Background:We evaluated heart rate (HR) and blood pressure (BP) trends when nicardipine (NCD) was co-administered during dexmedetomidine (DEX) sedation after spinal anesthesia.Methods:Sixty patients aged 19 to 65 were randomly assigned to the DEX or DEX-NCD groups. Five minutes after infusion of the loading dose of DEX, the NCD was administered intravenously at a rate of 5 μg/kg for 5 minutes in the DEX-NCD group. The study starting point was set at 0 minute when the DEX loading dose was initiated. The primary outcomes were the differences in HR and BP between the 2 groups during the study drug administration. Secondary outcomes included the number of patients whose HR was < 50 beats per minute (bpm) after the DEX loading dose infusion, and associated factors were evaluated. The incidence of hypotension in the postanesthesia care unit, postanesthesia care unit length of stay, postoperative nausea and vomiting, postoperative urinary retention, time to first urination after spinal anesthesia, acute kidney injury, and postoperative hospital length of stay were evaluated.Results:The HR was significantly higher at 14 minutes, and the mean BP was significantly lower at 10 minutes in the DEX-NCD group than in the DEX group. The number of patients with an HR < 50 bpm during surgery was significantly higher in the DEX group than in the DEX-NCD group at 12, 16, 24, 26, and 30 minutes. The DEX group and a low initial HR were independently associated with the occurrence of an HR < 50 bpm after DEX loading dose infusion. Postoperative outcomes were not significantly different between the 2 groups.Conclusions:Simultaneous administration of NCD during the administration of a loading dose of DEX prevented severe bradycardia. Co-administration of NCD may be considered in patients with a low initial HR when severe bradycardia is expected during the DEX loading dose infusion. NCD and DEX may be safely infused simultaneously without affecting postoperative complications (see Figure S1, Supplemental Digital Content,http://links.lww.com/MD/J241, Graphical abstract).