Infants are in negative iodine balance on current standard regimens of total parenteral nutrition, with a mean iodine intake of 3 µg/kg/day (150 ml/kg/day). The recommended enteral intake of iodine for preterm infants is 30 µg/kg/day. Gastrointestinal absorption of iodine is high, suggesting that parenteral intakes should approach enteral recommendations.
Iodine is essential for synthesis of thyroid hormones, and thyroxine is necessary for brain development. Transient hypothyroxinaemia in preterm infants is characterised by postnatal reductions in serum levels of total thyroxine, free thyroxine, and triiodothyronine, with normal levels of thyroid stimulating hormone.
1Transient hypothyroxinaemia is present in most infants of < 30 weeks gestation and is characteristically associated with reductions in intelligence quotient scores but also increased risks of cerebral palsy.2 The cause of transient hypothyroxinaemia is not clear, with contributions from withdrawal of maternal-placental thyroxine transfer, hypothalamic-pituitary-thyroid immaturity, developmental constraints on the synthesis and peripheral metabolism of iodothyronines, non-thyroidal illness, and iodine deficiency. 3 An enteral intake of at least 30-40 µg iodine/kg/day is required to achieve a positive iodine balance in healthy preterm infants. 4 Younger and sicker infants, 27-30 weeks gestation, can be in negative iodine balance for the first weeks, and 30 µg iodine/kg/day is the recommended enteral intake for extreme preterm infants.3 Increasing enteral intakes further to 40-50 µg iodine/kg/day in more mature preterm infants does not alter serum iodothyronine levels.5 Infants who were parenterally fed were excluded from all these studies. We now report iodine intakes and urinary iodine outputs in a cohort of infants of < 30 weeks gestation who were initially parenterally fed.
PATIENTS AND METHODSThirteen consecutive inborn infants were recruited: male/ female ratio, 6:7; gestation mean, 26.8 weeks (range 24-29); birth weight mean, 926 g (range 570-1260). All had intensive care support and survived at least 28 days.On day 1 of life all infants had parenteral dextrose/ electrolyte/amino acid solution (Vaminolact; Fresenius Kabi, Runcorn, Cheshire, UK) with a phosphate supplement (Addiphos; Fresenius Kabi). On day 2, and thereafter, this solution was supplemented with water soluble vitamins (Solvito N; Fresenius Kabi) and trace elements (Peditrace; Fresenius Kabi). In tandem, a fat emulsion (Intralipid 20%; Fresenius Kabi) with added fat soluble vitamins (Vitlipid; Fresenius Kabi) was infused, initially at 8 ml/kg/day, increasing maximally to 18 ml/kg/day by day 5. Enteral feeds were started as hourly boluses, 0.5-1 ml, increased as determined by the infants' clinical condition, with reciprocal reductions in parenteral solutions infused. No infant progressed beyond hourly bolus feeds.A 24 hour iodine balance was calculated for each infant at days 1, 6, 13, and 27. The types and volumes of all enteral and parenteral fluids used were recorded, and the io...
