The dose-effect relationship of propofol infusion and its effect on pain threshold in elderly patients

Objective To observe the changes of BIS,MAP,HR and pain threshold induced by different doses of propofol in elderly patients.Methods Forty elder patients(65-89 years old),ASA class Ⅰ or Ⅱ,scheduled for selective surgeries,were divided randomly and equally into 4 different doses of propofol(constant intravenous injection for 1 min) groups of 0.75 mg/kg(Ⅰ),1 mg/kg(Ⅱ),1.25 mg/kg(Ⅲ) and 1.5 mg/kg(Ⅳ).Responsiveness's OAA/S scores were used for judging sedation and hypnosis degree.Direct current potassium phoresis was used for detecting pain threshold.BIS,HR,MAP,low pain threshold and high pain threshold were monitored before propofol injection and at 1 min after propofol injection.Results 1 min after propofol injection,OAA/S scores in group Ⅰ and Ⅱ were 2 or 1,which in group Ⅲ and Ⅳ were 0.Data of BIS in group Ⅰ and Ⅱ were 70.4±12.3,68.7±6.4,and in group Ⅲ and Ⅳ were 56.3±13.3,48.3±9.8,respectively.BIS values in group Ⅲ and Ⅳ were significantly lower than those in group Ⅰand Ⅱ(P0.05 or P0.01).Dose of propofol was negatively correlated with BIS value(r=-0.648,P0.01),BIS=96.626-31.719×dose of propofol(r2=0.419,P0.01).HR of 4 groups as similar.At 1 min after propofol injection,MAP decreased remarkably compared with at before in all 4 groups(P0.01),which in group Ⅳ decreased significantly compared with at in group Ⅰ and Ⅱ(P0.05).At 1 min after propofol injection,the low pain threshold was higher in group Ⅲ or group Ⅳ(P0.01 or P0.05) than that in group Ⅰ,group Ⅱ or before propofol injection.The high pain threshold was higher at 1 min after propofol injection than that before(P0.05 or P0.01).Conclusion Dose of propofol is negatively and linearly correlated with BIS value.Propofol 1.25,1.5 mg/kg constant injection may meet the sedation and hypnosis demand of general anesthesia,with an increase of pain threshold and decrease of the sensitiveness of pain.