Application Of Intermittent Intraoperative Neuromonitoring Of The Recurrent Laryngeal Nervein Complicated Thyroid Surgery

Thyroid surgery is one of the most common surgical procedures in head and neck,and it also is the most common endocrine surgical procedure.Surgery is the best treatment option for many thyroid diseases,such as benign tumor,thyroid cancer,retrosternal goiter,tumor recurrence or persistence,hyperthyroidism,and so on.Recurrent laryngeal nerve paralysis is one of the most serious postoperative complications.Recurrent laryngeal nerve paralysis can cause the dysfunction of intra-laryngeal muscles except the cricothyroid muscle.Nerve injury may be transient or permanent.Transient recurrent laryngeal nerve paralysis is defined as recovery of nerve function within 6 months postoperatively;however,permanent recurrent laryngeal nerve paralysis is defined as no function recoverywithin 6 months.The typical symptom of recurrent laryngeal nerve paralysis is hoarseness.Nerve injury can also be either unilateral or bilateral paralysis.Patients with unilateral laryngeal nerve paralysis often present as hoarseness of voice.Patients with bilateral paralysismay present as more severe hoarseness,and some may have dyspnea and need tracheotomy.How to avoid recurrent laryngeal nerve paralysis is a critical issue during thyroidectomy.The methods to protect nerve function have evolved gradually,changing from no nerve exposure to routine exposure.And now the concept is widely accepted that routine exposure and meticulous surgical technique as a gold standard during thyroid surgery to protect the function of recurrent laryngeal nerve.However,the incidence of recurrent laryngeal nerve paralysis is still about 2% even the operations are performed in skilled hands.Many reasons can increase the incidence of nerve paralysis,such as low-volume surgeon,thyroid reoperation,thyroid cancer,and surgical extent.Second,anatomic variant of laryngeal nerve is another important reason,such as non-recurrent laryngeal nerve,and extralaryngeal bifurcation.Third,intact laryngeal nerve does not mean the function is normal.Some studies found that the nerve function is lost while the shape of nerve fibers is sill intact.And only about 10% of nerve injures can be recognized intraoperativelyby surgeons.During the past several decades,intraoperative neuromonitoring was successfully developed and applied in thyroid operations,aiming to identify the nerve,predict the function,and eventually reduce the incidence of nerve paralysis.Intraoperative neuromonitoring can verify nerve function by recording the electromyogram signal of intralaryngeal muscles,especially the thyroarytenoid muscle.NIM? system,which is developed by Medtronic,Inc,is most widely used.The role of intraoperative neuromonitoring during primary thyroid operations has been studied extensively.However,due to the low incidence of nerve injury,most of these studies did not support the concept that intraoperative neuromonitoring can reduce the incidence of nerve paralysis during primary thyroid operations.So special emphasis is given to the study of intraoperative neuromonitoring in complicated thyroid surgery.Complicated thyroid surgery,such as thyroid reoperation,has a higher risk of nerve injury due to the preexisting scar,which makes nerve exposure more difficult.So it is reasonable to hope that intraoperative neuromonitoring may reduce the incidence of nerve injury and eventually patients may benefit from intraoperative neuromonitoring.However,only a few studies have been published until now due to the relative uncommon of thyroid reoperation.This study aimed to explore the role of intraoperative neuromonitoring during complicated thyroid surgery.Part I Intermittent Intraoperative NeuralMonitoring Technology in Minimally InvasiveVideo-Assisted ThyroidectomyMethods(1)Clinical data of minimally invasive video-assisted thyroidectomies performed between October 2009 and August 2011 were continuously collected and analyzed retrospectively.(2)Patients were enrolled if all the following criteria were met: benign thyroid lesions evaluated by preoperative ultrasound imaging and with maximum diameter ?4.0 cm;no previous thyroid surgeries;no cervical radiation history.(3)Exclusion criteria included the following:(1)thyroid carcinoma diagnosed by intraoperative frozen sections;(2)operations converted to open surgeries.(4)Recurrent laryngeal nerve function was confirmed by fiberoptic laryngoscopy,which was done preoperatively and postoperatively.(5)All minimally invasive video-assisted thyroidectomies were performed by the same experienced surgeon.For patients in NIM group,a specialized endotracheal tube with two pairs of electrodes,as well as an intermittent neural monitoring system(Medtronic NIM-Response 2.0),was used to track EMG signals of laryngeal muscles.(6)The time of locating RLN was defined as the time interval after thyroid lobe exposure and before RLN identified definitely.The time of tracing and exposing RLN was defined as the time interval after RLN identified definitely and before thyroid lobe completed removed.(7)Temporary RLN paralysis was defined as recovery of complete function within six months postoperatively by fiberoptic laryngoscopy examination.If RLN function did not recover,permanent RLN paralysis was defined.(8)Student's t-test was performed for continuous variables,and Fisher's exact test was used for categorical variables.P <.05 indicated statistically significance.Results(1)A total of 108 patients underwent MIVAT during this period.Six patients were converted to traditional open thyroidectomy(three cases were due to adhesion between thyroid lobe and strap muscles,and three cases were due to thyroid carcinoma examined by intraoperative frozen section).Other five patients were excluded because thyroid lesions were located in isthmus and RLNs were not exposed.Eventually 97 patients were enrolled in this study.(2)All the patients did not complain about obvious incision pain postoperatively,and satisfied about cosmetic outcome of cervical incision.No patients developed skin edge drawing injury of incisions,and no patients developed skin scald with ultrasonic scalpel.(3)None of 46 cases in NIM group occurred equipment failure,and for 42 cases,tracheal intubation was completed at one time,4 cases needed the second intubation(one of which was induced by inserting into esophagus by error,and the other three cases were all induced by poor contact of tracing electrode with bilateral vocal cord)(4)47 RLNs were dissected and exposed in NIM group,and 60 RLNs were exposed for 51 cases in control group.In NIM group,10 males and 36 females,aged from 22 to 72 years old,with mean age of(46.02 ± 11.34)years old;in control group,9 males and 42 females,aged from 23 to 73 years old,with mean age of(44.71 ± 11.19)years old.The mean length of incision was(2.13 ± 0.22)cm and(2.09 ± 0.20)cm for NIM group and control group,respectively.(5)24 patients underwent lobectomy and 22 patients underwent subtotal lobectomy in NIM group;22 patients underwent lobectomy and 29 patients underwent subtotal lobectomy in control group.Neither of the patients in both groups developed postoperative hemorrhage.Postoperative routine pathological results indicated that in NIM group,36 cases of nodular goiter,6 cases of adenoma,2 cases of nodular goiter with chronic lymphocytic thyroiditis and 2 cases of occult papillary carcinoma;in control group,42 cases of nodular goiter,4 cases of adenoma,4 cases of nodular goiter with chronic lymphocytic thyroiditis and 1 case of occult papillary carcinoma.(6)Time to locate RLN was 6.06 ± 1.48 min in NIM group and 6.92 ± 1.34 min in control group(p =.02).Time to trace and expose RLN was 28.96 ± 4.75 min in NIM group and 32.17 ± 5.56 min in control group(p =.02).(7)There was one case of RLN temporary paralysis for both NIM group and control group.No hypoparathyroidism was developed.Part II Intermittent intraoperative nervemonitoring in thyroidreoperationsMethods(1)Patients who underwent thyroid reoperations in the Department of Thyroid and Neck between January 2012 and August 2014 were enrolled in this study.All enrolled patients were randomly assigned into either the nerve integrity monitor(NIM)group or the control group.(2)In the NIM group,RLNs were located and exposed with the assistance of intermittent IONM;whereas in the control group,RLNs were identified visually without IONM.(3)Enrolled patients were required to meet all the following inclusion criteria: thyroid operations were carried out at least once before;normal ipsilateral vocal cord function was detected by preoperative laryngoscopy;and previous surgical field(either thyroid bed or centralneck compartment),as well as ipsilateral RLN,would be exposed during reoperation.(4)Patients who met one of the following conditions were excluded: limited movement or paralysis of the ipsilateral vocal cord observed by preoperative laryngoscopy;and previous surgical field and ipsilateral RLNs were not exposed during reoperation.(5)All reoperations were carried out by one experienced thyroid surgeon who had more than 20 years' experience with thyroidectomy.(6)The RLNs of patients in the NIM group were monitored by the NIM Response 2.0(Medtronic Xomed,Jacksonville,FL),which had a specific type of endotracheal tube with 4surface electrodes.This study complied with the standard operating procedures of intermittent IONM.All vagus nerves in the NIM group were dissected out of the carotid sheath for further stimulation.During dissection,V1,R1,R2,and V2 signals were obtained sequentially by stimulation of the vagus nerve or RLN at given times.(7)Preoperative neck ultrasound was mandatory for all patients,as well as contrast-enhanced CT scans from the neck to the chest.These preoperative imaging evaluations could provide much useful information about the position and volume of thyroid remnant,the positional relationship between the remnant and tracheal wall,the status of lymph nodes in the central and lateral compartments,and the status of lung metastases.(8)Fiber-optic laryngoscopy was mandatory for all patients preoperatively and day 1 after reoperation.(9)If RLN paralysis occurred,laryngoscopy was carried out routinely at 1,3,and 6 months after operation.Temporary RLN paralysis was defined as recovery of RLN function within the first 6 months after thyroid reoperation,and permanent RLN paralysis was defined as no recovery of function during this period.(10)Data were analyzed by IBM SPSS statistics version 20.Student's t test was used for continuous variables,and data were presented as mean ±SD.The chi-square test or Fisher's exact test was used for categorical variables.And p <0.05 indicated statistical significance.Results(1)A total of 78 patients underwent thyroid reoperations during this period.Five patients were excluded because of RLN paralysis diagnosed by preoperative laryngoscopy;and 3 patients were excluded because the thyroid bed or central neck compartment was not involved during reoperations.Finally,70 patients were enrolled into this study.(2)Of these,33 patients with 41 RLNs at risk were enrolled into the NIM group,and 37 patients with 43 RLNs at risk were enrolled into the control group.(3)62.9%(44/70)of redo dissections were carried out due to recurrence or persistence of papillary thyroid carcinoma(PTC),followed successively by nontoxic multi-nodular goiter(16 of 70),follicular thyroid carcinoma(5 of 70),and medullary thyroid carcinoma(5 of 70).(4)The total RLN paralysis rate was 13.1%(11 of 84).The incidence of temporary RLN paralysis and permanent RLN paralysis was 9.5%(8 of 84)and 3.6%(3 of 84),respectively,12.2%(5/41)and 4.9%(2/41)in NIM group,7.0% and 2.3% in control group.No statically differences were observed.After the 6-month follow-up,71.4%(5 of 7)of paralytic RLNs in the NIM group and 75%(3 of 4)in the control group recovered function.(5)One patient in the NIM group and no patient in the control group underwent tracheotomy.Conclusion(1)Applying intermittent intraoperative neural monitoringin minimally invasive video-assisted thyroidectomy is feasible.(2)Intermittent intraoperative neural monitoring can help reduce the time to locate and trace the recurrent laryngeal nerve in minimally invasive video-assisted thyroidectomy.(3)Intermittent intraoperative neural monitoring could not reduce the incidence of recurrent laryngeal nerve paralysis in minimally invasive video-assisted thyroidectomy.(4)The incidence of recurrent laryngeal nerve paralysis is higher in thyroid reoperations than in primary thyroid operations.(5)Although intermittent intraoperative neural monitoring provided more intraoperative information about recurrent laryngeal nerve and helped predict postoperative nerve function,it still could not reduce the incidence of temporary and permanent paralysis,and it could not provide obvious benefits to skilled thyroid surgeons.Intermittent intraoperative neural monitoring could not reduce the incidence of paralysis caused by surgeon-related factors.(6)Routine exposure of recurrent laryngeal nerve is sill the gold standard to avoid nerve injuries during complicated thyroid operations.