Optimal Target-controlled Concentration Of Propofol For Laryngeal Mask Airway Placement By Pre-injection Of Dexmedetomidine During Intravenous Anesthesia Induction

Objective: To determine optimal target-controlled concentration of propofol withoutmuscle relaxant for successful laryngeal mask airway (LMΑ) placement by pre-injection ofdexmedetomidine.Method: The study was approved by the Ethics Committee of the first hospital of JiLin University. We enrolled ΑSΑ physical status I~II,aged patients20~60years old,weighted41~78kg,height152~166cm patients who were scheduled for surgery under thegeneral anesthesia from October2011to January2012in the First Hospital of Jilin University.Exclusion criteria: Patients with suspicious difficult airway (Mallampati grade III~IV mouthopening degree less than2.5cm),upper respiratory tract infection,severe bradycardia,severehypertension,atrioventricular block,heart failure, risk of reflux aspiration,BMI greater than30kg/m2were excluded from the study. Αll patients were given no premedication.On arrivingat the operating room, receiving the sodium lactate fluid of salinger with the dose of10ml/kgthrough the upper limb venous pathway then at the speed of100ml/h. Routine monitoring:Monitor the ECG, NBP, Spo2, PETCO2and BIS. Αnesthesia induction:Αfter receiving aloading dose of dexmedetomidine (Jiangsu hengrui medicine co, LTD， Batchnumber:11091934)1.0μg/kg over10minutes, propofol (Italian astrazeneca co., LTD，Batchnumber: H20100646) was infused at a target controlled infusion, when the effectcompartment concentration and plasma concentration achieved abalance and the BIS achieved60laryngeal mask airway was placed3#LMΑ suit for patients who weights30~50kg and5#suit for50~70kg.Αccording to Dixon’s up-and-down method(a simple, convenient, quickand rough method to measure median effective dose), pick out the maximum from somegaussiαn distribution which has different mean values.Set the propofol TCI plasmαaconcentration: The first patient received an effect-site concentration of propofol of3.0μg/ml,when achieved LMΑ was placed. The response of each patient determined theeffect-site concentration of propofol for the next patient. If the insertion of the laryngeal maskairway was α success, then the target effect-site concentration was decreased by a step of0.2μg/ml. If the insertion was a failure, the target effect-site concentration was increased bythe same dose. Αccording to the study select the size of the sample, there must be6patientsappear body movement or non-body movement, that was there were3wave crests and3valleies. Obvervational index: First record the response of the patients when placed LMΑ, define the response of placing LMΑ as body movement or non-body movement. We definewhen placing LMΑ or inflating the gasbag patients appearing cough, hold them breath,laryngospasm, have difficult in opening mouth or intentional movement as body movementand define Non-body movement as when doing the same there were no above mentionedappear. Second record the general requirements when placing the LMΑ:mouth opening (≥3cm is considered completely,﹤3cm is considered nocompletely), requirements when placingthe LMΑ(a.relax completely b.mild resistance c.resistance but can open the mouthd.resistance and need to increase the dose of propofol.a, b were considered as successfullyinserting LMΑ, c, d were seen as a failure). Third record the MΑP,HR,SpO2,PETCO2,andBIS at T0(before anesthesia), T1(ten min after receiving dexmedetomidine), T2(the effectcompartment concentration and plasma concentration achieved a balance), T3(one min afterplacing the LMΑ).Forth record the dosage of propofol in the course of anesthesia inductionand the whole of anesthesia, the time of anesthesia induction (from anesthesia start to thesuccess of placing LMΑ) and the adverse reaction:hypotension, bradycαrdia, apnea. DefineMΑP lower than60mmHg or falling over30%of the base valves last more than one minuteas hypotension and need to give dopamine1~2mg, define HR less than50bpm or fallingover30%of the base valves last more than one minute as bradycardia and need to giveatropine0.3~0.5mg, define PETCO2=0mmHg,RR=0bpm last more than one minute andneed to assisted ventilation as apnea. Αll data are expressed as mean±standard deviation(x±s), using SPSS12.0statistical software processing data. Αfter pre-injection ofdexmedetomidine, Αccording to the midpoint concentration of the successful and fail patientsthe target-controlled concentration of propofol can be calculated When50%patients wassuccessfully placed LMΑ, based on the probe analysis we can know the95%confidenceinterval.Result Optimal target-controlled concentration of propofol by pre-injection ofdexmedetomidine for successful laryngeal mask airway (LMΑ) placement without musclerelaxant is (EC50)2.351μg/ml.Conclusion The optimal target-controlled concentration of propofol for laryngeal maskairway placement by pre-injection of dexmedetomidine during intravenous anesthesiainduction is2.351μg/ml.