What it is:
TPN is a way of supplying all the nutritional needs of the body by bypassing the digestive system and dripping nutrient solution directly into a vein. (http://medical-dictionary.thefreedictionary.com/total+parenteral+nutrition)
When is it used:
TPN is used when individuals cannot or should not get their nutrition through eating. TPN is used when the intestines are obstructed, when the small intestine is not absorbing nutrients properly, or a gastrointestinal fistula (abnormal connection) is present. It is also used when the bowels need to rest and not have any food passing through them. Bowel rest may be necessary in Crohn's disease, pancreatitis, ulcerative colitis, and with prolonged bouts of diarrhea in young children. TPN is also used for individuals with severe burns, multiple fractures, and in malnourished individuals to prepare them for major surgery, chemotherapy, or radiation treatment. Individuals with AIDS or widespread infection (sepsis) may also benefit from TPN. It is also used for patients who have gastroparesis and cannot digest food properly. (http://medical-dictionary.thefreedictionary.com/total+parenteral+nutrition)
TPN is normally given through a large central vein. A catheter is inserted into the vein in the chest area under local anesthesia and sterile conditions. Often the placement is done in an operating room to decrease the chance of infection. Several different types catheters are used based on the reason TPN is needed and the expected length of treatment. Once the catheter is in place, a chest x ray is done to make sure the placement is correct.
Normally TPN is administered in a hospital, but under certain conditions and with proper patient and caregiver education, it may also be used at home for long-term therapy. TPN solution is mixed daily under sterile conditions. Maintaining sterility is essential for preventing infection. For this reason, the outside tubing leading from the bag of solution to the catheter is changed daily, and special dressings covering the catheter are changed every other day. (http://medical-dictionary.thefreedictionary.com/total+parenteral+nutrition
What the solution contains:
The contents of the TPN solution are determined based on the age, weight, height, and the medical condition of the individual. All solutions contain sugar (dextrose) for energy and protein (amino acids). Fats (lipids) may also be added to the solution. Electrolytes such as potassium, sodium, calcium, magnesium, chloride, and phosphate are also included, as these are essential to the normal functioning of the body. Trace elements such as zinc, copper, manganese and chromium are also needed. Vitamins can be included in the TPN solution, and insulin, a hormone that helps the body use sugar, may need to be added. Adults need approximately 2 liters of TPN solution daily, although this amount varies with the age, size, and health of the individual. Special solutions have been developed for individuals with reduced liver and kidney function.
Successful TPN requires frequent, often daily monitoring of the individual's weight, glucose (blood sugar) level, blood count, blood gasses, fluid balance, urine output, waste products in the blood (plasma urea) and electrolytes. Liver and kidney function tests may also be performed. The contents of the solution are individualized based on the results of these tests. (http://medical-dictionary.thefreedictionary.com/total+parenteral+nutrition)
Complications of TPN:
Mechanical complications are primarily related to the initial placement of a central venous catheter. Improper placement may cause pneumothorax, vascular injury with hemothorax, brachial plexus injury or cardiac arrhythmia.
Venous thrombosis is one of the two most common problems that occur after central venous access is established. The other is infection.
Venous thrombosis is associated with significant morbidity rates. Signs include distended neck veins and swelling of the face and ipsilateral arm. The risk of venous thrombosis is greater if patients are dehydrated, have certain malignancies, have had prolonged bed rest, have venous stasis, have sepsis, or have hypercoagulation.
Additional risk factors include morbid obesity, smoking, or ongoing estrogen therapy. (http://www.rxkinetics.com/tpntutorial/)
TPN imposes a chronic breech in the body's barrier system. The infusion apparatus from container to catheter tip may prove a source for the introduction of bacterial or fungal organisms.
Infection is one of the two most common problems that arise after central venous access is established. The other is venous thrombosis, discussed earlier. The mortality rate from catheter sepsis may be as high as 15%.
The primary preventive measures include adhering to strict aseptic procedure while establishing access and providing care of the dressing and line. (http://www.rxkinetics.com/tpntutorial/)
Metabolic complications fall into two broad categories: early and late complications. Those in the first category occur early in the process of feeding and may be anticipated. They are avoided by careful monitoring and appropriate adjustment of intake. Late metabolic complications are less predictable. They may be caused by an exacerbation of preexisting abnormalities, unpredictable long-term requirements, inadequate solution composition, or failure to monitor adequately. (http://www.rxkinetics.com/tpntutorial/)
Fluid and electrolyte:
Electrolyte management is one of the most difficult aspects of PN therapy. Often electrolytes are outside of the normal range based on an underlying cause rather than directly related to the PN solution. For this reason, no specific guidance can be given to adjust individual electrolytes based on laboratory serum concentration. Instead, incremental dose adjustments are made concurrent with treatment of the underlying cause of electrolyte abnormality. In general, supplemental electrolyte doses in response to an acute underlying condition are best managed outside of PN therapy. (http://www.rxkinetics.com/tpntutorial/)
Refeeding of severely malnourished patients may result in "refeeding syndrome" in which there are acute decreases in circulating levels of potassium, magnesium, and phosphate. The sequelae of refeeding syndrome adversely affect nearly every organ system and include cardiac dysrhythmias, heart failure, acute respiratory failure, coma, paralysis, nephropathy, and liver dysfunction.
The primary cause of the metabolic response to refeeding is the shift from stored body fat to carbohydrate as the primary fuel source. Serum insulin levels rise, causing intracellular movement of electrolytes for use in metabolism.
The best advice when initiating nutritional support is to "start low and go slow". (http://www.rxkinetics.com/tpntutorial/)