Phenylalanine content and total parenteral nutrition

Hyperphenylalaninaemia and outcome in intravenously fed preterm neonates

Hyperphenylalaninaemia is likely to have occurred in many infants fed the intravenous amino acid solution Vamin 9. In this study of 336 preterm infants plasma phenylalanine was measured weekly during their hospital stay. Reference data on plasma phenylalanine were prepared for 243 infants who did not receive Vamin. Only 1% of these infants had a peak plasma phenylalanine concentration greater than 150 mumol/l (maximum 202 mumol/l) compared with 23% in 93 infants fed Vamin 9, seven of whom had concentrations > 300 mumol/l (maximum 704 mumol/l). High concentrations only occurred when the total energy to protein energy ratio in the intravenous solutions decreased to less than 8.5:1 and always occurred with a ratio less than 6.5:1, implying that hyperphenylalaninaemia may be minimised with an intravenous energy intake of greater than 34 kcal (142 kJ)/g protein. Nevertheless, follow up at 18 months post-term showed that increased plasma phenylalanine in this instance was not associated with any impairment of the Bayley mental development index (or subscales including fine motor, cognitive, or language development), the psychomotor development index, or the social maturity quotient. Thus, despite theoretical concern, an adverse outcome after hyperphenylalaninaemia induced by intravenous feeding has not been observed.

Changes in the plasma aminogram of parenterally fed infants treated with dexamethasone for bronchopulmonary dysplasia

A substantial increase in the plasma concentration of most amino acids was observed in 59 preterm infants with chronic lung disease soon after the initiation of dexamethasone therapy. The size of increase appeared to be dose related. This phenomenon is likely to be the result of steroid induced protein catabolism. Interestingly, neither phenylalanine nor tyrosine concentrations were significantly increased.

Acid-base state of the preterm infant and the formulation of intravenous feeding solutions

An acidic intravenous source of phosphorus (Addiphos) was compared with dipotassium hydrogen phosphate in 25 preterm infants to study acid-base state. Eight infants were given either Addiphos or dipotassium hydrogen phosphate alternately for 48 hour periods and similar amounts of calcium and phosphorus were delivered. There were no significant differences in calcium and phosphorus intake, calcium and phosphate plasma concentrations, or acid-base state between study periods on the two solutions. Seventeen infants were given the two solutions alternately for 72 hour periods; Addiphos was used to increase the amounts of calcium and phosphorus being delivered. Calcium and phosphorus intake was decreased on dipotassium hydrogen phosphate, but Addiphos significantly increased calcium and phosphorus intake and plasma calcium and phosphate concentrations. It also lowered the pH of the urine and raised the titratable acidity. Acid-base state, however, was not significantly different. It is therefore possible to increase intake of calcium and phosphorus in preterm infants without causing a significant metabolic acidosis.

Plasma amino acid concentrations in parenterally fed preterm infants

One hundred and nine sick preterm infants were studied, and the data obtained show that hyperphenylalaninaemia is an extremely rare occurrence as long as an adequate source of energy is provided. High concentrations of the other aromatic amino acid (tyrosine) on the other hand, were often encountered and seem to be due to immaturity of an isolated hepatic enzyme as there was no correlation between phenylalanine and tyrosine concentrations. Possible adverse consequences of hypertyrosinaemia are discussed in relation to toxicity and the assessment of hepatic function. We provide reference centiles for plasma amino acid concentrations in this population.