Effects Of Different Doses Of Dexmedetomidine On Hemodynamics During Anesthesia Induction In Patients Undergoing Coronary Artery Bypass Grafting

Objective To observe the influences of continuous infusion of different doses of dexmedetomidine for 10 min before anesthesia induction on hemodynamics and myocardium oxygen consumption in patients undergoing off-pump coronary artery bypass grafting and discus the comparatively proper loading dose of dexmedetomidine.Methods Seventy-five patients,aged 45-70 years,weighing 55-80 kg,with BMI18.5-24.5 kg/m²,ASAⅡorⅢ,NYHAⅡorⅢand left ventricular ejection fraction≥45%,undergoing off-pump coronary artery bypass grafting,were randomly divided into groups D3,D6 and D9 using a random number table.There was no bradycardia（heart rate<50 times/min）or atrioventricular block above level II,no serious systematic diseases（liver and renal injury or serious respiratory diseases）and no anesthetic drug allergy history among these included patients.Dexmedetomidine 0.3,0.6 and 0.9μg/kg were infused intravenously for 10 min before induction of anesthesia in groups D3,D6and D9,respectively.Anesthesia was induced with lidocaine 1.5 mg/kg,midazolam 0.08mg/kg and sufentanil 0.6μg/kg.As BIS value≤75,0.12 mg/kg vecuronium bromide was infused intravenously.After induction of anesthesia,patients were tracheal intubated and mechanically ventilated when BIS value≤55.As BIS value≥60,0.5-1.0 mg/kg propofol was injected intravenously.The respiration parameters including tidal volume（V_T）8-10ml/kg,inspiratory/expiratory（I:E）1:2,respiratory rate（RR）10-12 times/min were set.General conditions including gender,weight,age,BMI,number of grafts and LVEF of patients were recorded.before dexmedetomidine infusion.2.HR,SBP,DBP and rate pressure product（RPP）which calculated using the formula RPP=HR×SBP were recorded before dexmedetomidine infusion（T₀）,5 and 10 min after dexmedetomidine infusion（T₁-₂）,immediately before intubation（T₃）and 1,3,5 min after intubation(T_4-6)3.The incidence of adverse cardiovascular events including hypotension,hypertension and bradycardia and respiratory depression were also recorded during anesthesia induction.Results Compared with T₀,HR was significantly decreased at T₁-T ₆ and RPP was significantly decreased at T₂-T₆ in groups D6 and D9（P<0.05）,SBP and DBP were significantly increased at T₁ in group D9（P<0.05）,while decreased at T₃ in all three groups（P<0.05）,and HR and RPP were increased at T₄ in group D3（P<0.05）.Compared with T₃,the HR,SBP,DBP and RPP were significantly increased at T₄ and T₅ in group D3（P<0.05）.Compared with group D3,SBP and DBP of groups D6 and D9 were significantly increased at T₃（P<0.05）,while HR and RPP were decreased at T₄（P<0.05）.The rate of hypotension was significantly lower in groups D6 and D9 than that in group D3（P<0.05）.While the incidence of hypertension,bradycardia and respiratory depression were significantly increased in group D9 than those in groups D3 and D6（P<0.05）.Conclusion Compared with 0.3 and 0.9μg/kg,dexmedetomidine 0.6μg/kg intravenous infusion is optimal to keep the stability of hemodynamics and the balance of myocardial oxygen delivery and consumption during anesthesia induction in patients undergoing coronary artery bypass grafting.