Surgical treatment for thyrotoxic hypokalemic periodic paralysis: case report.

Thyrotoxic hypokalemic periodic paralysis (THPP) is a rare, potentially life-threatening endocrine emergency. It is characterized by recurrent muscle weakness and hypokalemia. Because many THPP patients do not have obvious symptoms and signs of hyperthyroidism, misdiagnosis may occur. The published studies revealed that definitive therapy for THPP is control of hyperthyroidism by medical therapy, radioactive iodine or surgery, but the long-term post-operative follow-up result was not observed. We reported two cases of medically refractory THPP with recurrent paralysis of extremities and hypokalemia, and both were combined with thyroid nodules. Both patients were treated with total thyroidectomy; the pathology revealed that one is Graves' disease with thyroid papillary carcinoma, and the other is adenomatous goiter with papillary hyperplasia. No episode of periodic paralysis was noted and laboratory evaluation revealed normal potassium level during the post-operative follow up. Our experience suggests that total thyroidectomy by experienced surgeon is an appropriate and definite treatment for medically refractory THPP, especially in cases combined with thyroid nodules.

Detecting and identifying nonrecurrent laryngeal nerve with the application of intraoperative neuromonitoring during thyroid and parathyroid operation.

PURPOSE: The nonrecurrent laryngeal nerve (NRLN) is a rare anatomical variant but associated with high risk of nerve injury during thyroid and parathyroid operations. Therefore, intraoperative detection and verification of NRLN are necessary. METHOD: A total of 390 consecutive patients who underwent thyroid and parathyroid operations (310 RLNs dissected on the right side and 293 nerves on the left side) were enrolled. Electrically evoked electromyography was recorded from the vocalis muscles via an endotracheal tube with glottis surface recording electrodes. At an early stage of operation, vagal nerve was routinely stimulated at the level of inferior thyroid pole to ensure normal path of RLN. If there is a negative response from lower position but positive response from upper vagal stimulation, it indicates the occurrence of a NRLN, and we localize its separation point and path. RESULTS: Four right NRLNs (1.3%) without preoperative recognition were successfully detected at an early stage of operation. Three patients were operated on for thyroid disease, one for parathyroid adenoma and all were associated with right aberrant subclavian artery. All NRLNs were localized and identified precisely with intraoperative neuromonitoring. Functional integrity of all nerves was confirmed by the intraoperative neuromonitoring and postoperative laryngeal examination. CONCLUSIONS: Vagal stimulation at the early stage of operation is a simple, useful, and reliable procedure to detect and identify the NRLN.

Does extensive dissection of recurrent laryngeal nerve during thyroid operation increase the risk of nerve injury? Evidence from the application of intraoperative neuromonitoring.

PURPOSE: Extensive dissection of recurrent laryngeal nerve (RLN) is inevitable in some complicated thyroid operations. The study aimed to determine whether extensive dissection of RLN increases the risk of nerve injury. METHOD: Three hundred thirty-one patients (506 nerves at risk) who underwent thyroid operations with intraoperative neuromonitoring were included. The study chiefly focused on the 101 RLNs on which extensive nerve dissection from the thoracic inlet to the entry of larynx was performed and for which the nerve exposure was longer than 5 cm. Electromyographic (EMG) signals were obtained from the RLN and vagus nerve before and after complete RLN dissection, and these were defined as R(1), V(1) and R(2), V(2) signals, respectively. The RLN palsy rates and the change of EMG signals were evaluated and analyzed. RESULTS: Among 101 nerves with extensive dissection, 13 nerves were due to the operation for recurrent goiter; 41 nerves, for large goiter with substernal extension; and 47 nerves, for thyroid cancer with paratracheal nodal metastasis. No permanent palsy occurred, but 2 nerves experienced loss of EMG signal after complete RLN dissection from a large recurrent goiter and developed temporary palsy. The palsy rates were 2% (2/101) in the extensive dissection group and 2.5% (10/405) in the nonextensive dissection group (P = .77). Among 99 nerves with normal vocal function after operation, none experienced weakened signal after complete RLN dissection, and the mean amplitudes of R(2) and V(2) signals were not significantly different from those of R(1) and V(1) signals (R(2) vs R(1); 1038 vs 1030 µV; P = .74; V(2) vs V(1); 824 vs 816 µV; P = .75). CONCLUSIONS: The results of this study suggest that careful surgical dissection is well tolerated by the RLN.

The effectiveness of dexmedetomidine infusion for sedating oral cancer patients undergoing awake fibreoptic nasal intubation.

BACKGROUND AND OBJECTIVE: Dexmedetomidine is characterized with effects of sedation, analgesia, amnesia and lack of respiratory depression. Hence, it should be suitable for awake fibreoptic intubation (AFOI). METHODS: We enrolled 30 oral cancer patients with limited mouth openings who were undergoing AFOI for elective surgery. Patients were randomly allocated into two groups; the Dex group (n = 16) that received dexmedetomidine (1.0 microg kg(-1)) infusion and the Control group (n = 14) that received fentanyl (1.0 microg kg(-1)) infusion. Main outcomes were evaluated by grading scores presenting conditions for nasal intubation and postintubation. Other analysed parameters included airway obstruction, haemodynamic changes, consumption time for intubation, amnesia level and satisfaction. RESULTS: Intubation score (1-5) representing condition for nasal intubation was significantly better in the Dex group [2(1-3)] than in the Control group [3(2-5)] (P = 0.001). Postintubation score (1-3) representing tolerance to intubation also showed more favourable results in the Dex group [1(1-3)] than in the Control group [2(2-3)] (P = 0.002). The Dex group showed significantly reduced haemodynamic response to intubation than the Control group. Incidence requiring temporary haemodynamic support was higher in the Dex group but not of significance. Both levels of amnesia and satisfaction score were significant in the Dex group. Other analysed parameters such as consumption time for intubation, airway obstruction score and postoperative adverse events did not differ significantly. CONCLUSION: Combination of dexmedetomidine loading with topical anaesthesia provides significant benefit for AFOI in intubation condition, patient tolerance, haemodynamic response, amnesia and satisfaction. Dexmedetomidine is effective for AFOI in anticipated difficult airway with only minor and temporary haemodynamic adverse effects.

Feasibility of intraoperative neuromonitoring during thyroid surgery after administration of nondepolarizing neuromuscular blocking agents.

BACKGROUND: A short-acting depolarizing neuromuscular blocking agent (NMBA), succinylcholine, has been utilized for thyroid operations with intraoperative neuromonitoring (IONM). Because of its potential to cause serious side effects, this prospective study tried to determine the feasibility of IONM after administration of a nondepolarizing NMBA during thyroid operations. METHODS: Complete IONM data for 179 patients who had normal cord mobility were investigated: 90 patients received an induction dose of rocuronium (group R) and 89 received atracurium (group A). Electromyography signals were obtained from the vagus nerve before and after resection of the thyroid lobe and were defined as V(1) and V(2) signals, respectively. Accelerometry (percent twitch) was used to monitor the quantitative degree of neuromuscular blockade. RESULTS: V(1) and V(2) signals were obtained successfully in all patients. The percent twitch at the V(1) signal was significantly lower than that at the V(2) signal in both groups (39% +/- 20% vs. 69% +/- 26% in group R; 35% +/- 28% vs. 56% +/- 35 % in group A; both p < 0.01). However, the magnitude of the V(1) and V(2) signals did not differ significantly in either in group (473.8 +/- 290.8 microV vs. 528 +/- 316.2 microV in group R; 584.8 +/- 394.3 microV vs. 637.8 +/- 458.2 microV in group A; both p > 0.05). CONCLUSIONS: A single dose of either rocuronium or atracurium was feasible for IONM during thyroid surgery and provided adequate muscle relaxation for tracheal intubation.

Seizure after local anesthesia for nasopharyngeal angiofibroma.

We report a young male patient who experienced seizure after local injection of 3 mL 2% lidocaine with epinephrine 1:200,000 around a recurrent nasal angiofibroma. After receiving 100% oxygen via mask and thiamylal sodium, the patient had no residual neurologic sequelae. Seizure immediately following the injection of local anesthetics in the nasal cavity is probably due to injection into venous or arterial circulation with retrograde flow to the brain circulation. Further imaging study or angiography should be done before head and neck surgeries, especially in such highly vascular neoplasm.

Tracheostomy tube ignition during microlaryngeal surgery using diode laser: a case report.

Ignition of the tracheal tube during laser microlaryngeal surgery under general anesthesia is an uncommon complication with potentially serious consequences. We present here a case of a patient with glottic stenosis following endotracheal intubation, who experienced this potentially catastrophic combustion during endoscopic arytenoidectomy, using a diode laser under general anesthesia via 60% FiO2, with an airway fire occurring at the tracheostomy tube and causing tubal damage and obstruction. The anesthetic connecting tube was immediately disconnected and the tracheostomy tube replaced. No adverse consequences to this patient's upper airway were noted during follow-up visits. Higher oxygen concentrations, the presence of combustibles, and the narrowness of the surgical field during endolaryngeal diode laser surgery are risk factors for airway fires.

Comparative mid-term results between inguinal herniotomy and single-port laparoscopic herniorrhaphy for pediatric inguinal hernia.

BACKGROUND: Some recent papers have advocated single-port laparoscopic herniorrhaphy and obtained satisfactory results. The aim of this study was to compare the mid-term outcomes of conventional inguinal herniotomy and single-port laparoscopic herniorrhaphy. METHODS: Between April 2007 and March 2009, 202 records of infants and children with inguinal hernia treated were retrospectively reviewed. Of them, 86 patients were treated by conventional inguinal herniotomy (IH group), and 116 patients by single-port laparoscopic herniorrhaphy with preperitoneal hydrodissection, a totally extraperitoneal enclosing suture and extracorporeal knot tying (LH group). Follow-up data were collected using a telephone questionnaire and last outpatient follow-up. RESULTS: Mean follow-up was 35.7±7.2 months. Both procedures could achieve compete repair without recurrence. Operation time of unilateral repair was significantly longer in the LH group than in the IH group (40.1 vs. 20.0 min; P<0.001); however, operation time of bilateral repairs was comparable in both groups (46.0 vs. 37.5 min; P=0.291). Metachronous hernia developed in 6 of 80 patients (7.5%) initially presenting with unilateral hernia in the IH group and in no patient in the LH group (P=0.005). CONCLUSIONS: Accompanied by the method of preperitoneal hydrodissection and a totally extraperitoneal enclosing suture, single-port laparoscopic herniorrhaphy would be an effective procedure as conventional inguinal herniotomy. Single-port laparoscopic herniorrhaphy was associated with long operation time and a reduction in contralateral hernia development. However, every 4 patent processus vaginalis would require intervention to prevent 1 metachronous hernia.

Preliminary experience of one-trocar laparoscopic herniorrhaphy in infants and children.

OBJECTIVE: Laparoscopy is an alternative procedure for pediatric inguinal hernia, with a trend toward increasing use of extracorporeal knotting and decreasing use of working ports. The aim of this study was to evaluate the preliminary results of one-trocar laparoscopic herniorrhaphy in infants and children. METHODS: Between April 2007 and March 2010, 216 infants and children treated were retrospectively reviewed. Under laparoscopic guidance, the hernia defect was closed extracorporeally by a nonabsorbable suture, which was introduced into the abdomen by an 18-gauge vascular access on one side of the hernia defect and withdrawn on the opposite side by a homemade hook-pin through a stab incision. Preperitoneal hydrodissection was performed during the procedure. Being a developing technique, multiple linear regressions were used to model markers for the operating time, including descriptive data, diameter of scope, operation findings, and the procedural volume. RESULTS: A total of 308 procedures were successfully performed among 214 patients (99.1%) and the mean operating time was 42.9 ± 24.7 minutes (range: 9-255 minutes). Additional working instruments were necessary in 7 patients (3.3%). Only 2 (0.9%) recurrences were observed during this period. Male gender (ß = 7.507, P = .001), prematurity (ß = 10.051, P = .004), presence of incarcerated hernia (ß = 12.188, P = .016), and both sides simultaneous operation (ß = 7.057, P = .001) would increase the operating time, while being independent of age, weight, presence of sliding hernia, and diameter of scope. However, the operating time may decrease with procedural volume (ß = -0.119, P < .001). CONCLUSIONS: Without assistant working instrument, laparoscopy-assisted extracorporeal ligation of the hernia defect may be safely performed in most infants and children. The use of preperitoneal hydrodissection and extraperitoneal knot-tying could tautly enclose the hernia defect without peritoneal gaps and approach an accepted recurrence rate.

A comparative study between 1 and 2 effective doses of rocuronium for intraoperative neuromonitoring during thyroid surgery.

BACKGROUND: The goal of this study was to explore an ideal application of rocuronium to enable adequate muscle relaxation for intubation without significantly affecting the evoked potentials measured by intraoperative neuromonitoring during thyroid surgery. METHODS: A total of 80 patients were randomized to receive 1 (group 1, n = 40) or 2 (group 2, n = 40) effective doses (ED(95)) of rocuronium to facilitate electromyographic (EMG) endotracheal tube insertion. Evoked potentials were obtained every 5 minutes by stimulating the vagus nerve between the time period of 30 and 70 minutes after administration of rocuronium. The magnitude of evoked potentials at each time point and the tracheal intubating conditions were compared between groups. Accelerometry (twitch [% TW]) was used to monitor the quantitative degree of neuromuscular transmission at the adductor pollicis muscle. RESULTS: At 30 minutes after administration of rocuronium, the rate of positive EMG response was 100% (40/40) in group 1 and 53% (21/40) in group 2 (P < .001). Positive EMG signals were obtained for all patients in group 2 until 55 minutes after administration of rocuronium. The mean amplitude detected from the time point of 30 to 60 minutes was greater in group 1 than in group 2 (P < .01). The time to tracheal intubation was 208 ± 59 seconds in group 1 and 114 ± 26 seconds in group 2 (P < .001). The overall intubating conditions were better in group 2 than in group 1 patients (P < .001). CONCLUSION: A total of 1 ED(95) of rocuronium (0.3 mg/kg) is an optimal dose for intraoperative neuromonitoring during thyroid surgery. Positive and high EMG signals were obtained in all patients at an early stage of operation, and satisfactory intubating conditions were achieved in most patients.

Electromyographic endotracheal tube placement during thyroid surgery in neuromonitoring of recurrent laryngeal nerve.

Intraoperative neuromonitoring (IONM) is widely used in thyroid surgery. This study aimed to investigate the influence of neck extension on electromyographic (EMG) endotracheal tube displacement and to determine the necessity of routinely checking the final electrode position after the patient had been fully positioned. A consecutive 220 patients undergoing thyroidectomy were enrolled. All patients were intubated with the EMG endotracheal tube under direct laryngoscopy. The electrode position and tube displacement were routinely checked and measured by laryngofiberoscopy before and after patient positioning. The patients were divided into two groups. In Group I (n=110), the EMG tube was taped and fixed to the right mouth angle before full neck extension. In Group II (n=110), the EMG tube was disconnected from the circuit tube and was not taped until full neck extension. In all patients, we ensured that the final electrode position was the optimal position with laryngofiberoscopic examination. The tube displacement after neck extension ranged from 16 mm upward to 4 mm downward in Group I and from 12 mm upward to 5 mm downward in Group II. The rate of tube displacement greater than 10 mm was 12.7% in Group I and 3.6% in Group II. Successful monitoring was achieved in all patients after the final optimal position of electrodes was ensured routinely. The electrode position can be severely displaced after the patient has been fully positioned. Verification of ideal position of electrodes before the beginning of the operation is a necessary step to guarantee functional intraoperative neuromonitoring.

Anaphylaxis to benzalkonium chloride-coated central venous catheter.

Benzalkonium chloride (BAC) is commonly used as a bactericidal preservative and it may cause allergic reactions in some patients. An unusual case of anaphylactic shock in a 55-year-old woman following insertion of a central venous catheter (CVC) that was coated with BAC is presented. Assuming anaphylactic shock from the CVC, the catheter was removed immediately. Standard resuscitation was started with 100% oxygen, epinephrine, and saline infusion. The patient recovered without any sequelae. One month later, an intradermal skin test was positive for BAC.

Intraoperative neuromonitoring for early localization and identification of recurrent laryngeal nerve during thyroid surgery.

Early and definite identification of the recurrent laryngeal nerve (RLN) is an important step to avoid inadvertent nerve injury during complicated thyroid operations. This study aimed to determine the feasibility of routine use of intraoperative neuromonitoring (IONM) to localize and identify the RLN at an early stage of thyroid surgery. This prospective study enrolled 220 consecutive patients (333 RLNs at risk) who underwent thyroid operations with application of IONM. The RLN was localized and identified routinely with a nerve stimulator after opening the space between the thyroid and carotid sheath. The success rates of early RLN localization and identification were evaluated. The current for localization and the amplitude of evoked laryngeal electromyographic signals were also recorded and analyzed. All RLNs, including 87 (26%) nerves that were regarded as difficult to identify, were successfully localized and identified. The stimulation level for RLN localization was 2mA in 315 nerves (95%) and 3mA in the other 18 nerves (5%). The signal obtained from RLN localization (amplitude = 932 ±436µV) showed a clear and reliable laryngeal electromyographic response that was similar to that from direct vagus (amplitude=811±389µV) or RLN stimulation (amplitude=1132±472µV). The palsy rate was 0.6% and no permanent palsy occurred. RLN injury is rare if the nerve is definitely identified early in the thyroid operation. The conclusion of this study is that IONM is a reliable tool for early RLN localization and identification, even in complicated thyroid operations.

Electromyographic study of differential sensitivity to succinylcholine of the diaphragm, laryngeal and somatic muscles: a swine model.

Neuromuscular blocking agents (NMBAs) might diminish the electromyography signal of the vocalis muscles during intraoperative neuromonitoring of the recurrent laryngeal nerve. The aim of this study was to compare differential sensitivity of different muscles to succinylcholine in a swine model, and to realize the influence of NMBAs on neuromonitoring. Six male Duroc-Landrace piglets were anesthetized with thiamylal and underwent tracheal intubation without the use of an NMBA. The left recurrent laryngeal nerve, the spinal accessory nerve, the right phrenic nerve and the brachial plexus were stimulated. Evoked potentials (electromyography signal) of four muscle groups were elicited from needle electrodes before and after intravenous succinylcholine bolus (1.0 mg/kg). Recorded muscles included the vocalis muscles, trapezius muscle, diaphragm and triceps brachii muscles. The onset time and 80% recovery of control response were recorded and analyzed. The testing was repeated after 30 minutes. The onset time of neuromuscular blocking for the vocalis muscles, trapezius muscle, diaphragm and triceps brachii muscle was 36.3 ± 6.3 seconds, 38.8 ± 14.9 seconds, 52.5 ± 9.7 seconds and 45.0 ± 8.2 seconds during the first test; and 49.3 ± 10.8 seconds, 40.0 ± 12.2 seconds, 47.5 ± 11.9 seconds and 41.3 ± 10.1 seconds during the second test. The 80% recovery of the control response for each muscle was 18.3 ± 2.7 minutes, 16.5±6.9 minutes, 8.1±2.5 minutes and 14.8±2.9 minutes during the first test; and 21.5±3.8 minutes, 12.5 ± 4.3 minutes, 10.5 ± 3.1 minutes and 16.4 ± 4.2 minutes during the second test. The sensitivity of the muscles to succinylcholine, ranked in order, was: the vocalis muscles, the triceps brachii muscle, the trapezius muscle and the diaphragm. We demonstrated a useful and reliable animal model to investigate the effects of NMBAs on intraoperative neuromonitoring. Extrapolation of these data to humans should be done with caution.

Anatomical variations of recurrent laryngeal nerve during thyroid surgery: how to identify and handle the variations with intraoperative neuromonitoring.

Recurrent laryngeal nerve (RLN) palsy is the most common and serious complication after thyroid surgery. Visual identification of the RLN during thyroid surgery has been shown to be associated with lower rates of palsy, and although it has been recommended as the gold standard for RLN treatment, it does not guarantee success against postoperative vocal cord paralysis. Anatomical variations of the RLN, such as extra-laryngeal branches, distorted RLN, intertwining between branches of the RLN and inferior thyroid artery, and non-recurrent laryngeal nerve, can be a potential cause of nerve injury due to visual misidentification. Therefore, intraoperative verification of functional and anatomical RLN integrity is a prerequisite for a safe thyroid operation. In this article, we review the literature and demonstrate how to identify and handle the anatomical variations of the RLN with the application of intraoperative neuromonitoring in the form of high resolution photography, which can be informative for thyroid surgeons. Anatomical variations of the RLN cannot be predicted preoperatively and might be associated with higher rates of RLN injury. The RLN injury caused by visual misidentification can be rare if the nerve is definitely identified early with intraoperative neuromonitoring.

Influence of nondepolarizing muscle relaxants on intraoperative neuromonitoring during thyroid surgery.

OBJECTIVE: The objective of this study was to find a nondepolarizing muscle relaxant to replace succinylcholine during thyroid surgery with intraoperative neuromonitoring (IONM) because succinylcholine can cause severe adverse effects. DESIGN: Prospective study of 232 patients undergoing thyroidectomies. SETTING: A tertiary medical centre. METHODS: One hundred thirty-one patients received 0.5 mg/kg rocuronium (group R) and 101 patients received 0.5 mg/kg atracurium (group A) to facilitate electromyographic (EMG) endotracheal tube insertion. EMG signals were obtained from the vagus nerve before and after dissection of the recurrent laryngeal nerve and were defined as the V1 and the V2 signal, respectively. Accelerometry (twitch [% TW]) was used to monitor the quantitative degree of neuromuscular transmission at the adductor pollicis muscle. MAIN OUTCOME MEASURES: The amplitude (muV) of the V1 and V2 signals and the correlated degree of neuromuscular transmission (% TW). RESULTS: V1 and V2 signals were obtained from all patients successfully. The % TW at the V1 signal was significantly lower than that at the V2 signal in group R and group A. The mean recovery time from complete neuromuscular blockade to the initial twitch was 43.9 +/- 11 minutes. Only in the subgroup in which the correlated TW was 0% while eliciting the V1 signal were the amplitudes of the V1 signals significantly lower than those of the V2 signal in both groups. CONCLUSIONS: A single dose (0.5 mg/kg) of rocuronium and atracurium was feasible for IONM during thyroid surgery. This study showed that 44 minutes after administration of these two muscle relaxants is adequate for eliciting an EMG signal from the vagus nerve.

Accuracy of the central landmark for catheterization of the right internal jugular vein after placement of the ProSeal laryngeal mask airway.

OBJECTIVE: Catheterization of the internal jugular vein (IJV) after placement of a laryngeal mask airway (LMA) has been reported to be difficult. The purpose of this study was to evaluate the accuracy of the central landmark for catheterization of the right IJV after placement of a ProSeal LMA. METHODS: We enrolled 80 patients (30 men and 50 women) who were scheduled to undergo surgery under general anesthesia conveyed by a size 3 ProSeal LMA. A needle pathway based on the central landmark for right IJV catheterization was simulated. Ultrasound images were obtained, which we contrasted with the simulated pathway to evaluate whether the landmark accuracy remained unchanged after placement of the ProSeal LMA. Both frequency of simulated right carotid artery (CA) puncture and overlap between the right IJV and right CA were also investigated. RESULTS: The simulated needle pathway ran along the course of the right IJV in 60% (48/80) of subjects, and transected the CA in 31.3% (25/80) of subjects. Both events together occurred in 20% (16/80) of subjects. The central landmark had a medial bias of 6.8 mm (95% confidence interval, 5.3-8.4). In 83.8% (67/80) of subjects, the center of the right IJV was lateral to the central landmark. The possibility of overlap of the right IJV and CA was high after ProSeal LMA placement. CONCLUSION: After placement of the ProSeal LMA, the central landmark could not offer a good success rate at the first puncture attempt. When using the central landmark to catheterize the IJV after a ProSeal LMA placement, medial deviation of the central landmark should be considered. Ultrasound guidance may be helpful in difficult cases.

Optimal depth of NIM EMG endotracheal tube for intraoperative neuromonitoring of the recurrent laryngeal nerve during thyroidectomy.

BACKGROUND: Malpositioning of the endotracheal surface electrodes can result in dysfunction of intraoperative neuromonitoring (IONM) and increase the risk of recurrent laryngeal nerve injury. The purpose of this study was to investigate the optimal depth of the nerve integrity monitor (NIM) EMG endotracheal tube. METHODS: We enrolled 105 adult patients undergoing elective thyroidectomy. Each Medtronic Xomed NIM EMG endotracheal tube was placed with the middle of the exposed electrodes well in contact with the true vocal cords under direct laryngoscopy. Function of IONM was documented and the insertion depth was measured and analyzed. RESULTS: Ninety-nine (94.3%) patients had successful IONM with the initial endotracheal tube position. Six (5.7%) patients needed further tube depth adjustment under fiberoptic bronchoscopy. All patients were finally had successful IONM. The optimal mean depth was 20.6 +/- 0.97 cm in men and 19.6 +/- 1.0 cm in women (p < 0.01). There was the trend that taller subjects had a deeper tube depth (p < 0.05). CONCLUSION: We concluded that the mean depth of the NIM EMG tube would be a useful reference value for detecting the malposition of electrodes and adjusting the depth of tube during the operation.