You are working in the NICU as a registrar and have just admitted a 28 week premature baby weighing 1kg. The consultant would like to start parenteral nutrition as well as small volume trophic feeds of expressed breast milk.
- Parenteral nutrition is artificial nutritional support for patients who are unable to eat normally, or have impaired digestion and absorption.
- It contains amino acids, fats, glucose, trace minerals and vitamins. Adequate nutrition must be given to allow for full growth potential.
- Volume of parenteral nutrition administered will depend on the different energy requirements of a child (e.g. non ambulant child vs. a child at home with a stable chronic disease).
What is parenteral nutrition (PN)?
PN is artificial nutritional support delivered parenterally to patients in whom digestion and absorption are inadequate, or who are unable to eat normally. Prior to PN, children with intestinal failure or who cannot be fed enterally were unable to receive sufficient macronutrients, micronutrients, water and electrolytes and would suffer malnutrition and die.
The challenge in children is that their nutritional intake must not only be adequate for body function and to overcome any illness, but also for growth and development. Certain organs grow and differentiate at a rapid rate at a particular time in infancy, making timely initiation of PN crucial for normal development. An example is the brain, which experiences the most growth in the last trimester of pregnancy and in the first 2 years of life.
Why is early PN vital for preterm newborns?
A preterm baby weighing 1kg has sufficient reserve for just 4 days of starvation. A larger preterm baby will have enough for 12 days. Factor in the metabolic requirements for the often stormy perinatal period and this reserve may be halved to just 2 days in a small preterm baby.
When it is clear that enteral feeds will not be tolerated soon PN must be started shortly after birth.
What is in PN?
PN comprises mainly of the 3 principle calorie supplying nutrients: amino acids, glucose, and lipids. PN also has electrolytes and vitamins and trace elements.
How much PN should we give?
Basal metabolic rate is the energy expended by a recumbent child in a thermoneutral environment following a 12-18 hour fast just when the individual has awakened but before commencement of activities for the day. It is a reflection of energy expenditure for vital processes.
Resting energy expenditure is the energy expenditure of a person at rest in a thermoneutral environment.
These two values usually do not differ by more than 10%
Total energy expenditure is the sum total energy required for basal metabolism, thermic effect of digested food, thermoregulation and activity. In an older child, most energy is expended towards activity, so a hospitalised child lying in bed is reduced.
Data shows that in most cases there is little need to provide a post operative or critically ill child with much more than their resting energy expenditure. In contrast, a stable child on long term home PN who is growing and who has a relatively normal lifestyle will have a higher energy requirement.
By weight, the approximate requirements for parenteral nutrition in children is as follows:
|Weight||Total Fluid ml/kg/day||Total kcal/day|
|>20kg||1500ml + 20ml/kg/day for each kg over 20 kg||1500 + 20/kg for each kg over 20 kg OR 30-60/kg|
|15-20kg||1000ml + 50ml/kg/day for each kg over 10 kg||1000 + 50/kg for each kg over 10 kg OR 60-90/kg|
|10-15kg||1000ml + 50ml/kg/day for each kg over 10 kg||1000 + 50/kg for each kg over 10 kg OR 60-90/kg|
*From ESPGHAN Guidelines November 2005, taken from Sydney Children’s Hospital Paediatric Parenteral Nutrition Team’s Guidelines to PN
Can you give too much PN?
When glucose is delivered in excess amounts, the excess is directed to lipogenesis, which actually increases energy expenditure. An increase in lipogenesis leads to an excess of CO2 production relative to O2 consumption. Patients usually compensate by increasing their respiratory rate but problems may rise in cases of respiratory compromise. In addition, hyperglycaemia has been shown to be a risk factor for infection.
The preterm infant <2kg without intravenous lipids begins to show biochemical evidence of essential fatty acid deficiency by 7 days of life. Essential fatty acids must be provided or mobilisation of fatty acids from liver and adipose tissue occurs. Excess of lipids cause hypertriglyceridaemia, so cholesterol and triglyceride levels should be checked with other bloods.
Immunodeficiency associated with malnutrition is related more to protein malnutrition rather than energy malnutrition. Consequently, some recommend that amino acid requirements are attended to first when ordering PN. Some evidence has shown that amino acids contribute to PN associated cholestasis.
What lipid solutions are available?
Soy bean oil emulsions provide a reliable source of essential fatty acids but their high content of PUFA (polyunsaturated fatty acids) and limited alpha tocopherol, reduces alpha tocoferol and depletes antioxidant defences. These may lead to negative effects on the inflammatory response and immune system.
ClinOleic is an olive oil based lipid which reduces the risk associated with excessive intake of PUFA.
SMOFlipid contains 30% soybean oil, 30% MCT, 25% olive oil and 15% fish oil. The high content of omega 3 fish oil might be beneficial in providing an adequate balance of omegas 3 and 6 in the cell membrane phospholipids. SMOFlipid preserved liver function and showed increased serum alpha tocoferol in ICU patients.
What are the complications of PN?
Parenteral nutrition may cause immediate metabolic disturbances including hyperglycaemia, electrolyte imbalance and hypertriglyceridemia.
After a prolonged period of starvation, patients starting on PN may develop refeeding syndrome – hypokalemia, hypomagnesemia and hypophosphataemia. These patients require close monitoring and supplementation with potassium, magnesium and phosphate.
Patients on long term PN must be monitored for micronutrient deficiencies or excess.
Line sepsis is a common complication of PN therapy in children. The majority of line associated infections are gram positive organisms, mainly coagulase negative staphylococci. In patients with short bowel syndrome, translocation of gram negative gut organisms is also possible.
Thrombosis is associated with line infection. A cycle of line infections and thrombosis of the large central vessels may lead to the loss of central venous access sites and make provision of PN difficult.
Cholestatic liver disease manifestations secondary to PN include intrahepatic cholestasis, cholelithiasis, hepatic fibrosis, biliary cirrhosis and portal hypertension. PN associated cholestasis may progress to hepatic cirrhosis and then chronic liver failure. The main risk factors are prematurity, recurrent sepsis, previous gut surgery and lack of enteral feeds.
What can we do to reduce PN associated complications?
Even minimal enteral feeding should be considered in patients with a functioning gut. This is also the main strategy in treating PN associated cholestasis.
Prevention of infection by using strict aseptic technique when accessing the central line. Anticoagulation in conjunction with long term PN may reduce rate of thrombosis and preserve access sites in the long term.