until the patient can maintain weight and energy by oral intake alone. Doctors may do a trial of holding PN therapy for several days before discontinuing it completely. Depending on the indication, the total duration may be anywhere from just a few weeks to several years.
Can you eat while receiving TPN?
Depending on the condition and the reason for receiving TPN, you can consume food and beverages while on TPN therapy. If it is a possibility, oral intake is often encouraged to help expedite discontinuation. However, this should still be done cautiously under the direction of the prescriber and/or dietician because early oral intake may sometimes worsen the condition.
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Without insurance coverage of any kind, the cash price for 500 ml of TPN containing a basic mixture of amino acids, dextrose, and electrolytes is approximately $176 per day. The price may vary depending on the pharmacy. Additional additives may alter this estimate as well.
Quantity Per unit Price
500 (25 x 20 milliliters) $0.35 $176.33
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Dr. James Lee, PharmD, BCPS was born and raised in Arcadia, CA. He attended the University of the Pacific, Thomas J. Long School of Pharmacy and has been a practicing pharmacist for 5 years and is a Board Certified Pharmacotherapy Specialist. The most rewarding part of his job is solving problems. In his free time, he enjoys cooking and exercising.