If a patient is unable to follow an
oral diet, it is possible to inject nutrients by a parenteral access.
Nutrition can be done also by integrating the oral feeding by integrative feeding
of a parenteral access. It's possible also to use a naso - gastric tube with a
food mixture into a enteral sac. This procedure is indicated in a patient
affected by stroke and dysphagia.
We talk about supplemental parenteral nutrition or total parenteral nutrition when the parenteral route is the only source of nutrients.
The indications for this type of therapy include the preparation of undernourished patients for surgery, for chemotherapy or for radiotherapy; severe or prolonged disorders of the digestive system; major surgery, trauma and burns; prolonged coma or refusal of food; some cases of renal and hepatic insufficiency.
For parenteral nutrition a solution containing amino acids, glucose, lipids, electrolytes, minerals and vitamins is used by a central access.
This preparation is normally supplied in 3 liter bags.
In less severe clinical cases it is possible to directly employ 3-4 doses of 5%
glucose solution of 500 ml every 24 hours, but this parenteral feeding is
limited to a few days of treatment.
The patient's blood glycemia levels should always be monitored and medicated with rapid insulin if necessary.
In the case of protracted nutrition, central accesses are used, for example implantable systems (port-a-cath).
A single dose of vitamin B12 is given by
intramuscular injection; no regular administration is required unless total
parenteral nutrition does not last for many months. Folic acid is given at a
dose of 15 mg 1-2 times a week, usually with the nutritional solution.
The other vitamins are usually given every day by adding them to the parenteral
nutritional solution.
Alternatively, if the patient is able to take small amounts by mouth, vitamins can be given orally. The nutritive solution is administered by infusion through a central venous line inserted with a procedure controlled by the surgeon.
Alternatively, peripheral veins may be used, both for supplemental and total nutrition, for periods not exceeding one month, provided that there are suitable peripheral vessels; to prolong the cannula patency and to avoid thrombophlebitis, use pediatric polyurethane soft cannulas and use low pH neutral osmolarity liquids.
These infusion routes must be dedicated only to
the infusion of nutrients.
Before starting, the patient must be well oxygenated and with a normal
circulating volume; particular attention should be paid to renal function and
acid-base balance. First, appropriate biochemical tests must be performed and
any imbalances corrected. The nutritional status and electrolyte profile must be
monitored during treatment.
Complications of prolonged parenteral nutrition include biliary sand formation,
gallstones, cholestasis, and liver function test abnormalities. For other
details on prevention and treatment of the complications of parenteral nutrition.
refer to the consultation of specialized texts.
Proteins are administered as mixtures of essential and non-essential synthetic
L-amino acids. All essential amino acids and a selection of non-essential
substances should be provided to ensure adequate nitrogenous intake and electrolytes.
Amino acid solutions vary by composition; they also often contain energy sources
(usually glucose) and electrolytes. The energy supply is provided in an amount
of about 0.6-1.1 megajoules (150-250 kcal) for every gram of protein nitrogen.
This energy supply is necessary to make the best use of amino acids for the vitality of the tissues. A mixture of carbohydrates and lipids (generally with 30-50% lipids) gives a better use of amino acids than glucose alone.
Glucose is the preferred source of carbohydrates but. if more than 180 g is
given daily, it is necessary to check the blood sugar several times a day and
sometimes insulin should be given. 10 to 50% glucose solutions should be
administered via a central venous catheter to avoid thrombophlebitis.
In total parenteral nutrition, a portion of phosphates must also be provided to
allow glucose phosphorylation; in general, 20 to 30 mmoles of phosphate are
sufficient per day.
To avoid hyperglycemia with non-ketotic hyperosmolar acidosis fructose and sorbitol have been used, but these cause other metabolic disorders, as they cause xylitol and ethanol, which are rarely used.
Lipid emulsions have the
advantage of providing many calories in a reduced volume of liquids, have a
neutral pH and are isosmolar with plasma; finally they supply essential fatty
acids. It takes a few days of adaptation before reaching full dose. Side effects
include febrile episodes (usually only with 20% emulsions) and seldom allergic
reactions. If blood samples are taken without care to wash the venous line,
errors may occur in the determination of certain biochemical parameters such as
blood gas analysis and calcium. Complete plasma clearance should be assessed
daily in conditions of altered lipid metabolism. Only if the compatibility is
known, additives to lipid emulsions can be added.
Administration
Due to the complex requirements of parenteral nutrition, all details relating to
administration have been omitted. In all cases, please refer to the product data
sheets and specialized literature.