Dexmedetomidine is a useful sedative drug with various uses. We designed this study to investigate the clinical effects and complications of different loading doses, 0.5 and 1.0 µg/kg.

Forty six patients, of American Society of Anesthesiologists physical status I and II, who required elective and emergency operation under spinal anesthesia were randomly assigned to group L or group H. Group L received a loading dose of 0.5 µg/kg for 10 minutes while group H received 1.0 µg/kg. Bispectral index (BIS), systolic blood pressure, heart rate, and Ramsay score were recorded at T₀ (before loading), T_L (just after loading) and T_{10, 20, 30} (10, 20, 30 minutes after T_L). Complications, drug use, lowest BIS and time to reach BIS 80 after termination of dexmedetomidine were recorded during this study.

In group H, BIS value decreased significantly after T_L compared to the baseline (T₀), while in group L after T₁₀. Between two groups, BIS values showed a significant differences only at T₁₀, BIS of group H was lower than that of group L. Ramsay score showed no significant differences except in T_L; the score of group L was significantly lower than that of group H. Other vital signs and complications showed a minimal differences between two groups.

Higher loading dose (1.0 µg/kg) of dexmedetomidine can lead to faster sedation without any severe complications.