Does the use of an iodine-containing contrast agent to visualise the PICC tip in preterm babies cause hypothyroidism? A randomised controlled trial

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Preterm babies take time to reach their full quota of oral feeds so often require prolonged intravenous nutrition. Peripheral venous cannulas have a short life span and may result in damage to the skin’s integrity, as well as having a short life span. Long lines or peripherally inserted central catheters(PICC) have a significantly longer life span as the tip is positioned in a large vein.However PICC line insertions are not without complications. The tip of the catheter may reach deep inside the cardiac chambers or fall short of the caval veins and end in entirely unexpected locations. Extravasation of fluid from the catheters in each of these positions has led to serious, and occasionally lethal, complications. These can be avoided if the catheter tip can be precisely localised. The narrow calibre silastic line cannot always be seen on plain radiography but can be visualised with use of a small amount of radio-opaquae contrast. However the contrast available contains Iodine which may cause transient hypothyroidism in newborns. Concerns regarding this have resulted in some units including ours restricting use of contrast when determining line position. The data supporting this decision are very limited and it is unclear as to the role of iodine containing contrast in the development of hypothyroidism. The few studies that have assessed the relationship are either cohort studies, before-and-after study or case series, none being a randomized control trial. The results of these studies are contrasting without any clear answer as to whether perceived benefits of withholding contrast outweigh the risks of developing hypothyroidism. To confuse things further, asymptomatic hypothyroidism is not uncommon in the preterm population. The aim of our study is to compare thyroid function tests in preterm neonates after exposure to IV contrast with controls, to ascertain the impact of a small iodine exposure on the thyroid gland in relation to gestational age. The study will be a randomized control trial for babies less than 30 weeks old requiring insertion of a PICC line. Study infants will be randomised to use of contrast(0.3ml Iopamidol containing iodine 300mg/ml)to assess line position(previous Unit practice) or no contrast. Blood and urine tests will be performed to assess any impact on the thyroid gland of contrast use. Repeat thyroid function tests(TFT) for both case and control will be taken as baseline then 7 and 14days after insertion of the line. Further TFT will be taken if day 7 or 14 results are abnormal.