title: Effects of different loading doses of dexmedetomidine on bispectral index under stepwise propofol target-controlled infusion.
abstract: OBJECTIVE
  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 D(0), 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 (T(0)), 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 D(0) 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 D(0). 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Anesthesia, Zhongshan Hospital, Shanghai Medical College, Fudan University, Shanghai, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Wang
authors.forename: Shengjin
authors.initials: S
authors.lastname: Ge
authors.forename: Wanxia
authors.initials: W
authors.lastname: Xiong
authors.forename: Peiwen
authors.initials: P
authors.lastname: Zhou
authors.forename: Jing
authors.initials: J
authors.lastname: Cang
authors.forename: Zhanggang
authors.initials: Z
authors.lastname: Xue
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000008:administration & dosage*; D000328:Adult; D000771:Anesthesia, Intravenous; D018686:Anesthetics, Intravenous / Q000008:administration & dosage*; D001794:Blood Pressure / Q000187:drug effects; D056805:Consciousness Monitors; D020927:Dexmedetomidine / Q000008:administration & dosage*; D004311:Double-Blind Method; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D006993:Hypnotics and Sedatives / Q000008:administration & dosage*; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D015742:Propofol / Q000008:administration & dosage*; D056152:Respiratory Rate / Q000187:drug effects
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D018686:Anesthetics, Intravenous; D006993:Hypnotics and Sedatives; D020927:Dexmedetomidine; D015742:Propofol