Comparison of the hypnotic effect of propofol administered by TCI during day-time and night-time

Abstract

Objective To compare the hypnotic effect of propofol administered by target-controlled infusion (TCI) during day-time and night-time,in order to explore the effect of circadian rhythms on the sedative effect of propofol.Methods Sixty-five male ASA Ⅰ or Ⅱ patients aged 18-55 yr undergoing emergency minor hand surgery were divided into 2 gorups according to the time of the day when they received propofol TCI:day-time group (from 7:01 to 19:00) and night-time group (from 19:01 to 7:00).The pharmacokinetic parameters proposed by Schnider which predict effect-site concentration (Ce) were used.Four effect-site concentrations of propofol were set:0.8,1.2,2.0 and 4.0 μg/ml.Ce was increased step by step and each Ce was maintained for 5 min.The level of sedation at each Ce was assessed by BIS and OAA/S scores.BIS value and Ce of propofol were recorded and compared between the 2 groups when the patients lost consciousness (OAA/S score =2).Results There was 28 and 30 patients in day-time and nighet-time groups respectively.When Ce =1.2 and 2.0 μg/ml,the BIS values were significantly lower in night-time group than in day-time group.There was no significant difference in BIS value between the 2 groups when Ce =0.8 and 4.0 μg/ml.When the patients lost consciousness (OAA/S =2),the BIS value was comparable between the 2 groups,but Ce was significantly lower in night-time group than that in daytime group.Conclusion The hypnotic effect of propofol is greater during night-time than during day-time. Key words: Circadian rhythm; Propofol; Conscious sedation