Parenteral Nutrition: Principles, Indications and Complications

Parenteral nutrition is an alternative method of feeding a person who has had intestinal failures. Persons with intestinal failures have a problem with absorption of food, digestion or absorption of water. A patient  with intestinal failures cannot feed through the gastrointestinal tract. He/she may suffer from malnutrition and dehydration. The only way of meeting the nutritional needs of patients with intestinal failures is through the provision of nutrients, water or electrolytes directly into the bloodstream. A dietician may design  nutrients in accordance with the patient’s needs. Catheters provide the route of administration of the nutrients. Patients with irreversible intestinal dysfunction may depend on parenteral nutrition for the remainder of their lives. Others employ it for a short period. This method is advantageous to the patients, but the related complications account for the fact  the procedure has come in  a lot of criticism of late.

The aim of the parenteral nutrition formulations is to maintain the nutritional status for a long term. It can also serve to improve the status in case of deficiency of certain nutrients (Howard, 1995). The solutions contain all  essential nutrients, such as proteins, carbohydrates, energy, lipids, water, and electrolytes. Micronutrients are also vital. Dieticians include them in the design of the solutions. Although there are standard commercially available solutions, the formulations are most of the time individualized as per the patient’s nutritional needs (ASPEN, 2002). Standard solutions contain carbohydrates, proteins and fats at various volumes, while individualized solutions contain calculated amounts of electrolytes, vitamins, trace elements, and water according to the patient’s needs (ASPEN, 2002).

Carbohydrates and fats provide calories in the solution. A dietician or a pharmacist calculates energy requirements of each patient according to ordinary estimates of 25-35 k cal per kg per day (ASPEN, 2002). They may also use various formulas such as Harris- Schofield formula or Benedict equations. Carbohydrates in the form of glucose provide 60 percent of non-protein energy, while lipids in the form of essential fatty acids and triglycerides provide 40 percent (ASPEN, 2002). Proteins in the form of amino acids provide nitrogen as well as energy The formula used to calculate amino acids requirements is 3.0-3.5 Gm per kg per day for change in body compensation and an additional 2.2-2-5 gm per kg per day for normal growth (ASPEN, 2002). An optimal amino acids formulation contain essential amino acids, such as valine, methionine, leucine, isoleucine, phenylalanine, lysine, threonine and histidine, as well as, conditionally essential amino acids, cysteine, glutamine, tyrosine, proline, arginine, glycine and taurine). The solution should not contain an excess of methionine or glycine.

Catheters intravenously administer parenteral nutrition solutions into the bloodstream. The catheter used frequently is the silicone rubber catheter inserted to administer the solution to subclavian vein (Williamson, 2003). Other routes include jugular or femoral catheters. The doctor inserts catheter tip at the junction of the right atrium and superior vena cava. Two catheter types exist: peripherally inserted central catheters and peripherally inserted catheters. The tip of peripherally inserted central catheter is about 60 cm. It is centrally sited. They are for both long- and short-term use. Peripherally inserted catheters are 20 cm long and their tips usually sit in the axillary vein.

A standard cannula is most often used to administer parenteral nutrition solution directly into a peripheral vein for a short term to provide a bridge in central lines (Williamson, 2003). A feeding catheter fitted with a Dacron anchoring cuff or an implantable venous access port without an external catheter is preferable for long-term parenteral nutrition (Williamson, 2003). The device remains usable for many years if well cared.

Parenteral nutrition is most often used in patients whose gastrointestinal tract has malfunctions either by blockage or due to a fistula. Persons with intestinal failure in absorption of nutrients, electrolytes or water also require parenteral nutrition (ASPEN, 2002). Absorption impairments may be  a result of short bowel length, failure in intestinal movement, severe intestinal mucosal inflammation such as Crohn's disease, radiation enteritis, and chemotherapy mucositis (ASPEN, 2002). Enteral nutrition may not be successful or may sometimes be unable tot meet the  requirement of an individual’s nutritional needs.

An early growth deficit due to immature gastrointestinal motor function in children is also an indication for parenteral feeding (ASPEN, 2002). Preterm neonates do not have mature gastrointestinal tract (Howard, 1995). Hence, they  need parenteral nutrition to meet their needs. Gastrointestinal surgery is  a common indication as well. Doctors may resort to  parenteral nutrition when the bowel needs “rest” when there is a high output gastrointestinal fistula. Professionals recommend evidence based indications for parenteral nutrition due to increased complications (ASPEN, 2002).

Despite improving clinical outcomes of patients with gastrointestinal tract dysfunctions and persons with malnutrition, the use of parenteral nutrition poses serious complications. There are complications related to mechanical, vascular access, infections, and nutrition metabolism (Seiner, 2002). Mechanical complications may occur due to catheter malplacements, arterial damage, or infusion of fluid outside the catheter or vein. These include pneumothorax, catheter malposition, chylothorax, hydrothorax, arterial puncture brachial plexus injury, air embolism, and hemopericardium, and arrhythmias (Seiner, 2002). Catheter  fracture may lead to air embolism or distal migration of catheters. Catheter occlusion in the long term parenteral nutrition may occur due to backflow of solution components or blood fibrin into the catheter (Seiner, 2002).

Catheter-related sepsis is a complication of considerable concern. It causes mortality and morbidity in patients under the therapy (Seiner, 2002). A catheter can be the sole source of infection or pathogens may migrate from other sites and colonize the catheter. Sepsis may also occur at the exit of the catheter manifesting through local pain, erythema and discharge at the exit. Common bacteria causing catheter related infections include Staphylococcus aureus, Staphylococcus epidermidis, Enterococci, Klebsiella pneumoniae, and  fungus Candida albicans (Seiner, 2002).

Other common complications include Central Vein Thrombosis and Thrombophlebitis (Seiner, 2002). Thrombosis, characterized by painful swelling of a neck and arm and appearance of prominent collateral veins around the chest, is a common cause of disease and mortality related to parenteral nutrition. Risk factors for Thrombosis include dehydration, catheter infection, malposition of the catheter tip, hyperosmolar feeds and procoagulant states (Seiner, 2002). Additionally, mechanical trauma during catheter insertion, infection of catheters, and high osmolality feeding solutions may cause thrombophlebitis (Seiner, 2002).