Enteral feeding is the preferred means of nutritional support. Without any specific surgical contraindication, all patients should receive enteral feeding as soon as possible, preferably within 24 hours of admission. Enteral feeding provides nutrition and helps to maintain gastrointestinal tract integrity and function. However, not all patients can receive enteral nutritional support due to some contraindications. This requires the assistance of some extraneous source of energy and nutrients to support the body during times of stress.
Total parenteral nutrition (TPN) support is an important component of supportive therapy in hospitalized patients, particularly ICU patients. It is generally not necessary if the patient is likely to be able to recommence enteral feeding within a few days, unless the patient is already severely wasted or malnourished.
Typical Composition of Standard Total Parenteral Nutrition
Volume – 2.5 Litres
Nitrogen Source (9-14 g nitrogen) – L-amino acid solution
Energy Source (1500-2000 kcal) – Glucose and Lipid emulsion
Additives – Electrolytes, Trace Elements, Vitamins
Other Additives – Insulin and H2 blockers may be added if required
Practical Aspects of Parenteral Nutrition
TPN should be customized to a person’s requirements. Advice should be sought from dietitians or a parenteral nutrition team for specialized scenarios but a standard feed will suffice for most. Standard adult feeds are typically 2.5 litres a day, but smaller volume feeds are available for fluid-restricted patients.
Parenteral feeds are hypertonic and cause thrombophlebitis. Hence, they are preferentially given via central venous lines. However, high volume lower-osmolality feeds are now developed that can be given via peripherally inserted feeding lines called “Peripheral TPN”. It is a good practice to keep one lumen clean and dedicated for TPN.
Parenteral nutrition mixtures make good culture mediums for bacteria, so make sure not to break the line to give anything else. TPN is given by constant infusion over 24 hours and delivered by volumetric infusion pumps.
Monitoring Total Parenteral Nutrition
Advice should be sought from the nutrition team and dietitian. The following should be assessed on a daily basis to provide a well-tailored TPN to the patient.
- Fluid balance
- Urea, Electrolytes, Phosphate
- Glucose: An insulin infusion might need to be instituted to maintain blood sugar levels to an acceptable level. Close control of blood sugar levels have recently been shown to improve the outcome of critically ill patients.
- Adequate energy requirements: Clinical acumen is required to assess adequate energy requirements by degree of catabolism.
- Liver function (albumin, transferrin and enzymes) indicate adequate protein synthesis and give an early indication of TPN-related complications.
Complications of Total Parenteral Nutrition
- All complications of central venous access are an accompaniment of TPN.
- Metabolic derangement, particularly hyper- or hypoglycaemia, hypophosphataemia and hypercalcaemia, are quite common and require adequate adjustment of the feed.
- Hepatobiliary dysfunction, including elevation of liver enzymes, jaundice and fatty infiltration of the liver may occur. This is usually a consequence of the patient’s underlying disease processes and overfeeding. Reduce the volume of TPN and/or energy content in the feed to correct the same. If the serum becomes very lipaemic it may be necessary to reduce the fat content.