USA Surgery Today

Pediatric parenteral crystalline amino acid formulas provide essential and nonessential amino acids specifically balanced to meet the needs of the developing child. Neonatal-specific amino acid formulas (Aminosyn PF, Trophamine) are formulated to closely reproduce the plasma amino acid profile of breastfed infants. These formulas have led to greater weight gain and improved nitrogen balance in infants compared with standard amino acid formulas. Some amino acids such as cysteine, tyrosine, glycine, and taurine are considered conditionally essential to the child (Table 7-2). Taurine supplementation to premature infants is essential to promote bile acid conjugation and improve bile flow. Premature infants are at risk for taurine deficiency as a result of relatively high renal excretion and low synthetic capacity related to diminished cystathionase enzyme activity and can leap to inadequate retinal development (17). Amino acids are a source of energy (4 kcal per g) and nitrogen for protein synthesis. Parenteral amino acids should approximately provide 10% to 15% of total calories. Amino acids are generally started at 1 g per kg per day and advanced to goal over 2 to 3 days. To simulate intrauterine protein accretion rate, low birth weight infants may need up to 3.85 g per kg per day of amino acids (6,18). Amino acid requirements are 2.5 to 3 g per kg per day in term infants, 1.5 to 2 g per kg per day in older children, and 1 to 1.5 g per kg per day in adolescents. Amino acid doses should be adjusted based on the patient’s clinical condition and nutritional status. For example, higher amino acid doses may be required to heal a complex wound. Patients with liver failure require lower amino doses to avoid hyperammonemia. Higher amino acid doses are required in patients on renal dialysis or continuous renal replacement therapies to compensate for losses via the dialysis membrane and filter (19,20).

Hydrous dextrose is the major source of energy in PN and provides carbon skeletons for tissue accretion. Dextrose also acts as a protein-sparing substrate by preventing breakdown of somatic protein stores via suppression of gluconeogenesis. In children and adolescents receiving PN, parenteral dextrose usually provides 50% to 60% of total calories. The caloric value of hydrous dextrose is 3.4 kcal per g. In infants, PN should be initiated at a dextrose infusion rate of 4 to 8 mg per kg per minute to maintain adequate serum glucose concentrations. Lower amounts of glucose in a young neonate may lead to hypoglycemia due to inadequate hepatic production of glucose. Dextrose infusion is thereafter advanced at a daily rate of 2 mg per kg per minute until the nutritional goal is achieved. The maximum dextrose infusion rate should not exceed 10 to 14 mg per kg per minute, and this can usually be achieved when PN is administered through a central venous catheter (21).

Intravenous lipid emulsions are a condensed source of energy and essential fatty acids. The caloric density of lipid emulsions varies with the lipid concentration. Lipid emulsions at 10%, 20%, and 30% concentrations yield 1.1 kcal per mL, 2 kcal per mL, and 3 kcal per mL, respectively. Currently marketed intravenous lipid emulsions in the United States are made of long-chain triglycerides. Lipids usually provide 30% to 50% of the nonnitrogen caloric needs or about 20% to 30% of total calories in a patient on PN. Typically, lipid emulsions in infants and children are initiated at a dose of 1 g per kg per day and advanced by 1 g per kg per day to a maximum of 3 g per kg per day. Gradual increases in the daily lipid intake (0.5 or 1 g per kg per day) do not appear to improve lipid clearance. However, the lipid emulsion is better cleared (22) and lipid utilization is improved when lipid is infused continuously over 24 hours rather than intermittently or for part of the day. There are also differences between the clearances of different lipid emulsions. The 20% lipid emulsion is favored over the 10% emulsion due to a better plasma clearance because of a lower phospholipid content (23,24). Because lipid emulsions are derived from vegetable oils, they are also a natural source of vitamin K and vitamin E isomers. As lipid particles are metabolized to fatty acids and monoglycerides, free fatty acids may compete with bilirubin for albumin-binding sites and potentially displace free bilirubin into the serum. Although this phenomenon resulted in lipid restriction in hyperbilirubinemic patients in the past, more recent kinetic studies have failed to show that this represents a significant risk in terms of kernicterus, unless the child is at risk for exchange transfusion (25).

Pediatric parenteral multivitamins contain a combination of water and fat-soluble vitamins that are added to the daily PN. Several pediatric multivitamin formulas are available in the United States. However, no parenteral multivitamin products are currently available that specifically meet the needs of premature infants. Pediatric parenteral multivitamins provide relatively low vitamin A and high water-soluble vitamin doses to premature infants. Higher vitamin A intake may be helpful in low birth weight infants who are at increased risk for lung disease (26). Depletion of water-soluble vitamins occurs rapidly under conditions of physiologic stress.

Thiamine is a cofactor for normal dextrose metabolism. Dextrose is normally metabolized to pyruvate, which is then converted to acetyl coenzyme A prior to oxidation via the citric acid cycle. In the presence of thiamine deficiency, pyruvate is instead converted to lactate that can result in lactic acidosis (27). Lactic acidosis has been reported in patients who received dextrose infusions without thiamine supplementation, and fatalities from lactic acidosis due to thiamine deficiency were also reported during periodic multivitamin shortages in the United States.