Effects Of Dexmedetomidine On The EC₅₀ Of Propofol Target-Controlled Infusion At Loss Of Consciousness And Stress Reaction In Elderly Patients

Objective:To research the effects of different doses of dexmedetomidine at loss of consciousness?LOC? on the median effective concentration(EC₅₀) of propofol given by target-controlled infusion?TCI?, and the impact on hemodynamics and stress hormones in elderly patients, we expect to provide appropriate dexmedetomidine doses for pre-clinical anesthesia induced.Methods:One hundred cases of elderly patients of both sexes undergoing elective surgery under general anesthesia, ASA grade I or II, 65-75 years old, body mass index?BMI?between 18.5 kg/m2 and 30.0 kg/m2, were allocated into four groups? n = 25? by random number table: normal saline group?group C? and three different doses of dexmedetomidine groups?group D1-3?. Groups D1-3 were given dexmedetomidine0.3, 0.5, 0.7 ?g/kg by intravenous infusion?both diluted with normal saline to 50ml?,and the group C with an equal volume of saline, all the four groups were infused over 10 min. And 10 min later, target-controlled infusion?TCI? of propofol was started by using sequential method, which was began with 2.5 ?g/ml. The positive reaction was the patients loss of consciousness. When the patients consciousness disappeared, intravenous with sufentanil 0.3-0.5 ?g/kg and rocuronium 0.6 mg/kg.When the BIS value descended to 60, tracheal intuhation would be performed. The median effective concentration(EC₅₀) and 95%confidence interval of propofol TCI causing loss of consciousness were calculated each group. In four groups, the BIS,systolic blood pressure?SBP?, diastolic blood pressure?DBP? and HR were recorded at baseline?T0?, 10 min of giving dexmedetomidine or NS?T1?, the time that patients lossing of consciousness?T2?, 1 min before intubation?T3?, immediately after intubation?T4? and at 3, 5 min after intubation?T5-6?.Blood samples were taken from the right elbow venous at T0, T4, T6 time point, and radioimmunoassay was used to determine cortisol and norepinephrine levels in plasma.Result:1.There was no significant difference in the four groups of the general information.2.EC₅₀ and 95%confidence interval?CI? of propofol TCI at the time LOC were calculated each group.In group C and D1-3 patients with TCI propofol unconsciousness EC₅₀ and 95%CI was 2.92?2.81-3.02?, 2.67?2.56-2.79?, 2.20?2.03-2.39? and 1.95?1.81-2.11??g/ml. Compared with C group, D1-3 propofol group patients unconsciousness EC₅₀ was significantly lower?P <0.05?. At the time lost consciousness the EC₅₀ of propofol was significantly decreased in groups D2-3 than in group D1?P< 0.05?, and there were no obvious difference between D2 and D3?P>0.05?.3.Comparison of hemodynamic parameters and the BIS at each time point in the four groups.SBP, DBP, HR and BIS were no statistical difference in all four groups at T0.Compared with T0, SBP and DBP were no difference at T1?P > 0.05?, but HR was significantly decreased at T1 than at T0 in group D1?P< 0.05?, at the just moment of tracheal intubation,SBP, DBP and HR were obviously increased than that at T0; At T4, T5, T6, the patients' SBP, DBP and HR were comparable significant compared with at T3?P < 0.05?, but without statistical differences compared with group C?P>0.05?. Compared with T0, the SBP, DBP and HR were significant lower than T1 in the D2 group and D3 group, and the two groups at the moment of intubation, the patients' SBP, DBP and HR were lower than group C. In D2 group, the patients' SBP at T4 were higher than the level at T3, but still lower than the level at T0, which restored to the level at T3 when at T5 and T6, DBP and HR were no significantly differences between before intubation and after intubation, In the D3 group,compared with the level at T3, the SBP and DBP were no statistical difference at T4-6,but HR was lower at T5 and T6. BIS were significantly higher at T1 in group C than D1-3?P<0.05?, while lower at T2?P<0.05?.4.Comparison of COR and NE in four groups at different time point.COR and NE were no statical difference in four groups at T0?P>0.05?.Compared with the level at T0, COR and NE were obvious higher at T4 and T6 in group C and group D1?P<0.05?, and there were no difference in group D2 and group D3?P>0.05?.In group D2 and group D3 the level of COR and NE were lower than those in group C at T4 and at T6.Conclusion:In elderly patients, intravenous infusion of dexmedetomidine 0.5 ?g/kg is a suitable dosage before induction of anesthesia, which is not only decreasing the EC₅₀ of propofol TCI causing at loss of consciousness, but also effectively inhibiting the stress responses to tracheal intubation.