Attempts to feed directly into the bloodstream have been made ever since the circulatory system was first described by William Harvey in 1628. For example, Sir Christopher Wren infused ale and opium into dogs in 1656 using a bladder and sharpened quill.

In order for PN to be safely used in the clinical setting, suitable carbohydrate, protein, and lipid sources were required in a form that was stable in solution, nontoxic, and suitable to be infused directly into the bloodstream.

Carbohydrate energy sources trialed included fructose, sorbitol, ethanol, and glucose. Although glucose was metabolically the most suitable energy source, it was associated with venous thrombosis. It was only when Dudrick et al. in 1968 infused glucose into a large central vein that thrombophlebitis was avoided [3]. PN was first provided on a commercial basis from the late 1960s after a suitable lipid source was developed. The lipid was required in order to provide adequate calories without an excessive osmotic load as well as a source of essential fatty acids (EFA). An artificial “chylomicron” composed of soybean oil and egg phosphatides was developed by Wretlind and Schuberth in 1963 that is still in use today [4].

PN is a complex mixture of sterile nutrients in a suitable form to be safely infused directly into the bloodstream. It consists of carbohydrate lipid and amino acids with added vitamins and minerals.

Lipid is usually supplied as a separate infusion that also contains the fat soluble vitamins, that is, vitamins A, D, E, and K.

The standard carbohydrate source is dextrose. The amino acid formulation is usually based on egg protein and in the neonate, on breast milk .

Until the last few years soybean has been the only lipid source. However, more recently olive oil, fish oil, coconut oil, and an artificially structured lipid have been developed. See Table 47.2.

The lipid emulsion provides an energy-dense source of nonprotein calories and if includes soybean oil contains EFA, alpha-linolenic acid and linoleic acid.

Lipid should represent about 30 % of nonprotein energy and linoleic acid should be 1–2 % of total energy . The maximum lipid utilization rate is about 3.3–3.6 g/kg/day.

Minerals and vitamins are available in mixed formulations or can be added individually.

Iron is not routinely included since iron-associated liver cirrhosis can develop. However, it is often added when iron-deficiency anemia develops in children on prolonged treatment.

Additional substances that can be directly added to the formulation include the nonessential amino acid glutamine and certain medication, such as the H-2 receptor antagonist, ranitidine.

PN should be formulated in a licensed compounding unit. The unit should have access both to their own stability data and that available in specialist PN units elsewhere in the UK and Europe. An automated system in a specialized sterile unit is usually used to mix the PN ingredients according to international pharmaceutical standards. The final formulation is supplied in a sealed plastic bag. In most cases, the nutrients for a 24-h period are contained within two bags; one with the amino-acids, dextrose, electrolytes, trace elements, and water soluble vitamins, and the other with lipid and fat-soluble vitamins, that is, vitamins A, D, E, and K.

Stability of the PN formulation can be a major problem in children when compared to adults since they have relatively high calcium and phosphate requirements: two salts that readily precipitate.

PN can be sourced in three different ways:

It is essential that all attempts are made to feed a child enterally (unless contraindicated, e.g., intestinal obstruction, post-gastrointestinal surgery) before commencing PN. Once the need for PN has been established it usually needs to be commenced with some urgency.

The severity and complications of a chronic disease are worse in undernourished patients. Nutritional support should be begun early, for example, within 1–5 days if a child is unable to tolerate any enteral nutrition since nutritional reserves are limited. Age, nutritional state, and intestinal losses should be taken into account. It has been estimated that a small premature baby (1 kg) has sufficient reserves to survive only 4 days and a term infant up to 12 days [5]. When enteral nutrition is not tolerated or contraindicated, PN should be begun within 1–2 days of the intake/absorption becoming inadequate in the newborn infant, but can be delayed for up to 5–7 days in a well-nourished adolescent. Other than in the premature neonate, it is usually best practice to stabilize the patient and start PN during normal working hours. See Table 47.3 for the steps that need to be taken when commencing PN.

It is important to commence PN at the earliest opportunity and within 6 h of birth in the “high risk” premature neonate. Initially, PN at 60–90 ml/kg/day that includes both amino acids and lipid. See Table 47.5 for guidelines. Infusion can be commenced via an umbilical venous catheter UVC or peripherally inserted long line. If the child is clinically stable, trophic feeds of expressed breast milk (EBM) should also be commenced. “High-risk” neonates include those born prematurely at less than 32 weeks gestation, very low birth weight (VLBW) of under 1.5 kg, less than 35 weeks gestation with intrauterine growth retardation (IUGR) with weight < 9th centile and absent/reversed end-diastolic flow and those with congenital gastrointestinal malformations, such as gastroschisis . Other neonates at nutritional risk who may need PN are those with necrotising enterocolitis, gastrointestinal obstruction, those who need inotropic support, perinatal hypoxia/ischaemia, cyanotic or duct-dependent cardiac lesions or persistent pulmonary hypertension of the newborn (PPHN).