The Proper Depth Of Muscle Relaxants In Total Intravenous Anesthesia During Posterior Fossa Surgery

Objective Due to the Intraoperative Neurophysiological Monitoring(IONM) has been used more and more widely. There was a contradiction between the acquiring of electric signal and the depth of muscle relaxation. It is difficult to acquire the signal if the depth of muscle relaxant is too high. However, the patient may have body moving reaction when the degree of muscle relaxation is too low. Moreover, if don’t use muscle relaxant, we need increase the dose of anesthetic. It may lead to the instability of hemodynamics, delayed recovery and poor prognosis. So the purpose of the study is to find the proper depth of muscle relaxation in patients undergoing posterior fossa surgery using total intravenous anesthesia(TIVA) which did not affect electrophysiological monitoring.Method Forty ASA Ⅰ～Ⅱ patients of both sexes, aged24-76years, height150～178cm,weight45-89kg for elective surgery were studied. The course of disease is seven months to six years. The tumor’s diameter is2-6cm;22cases located on the right side, and18cases on the left side. All of the patients were divided to two groups: Group A without muscle relaxants, that used the traditional anesthesia method which did not use muscle relaxants after intubation until the EMG monitoring was completed; Group B used muscle relaxants to maintain the TOF at2%-25%in the process of electrophysiological monitoring. In the course of tumor resection,0.1～0.3mA intensity electrical stimulation were used to find the facial nerve. After determining the facial nerve and resecting the tumor, increased the amount of rocuronium gradually. TIVA were used to all patients, and the BIS value was maintained in range of40～60. Anesthesia was induced by intravenous injection of midazolam O.lmg/kg, followed by sufentanil0.3μg/kg, propofol2mg/kg,0.6mg/kg rocuronium. The target controlled infusion of propofol and sufentanil maintain their plasma concentrations were3～5μg/ml and0.2～0.5ng/ml respectively, blood pressure controlled between baseline blood pressure of±20%,Two electrophysiological data were recorded under different TOF value:continued EM G and evoked EMG. Respectively recorded the information of SBP, DBP, HR, temperature (T), BIS, TOF and the EMG under different TOF values in different time points: before induction (To), immediately after induction (Ti), surgery began immediately (T2), immediately craniectomy (T3), electrophysiological monitoring instantly (T4), electrophysiological monitoring the first five minutes (T5),10min (T6),15min (T7),20min (Ts),25min (T9),30min (T10), electrophysiological monitoring end (T11).Assess the patients facial nerve functionn a week before and after operation and six months after operation, according to the House-Brackmann (HB) facial nerve function assessment criteria, for the normal function of grade Ⅰ, Ⅱ grade mild dysfunction, grade Ⅲ moderate functional barriers, IV grade severe dysfunction, V level of severity of dysfunction.Statistical analysis The software SPSS16.0was used in analyzing measurement data, which was expressed as mean±standard deviation. The among groups were compared using the t test, level data using the Wilcoxon rank sum test, P <0.05was considered statistically significant.Result The electrophysiological monitoring were carried out successfully in all patients. Three patients in group A had body movement during the operation. Four cases in group B can not be performed electrophysiological monitoring when the TOF had three signals. Between the two groups:The dosage of propofol and rocuronium difference was statistically significant (P<0.05); The difference at the operation time, the amount of sufentanil, neuroprotective rate,gender, age, weight,SBP, DBP, HR was no statistically significant (P>0.05)Conclusion Maintaining TOF value in range of2～25%doesn’t affect intraoperative facial nerve monitoring during CPA surgery, as well as avoid intraoperative body movement and decrease the dose of anesthetic.