• Giuseppe Bello, Giorgia Spinazzola, Valentina Giammatteo, Luca Montini, Gennaro De Pascale, Alessandra Bisanti, Maria G Annetta, Eliana Troiani, Antonio Bianchi, Alfredo Pontecorvi, Mariano A Pennisi, Giorgio Conti, and Massimo Antonelli.
• Dipartimento di Scienze dell'Emergenza, Anestesiologiche e della Rianimazione; UOC di Anestesia, Rianimazione, Terapia Intensiva e Tossicologia Clinica; Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Roma; Istituto di Anestesia e Rianimazione; Università Cattolica del Sacro Cuore Largo A Gemelli 8, 00168 Rome, Italy. gsppbll@gmail.com.
• Respir Care. 2019 Oct 1; 64 (10): 1199-1207.

BackgroundSeveral respiratory abnormalities can be present in primary hypothyroidism and can be reversed with adequate hormone treatment. However, the role of thyroid hormone replacement therapy on the respiratory system in patients with nonthyroidal illness syndrome is still unclear. This physiologic study evaluated the effect of thyroid hormone treatment on respiratory muscle function in subjects with nonthyroidal illness syndrome and while on mechanical ventilation. The primary end point was neuromechanical efficiency, which provides an estimate of the efficiency of diaphragmatic contraction. Secondary end points were the transdiaphragmatic pressure-time product and the swing of the electrical activity of the diaphragm, which reflect the work of breathing and inspiratory effort, respectively.MethodsFifteen subjects on mechanical ventilation for ≥48 h and with a diagnosis of nonthyroidal illness syndrome who had a failed spontaneous breathing trial, received intravenous triiodothyronine. The hormone was administered as an intravenous bolus of 0.4 μg/kg triiodothyronine, followed by continuous perfusion at 0.6 μg/kg for 24 h. Neuromechanical efficiency was calculated as the ratio between the drop in airway pressure during an expiratory occlusion and the corresponding electrical activity of the diaphragm peak. Recordings were taken at baseline and after 3, 6, and 24 h.ResultsAfter study completion, free triiodothyronine serum concentrations increased in all the subjects (mean ± SD increase, 0.84 ± 0.34 pg/mL). Neuromechanical efficiency showed no significant changes throughout the study (mean ± SD baseline, 1.40 ± 0.87 cm H2O/μV; 3 h, 1.28 ± 0.64 cm H2O/μV; 6 h, 1.33 ± 0.87 cm H2O/μV; 24 h, 1.41 ± 0.96 cm H2O/μV). Similarly, no variations in transdiaphragmatic pressure-time product per min (mean ± SD baseline, 238.1 ± 124 cm H2O × s/min; 3 h, 242.5 ± 140.3 cm H2O × s /min; 6 h, 247.5 ± 161.7 cm H2O × s/min; 24 h, 281.2 ± 201.2 cm H2O × s/min) or swing of electrical activity of the diaphragm (mean ± baseline, 20.9 ± 13.1 μV; 3 h, 17.2 ± 8.3 μV; 6 h, 17.4 ± 11.3 μV; 24 h, 20.3 ± 13.7 μV) were observed during hormone administration.ConclusionsIn the subjects on mechanical ventilation who were admitted to the ICU with nonthyroidal illness syndrome, thyroid hormone replacement treatment did not yield any benefit on respiratory muscle function when assessed by neuromechanical efficiency, which indicated that, in these subjects restoring normal levels of serum thyroid hormones is debatable. (ClinicalTrials.gov registration NCT03157466.).Copyright © 2019 by Daedalus Enterprises.

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