TOTAL PARENTERAL NUTRITION (TPN)
Dr. Dineshkumar Chirla *
DM (Neo), MD. Rainbow Hospital, Hyderabad. *
Parenteral (intravenous) feeding is an expensive and complex way of providing nutrition, and should be reserved for those situations in which enteral feeds are not practicable. It should only be undertaken by experienced medical and nursing staff and where adequate biochemical, bacteriological and pharmaceutical services are available. In preterm infants with low body nutrient stores, cautious use of intravenous nutrition can prevent catabolism, with its resultant negative nitrogen balance, until enteral feeds are established. Infants with serious gut disorder may require total parenteral nutrition for several weeks.

Indications:
Indications for parenteral nutrition include:
  • gastrointestinal surgery
  • extreme prematurity
  • necrotizing enterocolitis
  • severe illness such as septicemia or cardiac failure - often with ileus
  • respiratory distress

(Preterm who will not reach full feeds in 3-4 days or term babies where oral feeds not possible for 7 days).

Nutrient supply:
Nutritional requirements and fluid volumes are similar to those of enteral nutrition.

Calories: are provided as glucose and as lipid emulsions. Protein should be utilized for growth and not metabolized for energy. Preterm babies require 50 cal/kg/d via TPN to maintain existing weight. For weight gain they need 100 cal/kg/day via TPN.

Carbohydrate: Glucose is the main source. Sick newborn infants, particularly preterm, may be relatively intolerant, necessitating a gradual increase. Usually start with 10% dextrose and reduce the concentration if hyperglycemic or increase if tolerated, to provide more calories. Dextrose concentrations of> 12.5% should be given via a central line to avoid phlebitis. Calculate the glucose infusion rate.

Protein: This is given as a synthetic crystalline amino acid solution. Special formulations are available for infants, although there is still uncertainly about the ideal composition of such solutions - whether to mimic placental supply or breast milk composition. If no exogenous protein is provided, preterm infants will catabolize about 1 g/kg/day; with at least 60 kcal/kg/day of non-protein calories to provide for resting energy expenditure will prevent this catabolism. Optimal protein requirements for growth are about 2 g/kg/day at term and 3-4 g/kg/day between 24-36 weeks. Start amino acids from day 1 and increase gradually.

Fat: Given as oil in water emulsion derived from egg phospholipid, soybean oil and glycerol. Fat provides a concentrated source of calories, but may be poorly tolerated by very small infants. Start at 0.5 g/kg/day increasing to 2.0 g/kg/day for preterm infants and 3.0 g/kg/day for term infants. Soybean oil is rich in essential fatty acids and 0.5-1.0 g/kg/day of "intralipid" will provide adequate amounts. Blood triglyceride levels can be measured keep levels below 150 mg/L. During period of suspected and proven sepsis, thrombocytopenia, acidosis and hyperbilirubinemia, lipid infusion should be reduced to 0.5-1.0 g/kg/day or stopped for 24 hours until the baby is stable. Close monitoring is necessary in children with lung and liver disease.

Guidelines for prescription of Parenteral nutrition in Newborn

Day of TPN

Volume Glucose (ml/kg/d)

Aminoacid (mg/kg/min)

Lipid
(g/kg/d)

(g/kg/d)

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6
80

100

120

140

150

150
4-6

4-6

6-8

6-8

8-10

8-10
0.5

1.0

1.5

2.0

2.5

2.5-3.0
0.5

1.0

1.5

2.0

2.5

3.0

Total fluid volume adjusted depending on the clinical status, electrolytes and phototherapy.

Minerals: The following are recommendations for term and preterm infants. Blood levels need to be closely monitored, particularly in the first week.
 

Term

Preterm

 
Sodium

Potassium

Chloride

Calcium

Magnesium

Phosphorus
2-3

1-2

1-2

1-2

0.25

1-2
3-5

1-2

2-3

2-4

0.25

1-3
mmol/kg/day

mmol/kg/day

mmol/kg/day

mmol/kg/day

mmol/kg/day

mmol/kg/day

NB it is often difficult to achieve the desired input of calcium and phosphate for preterm infants, because of solubility problems. This may improve with the availability of new organic phosphate solutions.

Trace elements: These are provided in a commercial mixture containing zinc, copper, manganese, selenium, fluorine and iodine. In prolonged, total PN use levels may need to measured, and other tract elements such as molybdenum and chromium may be required.

Vitamins: A full range of vitamins must be provided in intravenous nutrition. Both water and fat-soluble vitamins are available in commercial pediatric preparations, but vitamin B12 supplements are needed about 1 month.

Prescription and Preparation: It has been shown that pre-term infants will tolerate parenteral nutrition from day 1 and we aim to start within 24-48 hours in infants of < 1000 g birth weight in order to prevent catabolism. It is advisable to build up nutrient intake gradually. Larger infants with some boy nutrient stores, parenteral nutrition may be started later if enteral feeding is delayed. Clinical assessment of water requirement may make changes necessary. When considering the sodium requirement, take account of sodium in arterial line infusate, flushes, and any measured loses.

Commercial products are available for the provision of parenteral nutrition. The most common method of delivery is to mix a single bag of water-soluble components - dextrose, amino acids, minerals tract elements and water-soluble vitamins and to give lipid emulsion, with fat-soluble vitamins separately. The preparation must be carried out meticulously in a dedicated sterile area of pharmacy. The extent to which each baby's nutritional and metabolic needs can be individually met depends on local preference and staffing levels. A 24 hours supply is usually prepared.

Administration: Parenteral nutrition may be administered via peripheral or central venous lines. Peripheral lines should be resited as quickly as possible to avoid hypoglycemia. If given centrally, the caloric intake may be increased by the use of 15-20% glucose solutions. Arterial lines are not suitable routes for i.v. nutrition.

PN may be infused via a standard infusion pump with a two-entry port burette. There should be a suitable bacterial filter in line before a y-connector. The lipid emulsion is pumped into the other arm of this connector and thus into the baby. Both solutions should be protected from light.

Strict aseptic technique is necessary during preparation and administration. Ideally, a separate i.v. line should be used purely for PN. With a peripheral line drugs may be given, if essential so long as they are chemically compatible. They should be infected before the bacterial filter, and should be flushed through.

Glucose and amino acids are infused continuously. It used to be necessary to interrupt the lipid infusion for several hours, as lipid interferes with the measurement of serum sodium on laboratory analyzers. With modern analytical equipment, this is now rarely a problem except in cases of extreme lipaemia. Therefore lipid infusions can also be infused continuously over 24 hours. If in doubt, check with the local biochemist. Lipid levels should be determined during and after at least 8 hours of lipid infusion.

Cautions:
Potassium - Extra care must be exercised during renal impairment, and potassium omitted or reduced if hyperkalemic.

Hypocalcaemia - Occurs rarely as a result of excessive phosphate in the glucose-electrolyte mixture, and is corrected by reducing the phosphate concentration.

Never add bicarbonate - as it will precipitate as CaCO3.


Never add extra calcium to the glucose / amino acid mixture - as it will precipitate out phosphate.


Polyunsaturated fatty acids - are precursors of prostaglandins, and intravenous infusion may theoretically interfere with blood clotting, pulmonary artery vasodilatation, etc. Give with caution in sick infants. Toxic levels of some amino acids - may occur if high doses are given. If there is concern, urine amino acids should be measured.

Complications:
These can be classified into two main categories : infusion - related (usually problems with line) and infusate-related problems Infusion related problems

Sepsis: This can be minimized by meticulous nursing and medical care of lines. Percutaneous long-lines should be inserted and reconnections made, under full sterile conditions, and lines should be dedicated for PN.

Malposition: Check position with X-ray

Thrombosis: With peripheral lines thrombophlebitis and skin ulceration may occur. Avoidance is by frequent inspection and resiting of lines. If PN 'tissues' under the skin, intradermal injection of saline may prevent further damage, and should be considered in conjunction with a plastic surgery opinion.

Hemorrhage: May occur shortly after insertion, or if the line is dislodged or disconnected.

Monitoring
Clinical and laboratory monitoring is essential for all babies on parenteral nutrition.

Clinical monitoring. This should include the following regular observations: daily weight, urine volume, specific gravity, pH, glucose, protein and blood, blood sugar, 4 hourly on first day, then 8 to 12 hourly or more frequently if unstable.

Laboratory monitoring daily blood urea, electrolytes, creatinine, calcium initially, alternate days thereafter.

Magnesium, phosphate and bilirubin twice weekly until stable, then weekly.

Lipid levels: weekly on infusions of more than 2 g/kg/day, twice weekly above 3 g/kg/day.
Urine Na+, urea, creatinine: daily if there is an excessive Na+ requirement.
Total and indirect bilirubin, albumin, alkaline phosphatase, transaminases: weekly.
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