Pharmacodynamic Study On Tracheal Intubations To Myasthenia Gravis(MG) Patients In The Case Of Target Controlled Infusion (TCI) Of Propofol And Remifentanil

Objective This study is to determine the effect site concentration EC₅₀ and EC₉₅ of remifentanil based on the Target Controlled Infusion(TCI) of propofol-remifentanil to induce tracheal intubation after topical anesthesia of the airway with lidocaine for myasthenia gravis(MG) patients without muscle relaxant.Methods Forty-five of ASAâ… orâ…¡MG patients have been undergone trans-sternal thymectomy.Typeâ… 4 people;typeâ…¡a 13 people;typeâ…¡b 22 people;typeâ…¢4 people; typeâ…£2 people.Anesthesia was induced with both propofol(Cp) TCI with the concentration kept at 4μg/ml,and remifentanil by using effect site concentration(Ce) given by TCI.The concentration is set at 1.8,2.7,4.0,6.0 ng/ml and increased in degree with geometric proportion.Every one should always start from 1.8 ng/ml for initial induction.The time of intubating:5 minutes after balance achieved between propofol-remifentanil plasma concentration and effect site concentration while the patients have lost their consciousness.Laryngoscope should be put in if the patients lost the consciousness and BIS lowered to less than 60,meanwhile larynx anesthetic tube should be put in to the place underneath glottis if no body moving and choke cough is observed,in this case 2ml of 2%Lidocaine has to be infused through the larynx-anesthetic tube to carry out the internal surface anesthesia of airway,then the laryngoscope and larynx tube should be withdrawn for ventilation of 1-2 minutes again, the tracheal intubation now can be done.In case of consciousness disappeared but any body moving or choke cough during operating of laryngoscope and larynx anesthetic tube the operation has to be stopped,and remifentanil Ce should be increased in degree with geometric proportion from 1.8 ng/ml to 2.7,4.0,6.0 ng/ml,until the patient is able to accept the larynx anesthetic tube into the airway for surface anesthesia to complete of the intubation.BP,HR,SpO₂ and bispectral index(BIS) were monitored and recorded during induction and intubation.The total dose of propofol and remifentanil were recorded during induction.Results All of 45 patients accepted the tracheal intubation when the remifentanil was up to 4ng/ml.none of them needs to adjust the remifentanil concentration up to 6 ng/ml.Ten patients(22%) accepted the tracheal intubation as group T₁,among them there are 3 of typeâ…¡a,5 of typeâ…¡b,2 of typeâ…¢;there are 28 patients(62%) need Ce up to 2.7 ng/ml for the tracheal intubation as group T₂.among them there are 3 of typeâ… ,9 of typeâ…¡a, 13 of typeâ…¡b,2 of typeâ…¢,1 of typeâ…£;there are 7 patients(16%) with Ce up to 4 ng/ml as group T₃,among them.1 of typeâ… ,1 of typeâ…¡a,4 of typeâ…¡b and 1 of typeâ…£. Comparing with the basic value,BP,HR and BIS of whole groups significantly decreased(P＜0.01).There was no significant difference of BP.HR and BIS value between 1 rain before the intubation and by the time of the intubation completion(P＞0.05).For group T₁.3 minutes after the intubation,the DBP notably lowered down.3 or 5 minutes after the intubation,MBP,BIS notably lowered down too:for Group T₂,BP, HR and BIS were significantly decreased within 1,3,5 minutes after intubation:and for T₃,5 mins after the intubation,HR and BIS notably lowered down(P＜0.01),but the scope of decline is all around±20%～30%of the basic value,within the acceptable range of clinic.Comparison among the 3 groups:Comparing with group T₁,HR of all patients in T₂ and T₃ was lowered remarkably when equilibration between plasma and effect site concentration of remifentanil(P＜0.05);Comparing with T₂,the BP of T₃ patients notably lowered 1 minute before the intubation(P＜0.05).When the propofol plasma target concentration is 4μg/ml,the EC₅₀ of remifentanil Ce for intubation was 2.2 ng/ml,[95%CI 2.0～2.3 ng/ml],the EC₉₅ of remifentanil Ce for intubation was 3.0 ng/ml, [95%CI 2.8～3.5 ng/ml].Conclusion1.Without muscle relaxant,for MG patients undergoing trans-sternal thynaectomy,the propofol combined with remifentanil TCI and internal surface anesthesia availably restrain the intubatton reaction to accomplish tracheal intubation successfully.2.When propofol plasm target concentration up to 4μg/ml,the EC₅₀ of remifentanil Ce for intubation was 2.2 ng/ml,[95%CI 2.0～2.3 ng/ml],and the EC₉₅ of remifentanil Ce for intubation was 3.0 ng/ml,[95%CI 2.8～3.5 ng/ml].3.The effect site concentration of remifentanil is chosen as double of EC₅₀,4.4 ng/ml that is suitable when complax propofol plasm target concentration is 4μg/ml.