Aspects of nutrition, metabolism and growth of the low birthweight infant
A dextrose electrolyte solution (5.9mmol/dl sodium) administered alone or as a component of total parenteral nutrition was satisfactory for full term infants but produced significant hypernatraemia in infants of < 34 weeks gestation during their first few days of life. This hypernatraemia was prevented by the substitution of a solution of lower sodium content (2mmol/dl). Hyponatraemia was common between the second and fifth postnatal weeks in enterally fed preterm infants of < 1500g birthweight and a sodium intake of at least 3-4mmol/kg/day was necessary to maintain plasma sodium above 130mmol/l during this period. Plasma copper, zinc and albumin levels and alkaline phosphatase activity were recorded in infants of varying gestational age at birth. Plasma albumin and copper rose and alkaline phosphatase activity fell with increasing gestational age at birth, but no differences in plasma zinc values were noted in infants of between 28 and 41 weeks gestation. Plasma albumin and copper levels increased postnatally in preterm infants and did not differ from those of infants of a comparable postconceptual age (gestational age + postnatal age), in contrast to plasma zinc levels which declined below such standards. There was a significant correlation between the radiological features of rickets and plasma alkaline phosphatase activity which therefore may be used to screen for and monitor rickets in preterm infants. Routine dietary calcium supplementation reduced the incidence and severity of rickets in such infants. Hepatic dysfunction was detected in 14.6% of 122 infants who received total parenteral nutrition and a strong association was noted between bacterial infection and the development of hepatic dysfunction. Plasma bile salt measurements did not prove to be a more sensitive indicator of hepatic dysfunction than plasma direct bilirubin values. A comparative study of two feeding regimens was carried out in preterm infants of < 1500g birthweight. Fifty nine infants were allocated alternately to initial total parenteral nutrition or nasoduodenal feeding (enteral group). One third of the infants in the enteral group failed to establish nasoduodenal feeding during the first postnatal week. The gradual introduction of nasoduodenal feeding to infants in the parenteral group did not prevent the recognised deterioration in growth pattern associated with a rapid switchover from parenteral to enteral nutrition. The initial use of total parenteral nutrition did not produce any beneficial effects on growth between birth and the expected date of delivery and acquired bacterial infection associated with significant morbidity and mortality was more common in the parenterally fed infants. Parenteral nutrition should not be used routinely in very low birthweight infants but reserved for those in whom enteral feeding is not possible.