We report the clinical management of 2 adults with mental retardation because of trisomy 21 who were sedated with high-dose dexmedetomidine (DEX) alone during diagnostic cardiac catheterization (DCC). The first patient was a 25-year-old man with aortic regurgitation and ventricular septal defect. DEX increased his Ramsay sedation score; however, a high dose and bolus injection of DEX were required to perform an invasive procedure. Cardiovascular drugs were not administered and heart rate was maintained in the low 40s. The maximum predicted plasma concentration (pCp) of DEX was 2.3 ng/mL. The second patient was a 26-year-old woman who had developed hypoxia 20 years after palliative surgery for tetralogy of Fallot. High-dose DEX was administered to keep the bispectral index value below 70 and maintain an immobile state; her maximum pCp of DEX was 4.3 ng/mL. Percutaneous oxygen saturation was kept above 83%, because of the suspicion that DEX may increase the ratio of pulmonary artery flow to systemic artery flow. In both cases, no respiratory system complications occurred despite inspiration of room air, indicating the usefulness of DEX for DCC. However, because of DEX may affect DCC data, it is necessary to pay careful attention to the use of DEX during DCC.

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