Changes in thyroid hormone concentrations during neonatal extracorporeal membrane oxygenation

Indications for Intravenous T3 and T4

Therapy with thyroid hormones normally is restricted to substitution therapy of patients with primary or secondary hypothyroidism. Typically, thyroid hormones are given orally. There are few indications for intravenous use of thyroid hormones. Indications for parenteral application are insufficient resorption of oral medications due to alterations of the gastrointestinal tract, partial or total loss of consciousness, sedation in the intensive care unit or shock. In almost all cases, levothyroxine is the therapy of choice including congenital hypothyroidism. In preterm infants with an altered thyroid hormone status, studies with thyroid hormones including intravenous liothyronine showed a normalisation of T3 levels and in some cases an amelioration of parameters of ventilation. A benefit for mortality or later morbidity could not be seen. Effects on neurological improvements later in life are under discussion. Decreased thyroid hormone levels are often found after cardiac surgery in infants and adults. Intravenous therapy with thyroid hormones improves the cardiac index, but in all other parameters investigated, no substantial effect on morbidity and mortality could be demonstrated. Oral liothyronine therapy in these situations was equivalent to an intravenous route of application. In myxoedema coma, intravenous levothyroxine is given for 3 to 10 days until the patient can take oral medication and normal resorption in the gastrointestinal tract is achieved by restoring at least peripheral euthyroidism. Intravenous levothyroxine is the standard in treating patients with myxoedema coma. A protective effect on the heart of i.v. levothyroxine in brain-dead organ donors may be possible.

Developmental changes of the fetal and neonatal thyroid gland and functional consequences on the cardiovascular system

Thyroid hormones play an important role in the development and function of the cardiac myocyte. Dysregulation of the thyroid hormone milieu affects the fetal cardiac cells via complex molecular mechanisms, either by altering gene expression or directly by affecting post-translational processes. This review offers a comprehensive summary of the effects of thyroid hormones on the developing cardiovascular system and its adaptation. Furthermore, we will highlight the gaps in knowledge and provide suggestions for future research.

Frequency of thyroid dysfunction in pediatric patients with congenital heart disease exposed to iodinated contrast media - a long-term observational study

Background The thyroid gland of patients with congenital heart disease may be exposed to large doses of iodine from various sources. We assessed the thyroid response after iodine exposure during conventional angiography in cardiac catheterization and angiographic computer tomography in childhood. Methods Retrospective mid- to long-term follow-up of 104 individuals (24% neonates, 51% infants, 25% children) with a median age and body weight of 104 days [0-8 years] and 5.3 kg [1.6-20]. Serum levels of thyroid-stimulating hormone, free triiodthyronine and free thyroxine were evaluated at baseline and after excess iodine. We also assessed risk factors that may affect thyroid dysfunction. Results Baseline thyroidal levels were within normal range in all patients. The mean cumulative iodinate contrast load was 6.6 ± 1.6 mL/kg. In fact, 75% had experienced more than one event involving iodine exposure, whose median frequency was three times per patient [1-12]. During the median three years follow-up period [0.5-10], the incidence of thyroid dysfunction was 15.4% (n=16). Those patients developed acquired hypothyroidism (transient n=14, long-lasting n=2 [both died]) with 10 of them requiring temporary replacement therapy for transient thyroid dysfunction, while four patients recovered spontaneously. 88 individuals (84.6%) remained euthyroid. Repeated cardiac interventions, use of drugs that interfere with the thyroid and treatment in the intensive care unit at the index date were strong predictors for acquired thyroid dysfunction. Conclusions The incidence of acquired hypothyroidism after iodine excess was 15.4%. However, most patients developed only transient hypothyroidism. Systemic iodine exposure seems to be clinically and metabolically well tolerated during long-term follow-up.

Euthyroid sick syndrome in paediatric and adult patients requiring extracorporeal circulatory support and the role of thyroid hormone supplementation: a review

Non-thyroid disorders may modify thyroid hormone metabolism, resulting in an 'euthyroid sick syndrome'. Studies determining the association of cardiopulmonary bypass to thyroid function showed changes in line with this euthyroid sick syndrome. In some cases, cardiovascular dysfunction after cardiac surgery with cardiopulmonary bypass is comparable to that noticed in hypothyroidism associated with low cardiac output and elevated systemic vascular resistance. Numerous lines of research have proposed that triiodothyronine can behave acutely as a positive inotropic and vasodilator agent. The aim of this review is to present an update on the current literature about in what clinical situations the use of thyroid supplementation during the perioperative period of extracorporeal circulation in the adult and paediatric populations may impact outcome to any appreciable degree. The contribution of thyroid function in patients undergoing a ventricular assist device implantation is additionally reviewed and future study directions are proposed. This is a narrative review, where the search strategy consisted on retrieving the articles through an extensive literature search performed using electronic databases from January 1978 up to September 2019. All controlled trials randomly allocating to perioperative thyroid hormone administration in children and adults undergoing extracorporeal circulation for cardiac surgery were considered. Thyroid hormone supplementation may be recommended particularly in selected paediatric sub-populations. There is currently no firm evidence regarding the benefits of routine use of thyroid hormone administration in cardiac adult patients. Further studies are required to assess the beneficial effect of thyroid hormone on patients with end-stage heart failure supported by ventricular assist devices.