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Journal Information
Vol. 69. Issue 4.
Pages 231-242 (July - August 2018)
Vol. 69. Issue 4.
Pages 231-242 (July - August 2018)
Review article
DOI: 10.1016/j.otoeng.2017.06.017
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Recommendations on the Use of Neuromonitoring in Thyroid and Parathyroid Surgery
Recomendaciones sobre el uso de la neuromonitorización en cirugía de tiroides y paratiroides
José Luis Pardal-Refoyoa,b,
Corresponding author

Corresponding author.
, Pablo Parente-Ariasa,c, Marta María Arroyo-Domingoa,d, Juan Manuel Maza-Solanoa,e, José Granell-Navarroa,f, Jesús María Martínez-Salazarg, Ramón Moreno-Lunaa,e, Elvylins Vargas-Yglesiasa,h
a Comisión de Cabeza y Cuello y Base de Cráneo (SEORL CCC), Spain
b SACYL.Complejo Asistencial de Zamora, Zamora, Spain
c Complexo Hospitalario Universitario de A Coruña, A Coruña, Spain
d Hospital de Torrevieja, Alicante, Spain
e Hospital Universitario Virgen Macarena, Sevilla, Spain
f Hospital Universitario Rey Juan Carlos, Móstoles, Madrid, Spain
g Hospital Universitario del Sureste, Arganda del Rey, Madrid, Spain
h Hospital Universitario de Móstoles, Móstoles, Madrid, Spain
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Figures (2)
Tables (3)
Table 1. Reproductibility Recommendations on the Use of Neuromonitoring in Thyroid and Parathyroid Surgery. Situations Considered by the Work Group to Induce High Risk of Laryngeal Paralysis in Thyroid and Parathyroid Surgery.
Table 2. Recommendations on the Use of Neuromonitoring in Thyroid and Parathyroid Surgery. Recommended References in Neuromonitoring.
Table 3. Recommendations on the Use of Neuromonitoring in Thyroid and Parathyroid Surgery. Registration Parameters in Intermittent IONM.
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Additional material (1)

Thyroid and parathyroid surgery (TPTS) is associated with risk of injury to the recurrent laryngeal nerve, superior laryngeal nerve and voice changes. Intraoperative neuromonitoring (IONM), intermittent or continuous, evaluates the functional state of the laryngeal nerves and is being increasingly used. This means that points of consensus on the most controversial aspects are necessary.


To develop a support document for guidance on the use of IONM in TPTS.


Work group consensus through systematic review and the Delphi method.


Seven sections were identified on which points of consensus were identified: indications, equipment, technique (programming and registration parameters), behaviour on loss of signal, laryngoscopy, voice and legal implications.


IONM helps in the location and identification of the recurrent laryngeal nerve, helps during its dissection, reports on its functional status at the end of surgery and enables decision-making in the event of loss of signal in the first operated side in a scheduled bilateral thyroidectomy or previous contralateral paralysis. The accuracy of IONM depends on variables such as accomplished technique, technology and training in the correct execution of the technique and interpretation of the signal. This document is a starting point for future agreements on TPTS in each of the sections of consensus.

Recurrent laryngeal nerve
Patient safety

La cirugía de tiroides y paratiroides (CTPT) se asocia a riesgo de lesión del nervio laríngeo recurrente, nervio laríngeo superior y cambios en la voz. La neuromonitorización intraoperatoria (NMIO), intermitente o continua, en CTPT evalúa el estado funcional de los nervios laríngeos y se utiliza progresivamente con más frecuencia. Esto obliga a adoptar puntos de acuerdo en los aspectos más controvertidos.


Elaborar un documento de ayuda para orientar en la utilización de la NMIO en CTPT.


Consenso en grupo de trabajo mediante revisión sistemática y método Delphi.


Se identificaron 7 secciones sobre las que se establecieron puntos de acuerdo: indicaciones, equipo, técnica (parámetros de programación y registro), conducta en pérdida de señal, laringoscopia, voz e implicaciones legales.


La NMIO ayuda en la localización e identificación del nervio laríngeo recurrente, ayuda durante su disección, informa sobre su estado funcional al finalizar la cirugía y permite tomar decisiones en caso de pérdida de señal en el primer lado operado en una tiroidectomía bilateral programada o si había parálisis contralateral previa. La precisión de la NMIO depende de variables como la técnica realizada, la tecnología utilizada y la formación para la correcta ejecución de la técnica e interpretación de la señal. El documento presentado es un punto de inicio para futuros acuerdos en CTPT en cada una de las secciones de consenso.

Palabras clave:
Nervio laríngeo recurrente
Seguridad del paciente
Guía de práctica clínica
Full Text

Intraoperative neuromonitoring in thyroid and parathyroid surgery (TPTS) assesses the functional state of the laryngeal nerves (superior—SLN—and recurrent—RLN—) through the transformation into acoustic signal and electromiograph of the neuromuscular activity of the intrinsic muscles of the larynx after electric stimulus (directly or in the vagus nerve—VN—).

In TPTS the IONM helps to identify the RLN in its dissection and predict possible laryngeal paralysis (LP) by providing information on its functional state on termination of surgery.1

The laryngeal nerves may be injured through several mechanisms (sectioning, thermal mechanism, ligation, compression or traction).2

Thyroid surgery is associated with a relatively high proportion of changes in voice after surgery and a low prevalence of LP associated with variables such as the surgeon's experience or the performing of pre and postoperative laryngoscopy.3,4 The prevalence of LP and voice changes in parathyroidectomy has been less reported since few specific studies exist on IONM in parathyroidectomy.5

IONM in TPTS has controversial aspects, especially due to the non significant reduction of LP or its cost and the confusion generated by the large number of publications concerning it.5

In this regard, in 2016 the objective of the head and neck and skull base surgery commission was to design a document as guidance to the use of IONM in TPTS.

Material and Method

The methodology of this study is summarised in Fig. 1.

Figure 1.

Recommendations on the use of neuromonitoring in thyroid and parathyroid surgery. Working method recommendations.

* The search was adapted to each of the data bases consulted.

** Similar to other international surveys.17


The group worked in 2 areas. One concerned the text document using bibliographical review and another consisted of 3 rounds of successive surveys with web forms (Google Forms) applying the Delphi method.6 The questions contained multiple choice answer options and open-ended questions. In each round all members of the group were anonymously made aware of the answers of the others. Consensus was established when over 50% of members reached a final agreement.

Document Limitations

In general terms the text refers to thyroid surgery (although the concepts may be applied to parathyroidectomy), to RLN and to intermittent IONM—IONMi—(given the less widespread use of continuous IONM—IONMc—).


42 points of agreement were collected (Table 1 in Appendix A).

Table 1.

Reproductibility Recommendations on the Use of Neuromonitoring in Thyroid and Parathyroid Surgery. Situations Considered by the Work Group to Induce High Risk of Laryngeal Paralysis in Thyroid and Parathyroid Surgery.

  % Agreement 
High risk in thyroid surgery
Reintervention on the same side  100 
Advanced cancer, capsular rupture, infiltration  100 
Goitre with endothorasic extension  100 
Large volume goitre  80 
Circumferential goitre  70 
Association with recurrent neck dissection  100 
Association with lateral neck dissections (ii, iii, iv, v70 
Graves’ disease  70 
Thyroditis  60 
Contralateral paralysis  100 
Associated comorbidity: HBP, obesity, cardiopathy, diabetes, anticoagulation, anti-aggregation  60 
Any emergency surgery  60 
Any member of the team inexpert (surgeon, instrumentalist, anaesthetist)  60 
High risk in parathyroid surgery
Reintervention on the same side  100 
Negative location studies  90 
Thyroid diseases associated with high risk  100 
Revision surgery  100 
Bilateralexamination  40 
Adenomas large in size  50 
Contralateral laryngeal paralysis  100 
Parathyroids which are difficult to locate intraoperatively (ectopias, intraglandular)  70 
Associated comorbidity: HBP, obesity, cardiopathy, diabetes, anticoagulation, anti-aggregation  60 
Any emergency surgery  60 
Any member of the team inexpert (surgeon, instrumentalist, anaesthetist)  60 

HBP: high blood pressure.

The high risk surgery criteria are summarised in Table 1.

Seven sections were identified which were grouped into the topics discussed:

  • 1.


  • 2.


  • 3.

    Technique, parameters of programming and registration

  • 4.

    Signal loss behaviour

  • 5.


  • 6.


  • 7.

    Legal and ethical implications


The use of the IONM is justified because it helps with visual identification of RLN, increasing the rate of identification,7,8 facilitating dissection through successive checks,1,3,4 with a high positive precision for assessing the functional status of the RLN at the end of surgery (99.26% overall precision, 78.38% positive predictive value and 99.85% negative predictive value),1 guides decision making when there is a loss of signal,4 may lower the rate of bilateral paralysis9,10—probably due to postponing the second lobectomy when the signal is lost in the first one in a elective total thyroidectomy (TT),11—may reduce the rate of transitory paralysisysis12–15 (others do not find any difference14,16), increases the surgeon's confidence17 and is useful for teaching.18 In contrast it has been argued that it does not reduce the rate of permanent paralysis12,19,20 (in others it does21) and that it increases the cost.22 The IONM has to be assessed not just with regards to the LP rate but from other viewpoints (financial, convenience, medical and legal, patient safety, teaching).23

The American Academy of Otolaryngology and Head and Neck Surgery recommend carrying out IONM because it reduces the time in identifying RLN, the incidence of LP and helps to prevent bilateral LP.3

Bilateral LP is rare24 and it has been estimated that its incidence in patient series with IONM is lower than those in which only visual identification is made (2.43‰, 95% CI 1.55‰–3.5‰ and 5.18‰, 95% CI 2.53‰–8.7‰ respectively, with an absolute reduction of risk of 2.75‰, which suggests a necessary number of patients to treat of 364.13).10

In order to demonstrate a statistically significant reduction of the prevalence of paralysis with IONM compared with the single visual identification it would be necessary to carry out trials with over 150000 nerves per arm.25

IONM is progressively included in the practice of TPTS17 and preferably surgery where there is a high risk of paralysis, such as reinterventions,17,26,27 cancer,11,17,28 substernal extension,11,17 in preoperative LP,17,26,27 in Graves’ disease,17 on patient request,17 on patients with preoperative dysphonia,17 in toxic nodular goitre,17 in patients with a normal voice but who are referred with dysphonia,17 in TT,11 in central and lateral neck dissection,11,17 if there was previous cervical surgery11 and in thyroiditis.11

IONM work groups recommend its systemic use because it is not always possible to predict the degree of complexity in the preoperative period1,4 and all the less so in bilateral surgery, in revision surgery and in cases of pre-existing paralysis.3

Intraoperative Neuromonitoring in Minimally Invasive Video Assisted Thyroidectomy

Minimally invasive video assisted thyroidectomy was described by Miccoli in 1998, the most commonly endoscopic approach used being the treatment of modules under 4cm due to their reproductibiltiy, outcome (cosmetic, less pain and postoperative recovery) and easy conversion to the open technique.29 Despite the limited space of the approach (incision between 1.5 and 2cm), the complexity of IONM was increased, since the stimulation probe was comfortably inserted and easily controlled through endoscopic imaging.30 Although few studies exist on IONM in minimally invasive video assisted thyroidectomy, its use does not appear to affect rates of LP (transient or permanent), although it does reduce the time used in the search and dissection of the RLN.31

The technique is no different from that applied in open surgery. Electrodes are used, the surfaces of which are attached to the endotracheal tube (ETT). The thyroid lobe is laterally dissected and the middle thyroid vein is ligated, this is medially retracted, the carotid sheath is identified and the VN is stimulated with a 2mA current directly or through the sheath to obtain a signal (V1) which verifies the functioning of the nerve. Dissection is continued and once the oesophageal tracheal furrow is reached, stimulation is made with 1mA until the RLN has been located with obtainment of response (R1). Once the hemithyroid is resected, RLN and VN are stimulated using the same intensity as at the beginning of surgery, obtaining the corresponding electric responses (R2 and V2), which will help to verify nerve functioning.

Intraoperative Neuromonitoring in Thyroid Surgery Using Remote Approaches

The knowledge and outcome from open thyroid surgery are not directly transferable to these approaches. Dissection of the gland is technically similar, but there are relevant differences in approach and instruments used. The current standard of endoscopy is the high definition image which may also be 3D (routine in robotics). This may minimise the risk on enabling better identification of structures. Advanced cutting and coagulation systems are also essential and systematically used. In the most widespread published series, of over 1000 patients intervened using robotic BABA—Bilateral Axillo-Breast Approach—, 2 cases of permanent LP were reported (.2%).32

The most common option is to use ETT surface electrodes.33 According to the instrumentation and configuration of each operating theatre it is common to rotate the operating Table 180°. In underarm approaches the ipsilateral arm must be raised, and in all cases a wide subcutaneous breast dissection is made. In approaches without gas a large partition is also present. For all of these reasons there is a high risk of ETT movement, which should be appropriately fixed due to the risk of accidental extubation and poor positioning of the electrodes.

There are no technical limitations for the use of IONM in thyroid surgery using remote approaches (RATS). There are long stimulation probes (up to 230mm) which resolve the problem of distance up to the thyroid site.

Extensive literature already exists relating to RATS and there are several studies specifically aimed at IONM. Although in some initial publications there were no significant differences in the incidence of recurrent palsy in comparative studies,34 posterior series referred to comparable results.35 Lee et al. carried out a random prospective study in a group of 50 patients with papillary carcinoma of the thyroid using the robotic BABA approach, with and without IONM36 and described a zero rate of recurrent paralysis and an absence of differences in the vocal analysis except a faster recovery of the vocal range in the monitored group. Another study refers to the monitoring of the external branch of the SLN, and showed its clinical viability in BABA.37 Another laboratory study showed 2 cases of the use of the automatic usage of periodic stimulation of the vagus nerve in the transaxillary approach.38

To sum up, the IONM in the CTAA is probably a measure of appropriate safety for surgery which is technically complex and which is forced to maintain very demanding safety standards.

Recommendations from the work group:

  • It is always recommended that IONMi be performed in thyroidectomy.

  • In parathyroidectomy, the use of IONMi is recommended in cases considered to be high risk (Table 1).


The basic elements of the IONM system are the monitor (where the stimulation and registration parameters are programmed), the connection box, the ground and return electrodes, the stimulation electrode, (intermittent—monopolar, bipolar—or continuation; fine tip or spherical tip), the registration electrodes (with surface attached to the ETT which have already been configured by the manufacturer or adhesives), the needle electrodes inserted into the thyroarytenoid muscles through the cricothyroid membrane—transligamentary—and others—endolaryngeal needle inserted through direct laryngoscopy or endolaryngeal electrodes in contact with the retrocricoid area.4,39,40

The 2 most commonly used techniques and those referred to in the literature are the ones using surface electrodes in ETT and the transligamentary membrane.

The transligamentary technique is useful when there is a signature failure with ETT, when surgery is unpredictably complex where IONM was unplanned with a risk involved in ETT exchange, in tracheal stenosis with no possibility of using ETT and in patients who have or who need tracheotomy.

Recommendations from the work group:

  • The availability of neuromonitorisation equipment in the ENT services is considered necessary.

  • The equipment must include:

    • The possibility of configuring the stimulus and registration parameters.

    • The capacity for information storage and reproduction.

    • Automatic assessment of location and impedance of recording electrodes.

  • A recording electrode with the surface attached to the ETT is recommended.

  • Sharp or spherical tip stimulation electrodes may be used depending on the surgeon's preference.

  • Monopolar stimulation electrodes are recommended.

Technique, Programming and Registration Parameters4

Table 2 summarises the data which have to be recorded in the IONM.3,4,41

Table 2.

Recommendations on the Use of Neuromonitoring in Thyroid and Parathyroid Surgery. Recommended References in Neuromonitoring.

Information and informed consent document 
Preoperative laryngoscopy (p0L) 
Preoperative voice assessment 
Vagus nerve stimulation prior to thyroid dissection (V1) 
RLN stimulation in initial identification (R1) 
RLN stimulation on termination of thyroid dissection and complete haemostasis (R2) 
SLN stimulation in identification (S1) (optional) 
SLN stimulation in final dissection (S2) (optional) 
Stimulation of vagus nerve on termination of thyroidectomy and haemostasis (V2) 
Include the recording of the IONM in the patient's clinical history (recording of data and imaging for each side) 
Postoperative laryngoscopy (Lp1, Lp2, Lp3) 
Postoperative voice assessment 

Lp: laryngoscopy; RLN: recurrent laryngeal nerve; SLN: superior laryngeal nerve; IONM: intraoperative neuromonitoring.

IONM4,42,43 sequence:

1. During induction of anaesthesia and intubation:

  • a.

    Intubation with ETT with surface electrodes. Collaboration with anaestheology is important. The ETT diameter should be as large as possible with the electrodes positioned in the glottis area in contact with the vocal folds avoiding substances which make contact difficult (lubricants, saliva). Prevent the electrode of the ETT from twisting or getting trapped.

  • b.

    IONM equipment switched on.

  • i.

    Select thyroid screen.

  • ii.

    Configure the stimulation and registration parameters:

  • iii.

    Stimulus of 0.5–3mA (1mA is recommended, with posterior adjustment).

  • iv.

    Registration threshold ≥100μV.

  • v.

    Electrode impedance ≤5kΩ with a difference between both sides of <1kΩ.26

  • vi.

    Other parameters (with advanced configuration): volume of the sound, tone of warning, voice, maximum spread, visualisation of transitory events, latency view, detection of artefacts, monopolar or bipolar stimulation, period of rejection of artefacts of the actual electrical impulse (usually 1.2ms) and duration of stimulus (the most common configuration in IONMi is monopolar with frequency of 4 pulses and impulse duration of 100s43). For safety reasons, a warning must be configured when a stimulus of 3mA is reached.

2. After intubation:

  • a.

    Positioning of the patient. The hyperextension of the neck may change the position of the tube displacing it up to 33mm and electrode impedance must therefore be confirmed. Respiratory variations of the base line (30–70μV indicate good positioning).

  • b.

    Positioning of the earth electrodes (green, more remote positioning) and stimulus return (red, next to the larynx).

  • c.

    Connection of the electrodes to the connection box (earth, return and ETT) and to monitor.

  • d.

    Confirmation of the electrode impedance ≤5kΩ which indicates how the system works.

  • e.

    Keep a distance from the electric systems, place filter in the electrical scalpel wires.

3. In the surgical field at the start of the intervention:

  • a.

    Connection of the stimulation electrode to the connection box.

  • b.

    Confirmation of the system on the VN (V1). Check the degree of relaxation (recording of the level of blocking in the adductor muscle of the thumb).43 Stimulation of the VN may be performed directly, on the carotid artery or on the angle between the carotid and jugular vein without having to perform dissection through a small pouch in the fascia, with a supraliminal stimulus of up to 3mA with a spherical tip stimulation probe of 2.3mm which enables there to be pressure on the carotid, jugular or VN without injuring them.44 The recording has to be ≥100μV with dual-phase wave and throbbing sound.

  • c.

    Visual identification of the RLN (it is the standard pattern, preferably in relation to the inferior thyroid artery) and functional confirmation (register R1). Identification may be made in 3 reference points: in its emergence of the mediastinum, its relationship with the inferior thyroid artery or its relation with the Berry ligament. When there are doubts or difficulties the IONM helps in the location and identification of the RLN using successive confirmations (mapping).

  • d.

    Once lobectomy has been terminated, a functional confirmation of the RLN (R2 registration) is made.

  • e.

    Confirmation of the system with final stimulus on the VN (V2) which confirms the integrity of RLN function and differentiates lesion type 1 (segmentary, with distal signal in RLN and absence of proximal signal in VN) of type 2 (global, with absence of distal and proximal signal).4,45 Final V2 confirmation increases the predictive value.

The parameters of the signal are summarised in Table 3. Latency, width and duration would vary depending on the studies, nerve stimulated, the side, the disease and the method of registration.26,41

Table 3.

Recommendations on the Use of Neuromonitoring in Thyroid and Parathyroid Surgery. Registration Parameters in Intermittent IONM.

Breadth (μV)
Both sides  750±279μVa  1086±349μVa   
Right side  512μV (168–1593)b  623μV (207–1986)b   
Left side  460μV (138–1241)b  719μV (205–1767)b   
Latency (ms)
Both sides    3.96±0.69msa  3.56±0.49msa 
Right side  5.47±0.73msa
3.91ms (3.13–4.69)b 
2.73ms (1.95–3.91)b   
Left side  8.14±0.86msa
5.90ms (5–7.03)b 
2.73ms (1.95–3.91)b   
Duration (ms)
Right side  8.59ms (6.64–11.72)b  7.42ms (5.47–10.16)b   
Left side  9.38ms (7.42–11.72)b  7.42ms (5.47–9.77)b   

IONM: intraoperative neuromonitoring; RLN: recurrent laryngeal nerve; SLN: superior laryngeal nerve; VN: vagus nerve.


Expressed as mean and its standard deviation. Source: Lorenz et al.26


Expressed as median and its range (P10-P90). Source: Dionigi et al.41

Defects may occur in the signal which are analysed in the section called “signal loss behaviour” (absence, loss or reduction of intensity or increase of latency) or excess signal.

Excess signal is a false positive which may be due to a stimulus made on a nerve or vessel bridge, on the trachea, to interferences (electric, bipolar scalpel) or that the ETT has moved with respiratory movements, where the registration was not dualphased, had no relationship with the stimulus applied and lacked latency.46 The correct signal may be obtained by lowering the stimulus to 0.8mA or increasing the threshold (up to 200μV).

Signal losses may occur without LP (false positive, see the section on “signal loss behaviour”) and signal with LP (false negative) recordings.

Possible causes of false negative are:

  • Type 1 lesion (segmentary) or the RLN in which distal stimulus is obtained without there being a V2 signal.

  • Damage resulting after the last stimulus (in IONMi).

  • Delayed neuroapraxia.

  • Damage caused by the ETT in posterior branches of the RLN which lead to the interarytenoid vein.

  • Vocal immobility due to non neuromuscular causes.

Precision of the Test

IONM precision depends on technical aspects (stimulation and registration parameters, type of reference electrode, point of stimulation application—directly on the nerve or near it—, nerve stimulated—RLN, SLN, VN—type of stimulus—intermittent or continues—), the execution of the technique (visual identification of the RLN, obtainment of V1 and V2 references, sequence of references), of the experience in performing IONM (correct interpretation of the signal) and laryngoscopy (performing or not performing laryngoscopy and whether when performing it the detection of transient preoperative and postoperative paralysis increases).47,48

Obtainment of a V1 and V2 signal increases the precision of the IONMi, particularly in loss of signal due to lesion type 1 or in the case of the non recurrent inferior laryngeal nerve. Non recurrent inferior laryngeal nerve is more common on the right side (up to 3.6%), exceptional on the left side (.04%); IONM helps to correctly differentiate the motor branches of the sympathetic trunk fascicles,49 and using proximal stimulation on the VN (obtainment of the signal) and distal nerve (absences of the signal), allowing for the intraoperative establishment of the presence of the non recurrent inferior laryngeal nerve.50

The function of the SLN through IONMi is based on palpation of the cricothyroid muscle with a twitch present in all patients and in the electromiographical recording by glottis contraction present in 70%–80% of patients (anastomosis with RLN through Galen's anastomosis).51

Continuous Intraoperative Neuromonitoring28,52–55

Perhaps its best name would be IONM with “repetitive stimulation in pulses” since stimulation is not actually continuous.56

The stimulation electrodes applied to the VN may be open (S Shaped, Anchor or V3), semi-closed (Delta or Saxophone) or closed (APS—automated periodic stimulation—).56

Reference threshold programming recommended is of 100μV and stimulus of 1mA with 10 stimuli of 100ms duration.55

It is possible that the IONMi will not detect a lesion of the RLN between one stimulation and another28 with the result that the main advantage of IONMc is surveillance of RLN function in real time during mobilisation and dissection of the gland detecting events which may lead to an injury, helping the surgeon prevent or correct risk manoeuvres (traction, heat).28,53,54 Latency and amplitude are monitored and the events are classified into mild (reduction of breadth by 50%–70% and rise in latency of 5%–10%), severe (reduction of breadth>70% and increase of latency>10%) and loss of the signal when a response of <100μV28,53 is obtained.

The IONMc leads to the recognition of dysfunction which occurs during the RLN traction and modifies the said manoeuvres to prevent the loss of the signal, and help to identify the functional recovery of the nerve which occurs when ≥50% of baseline breadth is restored. We therefore recommend postponing the second lobectomy if this recovery has not taken place in the first side operated on in an electiveTT.56

IONMc precision is 99.5% in the prediction of the functional status of the RLN and is therefore useful in decision making during surgery and to prevent its injury.54

Recommendations by the work group:

  • RLN identification must be performed visually.

  • At the very least the RLN must be monitored.

  • Stimulation on the RLN in IONMi must be performed at the beginning and end in all cases (R1-R2).

  • Stimulation on the VN in IONMi must be performed at the beginning and end in all cases (V1-V2).

  • Registration of the superior layngeal nerve is not considered essential at the beginning (S1) and at the end (S2).

  • If visual identification of the RLN is impossible, functional identification is considered valid using IONM (R-V)

  • IONMc is considered useful in thyroid surgery in cancer with suspicion of extrathyroid extension, reinterventions or neck dissection.

  • IONMc is considered useful in parathyroid surgery associated with the above mentioned thyroid surgery and in reinterventions.

Guidelines for Loss of Signal

Signal loss is considered to have occurred when after stimulus4:

  • There is no signal.

  • The signal is <100μV with stimuli of 1 to 2mA (up to 3mA on the VN).

  • Checks are made with the area dry.

  • There is no twitch.

  • There is no laryngeal contraction using laryngoscopy.

The possible causes of signal loss are:

1. False positive:

  • The most common is the maladjustment of the ETT (rotated or displaced distally or proximally) or that it is small in diameter.57

  • Bad contact with the larynx due to saliva, blood or lubricant.

  • Connection failure.57

  • Badly programmed parameters (threshold too high, latency too short and initial artefact of the actual stimulus therefore recorded or stimulus insufficient for performance—optimum in mapping 2mA and during dissection 1mA—).

  • Low sound volume.

  • Activity of muscle relaxant activity.57

  • Deficiency of pseudocholinesterase (serum cholinesterase or type II).

  • Bad contact of stimulation probe (blood, fascias).

  • Malfunctioning of stimulation probe.

  • Artefacts and interferences.

  • Fatigue from repeated stimuli.

2. True positive:

  • Lesion of stimulated nerve (type 1—localised—or type 2—diffuse—).8

When signal is loss or the signal is <100μV, we would recommend checking (verification list):

  • 1st Position of the ETT (laryngoscopy).

  • 2nd Contact of ETT, earth and return electrodes.

  • 3rd Connections (box).

  • 4th Programmed parameters in the monitor (threshold, latency, stimulus, volume).

  • 5th Relaxation of the patient.

  • 6th Stimulation probe (status, contact, well dried surgical site).

  • 7th Contralateral V signal

  • 8th Laryngoscopy with stimulation in RLN or VN.

  • 9th Twitch with supraliminal stimuli (3–4mA).

After anterior confirmations9 on the first side of an elective TT we may wait for the signal to be restored after 20–30min (fatigue, neuroapraxia, relaxants),58 if there is recovery ≥0% of the signal (in IONMc) may be valued to continue with the second lobectomy or postpone it, and if paralysis has been confirmed on the contralateral side the IONM means that extuabation may be scheduled.59

The strategy in the case of signal loss in the first side or with previous contralateral paralysis may be summarised in the algorithm Fig. 2.

Figure 2.

Recommendations on the use of neuromonitoring in thyroid and parathyroid surgery. Algorithm of decision in the case of loss of signal on the first side operated on in an elective total thryodectomy or in previous contralateral paralysis depending on laryngeal motility confirmed with laryngoscopy and neuromonitoring signal.

RF: Respiratory failure; S1: side one; S2: side two; p0L: preoperative laryngoscopy; pL1: postoperative laryngoscopy performed between the first and third day; pL2: postoperative laryngoscopy performed between the fourth and sixth week; pL3: successive postoperative laryngoscopies; IONM: intraoperative neuromonitoring; V2: neuromonitoring signal obtained by stimulating the vagus nerve after termination of lobectomy; IONM V1-V2 sequence obtained with initial V1 and final V2 vagus signal; V1-R1-R2-V2: sequence of IONM obtained in 4 steps (initial vagus, in recurrent laryngeal nerve and R1 and R2 and final vagus V2).

* Strong level of indication: when other therapeutic alternatives do not have such a high probability of cure as total thyroidectomy.

** Weak degree of indication: when other therapeutic alternatives have a similar probability of cure as total thyroidectomy.

Taken and modified with the permission of Pardal-Refoyo et al.59


Recommendations from the work group:

  • If a neuromonitoring signal is not initially obtained after following the verification list it is recommended that the intervention be continued and that it be notified as a safety incident.

  • If there is a loss of signal in the first side in an elective TT it is recommended that the verification list be followed, if there continues not to be a signal, to postpone the second lobectomy.

  • If the decision is to postpone the second lobectomy and it is verified in the postoperative period that there is PL we recommend that the second lobectomy be planned according to the diagnosis obtained in the first one, the diagnosis obtained in the second one, symptomatology, comorbidity, therapeutic alternatives and the patient's opinion.

  • If a loss of signal occurs with the known contralateral LP, after having followed the verification list we would recommend to proceed with monitored laryngoscopy, reintubation when there are signs of laryngeal respiratory failure and tracheotomy when intubation is not possible.

  • Immediate surgical treatment in the larynx in a LP is not recommended.


Laryngoscopy should always be performed in the preoperative and postoperative period because the precision of the IONM will depend on the ability to detect the LP in the preoperative period (from 3.5% to 6.5% of patients with nodular goitre60,61) and in the postoperative period (to detect transient paralysis and false negatives).4,24,47,48 The detection of paralysis in studies with routine laryngoscopy duplicate those carried out for patients with voice disorders and probably both transient paralysis and permanent paralysis are being under diagnosed.3,62

In the preoperative period laryngoscopy would be performed when programming surgery and repeated when a voice problem arises prior to surgery.

Postoperative laryngoscopy may be performed immediately after extubation (with flexible fibroscopy or AirTraq®), in the medium term postoperative period (24–72h), in the late postoperative period (>1 month) and during follow-up after LP or dysphonia (up to 9–12 months follow-up63).

Flexible laryngoscopy is recommended due to easy execution, reproductibility and because video recording may be allowed64 with greater performance compared to examining with a mirror.3 The video stroboscopy leads to a more detailed examination in patients with voice disorders or with LP.3 Video laryngeal troboscopy is the technique of choice for assessing a possible compromise of the external branch of the SLN.65

Recommendations from the work group:

  • Laryngoscopy must always be performed before and after intervention.

  • Flexible laryngoscopy is recommended.

  • Preoperative laryngoscopy must be performed when surgery is scheduled if there are doubts about the situation changing, or if dysphonia has occurred at any time prior to surgery.

  • Immediate post-surgical laryngoscopy after extubation must be performed if there are signs of a suspicion of bilateral LP.

  • In the case of unilateral LP must be performed every 8–12 weeks.

  • Postoperative laryngoscopy in the medium postoperative period (24–72h) should be performed if the patient presents with dysphonia.

  • Postoperative laryngoscopy in the latepostoperative period (4–6 weeks) should always be performed.

  • Video documentation of the laryngoscopy exploration is recommended.


The prevalence of voice disorders in the general population is approximately 7.5%. 80% of patients present with a higher or lower degree of dysphonia after thyroidectomy and up to 4% may have persistent voice problems.3

Phonation disorders after thyroidectomy may be due to injury of the laryngeal nerves, trauma during intubation and extubation, dysfunction of cricothyroid articulation, dysfunction of the extrinsic laryngeal muscles, laryngeal tracheal fixation or psychological reaction to surgical intervention.66

The majority of studies refer to the identification and function of the RLN and it has not been demonstrated that identification and IONM of the external branch of the SLN reduce the rate of injury.65

We recommend assessing the voice preoperatively, taking precautions for protection of the SLN during surgery (identification, obtainment of the IONM signal and twitch)66 and recording whether there was a change in the voice between 2 weeks and 2 months after surgery.3

In the preoperative and postoperative period the patient should be asked if they have noticed any changes in their tone of voice, the volume, quality or resistance of it3 which may be documented using the Voice Handicap Index adapted into Spanish67 or other tools (V-RQOL, GRBAS or CAPE-V).3

Recommendations from the work group:

  • The patient should be asked if they had voice problems both pre and postoperatively.

  • A pre and postoperative voice study is recommended.

  • A voice questionnaire before and after surgery may be used.

Legal and Ethical Implications45,66

Attention should be focused on 2 aspects:

  • 1.

    Information and informed consent. Information on individual risks of injury or temporary or permanent dysfunction of the RLN and SLN, unilateral, bilateral or combined and its consequences on the respiratory pathway (blockage, tracheotomy), voice and swallowing. The patient must be informed on whether IONM will be used or not and in the case of non use, the reasons for this66 If selective use is made of IONM the patient must be informed (i.e. “if it is presumed that the neuromonitor is effective for complex cases, the surgeon must be capable of saying why it is not used in all cases”).66 The patient must be informed that situations of paralysis risk are unpredictable during the preoperative period.45

  • 2.

    Information on the limitations and usefulness of IONM. That its use is no guarantee of preventing nerve damage, LP from other causes or dysphonia without nerve injury (anatomical integrity of the nerves does not have to be associated with normal function). As with all technology using devices false negatives or false positives may arise where the results affect other variables such as anaesthesia or technical assistance.66 The patients should be informed about the real use of IONM which is merely technical (helping to identify nerves during dissection, for taking decisions during surgery on the functional status of the RLN, and eventually on the SLN, on termination of surgery). Information should be given on the possibility of postponing the second lobectomy in an elective TT if the signal is lost in the first side operated on, to prevent potential bilateral paralysis.45,66

Recommendations from the work group:

  • Information on the results of the neuromonitoring should be included in the patient's clinical record.

  • If a survey is made no opinion should be given on the need for neuromonitoring because there are no conclusive results in the literature.

  • The patient must be informed that problems may arise with their voice after thyrodectomy, even though there is no laryngeal paralysis.

  • The patient must be informed of the possibility that, if there is a loss of signal in the first side, the second lobectomy may need to be postponed.


Laryngeal or voice motility after TPTS depends on variables such as the technique used or the technology applied.

IONMi helps in the location and identification of RLN, during its dissection and provides information on its functional status on termination of surgery.

IONM precision depends on variables such as the technique used, the technology used and the training for correct execution and interpretation of the signal. The degree of difficulty is not always predictable and may arise during surgery. For this reason training is required so that the appropriate technique may be carried out and interpretation of the signal may be made in any situation, even in complex cases.

Obtaining registration using final V2 stimulus increases precision.

Due to its precisions, both IONMi and IONMc make it easier to take decisions when there is loss of signal in the first side operated on or when extubation is planned if there was previous contralateral paralysis.

IONM helps to reduce the rate of bilateral LP, increasing patient safety.

IONM may help to reduce the rate of transient LP.

IONMi must be performed in all thyrodectomies and in high risk parathyroidectomies.

IONMc has a higher capacity to predict nerve injury under circumstances with increased latency or a reduction of the breadth of the signal and may be useful in high risk surgery.

IONM increases the surgeon's confidence during surgery.

IONM is useful for teaching and helps in continuous professional training, identifying variants in anatomical pathways of the laryngeal nerves.

IONM facilitates the recording of data for research.

Conflict of Interests

The authors have no conflict of interests to declare.

Appendix A
Supplementary data

The following are the supplementary data to this article:

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Please cite this article as: Pardal-Refoyo JL, Parente-Arias P, Arroyo-Domingo MM, Maza-Solano JM, Granell-Navarro J, Martínez-Salazar JM, et al. Recomendaciones sobre el uso de la neuromonitorización en cirugía de tiroides y paratiroides. Acta Otorrinolaringol Esp. 2018;69:231–242.

Copyright © 2017. Sociedad Española de Otorrinolaringología y Cirugía de Cabeza y Cuello
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