Effects of Different Loading Doses of Dexmedetomidine on Bispectral Index under Stepwise Propofol Target-Controlled Infusion

Abstract

Background and Purpose: Stepwise propofol target-controlled infusion (TCI) can achieve a less disturbed condition of hemodynamics and respiration. Its combination with dexmedetomidine may have some advantages for patients. We studied the effects of different loading doses of dexmedetomidine on the bispectral index (BIS) under stepwise propofol TCI. Methods: Forty patients were randomly assigned into groups D_1.0, D_0.5, D_0.25 and D₀, in which dexmedetomidine at 1.0, 0.5, 0.25 or 0 µg•kg^–1 was infused over 10 min followed by 0.5 µg•kg^–1•h^–1 and stepwise propofol TCI, which was administered with target effect site concentration (Ce) at 0.5 µg•ml^–1, and increased until 2.5 µg•ml^–1 by 1.0 µg•ml^–1 after 5 min reaching target Ce. BIS, heart rate, MAP, pulse oxygen saturation, RR and end-tidal carbon dioxide pressure were recorded before loading dose (T₀), at 5 min (T_{5 min}) and 10 min (T_{10 min}) after starting infusion, after 5 min reaching Ce of 0.5, 1.5 and 2.5 µg•ml^–1 (T_p0.5, T_p1.5 and T_p2.5). Results: BIS values in group D_1.0 were significantly lower compared with those in group D₀ since T_{10 min} and those in groups D_0.5 and D_0.25 since T_p0.5. In group D_1.0, heart rate decreased significantly at T_{5 min} and T_{10 min}, heart rate at T_{10 min} was significantly lower compared with that in group D₀. MAP remained stable during the loading dose infusion and decreased to some degree after propofol infusion in all groups. Changes in pulse oxygen saturation, RR and end-tidal carbon dioxide pressurewere similar among the groups without respiration depression. Conclusion: A loading dose of dexmedetomidine of 1.0 µg•kg^–1, not 0.5 µg•kg^–1 or less, over 10 min followed by 0.5 µg•kg^–1•h^–1 can definitely decrease the BIS under stepwise propofol TCI with clinically stable blood pressure and without respiration depression, while attention should be paid to decreased heart rate.