Total parenteral nutrition – TPN

Total parenteral nutrition (TPN)

A look at TPN

TPN is a highly concentrated, hypertonic nutrient solution administered by way of an infusion pump through a large central vein. For patients with high caloric and nutritional needs due to illness or injury, TPN provides crucial calories, restores nitrogen balance, and replaces essential fluids, vitamins, electrolytes, minerals, and trace elements. TPN also promotes tissue and wound healing and normal metabolic function; gives the bowel a chance to heal; reduces activity in the gallbladder, pancreas, and small intestine; and is used to improve a patient’s response to surgery.

Understanding common TPN additives

Common components of total parenteral nutrition (TPN) solutions such as glucose, amino acids, and other additives are used for specific purposes. For instance, glucose provides calories for metabolism. Here’s a list of other common additives and the purposes each serves.

TPN triggers
Common illnesses or treatments that can trigger the need for TPN include inflammatory bowel disease, ulcerative colitis, bowel obstruction or resection, radiation enteritis, severe diarrhea or vomiting, acquired immunodeficiency syndrome (AIDS), chemotherapy, and severe pancreatitis, all of which hinder a patient’s ability to absorb nutrients. Also, patients may benefit from TPN if they’ve undergone major surgery or if they have a high metabolic rate resulting from sepsis, trauma, or burns of more than 40% of total body surface area. Infants with congenital or acquired disorders may need TPN to promote proper growth and development.

TPN has limited value for well-nourished patients with GI tracts that are healthy or are likely to resume normal function within 10 days. The treatment also may be inappropriate for a patient with a poor prognosis or when the risks of TPN outweigh its benefits.

Lipid emulsions

Lipid emulsions are thick emulsions that supply patients with both essential fatty acids and calories. These emulsions assist in wound healing, red blood cell (RBC) production, and prostaglandin synthesis. They may be piggybacked with TPN, given alone through a separate peripheral or central venous line, or mixed with amino acids and dextrose in one container (total nutrient admixtures) and infused over 24 hours.

How to infuse TPN

TPN must be infused through a central vein. As a hypertonic solution, it may be up to six times the concentration of blood and, therefore, too irritating for a peripheral vein.

TPN may be infused around the clock or for part of the day for instance, as the patient sleeps at night. A sterile catheter made of polyurethane or silicone is inserted into the subclavian or jugular vein. A polyurethane catheter is rigid during insertion but softens at body temperatue. It’s biocompatible, so tissues don’t react to the material and it’s less thrombogenic than earlier types of manufactured catheters. A Silastic catheter may be a better alternative for therapy lasting months or years because it’s more flexible and durable and it’s compatible with many medications and solutions.

Looking to the peripheral

A peripherally inserted central catheter, a variation of central venous therapy, can be used for therapy lasting 3 months or more. The catheter is inserted through the basilic or cephalic vein and threaded so that the tip lies in the superior vena cava.

The patient generally experiences less discomfort with a peripheral catheter, especially if he can move around easily. Movement stimulates blood flow and decreases the risk of phlebitis. Peripherally inserted central catheters are often used for intermediate-term therapy, both at home and in the health care facility.

The sugar situation

• Monitor serum glucose levels every 6 hours initially, then once a day. Watch for thirst and polyuria, which are indications that the patient may have hyperglycemia. Periodically confirm glucometer readings with laboratory test results. Serum glucose levels should be less than 200 mg/dl. This indicates the patient’s tolerance of the glucose solution.
• Monitor for signs and symptoms of glucose metabolism disturbance, fluid and electrolyte imbalances, and nutritional problems. Some patients may require insulin added directly to the TPN for the duration of treatment.
• Monitor electrolyte levels daily at first, and then twice a week. Keep in mind that when a patient is severely malnourished, starting TPN may spark refeeding syndrome, which includes a rapid drop in potassium, magnesium, and phosphorus levels. To avoid compromising cardiac function, initiate feeding slowly and monitor the patient’s electrolyte levels closely until they stabilize.
• Monitor protein levels twice a week. Albumin levels may drop initially as treatment restores hydration.
• Check renal function by monitoring blood urea nitrogen (BUN) and creatinine levels; increases may indicate excess amino acid intake.
• Assess nitrogen balance with 24-hour urine collection.
• Assess liver function with liver function tests, bilirubin, triglyceride, and cholesterol levels. Abnormal values may indicate intolerance.
• Review the patient’s serum chemistry and nutritional studies, and alert the practitioner of abnormal results, which may indicate that the TPN fluid concentration or ingredients may need to be adjusted to meet the patient’s specific needs.
• Avoid an adverse reaction by starting TPN slowly usually 60 to 80 ml/hour for the first 24 hours and increasing gradually. Continually monitor the patient’s cardiac and respiratory status.
• Use an infusion pump for rate control.